Sleeve Valve Report

116
Cranfield University Adriaan Moolman Modelling of a 4-Stroke Sleeve Valve Engine School of Engineering MSc Automotive Product Engineering

Transcript of Sleeve Valve Report

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Cranfield University

Adriaan Moolman

Modelling of a 4-Stroke Sleeve

Valve Engine

School of Engineering

MSc Automotive Product Engineering

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Cranfield University

School of Engineering

MSc Automotive Product Engineering

Academic Year 2006-2007

ADRIAAN MOOLMAN

Modelling of a 4-Stroke Sleeve Valve

Engine

Supervisor: Professor Douglas Greenhalgh

August 2007

This thesis is submitted in partial fulfilment of the requirements for the degree of

Masters in Science

© Cranfield University 2007. All rights reserved. No parts of this publication may be

reproduced without the written permission of the copyright owner.

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ABSTRACT

In the highly competitive automotive industry where ever increasing demand on

higher performance is overshadowed by emission regulations, downsizing engines

becomes an attractive solution. To ensure sufficient breathing capacity of the

downsized engine, the higher possible valve area of the sleeve valve coupled with the

possibility to optimize the combustion chamber and the reduced mechanical losses

present a plausible alternative to poppet valve engines.

The aim of this study is to develop a simulation model in order to predict the

performance of a sleeve valve engine. Little theoretical or empirical models are

available for sleeve valve engines because the use of sleeve valve engines deteriorated

before the widespread use of computer simulations. The major focus for the

simulation is on the modelling of the flow through the sleeve valves. The modelling

consists of the exact valve areas and the accompanying valve discharge coefficients.

The study subsequently developed a method of determining the valve areas as a

function of the engine crank angle from the arbitrary shaped valve profiles. It also

identified experimental discharge coefficients in the open literature that could be used

for flow analyses and it determined a new set of discharge coefficients by way of CFD

simulations. These CFD derived discharge coefficients compared well with the

experimental coefficients and can subsequently also be used for sleeve valve

modelling.

WAVE models were developed for a sleeve valve engine using the sleeve valve models

as determined in the study. These WAVE models produced satisfactory results,

reiterating the need for accurate valve models.

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ACKNOWLEDGEMENTS

Firstly I thank my Lord and Saviour Jesus Christ for the opportunity He gave me to

study this course and for the abilities and intellect to complete this study.

I thank my parents for all their support and love, emotionally and financially and I

thank my brother and sister for their support and love as well.

My thanks go to my supervisor for his help and guidance during this study as well as

my fellow students working with me on the sleeve valve project for their support and

help. I thank Mahle for providing the experimental engine as well as help and

assistance regarding this project.

I thank my flatmates and my classmates who helped me through this year of study and

for helping me make this a very memorable year in my life. I also thank the staff of the

Automotive Product Engineering course for their teachings and guidance throughout

the year.

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TABLE OF CONTENTS

Abstract ....................................................................................................................... iii

Acknowledgements...................................................................................................... iv

Table of Contents .......................................................................................................... v

List of Figures .............................................................................................................. vii

Notation ....................................................................................................................... x

1. Introduction .......................................................................................................... 1

2. Literature Review .................................................................................................. 4

2.1 Engine Downsizing .......................................................................................... 4

2.2 The Use of Sleeve Valve Engines ..................................................................... 7

2.2.1 Brief History of Sleeve Valve Engines ....................................................... 7

2.2.2 Sleeve Valve Operation ............................................................................ 7

2.2.3 Advantages of Sleeve Valves .................................................................. 10

2.2.4 Disadvantages of Sleeve Valves .............................................................. 12

2.3 Engine Modelling .......................................................................................... 13

2.3.1 Sleeve Valve Flow Coefficients ............................................................... 14

2.3.2 Sleeve Valve Area .................................................................................. 20

2.3.3 Heat Transfer in Small Engines ............................................................... 21

2.4 Conclusion .................................................................................................... 22

3. Initial WAVE Model ............................................................................................. 23

3.1 Determining the Port Positions ..................................................................... 23

3.2 Determining the Valve Areas......................................................................... 28

3.2.1 Initial Method of Calculation .................................................................. 28

3.2.2 Automated Method of Calculation ......................................................... 30

3.3 Valve Models ................................................................................................ 35

3.4 Intake Flow Path ........................................................................................... 38

3.4.1 Geometry .............................................................................................. 38

3.4.2 Heat Transfer ......................................................................................... 41

3.4.3 Junction ................................................................................................. 45

3.5 Engine Model ................................................................................................ 46

3.5.1 Engine Geometries ................................................................................ 46

3.5.2 Combustion Model ................................................................................ 50

3.5.3 Engine Heat Transfer ............................................................................. 50

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3.6 Exhaust Flow Path ......................................................................................... 57

3.6.1 Ducts ..................................................................................................... 57

3.6.2 Junction ................................................................................................. 59

3.7 Initial Results and Discussion ........................................................................ 60

3.8 Conclusion .................................................................................................... 65

4. Valve Discharge Coefficients with Computational Fluid Dynamics ....................... 67

4.1 Model Generation......................................................................................... 67

4.1.1 Model Layout ......................................................................................... 68

4.1.2 Valve Geometry ..................................................................................... 69

4.1.3 Gambit Models ...................................................................................... 70

4.1.4 Meshing ................................................................................................. 71

4.2 Simulation Specifications .............................................................................. 72

4.2.1 Solver Models ........................................................................................ 72

4.2.2 Boundary Conditions ............................................................................. 74

4.2.3 Convergence .......................................................................................... 75

4.3 Post Processing ............................................................................................. 76

4.4 Results and Discussion .................................................................................. 79

4.5 Conclusion .................................................................................................... 83

5. Experimental Facility ........................................................................................... 85

5.1 Assembly of Test Setup ................................................................................. 85

5.1.1 Belt Driven ............................................................................................. 86

5.1.2 Direct Coupling ...................................................................................... 87

5.2 Conclusion .................................................................................................... 89

6. Final WAVE Model ............................................................................................... 91

6.1 Changes from Initial Model ........................................................................... 91

6.2 Equivalent Poppet Valve Model .................................................................... 92

6.3 Results and Discussion .................................................................................. 94

6.3.1 Initial Model vs. Updated Model ............................................................ 94

6.3.2 Sleeve Valve Model vs. Poppet Valve Model .......................................... 96

6.4 Conclusion .................................................................................................... 99

7. Final Conclusion and Further Work.................................................................... 101

7.1 Conclusion .................................................................................................. 101

7.2 Recommendations for Further Work........................................................... 102

8. References ........................................................................................................ 104

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LIST OF FIGURES

Figure 1: VSC Core Engine (Hendrickson, 1999) ........................................................... 6

Figure 2: Sleeve Valve Motion ..................................................................................... 8

Figure 3: Various Sleeve Port Arrangements (Ricardo, 1931) ....................................... 9

Figure 4: Maximum Available Valve Areas (Ricardo, 1931) .......................................... 9

Figure 5: Cylinder “Junk” Head (Dardalis, 2004) ......................................................... 10

Figure 6: Typical Valve Flow Coefficient for Poppet Valves (Cole, 2006)..................... 15

Figure 7: Shape of Sleeve Valve Openings (Waldron, 1940) ....................................... 15

Figure 8: Cylinder of Waldron Experimental Engine (Waldron, 1940) ........................ 16

Figure 9: Flow Coefficients for Centre Inlet Valve (Waldron, 1940) ............................ 17

Figure 10: Flow Coefficient for Centre Valve at Different Openings (Waldron, 1940) . 18

Figure 11: Flow Coefficient for End Inlet Ports (Waldron, 1940) ................................ 18

Figure 12: Manifold Pressure with All Inlet Ports Open (Waldron, 1940) ................... 19

Figure 13: Flow Coefficient for Exhaust Valves (Waldron, 1940) ................................ 20

Figure 14: Valve Movement with Respect to Crank Angle (Hendrickson, 1999) ......... 21

Figure 15: Traced Sleeve Ports................................................................................... 24

Figure 16: Traced Cylinder Wall Ports ........................................................................ 24

Figure 17: Coordinate Points on Sleeve Port Profiles ................................................. 25

Figure 18: Coordinate Points on Cylinder Wall Port Profiles....................................... 25

Figure 19: Port Layout at 0° Crank Angle ................................................................... 26

Figure 20: Elliptical Motion of Sleeve ......................................................................... 26

Figure 21: X and Y Coordinates of Ellipse at Crank Angle α ........................................ 27

Figure 22: Curves Fitted to Points Describing Sleeve Port .......................................... 29

Figure 23: Points Describing the Sleeve Port Profile................................................... 31

Figure 24: Piston Movement with Crank Angle .......................................................... 33

Figure 25: Trapezoid from Adjacent Valve Opening Points ........................................ 34

Figure 26: Valve Areas Plotted Against Crank Angle ................................................... 35

Figure 27: Typical Input Page for Effective Valve Area ............................................... 36

Figure 28: Discharge Coefficients as taken from (Waldron, 1940) .............................. 37

Figure 29: Input Page for Valve Discharge Coefficient ................................................ 37

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Figure 30: WAVE Layout of Intake Flow Path ............................................................. 38

Figure 31: Inlet Manifold Duct and Cylinder Barrel .................................................... 39

Figure 32: Inlet Manifold Geometry .......................................................................... 39

Figure 33: WAVE Layout of Intake Including Heat Transfer Ducts .............................. 44

Figure 34: 3-D Layout of Y-Junction Element for Intake Manifold .............................. 46

Figure 35: Volumes for Compression Ratio Calculation .............................................. 48

Figure 36: Fin Geometry and Equations ..................................................................... 54

Figure 37: Efficiency of a Rectangular Annular Fin (Incropera & De Witt, 1996) ......... 56

Figure 38: Schematic of Exhaust Flow Path ................................................................ 58

Figure 39: 3-D Layout of Y-Junction Element for Exhaust Pipe ................................... 60

Figure 40: Brake Power and Torque Calculated with Initial Model ............................. 61

Figure 41: Volumetric and Thermal Efficiency Calculated with Initial Model .............. 61

Figure 42: Indicated and Brake Mean Effective Pressure Calculated with Initial Model

................................................................................................................................... 62

Figure 43: P-V Diagram Calculated with Initial Model at 4000 rpm ............................ 62

Figure 44: Effective Valve Areas for Initial Model ...................................................... 63

Figure 45: Mass Flows through Valves Calculated with Initial Model ......................... 64

Figure 46: Pressure Difference across the Valves ....................................................... 65

Figure 47: Layout of CFD Model................................................................................. 68

Figure 48: Indication of Valve Opening Profiles Simulated ......................................... 70

Figure 49: Solver and Viscous Model Input Pages of Fluent ....................................... 73

Figure 50: Centre Inlet Valve Discharge Coefficients .................................................. 79

Figure 51: End Inlet Valve 1 Discharge Coefficients.................................................... 80

Figure 52: End Inlet Valve 2 Discharge Coefficients.................................................... 81

Figure 53: (Waldron, 1940) End Inlets (left) vs. Experimental Engine End Inlets (right)

................................................................................................................................... 81

Figure 54: Exhaust Valve 1 Discharge Coefficients ..................................................... 82

Figure 55: Exhaust Valve 2 Discharge Coefficients ..................................................... 83

Figure 56: Experimental 4-Stroke Sleeve Valve Engine............................................... 85

Figure 57: Engine Belt and Pulley Layout ................................................................... 87

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Figure 58: Engine CV Joint Layout .............................................................................. 88

Figure 59: Engine Mountings ..................................................................................... 89

Figure 60: Updated Discharge Coefficient Input Page for Inlet Valve ......................... 91

Figure 61: Updated Discharge Coefficient Input Page for Exhaust Valve .................... 92

Figure 62: Valve Configuration for Poppet Valve Model ............................................ 93

Figure 63: Brake Power and Torque Calculated with Updated Model ........................ 94

Figure 64: Effective Valve Areas – Updated Model Left & Initial Model Right ............ 95

Figure 65: Valve Mass Flow Rates – Updated Model Left & Initial Model Right .......... 95

Figure 66: Brake Power and Torque Calculated with Poppet Valve Model ................. 96

Figure 67: Valve Effective Areas – Sleeve Valve Model Left & Poppet Valve Model

Right ........................................................................................................................... 97

Figure 68: Valve Mass Flow Rates – Sleeve Valve Model Left & Poppet Valve Model

Right ........................................................................................................................... 97

Figure 69: Brake Power of Sleeve and Poppet Valve Models ..................................... 99

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NOTATION

Variables

Variable Description

Speed of sound

Constants

Area

Flow coefficient

Discharge coefficient

Specific heat at constant pressure

Compression ratio

Diameter

Hydraulic diameter

Discretization length

Heat transfer coefficient

Height

Thermal conductivity

Connecting rod length

Mass flow rate

Length, lift

Number of fins

Nusselt number

Static pressure

Total pressure

Prandtl number

Wetted perimeter

Crank shaft radius, radius

Universal gas constant

Reynolds number

Surface area, fin and adjacent wall thickness

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Piston vertical position

Time, thickness

Temperature

Volume, velocity

Greek Symbols

Variable Description

Coordinates

Crank angle

Emissivity

Efficiency

Ratio of specific heats

Viscosity

Density

Sleeve angle

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1. INTRODUCTION

The automotive industry is a very contradictive industry in that the research and

development is driven by two conflicting factors. It is dictated by regulations and

legislations set out by governments, which at this point in time focuses on

environmentally friendly and safety driven vehicles. Direct consequences of these

focuses are vehicles with lower performance in order to emit less harmful exhaust

gasses and slower vehicles in order to be safer. However, the automotive industry is

dependent on its customers to survive financially and the customers desire faster

vehicles with ever increasing performance. It is therefore the task of the automotive

engineer to satisfy the customers while adhering to the regulations and legislations.

The reduction of carbon dioxide and other harmful exhaust gas emissions are very

important issues and consume vast amounts of research and development resources.

Various techniques are investigated and employed, and one of the techniques

currently being developed is “downsizing”. This consists of decreasing the engine

displacement in order to reduce the exhaust gas emissions. It is, however important to

maintain satisfactory performance and therefore boosting is usually employed with

downsizing.

Decreasing the engine displacement involves reducing the piston bore and stroke.

When reducing the piston bore, the diameter of the conventional poppet valves

subsequently also reduces, resulting in smaller air flow area and increased pumping

losses due to increasing friction of the flow and the surrounding surfaces. Decreasing

the air flow into the engine will reduce the amount of fuel that can be burnt per cycle,

thus, together with the increased pumping losses, reducing the engine performance.

One possible way to counter this problem is by using sleeve valves to facilitate the air

induction and exhaust gasses of the engine. However, sleeve valve engine design have

not enjoyed as much research and development as the poppet valve engine designs

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and problems with high harmful exhaust emissions, unwanted sleeve friction and

ineffective sealing still needs to be resolved before sleeve valve engines can be used

productively. The majority of the sleeve valve development occurred before the

1950’s, therefore before the widespread use of computer simulation software to

determine engine performance and optimize designs. The present study thus is aimed

at developing models for simulating sleeve valve engine using present engine

simulation software and an experimental 4-stroke sleeve valve engine. Attention will

also be paid to develop these models so that it could be utilized in simulation of

downsized engines employing sleeve valve engines. The software that will be used is

called WAVE. It is a 1-dimensional engine simulation package developed by Ricardo.

From the onset of the project the importance of accurately determining the sleeve

valve area was realised. Accompanying the sleeve valve areas are the discharge

coefficients that combine to produce the effective area of the valves. A major focus of

this report was to determine these two valve characteristics for an experimental sleeve

valve engine provided by Mahle for this study. A method of calculating the valve areas

from traced drawings of the port profiles are presented. Valve discharge coefficient

from available literature is presented as well as a set of simulated discharge

coefficients specifically characteristic to the valves of the experimental engine. These

coefficients were simulated using computational fluid dynamic (CFD) software.

It was planned to perform experiments with the engine and to use the experimental

results to calibrate the WAVE engine models. However, due to unforeseen

circumstances and the time constraint on this project, the experimental results did not

materialise, but still a chapter was dedicated to explaining the experimental setup and

lessons learned during the attempts to acquire these results.

Three WAVE models were developed and the results compared in order to gain

understanding into simulating sleeve valve engines. One model was done with

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discharge coefficients found in the open literature, one model with CFD derived

discharge coefficients and one model with poppet valves.

Finally conclusions were drawn and further recommended work discussed. This

project served as one in four projects performed on the particular sleeve valve engine.

The other projects address different parts of the engine and although the projects

were all separate, some information and knowledge were shared. The other projects

are (Chabert, 2007), (Franco Sumariva, 2007) and (Vasudevan, 2007).

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2. LITERATURE REVIEW

In order to gain a better understanding of sleeve valve engines, a literature review was

undertaken. It also serves as a tool in performing the project and identifies previous

work done in the relevant fields so that unnecessary duplication of work will be

avoided. The literature review firstly focuses on the topic of engine downsizing after

which the focus is shifted towards sleeve valve engines and then the modelling of this

type of engines. A few key modelling issues are identified and existing literature

assembled to aid in the understanding and completion of the task at hand.

2.1 ENGINE DOWNSIZING

One of the possible methods of reducing engine exhaust emissions while maintaining

sufficient performance is by downsizing the engine. The problem with current

production small engines is that they are not designed to meet any emission

regulations and fuel consumption is of low importance. These two factors, however,

are major design criteria for modern automotive engines.

Small engines show the tendency to produce low brake thermal efficiencies and (Lowi,

2003) describes a few causes for this. When downsizing an engine the surface to

volume ratio becomes an important design consideration. The smaller cylinder exhibit

higher heat transfer areas which could result in over cooling thereby impairing

effective combustion, but the cylinder head has the tendency to under-cool resulting

in excessive spark plug temperatures. The cooler cylinder walls do however reduce the

tendency for end gasses to auto ignite, allowing the use of higher compression ratios.

Downscaling of the cylinder results in viscous effects influencing the air stream and

causing small scale turbulence. This causes insufficient air/fuel mixture and flame

speeds which can be resolved by introducing large flow areas into the cylinder. This is

however difficult to achieve with conventional poppet valves, thus promoting the use

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of sleeve valves. (Yagi et al. 1970) also states that one of the major design

considerations to achieve high volumetric efficiency is to maximize the valve area in

order to increase engine breathing.

Furthermore, using carburetion with a short inlet manifold will cause incomplete

vaporization of the fuel (especially wide-boiling hydrocarbon fuels) resulting in

unburned fuel being passed through the engine causing high fuel consumption and

hydrocarbon emissions. Port- or direct fuel injection might solve this when high

atomization injection is used. These factors must be taken into account when

simulating and designing a downsized engine.

The design of the combustion chamber is one of the most important components in

designing a small engine. A high compression ratio and combustion speed is required

in order to maximize the thermal efficiency while flame travel and heat transfer must

be minimized so that higher indicated efficiency can be reached. Decreasing the travel

that the flame must undergo to engulf the end gasses will result in a higher usable

compression ratio. In order to ensure sufficient turbulence in the air flow into the

cylinder, the combustion chamber design in a small engine needs to promote swirl

motion of the air. Careful consideration is required not to invoke excessive turbulence

so that the flame kernel is extinguished before the fuel is burnt completely.

(Lowi, 2003) describes the design considerations for a combustion chamber of a small

cylinder engine and concluded that the design used by (Hendrickson, 1999) is

sufficient. This design consists of a small spherical open chamber with a spark plug

locater centrally with a small squish land on the cylinder perimeter. (Ricardo and

Company, 1947) also confirmed that decreasing the combustion chamber diameter

with the use of a squish land on the cylinder perimeter increases the swirl inside the

combustion chamber. This minimized the volume of the chamber as well as the flame

travel and the surface area. This arrangement however, deems it improbable to use

poppet valves and (Hendrickson, 1999) also describes using sleeve valves to overcome

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the lack of area in the combustion chamber to yield to the poppet valves. Figure 1

illustrates the so called “VSC core engine” by (Hendrickson, 1999). Note the

combustion chamber shape as described above and the lack of space for poppet valves

in the combustion chamber, necessitating the use of a sleeve valve.

Figure 1: VSC Core Engine (Hendrickson, 1999)

Turbocharging a downsized engine may lead to impractically small turbomachinery.

Too tiny components would have to run at too high rotational speeds resulting in low

Reynolds numbers which is not practical for manufacture and service. In these cases

positive displacement pumps would result in a more practical solution (Hendrickson,

1999).

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2.2 THE USE OF SLEEVE VALVE ENGINES

2.2.1 Brief History of Sleeve Valve Engines

In 1903 Charles Yale Knight designed the first sleeve valve engine. This sleeve valve

mechanism consisted of a double sleeve arrangement with reciprocating movement.

Six years later two separate designers filled patents for single sleeve valve mechanism

combining reciprocating and rotating movements to produce an elliptical path of valve

movement. These two inventers were Peter Burt and James H K McCollum (Wells).

Various sleeve valve engine designs enjoyed moderate success in the automotive

industry with the high production cost of the engines limiting their use to upmarket

vehicles. Sir Harry Ricardo noticed the sleeve valve engine and realized its potential as

a high performance aero engine. He performed much development work on sleeve

valve engines and many different sleeve valve design aero engines were employed

during the Second World War. Among them the Bristol Centaurus and the Napier

Sabre, two of the world’s most powerful spark ignition engines.

The sleeve valve engine was a very competent alternative to the poppet valve engine,

showing very high levels of performance for spark ignition engines and many other

advantages (as described in the subsequent sections). The advent of the jet engine in

the aero industry however, halted the use of the sleeve valve engine in that industry.

At that stage no other markets existed for very high performance spark ignition

engines and subsequently sleeve valve engines was lost to the world.

2.2.2 Sleeve Valve Operation

The sleeve is located between the cylinder wall and the piston. Port openings at

various locations along the cylinder wall serve as inlet and outlet passages. The sleeve

consists of a number of pie-shaped openings situated along its circumference. These

openings are aligned with the applicable ports in the cylinder wall at the appropriate

sectors in the intake and exhaust strokes, thereby creating inlet and outlet valves

respectively. The sleeve motion is produced by a gear driven cam connecting to the

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sleeve and delivering reciprocating as well as rotating motion to result in an elliptical

path being followed by the sleeve (Figure 2).

Figure 2: Sleeve Valve Motion

Various port arrangements are illustrated in Figure 3, with the subsequent maximum

valve areas available for some of these arrangements at different bore diameter

illustrated in Figure 4.

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Figure 3: Various Sleeve Port Arrangements (Ricardo, 1931)

Figure 4: Maximum Available Valve Areas (Ricardo, 1931)

At TDC the sleeve ports are above the “junk” head rings (Figure 5), effectively

shrouding the ports from the combustion chamber and protecting the ports from the

combustion gasses. This is however a place of concern when sealing is considered and

blow-by of gasses occur around these rings.

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Figure 5: Cylinder “Junk” Head (Dardalis, 2004)

2.2.3 Advantages of Sleeve Valves

Sir Harry Ricardo realised the potential of the sleeve valve engine as a high

performance aero engine, but described the following advantages of the general use of

sleeve valve engines (Lowi, 2003):

The spark plug could be located in the centre of the combustion chamber,

thereby minimizing the required flame travel to engulf all the charge in the

combustion chamber. This is also applicable to very small cylinder engines and

is exactly the design consideration required as described in Section 2.1. This

use of sleeve valves which permits the designer to optimize the combustion

chamber shape for desired combustion was also realized by (Hendrickson,

1999) and (Lowi, 2003).

The lack of high temperature resistant materials in the early part of the 20th

century caused problems for exhaust poppet valve design. The use of sleeve

valves eliminated problematic exhaust poppet valves while also eliminating the

source of unwanted auto ignition in the form of the hot exhaust valves. The

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absence of the hot exhaust valves subsequently allows for higher tolerable

compression ratios, thereby increasing engine performance.

The geometry and layout of the sleeve valve generates high levels of natural

turbulence (in the form of swirl) when the valves initially opens aiding in

air/fuel mixing and flame propagation. These high levels of swirl was studied

and documented by (Ricardo and Company, 1947).

The sleeve valve results in a breathing capacity (in other words flow area) at

least equal to that of any accommodated poppet valve arrangement and that

this larger valve area could be opened more rapidly than a poppet valve

counterpart.

The use of a sleeve valve mechanism results in a more compact and less

complex engine with a smaller frontal area.

Sleeve valve engines also showed higher mechanical efficiencies due to

reduced friction and lower actuation force of the valve train. The lower friction

also resulted in less wear of the engine components.

The sleeve valve ensures noiseless operation (Ricardo, 1931).

It is more robust than the poppet valves and requires less attention.

Opposed to the sleeve valve, (Yagi et al. 1970) describes abnormal valve motion of

poppet valve trains as a major obstacle in high speed engines. The rigidity and the

inertia of the valve train is a source of loss in the engine, reducing the volumetric

efficiency. Sleeve valves reduce these mechanical losses due to a lower power

consumption of the valve train.

One of the limitations on engine speed of a normal poppet valve engine as pointed out

by (Lumley, 2001) is valve float. This happens when the engine speed becomes too

high, and the valve spring is not strong enough to prevent the valve from breaking free

from the cam profile. When using a sleeve valve, this limitation in engine speed is

eliminated entirely, because the sleeve valve is operated by a fixed cam and not

controlled by a spring.

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At first it was believed that the extra surface contact areas between the piston and the

sleeve, and the sleeve and the cylinder wall would increase mechanical friction,

thereby reducing engine performance. However, according to (Dardalis, 2004)

experiments have shown that the total friction of the sleeve valve was “usually lower”

than conventional poppet valve designs, believed to be due to the rotary movement of

the sleeve.

The maintanance records of over 60 000 sleeve valve engines used during the war

suggested the absence of localized cylinder wear paterns, observed in engines without

the resiprocating sleeve valve, and 10 times lower overall bore wear (Dardalis, 2004).

The wear was so low that it did not determine the engine life as was the case in more

conventional engines. Unfortuanately the major manufacturers at the time, Bristol

and Napier, was more conserned about engine performance than cylinder wear (or

lack thereof in this case) and very little effort was spent on quantifying this benefit.

According to (Dardalis, 2004), the sleeve valve engines illustrated high values of BMEP

and the engines could be maintained indefinitely at these peak pressures rather than

only 15 minutes as the poppet valves was limited to.

Sleeve valve engines are relatively insensitive to high exhaust pressures because of the

increased exhaust valve area allowing quick discharge of exhaust gasses through the

exhaust ports. This results in ideal conditions for using a turbocharger with the sleeve

valves.

2.2.4 Disadvantages of Sleeve Valves

Sleeve valve engines were developed at a stage where emission control was absent,

and therefore the current design of these engines will not meet modern emission

regulations. The extra set of ring in the junk head attribute to higher hydrocarbon

emissions by trapping fuel and preventing it from combusting during the combustion

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process. These stationary rings in the junk head also cause sealing problems and

subsequent blow-by is observed. This will cause inaccuracies in engine simulations and

therefore the blow-by must be accounted for in the engine model.

The piston movement can restrict the port area when a short stroke is employed.

Furthermore, the sleeve hampers heat dissipation of the piston to the cooling capacity

of the cylinder wall. This justifies research into sleeve materials that would allow

increased heat transfer from the piston.

Companies like Rolls Royce started developing high performance sleeve valve engines

and experimental ultra-high performance 2-stroke sleeve valve engines for aero

applications. However, the advent of the jet engine in the aero industry halted the

production of these engines as well as further development of sleeve valve engines.

2.3 ENGINE MODELLING

“Design refers to a situation where the characteristics of a system must be specified so

that it will enable execution of specific functions at an acceptable level of

performance. Simulation on the other hand generally refers to a situation where the

characteristics of the system are known and models must be set up to predict its

functionality and performance level” (Rousseau, 2002).

The goal of this study is to simulate the sleeve valve engine in order to be able to use

the simulations to optimize the design. To do this, known models must be employed

to accurately predict the performance so that effective optimization can be done. The

level of complexity of the simulations will be dictated by the available models for

different simulated sections of the entire engine. The thermal fluid flow through the

engine ducting will for instance be modelled with theoretical models based on

fundamental principles. The flow through the valves can also be modelled with

theoretical principles (approximated with orifice flow), but empirical correlations

determined experimentally should produce more accurate results, as observed by

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(Waldron, 1940). The theory is not always completely understood and in such

scenarios empirical model must be used to acquire accurate results.

The sleeve valve engine will be modelled using the Ricardo WAVE software package.

This software is used by many automotive companies and research institutions

(Farrugia, 2004). It is a 1-dimensional simulation package which combines accurate

general model simulations with improved simulation time compared to 3-dimensional

CFD simulations.

2.3.1 Sleeve Valve Flow Coefficients

The major fundamental difference between the poppet valve and the sleeve valve

engines is the airflow into and out of the cylinder. Therefore, the major difference in

the modelling of these two types of engines will be the modelling of the valves. The

fact that the pressure drop across the valves has a significant influence on the engine

performance deems it necessary to accurately model the flow coefficients across the

valves. Figure 6 illustrates a typical flow coefficient curve for normal poppet valves as

a function of the valve lift used in the valve model of Ricardo WAVE. It is therefore

necessary to acquire a similar flow coefficient curve for sleeve valves.

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Figure 6: Typical Valve Flow Coefficient for Poppet Valves (Cole, 2006)

A first method of obtaining such a flow coefficient curve for a sleeve valve is to search

the open literature. This was done and a 1940 NACA report (Waldron, 1940) was

obtained describing the construction of flow coefficients for sleeve valves. The author

used an experimental setup which employed a very similar sleeve valve arrangement

as the engine being used for the present study. In both cases a single sleeve is used

with an elliptical path consisting of 3 inlet valves and 2 exhaust valves.

Figure 7: Shape of Sleeve Valve Openings (Waldron, 1940)

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Figure 7 illustrates the shape of the sleeve and cylinder ports that was used in the

experimental engine of Waldron. Figure 8 illustrates the cylinder and port

arrangement. The experimental engine of the present study consist of a very similar

setup, with three inlet ports spread across 180° of the cylinder and the two exhaust

ports located in the remaining half of the cylinder wall. The inlet duct is also aligned

with the one centre port after which it branches to the two end ports resulting in the

inlet flow entering the end ports tangentially.

Figure 8: Cylinder of Waldron Experimental Engine (Waldron, 1940)

Waldron describes the experimental setup and methods used in measuring the

pressure drop as well as the assumptions made during the entire process and the

claimed accuracy of the results. He calculates the flow coefficient as a function of the

pressure across the valves and it is presented in the following equations.

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(1)

(2)

Waldron’s results are illustrated for the different valves in the following figures.

Figure 9: Flow Coefficients for Centre Inlet Valve (Waldron, 1940)

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Figure 9 illustrates the flow coefficients for the centre inlet valve for different

approaching flow field conditions. It can be seen that the flow coefficients are quite

high (>0.8) and that they are independent of approaching flow field conditions. It

should be noted that Waldron ensured that inlet manifold acoustics did not influence

the results.

Figure 10: Flow Coefficient for Centre Valve at Different Openings (Waldron, 1940)

Figure 10 illustrates the flow coefficients for the centre inlet valve for different valve

openings, showing that the flow coefficients are independent of the valve opening.

Figure 11: Flow Coefficient for End Inlet Ports (Waldron, 1940)

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Figure 11 illustrates the flow coefficients of the end inlet valves. Although they are

lower than that of the centre inlet valve (0.62 – 0.78), the flow coefficient still seems to

be high.

Figure 12: Manifold Pressure with All Inlet Ports Open (Waldron, 1940)

Figure 12 illustrates the pressure in the inlet manifold just upstream of the respective

valves in the case where all the inlet valves are opened simultaneously. It shows that

when the valves are fully open, the pressure just upstream of the end valves are lower

than that just upstream of the centre valve, indicating a pressure drop as a result of

the flow curvature.

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Figure 13: Flow Coefficient for Exhaust Valves (Waldron, 1940)

Figure 13 illustrates the flow coefficients for the exhaust valves at different valve

openings. It is clear that the flow coefficients are independent of valve opening.

These results seem to be very useful for developing a model for simulating the sleeve

valves. However, careful consideration must be done to ensure that the definition of

the flow coefficients as calculated by Waldron is exactly the same as the definition of

the flow coefficients used to describe the eventual valve model. This process will be

described in a later Section where the valve model will be described in detail.

2.3.2 Sleeve Valve Area

The area of the sleeve valves as a function of the crank angle together with the flow

coefficients described in the previous section is used to calculate the flow through

these valves. There is no exact equation for calculating the area for the sleeve valve

areas and therefore the drawings and physical measurements of the experimental

engine will be used to determine the areas graphically.

Figure 14 illustrates the valve movement presented as flow area with respect to crank

angle for the VSC core engine of (Hendrickson, 1999). It shows the upwards

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movement of the piston covering the ports, resulting in a reduced flow area. This must

be considered when calculating the valve areas of the experimental engine being used

in this study.

Figure 14: Valve Movement with Respect to Crank Angle (Hendrickson, 1999)

2.3.3 Heat Transfer in Small Engines

The increased heat transfer area in small engines causes cooler cylinder walls. This

heat transfer phenomena of the small bore engines can adversely affect the efficiency

and torque and must subsequently be taken into consideration when simulating and

designing engine performance of a downsized engine (Lowi, 2003).

In the design process of a small cylinder sleeve valve engine, (Lowi, 2003) used the

following models that influence the combustion process:

Fuel properties and mixture as well as unburned mixture and residual gas

fractions.

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Geometry of the combustion chamber including spark plug location and surface

to volume ratio.

Heat transfer characteristics which are based on the mean velocity, a measure

of the turbulence and the swirl ratio.

These suggested models will be taken into account when preparing the final models

for the engine simulations and will therefore be described in more detail in subsequent

sections.

2.4 CONCLUSION

In this review, a brief description of the sleeve valve engine was given as well as some

comments on the downsizing of spark ignition engines. It was found that the sleeve

valve engine consists of many advantages and therefore justifies a closer inspection.

The fact that the current designs of sleeve valve engines will not meet the modern

emission regulations, together with the advantages of the sleeve valve engines justifies

research into minimizing the emissions of these engines. It was also shown that sleeve

valve engines present a plausible solution for maintaining sufficient breathing for

downsized engines.

With this in mind and the lack of sleeve valve simulation models due to the halted use

of these engines in the non-computer age necessitates the need for accurate

performance prediction models to aid in sleeve valve engine optimization. The major

simulation difference between poppet and sleeve valve engines will be the valve flow

models. Sleeve valve flow coefficients for a very similar sleeve valve was found and

described, but the detail description of the valve model will be described in further

sections of this report. For these models the valve areas of the experimental engine

must be determined and the flow coefficient described in this literature review must

be adapted to serve in the WAVE software.

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3. INITIAL WAVE MODEL

The main aim of this project is to model the 4-stroke sleeve valve engine. This will be

done with specialised engine simulation software called WAVE, being developed by a

company called Ricardo. The software is a 1-dimensional fluid simulation package,

which uses model elements to represent certain parts of typical engine components.

The detail theory behind the models will not be addressed as it comprises mostly of

widely published thermal fluid mechanics.

An initial engine simulation was needed in order to use the experimental data to

calibrate the model. In order to develop an initial WAVE model, various geometries

were needed from the engine. As the engine was available for testing, the engine was

taken apart before any testing was done, to acquire the required geometrical

dimensions. The most important geometries needed for the WAVE model is any

geometrical dimensions determining the flow path of air and exhaust gas through the

engine. The sleeve valve port openings are very important geometries and special care

was taken to acquire these values because of their rather arbitrary and complex

shapes.

This chapter explains the determination of acquiring the sleeve valve flow areas as well

as initial sleeve valve flow coefficients and the subsequent development of an initial

WAVE model.

3.1 DETERMINING THE PORT POSITIONS

With the engine taken apart, the ports in the sleeve as well as the ports on the inside

of the cylinder wall were exposed. There are five ports in the cylinder wall, being one

centre inlet port, two end inlet ports and two exhaust ports. The sleeve has four ports,

as two ports overlap the inlet cylinder wall ports; one overlaps an exhaust cylinder wall

port and the final sleeve port overlapping an inlet and exhaust cylinder wall port.

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The shape of the both sets of ports was captured by fixing a sheet of paper around the

sleeve and around the inside of the cylinder respectively and tracing the particular port

shapes with a pencil. Great attention was paid to obtaining accurate copies of the

shapes and two copies of both sets of ports were made and compared in order to

ensure repeatability of the copying process. Both copies produced the same port

profiles and it was therefore assumed to be sufficiently accurate and repeatable.

Scaled down pictures of the traced sleeve ports and of the cylinder ports are presented

in Figure 15 and Figure 16 respectively.

Figure 15: Traced Sleeve Ports

Figure 16: Traced Cylinder Wall Ports

The next step was to copy these images onto graphical paper in order to determine

coordinates for various points on the profiles of the ports. The profiles were copied

onto the graphical paper and many points along the ports’ shapes were identified so

that the coordinates of these points would describe the respective port shapes.

Figure 17 and Figure 18 illustrates these coordinate points for the sleeve and cylinder

wall port profiles respectively.

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Figure 17: Coordinate Points on Sleeve Port Profiles

Figure 18: Coordinate Points on Cylinder Wall Port Profiles

The X and Y coordinates of all the various points as they occur on the graphical paper

were read into and Excel spreadsheet and X and Y offset values were added in order to

replicate the positions of the port openings at top dead centre (TDC) for the start of

the combustion stroke (assumed as 0° crank/cycle angle). The origin of the Y-axis was

selected to be the outer rim of the piston at bottom dead centre (BDC) and the origin

of the X-axis was selected to be between the centre inlet wall port and one of the end

inlet wall ports. This position was marked on the traced drawings of the sleeve and

cylinder wall ports in order to obtain the correct X offset values. The circumference of

the sleeve outside diameter and the cylinder inside diameter were “rolled out” on the

X-axis, and therefore the X-axis stretched from 0 mm to approximately 278 mm (sleeve

outside diameter ≈ 89 mm). Figure 19 illustrates the positioning of the various ports at

0° crank angle as reproduced in the Excel workbook. Note the horizontal line

representing the piston at TDC.

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Figure 19: Port Layout at 0° Crank Angle

The procedure described above produced the port positioning of all the ports at TDC.

To determine the port positions at any given crank angle, the port coordinates at TDC

was used as the base coordinates whereby dynamic X and Y offset values would be

added for a certain crank angle. These offset values are determined by the sleeve

motion produced by the rotation of the crank shaft.

Figure 20: Elliptical Motion of Sleeve

(3)

60

80

100

120

140

160

180

0 50 100 150 200 250

Wall Port 1 (End Inlet) Wall Port 2 (Exhaust) Wall Port 3 (Exhaust) Wall Port 4 (End Inlet) Wall Port 5 (Centre Inlet)

Combined Sleeve Port Exhaust Sleeve Port End Inlet Sleeve Port Centre Inlet Sleeve Port Piston

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The mechanism driving the sleeve produces an elliptical motion of the sleeve as

illustrated in Figure 20. The X and Y offset values can therefore be calculated with the

equation describing an ellipse as presented in Equation (3).

Figure 21: X and Y Coordinates of Ellipse at Crank Angle α

Figure 21 illustrates the sleeve at crank angle α (coordinates (x,y)), which represents

sleeve angle θ, with the sleeve angle being half that of the crank angle. The sleeve at

TDC is located at the upper most point on the ellipse (coordinates (0,a)). This leads to

an X value as function of the sleeve angle as calculated by Equation (4) and a Y value as

a function of the X value as calculated by Equation (5).

(4)

(5)

X

Y

θ

a

b

y

x

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The values of x and y is subsequently adapted to produce the values for the X and Y

offsets and added to the base X and Y values of the sleeve at TDC in order to locate the

sleeve ports at any given crank angle, α.

3.2 DETERMINING THE VALVE AREAS

In order to correctly simulate the flow through the engine the valve areas must be

known throughout the 720° crank angle cycle. Therefore the valve areas must be

calculated for every crank angle. This can be done by tracing the overlapping sleeve

and cylinder wall port profiles onto a piece of graphical paper and counting the square

millimetre blocks confined within the traced port outline. However, as this must be

done for all five valves at 720 different crank positions, it will result in a very time

consuming and inaccurate process due to the difficulty in correctly tracing the

overlapping port shapes in the confined space of the cylinder. It was subsequently

decided to use the coordinates of the sleeve and cylinder wall ports as determined in

the previous section to calculate the valve areas for all 720° crank angles.

3.2.1 Initial Method of Calculation

At first it was thought to perform “curve fitting” to various sections of the coordinated

points identified in the port profiles and then to determine the integral of these curves

over their various ranges of applicability and finally to add these areas in order to

obtain the total area of a certain port. Figure 22 illustrates the curves fitted and their

accompanied equations to eight different zones identified around the sleeve port

profile.

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Figure 22: Curves Fitted to Points Describing Sleeve Port

A number of problems arose with this method however. Firstly, the equations for the

curves changes with every change in crank angle (subsequent change in position) and

therefore the integrals must be repeated for every crank angle, resulting in a very

laborious and time consuming process. Secondly, when the ports overlap, the exact X

coordinates where the port profiles overlap are unknown and hence the ranges of the

applicable integrals are unknown, resulting in incorrect calculations of the areas.

Finally, because the curve fittings are just a mathematical approximation, the curves

does not exactly represent the various profiles, resulting in inaccurate calculation of

y = 0.045x3 - 7.623x2 + 424.2x - 7747.y = 120.4

y = -0.016x3 + 1.527x2 - 47.75x + 617.9

y = 3.331x + 45.36

y = 0.5x + 143.2y = -0.003x2 + 0.303x + 154.5

y = -0.165x2 + 15.69x - 210.0

y = -0.124x2 + 10.40x - 47.03

110

120

130

140

150

160

170

0 20 40 60 80

1

2

3

4

5

6

7

8

Poly. (1)

Linear (2)

Poly. (3)

Linear (4)

Linear (5)

Poly. (6)

Poly. (7)

Poly. (8)

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the area. This was realised when the area of the port shown in Figure 22 was

calculated using the method described above. This value was compared to the area

determined by counting the square millimetre blocks on the graphical paper for the

sleeve port in question. Although counting the blocks is also a time consuming

process, it is very accurate and the area calculated using this method resulted in

approximately 1200 mm² compared to an area of roughly 1400 mm² calculated with

the curve integrals. This confirms the need for a more accurate, generic and quicker

method of calculating the port areas.

3.2.2 Automated Method of Calculation

The points identified on the port profiles are located so that when the points are

connected with a straight line it would still yield a very similar profile as the actual

shape. On curved parts of the profiles the points are highly populated and on

straighter parts the points are more sparsely populated. The region between two

adjacent points could therefore be approximated with a straight line and the area can

easily be calculated as the area of a trapezoidal, being the area from the X-axis to the

straight line for the range on the X-axis.

The port area is subsequently obtained by subtracting the area of the bottom part of

the port profile from the area of the top part of the profile. However, this procedure

works well only when calculating the area of an entire port. Problems arise however,

when the sleeve port and the cylinder wall port overlap and only a certain part of each

profile must be taken into account and the exact points of overlap is unknown. To

overcome this problem, the entire range of each port on the X-axis was divided into

0.25 mm sections. New points were created by linearly interpolating between

adjacent points in order to have points at every 0.25 mm intervals. The linear

interpolation was done by Equation (6) where (x1,y1) and (x2,y2) are two original

adjacent points and (x,y) is the newly created points with at intervals of

0.25 mm.

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(6)

Figure 23 illustrates the original points describing one of the sleeve port profiles

together with the linearly interpolated added points at 0.25 mm intervals. This

procedure was done for all the cylinder wall ports as well as for the sleeve ports.

Subsequently, the biggest interval in X values is 0.25 mm resulting in a very small

potential error in determining the exact point of intersection in the case of port

overlap.

Figure 23: Points Describing the Sleeve Port Profile

The coordinates of the cylinder wall ports remain unchanged when the crank angle

changes, but as described in the previous section, the sleeve port coordinates change.

The procedure of adding points at every 0.25 mm interval on the X-axis was done for

the sleeve ports as well and it is subsequently easy to determine the points of

intersection between the wall and sleeve ports to within 0.25 mm.

120

125

130

135

140

145

150

155

160

165

24 29 34 39 44 49 54 59

Y-A

xis

X-Axis

Original Points Added Points (0.25mm Intervals)

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This results in the range of X values where the wall and sleeve ports overlap being

known, as well as the Y values accompanying these X values, so that the area of the

open valve can be calculated. However, the issue of whether the piston will mask the

valve area at certain crank angles is still unattended. As illustrated by (Hendrickson,

1999) the piston movement covered the valve openings when moving up to TDC in the

exhaust stroke and moving down from TDC in the intake stroke, effectively reducing

the valve areas. An equation presented by (Bosch, 2004) was used to describe the

piston movement and an appropriate Y offset value was added in order to ensure the

piston is at Y = 0 at BDC. The equation for the piston movement is given by

Equation (7).

(7)

The resulting piston movement is presented in Figure 24. A horizontal line was added

to the port coordinates and taken into account when determining the Y values for the

valve opening.

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Figure 24: Piston Movement with Crank Angle

Finally all the necessary data are available to calculate the valve opening area. This

includes the range of X values at which a cylinder wall port and its associating sleeve

port overlap, as well as the accompanying Y values that describes the open part of the

overlap. These Y values also include the presence of the piston where applicable. It

was decided to use the equation for calculating the area of a trapezoid because two

adjacent X values and their respective two associated Y values are situated in the form

of a trapezoid as illustrated in Figure 25. The equation is presented in Equation (8) and

Figure 25 also illustrates the definitions of the terms used in the equation.

(8)

0

10

20

30

40

50

60

70

80

90

0 100 200 300 400 500 600 700

Y-A

xis

[mm

]

Crank Angle [deg]

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Figure 25: Trapezoid from Adjacent Valve Opening Points

All the small trapezoid areas describing each valve opening were added together to

produce the total valve opening for each valve. This was done at all the crank angles

for 1 full cycle (0° to 720°) and plotted to produce Figure 26. Note the sudden drop-

offs in the range between 300° to 400° due to the piston masking the valve openings.

91

92

93

94

95

96

97

98

99

100

48.2 48.25 48.3 48.35 48.4 48.45 48.5 48.55

Y -

Axi

s

X - Axis

(x1t,y1t)

(x1b,y1b)

(x2t,y2t)

(x2b,y2b)

Δy1 Δy2

Δx

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Figure 26: Valve Areas Plotted Against Crank Angle

3.3 VALVE MODELS

The WaveBuild software has a number of options available to specify the valve models

with. Unfortunately, there are no models which are directly applicable to sleeve valves

and it was subsequently decided that the best alternative would be to use the effective

area valve model. This model requires the valve area as function of the crank angle, a

diameter and the valve flow coefficients as function of the pressure ratio across the

valve and the valve lift.

As described in the previous section, the valve area was determined as function of the

crank angle. The area data was entered into a file in the format as specified by the

WAVE user manual for valve effective area files. These files were then specified as the

areas for the various valves leading to input pages similar to the one presented in

Figure 27. Notice that WAVE automatically converts the effective area to valve lift

values.

-100

0

100

200

300

400

500

600

700

800

900

0 100 200 300 400 500 600 700 800

Are

a [m

m^

2]

Cycle Angle [deg]

End Inlet 1 Valve Area [mm^2] Exhaust 1 Valve Area [mm^2] Exhaust 2 Valve Area [mm^2]

End Inlet 2 Valve Area [mm^2] Centre Inlet Valve Area [mm^2]

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Figure 27: Typical Input Page for Effective Valve Area

The valve diameter is used to convert the effective area plot to a valve lift plot

, plotted against crank angle. In the simulations this will be converted

back to an effective area and therefore, any reasonable diameter can be used, as long

as it is used consistently. For the initial model, all the valve diameters were specified

as 20mm.

This leaves only the discharge coefficients to be determined. Due to the fact that this

is an initial WAVE model, it was decided that the coefficients as described in Section

2.3.1 will be sufficient. Discharge coefficient determined from the figures presented

by (Waldron, 1940) was copied into a file with the format of the file as specified by the

WAVE user manual for valve discharge coefficient files. These files were then specified

in the WAVE model as the discharge coefficients for the various valves. Figure 28

illustrates the coefficients used. Notice only one profile per valve, as (Waldron, 1940)

concluded that very similar coefficients were acquired for different valve openings.

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Figure 28: Discharge Coefficients as taken from (Waldron, 1940)

These discharge coefficients were entered as a function of the pressure ratio and

repeated for two different valve lifts, one small lift value (0.1 mm) and one large lift

value (15 mm), resulting in a typical input page presented in Figure 29 (centre inlet

valve in this case).

Figure 29: Input Page for Valve Discharge Coefficient

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.0000 1.5000 2.0000 2.5000 3.0000 3.5000 4.0000 4.5000

Dis

char

ge C

oe

ffic

ien

t

Pressure Ratio

Centre Inlet Valve End Inlet Valves Exhaust Valves

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3.4 INTAKE FLOW PATH

The flow path of the intake system comprises of an inlet pipe, throttle valve of the

carburettor and then the inlet manifold leading into the three inlet valves. The inlet

pipe and the inlet manifold are modelled using duct elements and these two parts are

joined by a Y-junction element. The throttle is specified as an orifice, splitting the inlet

pipe into two sections before entering the junction element. A fuel injector is also

added to the second part of the inlet pipe to facilitate fuel delivery to the system. The

injector was set to deliver an air fuel ratio (AFR) of 14.7, thereby assuming

stoichiometric combustion. This layout is presented in Figure 30.

Figure 30: WAVE Layout of Intake Flow Path

3.4.1 Geometry

The carburettor is connected to an inlet manifold. The manifold comprises of a C-

shaped steel ducting that bolts over the exposed ports in the cylinder wall. This

ducting directs the flow towards the three inlet ports which are situated at roughly 90°

intervals around the barrel. The area around the ports is cleared of cooling fins in

order for the ducting to attach onto the outside of the cylinder barrel. The side of the

manifold connecting to the barrel is open, thus using the barrel as one of the sides

enclosing the inlet flow path. Figure 31 illustrates these components.

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Figure 31: Inlet Manifold Duct and Cylinder Barrel

The geometry of the inlet manifold duct therefore defines the flow path of the air and

it is graphically presented in Figure 32, showing the main dimensions. Inside the

ducting there are no obstructions and the air is free to move undisturbed. The

curvature of the flow around the barrel to the two end inlet valves are supported by

slopping cut-out sections into the barrel to maximize the flow area.

Figure 32: Inlet Manifold Geometry

191

139

26 26

30

30

15

9

0

Ø38

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As illustrated in Figure 30 the inlet flow path will be modelled by using duct, orifice and

Y-junction elements. The input geometrical values for the various duct elements are

taken from Figure 32, with the carburettor having the same diameter as the pipe it

connects to. The two pipes leading to the two end inlet valves are noncircular and

therefore the hydraulic diameter equation (Equation (9)) was used to determine the

input diameter values for the ducts.

(9)

The resulting geometrical input values for the ducts of the intake system are presented

in Table 1. It should be noted that the friction multiplier for the three ducts leading to

the inlet valves are set at 0, implying no pressure loss due to friction. This is done

because the pressure loss due to friction is already taken into account in the discharge

coefficients of the valves.

Table 1: Geometrical Input Values for Intake Flow Path Ducts

Left

Dia

me

ter

[mm

]

Rig

ht

Dia

me

ter

[mm

] D

iscr

etiz

atio

n

[mm

]

Ove

rall

Len

gth

[m

m]

Ben

d A

ngl

e

[deg

]

Fric

tio

n

Mu

ltip

lier

Hea

t Tr

ansf

er

Mu

ltip

lier

Carb1 38 38 15 100 0 1 1

Carb2 38 38 15 15 0 1 1

DuctEI1 33.53 30.875 15 90 90 0 1

DuctCV 38 38 15 10 0 0 1

DuctEI2 33.53 30.875 15 90 90 0 1

The discretization lengths were calculated with an equation given in the WAVE user

manual, Equation (10). The manual suggests using this equation to calculate the

discretization size in order to acquire the best compromise between accuracy and

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computing time, as minimizing the discretization length will increase the accuracy but

also increase the computing time.

(10)

with

where is the engine speed in revolutions per minute, and is the speed of sound.

As the engine will probably not be ran above 6000 rpm, it was decided to calculate the

discretization for this speed and subsequently it will be sufficient for lower speeds.

This resulted in a discretization of approximately 15 mm.

3.4.2 Heat Transfer

Heat transfer inherently implies the transfer of heat from a medium which consist of

heat to a medium which consists of less heat. This phenomenon is therefore driven by

a difference in heat between two mediums which imply a temperature difference

between the two mediums. The three methods of heat transfer are convective,

conductive and radiation heat transfer. All these methods rely on a temperature

difference between two mediums and a higher temperature difference implies higher

heat transfer.

Consider the intake system, remembering that this is a normally aspirated engine.

Therefore, the temperatures throughout the intake system will be at a similar

temperature as the ambient surrounding temperature. Subsequently very little heat

transfer will take place and it was therefore decided not to simulate heat transfer in

the intake system. However, it was realised that a part of the two intake ducts leading

to the end inlet valves are directly in contact with the cylinder barrel which will be at a

considerably higher temperature as the ambient temperature and thus a significant

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amount of heat transfer will take place. It is hence imperative that the heat transfer in

these two ducts is simulated.

A first thing to notice is that the heat transfer multipliers as specified in Table 1 in the

previous section are all set to 1, even for the ambient temperature intake ducts. The

heat transfer calculated in that case is convective heat transfer between the fluid

stream in the duct and the boundary layer. Due to the friction between the boundary

layer and the duct wall it was decided to consider this convective heat transfer.

However, the conductive and radiation heat transfer of the ambient inlet ducts will be

ignored, but these heat transfer terms will be included in the analyses of the two ducts

which are in contact with the cylinder barrel.

A problem arises when attempting to activate the conduction and radiation heat

transfer to the two ducts which are in contact with the cylinder barrel. The problem is

that only one side of the duct is connected to the hot cylinder barrel and if the

geometries of theses ducts remain as they are specified in Table 1, excessive heat

transfer will take place due to the heat transfer area (the outside area of the duct)

being larger than the actual heat transfer area (only the one side). Thus, a way must

be found to decrease the heat transfer area without affecting the pressure loss and

mass flow rate through these ducts or their acoustic behaviour. In order to keep the

mass flow rate in tact the same diameters must be used as specified in the table. As

far as the pressure loss is concerned, altering the length of the ducts will not affect the

pressure loss, because the pressure loss of these ducts is already accounted for in the

discharge coefficients of the valves. Therefore, the length and thickness of these ducts

can be altered in order to accurately specify the heat transfer area. The thickness has

no affect on either the mass flow rate or pressure loss.

Unfortunately, altering the length of the pipe will affect the acoustic pressure wave in

the duct and ultimately the effective mass flow rate. It was subsequently decided to

divide each of the two intake ducts that lead to the end inlet valves into two separate

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ducts. The combined length of these two ducts will be the same as the geometrical

length of the duct, one of the ducts will model conduction and radiation heat transfer

while the other duct will model the convective heat transfer.

In order to calculate the input values the area and volume of the duct with conduction

and radiation must be equal to the area of the cylinder barrel that is in contacts with

the flow and the volume of that part of the barrel. According to the engine drawings,

that part of the barrel is roughly a block of 50 mm long, 38 mm high and 25 mm deep.

The contact area is only one face in the length and one face in the depth of the block.

Assuming that this duct will be placed adjacent to the valve, the diameter of the duct

will be 30.875 mm as presented in Table 1. Therefore,

and

thus

and

Solving these equations simultaneously leads to a duct length, , of 14.13 mm and a

thickness, , of 16.67 mm and a new length of the accompanying duct of 75.87 mm.

The new input values for these ducts are presented in Table 2 and the layout is

presented in Figure 33.

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Figure 33: WAVE Layout of Intake Including Heat Transfer Ducts

The cylinder barrel is a cast aluminium, air cooled cylinder block. (Incropera & De Witt,

1996) provides the following properties for cast aluminium:

Density – ρ = 2790 *kg/m³+

Specific heat – cp = 883 [J/kg.K]

Thermal conductivity – k = 168 [W/m.K]

Emissivity – ε ≈ 0.8

This leads to a heat capacity of roughly 2.46 x 106 [J/m³.K]. The temperature of the

cylinder barrel was assumed to be 400K, but should be calibrated once experimental

data becomes available.

Table 2: Input Values for Intake Heat Transfer Ducts

DuctEI1 DuctHTEI1 DuctEI2 DuctHTEI2

Left Diameter

[mm] 33.53 30.875 33.53 30.875

Right Diameter

[mm] 30.875 30.875 30.875 30.875

Discretization

[mm] 15 14.13 15 14.13

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DuctEI1 DuctHTEI1 DuctEI2 DuctHTEI2

Overall Length

[mm] 75.87 14.13 75.87 14.13

Bend Angle [deg] 90 0 90 0

Friction Multiplier 0 0 0 0

Heat Transfer

Multiplier 1 0 1 0

Outer Wall

Thickness [mm] - 16.67 - 16.67

Heat Capacity

[J/m³.K] - 2.46 x 106 - 2.46 x 106

Conductivity

[W/m.K] - 168 - 168

Convective Field

Temperature [K] - 400 - 400

Radiation Field

Temperature [K] - 400 - 400

Emissivity - 0.8 - 0.8

3.4.3 Junction

The modelling of the intake flow path consists of a Y-junction model that connects the

inlet pipe, following the carburettor throttle valve, and the three inlet manifold ducts.

A Y-junction element was used and specified with a diameter of 38 mm. The friction

and heat transfer multipliers were specified as 1 to account for the friction and

convection heat transfer, but because the junction does not contact any part of the

hot cylinder barrel, the conduction and radiation heat transfer were omitted. The

junction openings were set up as presented in Figure 34.

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Figure 34: 3-D Layout of Y-Junction Element for Intake Manifold

3.5 ENGINE MODEL

The engine model comprises of the basic engine geometries, combustion model and

heat transfer specifications. It is therefore only logical to divide this section into these

subsections.

3.5.1 Engine Geometries

The engine geometries were measured on the engine drawings and verified with the

measurements on the actual engine. The geometry tab of the engine model window

was subsequently populated with the values presented in Table 3.

Table 3: Engine Geometry Inputs

Variable Name Value Units

Number of cylinders 1 -

Strokes per cycle 4 -

Engine type Spark ignition -

Bore 85 mm

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Variable Name Value Units

Stroke 84.5 mm

Connecting rod length 171 mm

Wrist pin offset 0 mm

Clearance height 21 mm

The friction correlation constants were specified with the default values as no

numerical data on sleeve valve friction could be obtained. This is sufficient for the

initial WAVE model, but the friction model needs to be correlated with the

experimental results for the final WAVE model. The detail geometry of the piston

were specified with the default values of 0, because the swirl model is not used,

therefore not requiring the piston detail.

The compression ratio was more complicated to determine and therefore the

following subsection is dedicated to this matter.

3.5.1.1 Compression Ratio

In order to determine the compression ratio of the engine it was decided to use a

mathematical process. Using the known geometries of the piston and cylinder head,

the volumes needed to calculate the compression ratio could be calculated. The

equations that describe the piston at TDC and BDC as well as the cylinder head were

integrated in order to obtain their respective volumes. The various curves describing

these volumes along with the coordinates defining the curves are illustrated in

Figure 35.

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Figure 35: Volumes for Compression Ratio Calculation

It was assumed that the curves are round and therefore the various points on the

curves as illustrated in the figure were substituted in the standard equation describing

a circle. The coordinates of the points were determined by measurements from the

engine drawings and the measurements from the actual engine. This lead to the

following equations for the various curves:

(11)

To obtain the volume of a curve in the XY-plane revolved around the Y-axis,

Equation (12) can be used.

Y

X

Piston BDC

Volume 2 (42.5,0)

(0,8.5)

(42.5,84.5)

(42.5,106.5) (0,98)

Piston TDC

Volume 1

Cylinder Head

Volume 3

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(12)

where is the function describing the curve. Using this equation to determine the

volume is similar for all three different curves, and hence only the derivation of the

piston at TDC (volume 1) will be shown.

Consider

then

Volumes 2 and 3 were calculated in a similar way, resulting in and

, and subsequently the compression ratio could be calculated

with Equation (13), resulting in a compression ratio of 7.312 : 1.

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(13)

3.5.2 Combustion Model

The standard SI Wiebe model is specified for the combustion model. As initial values,

the 50% burn point was specified at 8° and the combustion duration was specified as

30°, while the rest of the variables were kept at their respective default values. These

input values was chosen in order to acquire the prescribed ignition timing of roughly

20° before TDC, but the values should however be calibrated with the experimental

data.

3.5.3 Engine Heat Transfer

There are two input pages to consider when modelling the heat transfer in the engine

model. The first is the heat transfer page and refers to the heat transfer between the

combustion gas and the surrounding surfaces. The second is the conduction page and

accounts for the conduction through the piston, cylinder wall and head, as well as the

cooling of these components. The inputs for these pages are described next.

3.5.3.1 Heat Transfer Inputs

This heat transfer model will be simulated by the original Woschni model as

predefined in the WAVE software. The heat transfer multipliers for open and closed

intake valves will be kept at the default values of unity. This indicates similar heat

transfer for open and closed valve situations. The average surface temperature of the

piston, cylinder head and liner were specified as 400°C, 470°C and 440°C respectively

as suggested by (Vasudevan, 2007). This is however a gross simplification as these

values will vary with different engine operating conditions, but these values should be

correlated when experimental data is available. The area multipliers, however has to

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be adjusted as a value of 1 indicates a flat piston and cylinder head and this is not the

case.

The actual surface area of the piston and the cylinder head is the same, as these to

shapes follow the same curve, only as mirror images of each other. Rewriting

Equation (11), which describes the profile of the piston and cylinder head, and using it

together with Equation (14) will provide the actual surface area from which an area

multiplier can be calculated.

(14)

where the curve is expressed as and is continuous on and

for . The surface is produced when the portion to is revolved

around the Y-axis. This leads to the following calculation:

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With the area of a flat piston with a diameter of 85 mm being 5674.5 mm² this results

in an area multiplier of 1.04. The multiplier is the same for both the piston and the

cylinder head.

The final input is the swirl ratio. According to (Ricardo and Company, 1947), sleeve

valve engines are high natural swirl engines and a swirl ratio of 0.716, as suggested by

(Vasudevan, 2007), will be used. This is however only a speculative value and should

be correlated with experimental results.

3.5.3.2 Conduction Inputs

The conduction input page consists of two sub-pages. The one contains information

on the engine component walls and the other information on the cooling side of the

engine components.

The cylinder head, barrel and piston were assumed to be cast aluminium and the

properties are presented in (Incropera & De Witt, 1996).

Density – ρ = 2790 *kg/m³+

Specific heat – cp = 883 [J/kg.K]

Thermal conductivity – k = 168 [W/m.K]

Volumetric heat capacity – 2.46 x 106 [J/m³.K]

Firstly considering the piston, as it was simplified to a hollowed circular cylinder with a

height of 60 mm and a thickness of 6 mm as measured on the drawings. This resulted

in a volume of:

(15)

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The area of the coolant side of the piston is difficult to determine, because the

drawings of the piston is not detailed enough, but it was assumed sufficient to use an

area equal to that of the piston face, calculated in Section 3.5.3.1 as

.

The cylinder head was also assumed to be a hollowed out cylinder with height of 125

mm and a thickness of 18 mm as measured on the drawings. Using Equation (15) again

results in a volume of . The area of the coolant side of the

cylinder head consists of a number of cooling fins. According to the drawings the fins

are 65 mm by 40 mm and there are 20 fins. This results in an area of approximately

.

The barrel unit also consists of cooling fins and is therefore difficult to determine the

volume. However, it was measured at 6.23 kg, but it is assumed that roughly only two

thirds of that mass is the part of the barrel that is in contact with the piston and which

contributes directly to the heat transfer. With a density as specified above, this leads

to a volume of the cylinder barrel of .

The next step is to calculate the area of the coolant side. Figure 36 illustrates the

geometry of the barrel and fin setup with the accompanying equations. The following

are the geometries describing the barrel of the experimental engine:

H = 85 mm

S = 10 mm

N = 9

t = 2 mm

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L = 26 mm

r1 = 69.5 mm

r2 = 95.5 mm

This leads to a coolant side area, including the fins, of . The

thickness of the barrel is the difference between the two radii, which is 26 mm.

Figure 36: Fin Geometry and Equations

This concludes the inputs for the component walls sub-page and the next sub-page

requires information on the cooling side of the components. The required information

includes the heat transfer coefficients and temperatures of the cooling sides of the

piston, cylinder head and barrel.

Drop-down menus provide options for calculating the heat transfer coefficients for the

various components. The piston heat transfer coefficient will be determined via a

splash correlation hardcoded in the WAVE software. Determining the heat transfer

coefficients for the cylinder head and barrel will however be calculated by hand and

r1

r2

L

H

S

t

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specified as a fixed value. The correlation for these values considers nucleate boiling,

which is associated with water-cooled engines. This engine is air cooled and therefore

a pre-calculated fixed value will be used as opposed to the correlation.

The heat transfer coefficient of the cylinder head and barrel will be the product of a

forced convection heat transfer coefficient of just the barrel without the fins and the

total fin efficiency. The forced heat transfer coefficient will be generated by a cooling

fan blowing cool air over the stationary engine.

The barrel was considered as a cylinder in a cross-flow application. (Incropera & De

Witt, 1996) provides properties of the cooling air at 293 K and it is listed below.

Density – ρ = 1.194 [kg/m³]

Specific heat – cp = 1.00686 [J/kg.K]

Thermal conductivity – k = 0.02574 [W/m.K]

Viscosity – μ = 1.811 x 10-5 [N.s/m²]

Prandtl number – Pr = 0.70882 [-]

With the cooling fan ratted at 173 m³/min and a diameter of 650 mm, it results in an

air speed of approximately 8.7 m/s. The diameter of the barrel is 139 mm and using

Equation (16) the Reynolds number was calculated as 79,635.

(16)

According to Table 7.2 in (Incropera & De Witt, 1996) for a Reynolds number between

40,000 and 400,000, the values of and must be used in

Equation (17) to determine the average heat transfer coefficient. This resulted in a

forced convection coefficient of .

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(17)

The next step is to calculate the fin efficiency of the barrel fins. Using the equations

presented in Figure 36 along with the calculated forced convection coefficient and

Figure 37, results in a single fin efficiency of . Equation (18) is subsequently

used to calculate the overall fin efficiency of all the fins, resulting in .

(18)

Figure 37: Efficiency of a Rectangular Annular Fin (Incropera & De Witt, 1996)

The forced convection coefficient and the overall fin efficiency are multiplied to

produce an effective heat transfer coefficient for the coolant side of the cylinder

barrel. This resulted in a value of . Although the cylinder head

has differently shaped fins, it was assumed that the same effective heat transfer

coefficient could be used for the coolant side of the cylinder head.

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Finally, the coolant temperatures of the cooling flows were specified. For the oil

temperature, the default value of 380 K was used, but the cylinder head and liner

coolant temperatures were specified as 293 K, representing the cooling air and not

cooling water as is the case of the default values.

3.6 EXHAUST FLOW PATH

The exhaust flow path of the experimental engine only consists of an exhaust pipe.

The engine was used for racing purposes and hence there are no catalytic converters

or silencers. Therefore the modelling of the exhaust flow path will only consist of

ducts and junctions. The exhaust gas will be at a high temperature compared to the

ambient temperature and thus heat transfer must be added to the simulation models.

It was assumed that the exhaust temperature would be in the region of 1000 K.

3.6.1 Ducts

The geometry of the exhaust system is illustrated schematically in Figure 38. The

exhaust bolts directly onto the cylinder barrel covering the exhaust ports. The pipe is

manufactured from stainless steel and the following properties are described in

(Incropera & De Witt, 1996) at a temperature of 1000 K:

Density – ρ = 8055 *kg/m³+

Specific heat – cp = 606 [J/kg.K]

Thermal conductivity – k = 25.4 [W/m.K]

Emissivity – ε ≈ 0.35

This leads to a heat capacity of roughly 4.88 x 106 [J/m³.K]. Using Equation (10) again

to calculate the discretization length yields a discretization length of approximately

30 mm. The assumed exhaust temperature of 1000 K increased the speed of sound

which subsequently increased the discretization length from the value calculated for

the intake ducts.

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Figure 38: Schematic of Exhaust Flow Path

The geometry and heat transfer data presented above, leads to the input data for the

exhaust system as presented in Table 4.

Table 4: Input Values for Exhaust System Ducts

DuctHTX11 DuctHTX12 DuctHTX21 DuctHTX22 DuctHTX

Left Diameter

[mm] 32 32 32 32 47

Right Diameter

[mm] 32 32 32 32 47

Discretization

[mm] 30 30 30 30 30

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DuctHTX11 DuctHTX12 DuctHTX21 DuctHTX22 DuctHTX

Overall Length

[mm] 430 170 430 170 400

Bend Angle

[deg] 135 90 135 90 0

Friction

Multiplier 1 1 1 1 1

Heat Transfer

Multiplier 1 1 1 1 1

Outer Wall

Thickness [mm] 1 1 1 1 1

Heat Capacity

[J/m³.K] 4.88 x 106 4.88 x 106 4.88 x 106 4.88 x 106 4.88 x 106

Conductivity

[W/m.K] 25.4 25.4 25.4 25.4 25.4

Convective

Field

Temperature

[K]

293 293 293 293 293

Radiation Field

Temperature

[K]

293 293 293 293 293

Emissivity 0.35 0.35 0.35 0.35 0.35

3.6.2 Junction

A Y-junction was used to simulate the junction of the two exhaust pipes into one final

pipe. The junction was specified with a diameter of 32 mm and it was also deemed

necessary to simulate the heat transfer. The input values for the heat transfer was

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specified as the same values as presented for the ducts in the previous section. The

junction openings were set up as illustrated in Figure 39.

Figure 39: 3-D Layout of Y-Junction Element for Exhaust Pipe

3.7 INITIAL RESULTS AND DISCUSSION

The simulation was set up for different engine speeds, ranging from 1000 rpm to 6500

rpm at intervals of 500 rpm. The engine speed was limited to 6500 rpm because above

this value the average piston speed is in excess of 18 m/s and therefore above a

recommended safe operating speed. The WAVE software produces many different

results ranging from temperature and pressure through the engine to engine

performance, fuel consumption and emission levels. Not all these results will be

discussed, only some of the relevant results will be presented and discussed.

The engine performance is always of high importance and the discussion will therefore

start there. The engine brake power and brake torque is presented in Figure 40. The

maximum power is 23.07 kW at 6500 rpm and the maximum torque is 34.95 Nm at

6000 rpm.

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Figure 40: Brake Power and Torque Calculated with Initial Model

The torque curve illustrates two troughs at 2000 rpm and 4000 rpm respectively.

When examining the efficiencies, Figure 41, it can be seen that these troughs coincide

with two troughs in the volumetric efficiency curve. These troughs in the volumetric

efficiency indicate that the inlet acoustics are detrimental to the engine breathing,

causing low engine power outputs at these speeds.

Figure 41: Volumetric and Thermal Efficiency Calculated with Initial Model

The indicated and brake mean effective pressures are presented in Figure 42. As

suggested by (Greenhalgh, 2006), the maximum break mean effective pressure of

roughly 9.1 bar is in the range of typical naturally aspirated spark ignition engines.

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Figure 42: Indicated and Brake Mean Effective Pressure Calculated with Initial Model

The cycle analysis was also investigated and the first to consider is the P-V diagram.

Figure 43 illustrates this diagram at 4000 rpm. It is clear from the diagram that it

seems to resemble a 4-stroke spark ignition engine, meaning that the basic parameters

of the engine simulation seems to be correctly specified.

Figure 43: P-V Diagram Calculated with Initial Model at 4000 rpm

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The main difference between the poppet and sleeve valve engines is the flow through

the valves. It is therefore of main concern to study the results of the valves. Firstly

consider Figure 44 illustrating the effective valve areas. This figure presents the valve

areas multiplied by the discharge coefficient. It can be seen that the basic profile of

the area curves as presented in Figure 26 are retained, but the values have reduced

due to discharge coefficients being lower than 100%. It can also be seen that the one

inlet valve (the centre inlet valve) has a much higher peak than the other two inlet

valves. This is because the discharge coefficients given by (Waldron, 1940) for the

centre inlet valve is higher than that of the two end inlet valves.

Figure 44: Effective Valve Areas for Initial Model

Consider Figure 45, illustrating the mass flow through the various valves plotted

against crank angle at 4000 rpm. The difference in the mass flow through the centre

valve and the two end valves is very clear. The centre valve mass flow rate is about

300 kg/hr, whereas the end inlet valves are roughly 50 kg/hr each. The difference in

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effective valve area as described from the above figure assists in this phenomenon, but

is not the only cause. The duct leading to the two end valves are longer and they are

bent, causing higher flow losses than the straight, short duct leading into the centre

valve. Therefore, the flow will naturally follow the path of least resistance, causing the

higher flow rate in the centre inlet duct. Furthermore, the two ducts leading to the

two end inlet valves are in contact with the cylinder barrel, causing the flow to heat up

as it flows towards the valve inlets. The higher temperature of the air causes the

density of the flow to reduces, further reducing the mass flow rate through the end

inlet valves. These are therefore design considerations that need to be taken into

account when designing a sleeve valve engine like this. To maximize air flow through

the valves, ensure that the inlet ducts are not heated by the cylinder barrel and try to

minimize the flow losses in the ducts. In this case it was difficult as this is a motorcycle

engine and packaging was a major design specification.

Figure 45: Mass Flows through Valves Calculated with Initial Model

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The following step in this project was to determine discharge coefficients that are

applicable to the available experimental engine. The discharge coefficients are

presented in WAVE as values plotted against valve lifts and pressure ratio across the

valves. Therefore, one final result that is of worth is presented in Figure 46. The figure

shows the pressure difference across the various valves. Assuming 1 bar pressure in

the cylinder chamber during the intake stroke and 1 bar pressure in the exhaust during

exhaust stroke, this provides a pressure ratio range for the inlet valves of 1 to 2 and for

the exhaust valves of 1 to 6.

Figure 46: Pressure Difference across the Valves

3.8 CONCLUSION

Two of the major aims of this project have been addressed in this chapter. Firstly, a

method was presented on how to determine the sleeve valve areas accurately from

detail sketches of the ports. This is very important as the detail knowledge of the valve

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areas is fundamental in simulating the engine. This method works well when the

engine has already been designed and needs to be analysed from sketches and

measurements. However, in the modern computer aided design (CAD) atmosphere

this method might be redundant as the design software will probably be able to

automatically calculate the valve areas. Nonetheless, working through this method

still provides a proper understanding of the sleeve movement during the engine cycle

and could aid in the design of new sleeve valve configurations.

Secondly, a set of sleeve valve discharge coefficients found in the open literature,

(Waldron, 1940), has been identified and put to practical use in an engine simulation

with satisfactory results. These discharge coefficients provide an excellent starting

point for similar sleeve valve analyses. It is however suggested that a more detailed

method of determining discharge coefficients should be undertaken when more

detailed simulations are done, especially when the sleeve and cylinder wall ports have

different profiles than that used in the (Waldron, 1940) experiments. The next step in

this project is therefore to determine discharge coefficients characteristic to the

experimental engine’s specific sleeve valves.

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4. VALVE DISCHARGE COEFFICIENTS WITH

COMPUTATIONAL FLUID DYNAMICS

In developing the initial WAVE model, it became clear that the air flow through the

valves is very influential in determining the performance of the engine. It is therefore

crucial that the discharge coefficients of the valves are determined correctly. For the

initial WAVE model the discharge coefficients provided by (Waldron, 1940) was used,

but those coefficients were determined on slightly different valve geometries than the

engine used in this study and hence it was decided to determine discharge coefficients

that is characteristic to this engine and its specific valve profiles.

The discharge coefficients could either be determined experimentally or

mathematically by the use of computational fluid dynamics (CFD). However, the use of

experimental results required the construction of an experimental setup and due to

the limited amount of time available for this project it proved to be a detrimental

constraint. It was decided to use CFD methods to determine the discharge coefficients

of the valves. This way the author could gain knowledge in the use of CFD simulations

and acquire a further skill in the use of CFD software.

The discharge coefficients are specified in WAVE as an external data file, and consists

of the discharge coefficients as a function of pressure ratio and valve lift. The valve lift

represents the area of the valve. This chapter describes the process undertaken to

determine these discharge coefficient profiles for the valves using CFD simulations.

4.1 MODEL GENERATION

The CFD simulates the fluid flow in a volume bounded by certain boundary conditions

with the volume being the space occupied by the fluid. This is done by dividing

(meshing) the volume into very small elements in order for the CFD software to solve

the continuity equations (continuity of mass, momentum and energy) for each small

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element bounded by adjacent elements. The first step in the CFD process is to

generate a model of the volume being studied and meshing the model for the CFD to

perform the calculations on. The following sections describe the process undertaken

to create the meshed models for this project.

4.1.1 Model Layout

A valve setup comprising of the cylinder bore, port in the cylinder wall and exhaust

duct for exhaust valves and inlet duct for inlet valves, was simplified for the CFD

analyses to an orifice type setup. This comprised of a large round duct representing

the cylinder, the detail valve geometry as determined in Section 3.2 and an inlet or

exhaust duct representing the inlet or exhaust pipe respectively. This layout is

presented in Figure 47.

A round duct with a diameter equal to that of the bore (85 mm) and a length equal to

that of the stroke (84.5 mm) of the engine was used to represent the cylinder volume.

A round duct with a diameter equal to that of the height of the intake channel (38 mm)

was used for the intake duct and equal to the diameter of the exhaust pipe (32 mm)

was used for the exhaust duct. In both these cases, the length of the duct was

selected to be 6 diameter lengths in order to ensure that fully developed flow has been

established inside the duct. This led to respective heights of 228 mm and 192 mm.

Figure 47: Layout of CFD Model

6D = (228 mm Intake / 192 mm Exhaust)

Inlet for Intake Valves

Outlet for Exhaust Valves

Inlet for Exhaust Valves

Outlet for Intake Valves

84.5 mm

85

mm

D =

38

mm

(In

take

) /

D =

32

mm

(Exh

aust

)

Valve Profile Volume

(2 mm thick)

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4.1.2 Valve Geometry

The valve profile volume consists of the exact valve profile, at a certain pre-determined

crank angle, extruded to a thickness of 2 mm, representing the thickness of the sleeve.

This volume is then placed between the two ducts described in the preceding

paragraph (see Figure 47).

The exact profile is described by the points as determined in Section 3.2.2, but it was

necessary to establish at which different crank angles the simulations would be done.

Although suggested by (Waldron, 1940) that the coefficients remain similar for

different valve openings, it was deemed necessary to simulate the discharge

coefficient at different valve openings. The first simulations were done at

approximately maximum valve opening for all the valves. Simulations were then done

at a very small valve opening (approximately 1/32 of maximum opening) followed by

simulations at valve openings between these extremes.

At first it was believed that the biggest variation in coefficients occur at smaller valve

openings, hence the simulations were focused at valve openings smaller than half of

the maximum valve area. This proved not to be sufficient and simulations at 3/4 valve

opening was also necessary in order to fully describe the trends of the coefficients.

Figure 48 illustrates the locations of the valve profiles on the area/crank angle graph.

Valve profiles at the intersections of the solid black horizontal lines (also the two

vertical lines at maximum openings) and the graphs were used for the simulations.

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Figure 48: Indication of Valve Opening Profiles Simulated

Upon closer inspection, it should be noticed that only valve profiles on the opening

slope of the valves were simulated. This was because the WAVE software does not

distinguish between the opening and closing instances of the valves, assuming the

areas are the same in both cases. This is true for poppet valves, but not for sleeve

valves. For this study it was therefore decided to use only the opening profiles to

determine the discharge coefficients. This was assumed because the highest pressure

ratios across the valves occur when the valves opens initially. The mass flow rates will

be the highest in these cases of high pressure ratios and thus the discharge coefficient

will have the greatest influence. Further comments regarding this matter will be made

when the results of the CFD simulations are described at the end of this chapter.

4.1.3 Gambit Models

The setup as presented in Figure 47 was constructed in Gambit (CFD meshing

software) after which a mesh was generated for use in the Fluent CFD software

package. One of the most important factors of these simulations was that the exact

-100

0

100

200

300

400

500

600

700

800

900

0 100 200 300 400 500 600 700

Are

a [m

m^

2]

Cycle Angle [deg]

End Inlet 1 Valve Area [mm^2] Exhaust 1 Valve Area [mm^2] Exhaust 2 Valve Area [mm^2]

End Inlet 2 Valve Area [mm^2] Centre Inlet Valve Area [mm^2]

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valve profile was used. Constructing the exact profile in Gambit is a very labour

intensive and time consuming job, because the profile is described by many points as

determined in Section 3.2.2. In some cases more than 200 points describe the profile

and all these points have to be created in Gambit, then they need to be joined to form

lines and all the lines need to be joined to form a face. Fortunately, Gambit uses a

journal file to record all the actions taking place in a work session. These saved journal

files can be accessed to repeat a certain work session if need be, and subsequently it

was decided to create journal files with a text editor and just import the journal files to

create the model.

Since all the required points are known in the Excel workbook as described in

Section 3.2.2, a Macro was added to the workbook that creates journal files for all the

valves. The user then only needs to decide which valve area is needed, enter the crank

angle into the Excel file to obtain the required valve area and run the Macro which

produces a journal file for each valve, producing the valve profile as it will be at that

crank angle. The journal file is then run in Gambit where after only a few commands

are added and the mesh is ready for import into the Fluent software, the entire

process taking at most 5 minutes instead of hours of Gambit modelling. This was

especially helpful since this study included 27 different geometrical setups.

4.1.4 Meshing

The meshing of the volumes is a very important aspect of the CFD model. Care must

be taken when generating the mesh in order to produce accurate and representative

results. The author, however, is not a CFD expert and is not experienced in creating

meshes and therefore decided to use a standard automated meshing scheme, namely

the Cooper scheme. This automated scheme is available in the Gambit software.

Further, to determine the flow coefficient from the CFD simulations, only the mass

flow rate through the valve and the inlet density are needed, and the detail flow field

is of no concern. This allowed for a non-perfect mesh to be sufficient.

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The entire volume was meshed using the automated Cooper meshing scheme with

hex/wedge element type. For the inlet and outlet duct a spacing of 2 mm was used,

resulting in almost 70,000 elements for the duct representing the cylinder and about

30,000 elements for the duct representing the inlet or outlet duct. The valve volume

was meshed using a spacing representative of its size. For most of the meshes it was

0.5 mm, but for the very small area profiles the spacing was chosen as 0.2 mm. This

resulted in element numbers ranging from 5,000 to 20,000 elements for the valve

volume.

In all the cases the quality of the mesh was checked using the mesh examiner provided

by Gambit. As a guideline, the skewness of the elements should be as low as possible

on a 0 to 1 scale. It was decided to ensure that the skewness of all the elements

should be kept below 0.5. In almost all the cases (with the exception of the very small

valve area cases) all the elements had a skewwnes of less than 0.5. In the cases where

the skewness was greater than 0.5, it was less than half a percent of all the elements,

and the skewness remained below 0.7 for all the elements. It was assumed that less

than half a percent of all the elements is a small enough number of elements to

provide an acceptable mesh.

4.2 SIMULATION SPECIFICATIONS

The Gambit models were exported as mesh files to be used in the Fluent CFD software.

The important specifications used in the software are presented in the following

sections.

4.2.1 Solver Models

The geometrical models and meshes were created in 3-dimensional orientation and

therefore the 3-D version of the Fluent software was used. A segregated solver was

specified with the use of implicit mathematical formulation. Only steady state

solutions were considered and the gradient option was set as cell-based and not node-

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based. The energy equation was activated and the k-ε turbulence model was used

with the default model constants as prescribed by the software. Figure 49 illustrates

the input pages of the Fluent software for the solver and viscous models.

The SIMPLE algorithm was selected for the pressure-velocity coupling and the

discretization of the pressure set to second order. The discretization of the density,

momentum, turbulence kinetic energy, turbulence dissipation rate and the energy

were all set to second order upwind. The second order discretization leads to more

accurate results, albeit at a higher consumption of computing resources, resulting in

longer simulation times. The gain in accuracy however, justified the longer simulation

times. The under-relaxation factors were all left at their default values, however, in

some cases they had to be altered in order to avoid divergence of the solution. There

are no set values that were used, and the author experimented with different values

until satisfactory convergence was reached.

Figure 49: Solver and Viscous Model Input Pages of Fluent

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In all the simulations, air was used as working fluid. The default properties as given by

Fluent were used except the formulation of the density, which was specified as an

ideal gas instead of having a constant value. This was done because high pressure

values (up to 6 bar) were used in the simulations which significantly affect the value of

the density. Table 5 presents the values used for the material properties of air.

Table 5: Properties of Air for CFD Simulations

Property Value Unit

Density Ideal-gas kg/m³

Cp 1006.43 J/kg.K

Thermal Conductivity 0.0242 W/m.K

Viscosity 1.7894 x 10-5 kg/m.s

Molecular Weight 28.966 kg/kMol

4.2.2 Boundary Conditions

The boundary conditions define the simulation and establish flow inside the volume

being studied. These boundary conditions include wall specifications, inlet- and outlet

pressure.

The inside walls of the ducts and the valve profile were specified with a surface

roughness of 0.015 mm as found in (Shames, 1992). This is to simulate the pressure

drop through the ducts due to friction of the fluid against the non-smooth wall

surfaces. The value found in (Shames, 1992) is for drawn tubing and might be too

rough for the cylinder wall, but too smooth for the inlet and outlet ducts. This value

was therefore assumed to be a compromise between the two extremities.

The inlet- and outlet pressure boundary conditions are specified in Table 6. The table

presents the specified outlet pressure for the intake valve cases and the specified inlet

pressure for the exhaust valve cases. The inlet pressure of the intake valves and the

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outlet pressure of the exhaust valves were specified as 0 Pa. These are all gauge

pressure readings; resulting in a pressure setting of 100,000 Pa (the setting of the

initial conditions is 100,000 Pa). This will replicate an atmospheric intake pressure for

the intake valves and an atmospheric outlet pressure for the exhaust vales.

The negative pressure set for the outlet of the intake valves replicates the piston

movement creating a pressure lower than atmospheric pressure inside the cylinder

chamber. In contrast, the positive inlet pressure set for the exhaust valve cases

replicates the high pressure inside the combustion chamber after combustion took

place, blowing down to atmospheric pressure at the outlet. However, it should be

noted that the working fluid is air and not typical combustion residual gasses. The

temperature for all the cases is set at 300 K, which is a simplified assumption for the

exhaust cases.

Table 6: Boundary Pressure Settings for CFD Cases

Case Inlet Pressure [Pa] Outlet Pressure [Pa] Pressure Ratio

Intake Valve Case 1 0 -5,000 1.0526

Intake Valve Case 2 0 -15,000 1.1765

Intake Valve Case 3 0 -30,000 1.4286

Intake Valve Case 4 0 -50,000 2

Exhaust Valve Case 1 10,000 0 1.1

Exhaust Valve Case 2 50,000 0 1.5

Exhaust Valve Case 3 100,000 0 2

Exhaust Valve Case 4 300,000 0 4

Exhaust Valve Case 5 500,000 0 6

4.2.3 Convergence

The CFD software uses an implicit method to solve the simultaneous continuity

equations for all the elements. It uses initial values at the boundaries in order to

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calculate new values at the boundaries and then the differences between the initial

and the newly calculated values are the residuals. A simulation has not reached

convergence until these residual values are small enough and hence the results cannot

be trusted unless the residuals are sufficiently small. The various criteria’s suggested

for the different variables in this study is presented in Table 7. Simulations were

continued until the residuals reasonably steadied out at values satisfying the criteria’s

as specified in the table. In almost all the cases the specified criteria’s were met and it

was assumed that the results could be trusted.

Table 7: Convergence Criteria’s

Criteria Variable Convergence Value

Continuity 1 x 10-3

X-Velocity 1 x 10-3

Y-Velocity 1 x 10-3

Z-Velocity 1 x 10-3

Energy 1 x 10-6

k 1 x 10-3

ε (epsilon) 1 x 10-3

4.3 POST PROCESSING

The aim of the entire CFD exercise in this project was to determine the valve discharge

coefficients for use in the WAVE effective area valve model. Thus, to determine these

coefficients one must first examine the definition of the discharge coefficients for the

WAVE model. The discharge coefficient is defined by Equation (19) as found in the

WAVE user manual. The geometrical area, , is defined by the area of a poppet

valve skirt area, , with the lift of a poppet valve with diameter .

(19)

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The discharge coefficient can thus be calculated when the effective area, , is

known. To determine the effective area, the mass flow rate calculated with the CFD

simulations is used. The mass flow rate at any point through the orifice setup is given

by Equation (20).

(20)

Rewriting the equations leads to the effective area, Equation (21). The effective area is

actually the area of the vena contracta and therefore the isentropic velocity, , and

the density, , at the throat must be used.

(21)

It is very difficult to accurately determine the velocity and density at the vena

contracta from the CFD results. This is because the exact location of the vena

contracta is not known and it differs for different boundary conditions. The WAVE

user manual, however, provides equations to calculate the isentropic velocity and the

throat density. Further, considering that these would be the same equations that

WAVE uses to determine the mass flow rate from the discharge coefficient, it seems to

be the most accurate method to use these equations for determining the discharge

coefficients. These equations are presented in Equations (22) and (23).

(22)

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(23)

Prior to using these equations, however, the pressure ratio, , must be compared

with the critical pressure ratio given in Equation (24) as presented by (Shames, 1992).

If the pressure ratio exceeds the critical pressure ratio, the flow will choke (the flow

velocity reaches the speed of sound), preventing the mass flow to increase even if the

pressure ratio increases. Therefore, if the pressure ratio across the valve exceeds the

critical pressure ratio, the pressure ratio terms in Equations (22) and (23) must be

replaced with the critical pressure ratio (Equation (24)) so that the velocity (and

subsequent mass flow rate) will not be overestimated.

(24)

The equation presented by the WAVE manual for calculating the critical pressure ratio

is slightly different from the one given by (Shames, 1992) and produces an

unrealistically low pressure ratio as the critical pressure ratio. The pressure ratio

calculated with the equation given by (Shames, 1992) provides a much more realistic

critical pressure ratio, which results in a velocity very close to that of the widely know

value for the speed of sound for normal air (approximately 330 m/s). It was therefore

assumed that the equation in the WAVE manual might be a typing error and the

equation given by (Shames, 1992) was used.

Finally, the mass flow rate and inlet density calculated by the CFD software were the

only results used for the calculation of the discharge coefficients. These results were

used for all the different cases (varying pressure ratios for all different geometries, for

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all the valves) and the various discharge coefficients calculated. These coefficients are

presented in the following section.

4.4 RESULTS AND DISCUSSION

The resultant discharge coefficients are presented in this section together with the

flow coefficients presented by (Waldron, 1940) in order to make a comparison. For

the centre inlet valve, Figure 50, the coefficients compare very well. The profiles of the

coefficients are very similar and the magnitudes of the values are in the same range.

This is a good validation for the CFD results, and the advantage is that the CFD results

cover a wider range of different valve area openings. (Waldron, 1940) only considered

two different area opening, approximately full- and half valve openings, with both

yielding very similar results.

Figure 50: Centre Inlet Valve Discharge Coefficients

The two end inlet valves, Figure 51 and Figure 52, produces results very similar to the

centre inlet valve. It also produces results showing similar profiles to that of the

0.7

0.75

0.8

0.85

0.9

0.95

1

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Dis

char

ge C

oe

ffic

ien

t

Pressure Ratio

Centre Inlet Valve

100 % Open 73 % Open 48 % Open 24 % Open 3 % Open Waldron Coefficients

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(Waldron, 1940) coefficients, but at higher magnitudes. This is due to the

simplification of the CFD geometry to a straight duct orifice setup, while in reality the

end inlet ducts are curved. The lower flow disturbance of the lower curvature results

in higher coefficients, while the experimental results of (Waldron, 1940) takes into

account the duct curvature and it is represented in his results being of lower

magnitude.

Figure 51: End Inlet Valve 1 Discharge Coefficients

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Dis

char

ge C

oe

ffic

ien

t

Pressure Ratio

End Inlet Valve 1

100 % Open 73 % Open 48 % Open 25 % Open 3 % Open Waldron Coefficients

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Figure 52: End Inlet Valve 2 Discharge Coefficients

However, consider the end inlet ducts for the different engines as presented in

Figure 53. On the left hand side, the (Waldron, 1940) engine can be seen with very

sharp edges on the intake port of the cylinder wall, whereas the experimental engine

on the right shows a smoothly curved path cut-out of the cylinder wall in order to

decrease flow curvature towards the end inlet valves. It was therefore assumed that

the higher discharge coefficients produced by the CFD results could be used due to the

costumed flow path of the experimental engine.

Figure 53: (Waldron, 1940) End Inlets (left) vs. Experimental Engine End Inlets (right)

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Dis

char

ge C

oe

ffic

ien

t

Pressure Ratio

End Inlet Valve 2

100 % Open 74 % Open 49 % Open 25 % Open 3 % Open Waldron Coefficients

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The results for the exhaust valves are illustrated in Figure 54 and Figure 55. Both

exhaust valves yielded very similar results and compared fairly well with the (Waldron,

1940) coefficients. As in the cases of the inlet valves, the profiles of the coefficient

curves compare very well, but in this case the magnitudes are slightly different, with

the (Waldron, 1940) coefficients having greater extremities. The flattening of the

curves at higher pressure ratios can be attributed to the critical pressure ratio being

reached and choked flow occurring in the valves.

Figure 54: Exhaust Valve 1 Discharge Coefficients

0.7

0.72

0.74

0.76

0.78

0.8

0.82

0.84

0.86

0.88

0.9

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Dis

char

ge C

oe

ffic

ien

t

Pressure Ratio

Exhaust Valve 1

100 % Open 80 % Open 53 % Open 27 % Open 13 % Open 3 % Open Waldron Coefficients

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Figure 55: Exhaust Valve 2 Discharge Coefficients

Finally, in Section 4.1.2 it was described that only valve profiles on the opening slope of

the area chart was used. From the results it was realized that the different profiles of

the different valves resulted in similar discharge coefficients and hence it was assumed

sufficient to only use the opening valve profiles and not the closing valve profiles to

acquire representative discharge coefficients. However, should sleeve valve

technology continue to be studied as a viable engine design option, it is suggested that

the developers of the WAVE software be requested to develop a sleeve valve model

which will incorporate both opening and closing discharge coefficients for the sake of

comprehensive simulations.

4.5 CONCLUSION

In conclusion it can be said that the aim of attaining discharge coefficients for specific

sleeve valve profiles has been addressed. CFD is a powerful tool that can be used to

minimize experimental costs and in this case it also yielded results which compared

very well to existing experimental results. The only discrepancy was in the case of the

0.7

0.72

0.74

0.76

0.78

0.8

0.82

0.84

0.86

0.88

0.9

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Dis

char

ge C

oe

ffic

ien

t

Pressure Ratio

Exhaust Valve 2

100 % Open 80 % Open 54 % Open 27 % Open 13 % Open 3 % Open Waldron Coefficients

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end inlet valves, where the experimental results included the extra flow resistance of

the bend in the duct. However, it is all a case of perspective, and the designer must be

careful when analysing the valve flow. If the flow losses were to be considered in the

adjacent duct elements, then using the CFD discharge coefficients will yield similar

results to the use of the experimental discharge coefficients which inherently account

for those losses.

Now that the specific discharge coefficients have been determined, it will be used in

the WAVE model in order to analyse and compare the results. This is done in

Chapter 6.

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5. EXPERIMENTAL FACILITY

The experimental 4-stroke sleeve valve engine supplied by Mahle Powertrain Ltd.,

Northampton UK, is presented in Figure 56. Various items were manufactured in order

to set the engine up for testing purposes. Ultimately the engine could not be brought

to an operational state before the end of the project as the project is fixed to the

academic year. This chapter describes the assembly of the test setup and the

subsequent lessons learned from the experience.

Figure 56: Experimental 4-Stroke Sleeve Valve Engine

5.1 ASSEMBLY OF TEST SETUP

After taking the engine apart and measuring the required dimensions, the engine was

reassembled and sealed for operational purposes. Engine mounting brackets and a

mounting base were manufactured and the engine was attached to these mountings.

The mounting brackets were attached to sliders channels on the mounting base to

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permit the engine placement to be adjusted left to right. Similarly, the mounting base

was attached to slider rails in the floor which permitted the engine placement to be

adjusted closer or further from the dynamometer.

An oil tank was also manufactured and attached onto one of the engine mounting

brackets. The next step was to link the engine to the dynamometer as the

dynamometer would be used to start the engine and measure the engine torque

produced when running.

5.1.1 Belt Driven

A previous project made use of a 2-stroke sleeve valve engine, which was connected to

the dynamometer with a pulley and belt system and it was thought to use the same

system components to connect the 4-stroke sleeve valve engine.

In order to connect the 4-stroke sleeve valve engine to the dynamometer using the

pulley and belt system, a number of components were manufactured. Firstly, a

connector was manufactured which bolted onto the end of the crank shaft and

contained a square stub end where the pulley was fastened onto. At the end of the

pulley, an aluminium disc was attached with a steel bolt on the outer rim which acted

as pickup for the electronic ignition system.

A plate was manufactured which attached to the base mounting and served as

attachment for the ignition system and timing sensor. Covering plates were also

added around all the rotating parts which served safety purposes. Figure 57 illustrates

the layout at the end of the engine crank shaft, displaying the components mentioned

above, excluding the covering plates.

This setup created many challenges and difficulties. Very precise adjustment was

needed fastening all the components to the end of the crank shaft to eliminate any

unbalanced forces. Careful alignment was also required in order to align the pulleys on

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the engine and dynamometer respectively. Thereafter the engine was motored by the

dynamometer, but the belt jumped on the pulleys. Tightening the tension in the belt

caused the belt to break. Although an extra belt was available, it was realised that the

alignment and jumping problems justified a change in connecting the engine to the

dynamometer. Over tightening of the belt could also lead to excessive forces exerted

on the crank shaft bearing, possibly causing it to fail.

Figure 57: Engine Belt and Pulley Layout

5.1.2 Direct Coupling

It was subsequently decided to use a direct coupling by means of a constant velocity

(CV) joint. This setup solved both the problem of alignment and the jumping belt and

should not apply unwanted forces on the crank bearings.

An available CV joint was used and fixed to the dynamometer. The connector used for

the belt setup was adjusted to fit to the joint and holes were machined into the

Connector

Pulley & Belt

Aluminium End Disc & Bolt

Timing Sensor

Ignition System Plate

Ignition System

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connector in order for shear pins to be used to protect the engine from excessive force

transmission which could damage the engine. The ignition system plate was moved

and a new cover plate was constructed which also housed the ignition timing sensor.

The new layout however, required the engine to be lifted in order for the crank shaft

to be at the same height as the shaft of the dynamometer. Two steel columns were

constructed which fitted in between the mounting base and the engine mounting

brackets. The new setup is presented in Figure 58 and Figure 59.

Figure 58: Engine CV Joint Layout

Using this setup, the engine was brought up to about 2400 rpm with the

dynamometer. The carburettor was connected to a tank with unleaded fuel and the

ignition system switched on. The engine fired, but it was uncertain whether the engine

was running on its own or being driven by the dynamometer and just firing randomly.

Timing Sensor

Dynamometer

New CoverPlate with CVJoint underneath

Ignition System

Ignition Coil

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It is therefore suggested that a type of clutch should be connected between the

dynamometer and the engine in order to let the engine run free.

Figure 59: Engine Mountings

This was the point where it was realised that there was not sufficient time to get the

engine running and complete this report. Before the engine could be started again,

the laboratory exhaust system would have to be fixed as there is some sort of a

blockage and the carburettor settings would have to be inspected.

5.2 CONCLUSION

The aim of the experimental setup was to acquire pressure, temperature and engine

output reading and to use these values to calibrate the WAVE model of the engine.

Variables such as heat transfer coefficients, ambient temperature and pressure,

surface temperatures of thepiston, cylinder wall and head, ignition timing and friction

factors can be calibrated using the experimental data. However, the lack of

experimental data prohibited the calibration of the engine model.

Steel Columns

Engine Mounting Brackets

Mounting Base

Oil Tank

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Nonetheless, a great deal was learned through the experience of attempting to acquire

experimental results. Should work on this engine be continued, it is suggested that the

direct coupling that presently set up between the engine and dynamometer be

improved by adding a clutch between the two machines. This will ease the starting of

the engine.

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6. FINAL WAVE MODEL

Due to the lack of experimental results, this study concludes with the update of the

initial engine model to include the CFD derived valve discharge coefficients. The

results generated with the new model will be compared to the results of the initial

model and subsequent conclusions will be made.

Furthermore, a model was set up with poppet valves instead of sleeve valves in order

to see if the sleeve valves boast any performance advantages in this engine. Exactly

the same model was used as the sleeve valve model, except the valve definitions.

6.1 CHANGES FROM INITIAL MODEL

The only changes made to the initial model was to replace the valve discharge

coefficients taken from (Waldron, 1940) with the values obtained by means of CFD

analyses as described in Chapter 4. This resulted in the discharge coefficient input

pages as presented in Figure 60 for one of the inlet valves and Figure 61 for one of the

exhaust valves.

Figure 60: Updated Discharge Coefficient Input Page for Inlet Valve

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Figure 61: Updated Discharge Coefficient Input Page for Exhaust Valve

The rest of the model was left unchanged and this provided an excellent opportunity

to evaluate the influence of the discharge coefficient on the final results of the

simulation. These results will be discussed at the end of this chapter.

6.2 EQUIVALENT POPPET VALVE MODEL

As a comparison between sleeve and poppet valve engines, a model of a similarly sized

engine was set up which consist of poppet valves instead of sleeve valves. This was

done purely to see if there are any performance advantages in using sleeve valve

engines. The same engine model as the sleeve valve engine was used, with only the

valve models being changed to represent poppet valves. It is true that a similar sized

poppet valve engine would have different geometries, especially intake and exhaust

systems, but the same model was used in order to only distinguish the differences

caused by the different valves.

The first thing was to determine the size of the valves. A similar valve configuration,

three inlet and two exhaust valves, was used. The constraint here is that the valves

should fit into the cylinder head, limiting the sizes of the valves. It was decided to use

a graphical method to determine the maximum valve sizes. It was assumed that the

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cylinder head is flat, resulting in a final valve configuration as presented in Figure 62.

The blue circles representing the inlet valves and the smaller red circles representing

the exhaust valves.

Figure 62: Valve Configuration for Poppet Valve Model

This layout was achieved with 30.5 mm inlet valves and 27 mm exhaust valves. The

respective valve lifts were calculated by assuming that the maximum skirt area

is equal to the valve area . This resulted in an inlet valve lift of roughly

7.7 mm and an exhaust valve lift of roughly 6.8 mm.

The valve movement for the inlet and exhaust valves were specified with the

predetermined “fast” polynomial as hardcoded in the WAVE software. The open

duration and crank timing input variables were specified so that the valves open and

close at exactly the same crank angles as with the sleeve valves. The open duration

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and crank timing for the inlet valves were 333° and 465.5° respectively, resulting in an

inlet valve opening at 299° crank angle and inlet valve close at 632° crank angle. To

achieve an exhaust valve opening at 91° and closing at 400° the open duration for the

exhaust valves was specified as 309° and the crank timing as 245.5°.

The model was solved and the results compared to the results of the updated sleeve

valve engine model to analyse the performance differences.

6.3 RESULTS AND DISCUSSION

The results of the model specified with CFD derived discharged coefficients and the

model specified with poppet valves were studied and some conclusions drawn.

6.3.1 Initial Model vs. Updated Model

The results for the updated sleeve valve model are very similar than the results of the

initial model. The brake power and torque curves (see Figure 63) have similar profiles

and very similar values with a power output of the updated model of 23.23 kW at 6500

rpm and torque of 35.17 Nm at 6000 rpm. It is 0.16 kW and 0.23 Nm more than the

initial model.

Figure 63: Brake Power and Torque Calculated with Updated Model

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In the same way, all the results compare similarly for these two models. There is

however differences when examining the effective areas of the valves and the mass

flow rate through the valves.

Figure 64: Effective Valve Areas – Updated Model Left & Initial Model Right

The effective area plots, Figure 64, illustrates the effect of the higher discharge

coefficients for the end inlet valves of the updated model (left), compared to the lower

effective areas of these valves in the initial model (right). The difference in effective

areas leads to the different mass flow rate plots as presented in Figure 65. Notice the

smaller difference between the profiles in the range of 360° and 540° on the updated

model plot (left).

Figure 65: Valve Mass Flow Rates – Updated Model Left & Initial Model Right

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When considering the mass flow rate of all the inlet valves combined, however, a very

similar value is obtained. This can be observed in the mass flow rates calculated

through the carburettor element. For the initial model it is 0.02933 kg/s and for the

updated model it is 0.02949 kg/s. Further, it can be shown that the power produced

by the engine is a function of the engine speed, air-fuel-ratio, fuel heating value, fuel

conversion efficiency and the air mass flow rate. Considering that for the two different

engine models, all these variables are equal except the mass flow rate, it is clear that

the performances are very similar because the air mass flow rate values are very

similar.

6.3.2 Sleeve Valve Model vs. Poppet Valve Model

The comparison of these results was done using the sleeve valve model with discharge

coefficients derived from the CFD analyses. The results of the poppet valve engine are

very similar to the sleeve valve engine model results. Figure 66 illustrates a very

similar performance profiles. The brake power and torque calculated for the poppet

valve model are 22.83 kW at 6500 rpm and 34.63 Nm at 6000 rpm respectively. It is

only 0.4 kW and 0.54 Nm less than the sleeve valve model.

Figure 66: Brake Power and Torque Calculated with Poppet Valve Model

The only difference between these two models is the definition of the valves.

Different valve areas are specified and different discharge coefficients are specified for

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the two models. Therefore it is logical to also compare the effective valve areas and

mass flow rates through the valves. Figure 67 illustrates the much higher effective

valve areas of the sleeve valve model (right), with a maximum of just more than

600 mm² compared to the maximum for the poppet valve model of just more than

400 mm². This difference can be contributed to more area available for valves ports in

the case of the sleeve valve engine and the higher discharge coefficients of the sleeve

valves due to less flow obstruction.

Figure 67: Valve Effective Areas – Sleeve Valve Model Left & Poppet Valve Model Right

The respective effective valve areas results in the mass flow rates as presented in

Figure 68. Although the peaks of the poppet valve model (left) are lower than the

peaks of the sleeve valve model, the mass flow rates through the carburettor element

presents similar flow rates, 0.02947 kg/s compared to 0.02949 kg/s.

Figure 68: Valve Mass Flow Rates – Sleeve Valve Model Left & Poppet Valve Model Right

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As explained in Section 6.3.1, the similar air mass flow rates into the engine results in

very similar performance figures. The question now arises, can any of the so called

performance benefits of the sleeve valve engine be seen with simulations or not. To

answer this question for these specific simulations, higher engine speeds will have to

be considered. At the engine speeds considered up to now, the required mass flow

rate induced by the piston movement could be delivered by the valves, sleeve and

poppet valves, because sonic conditions has not been reached yet. In all the cases, the

effective areas of the valves were sufficient to avoid choked flow. However, when

increasing the engine speed, the mass flow rate demand will also increase,

subsequently increasing the velocity of the flow through the valves (see Equation (20)).

As seen in Figure 67, the effective areas of the sleeve valves are greater than that of

the poppet valves, and therefore it is believed that the flow through the poppet valves

will choke prior to the flow through the sleeve valves when increasing the engine

speed. To test this, the two models compared here was analysed again, this time at up

to higher engine speeds, to see if the poppet valve performance succumb to that of

the sleeve valve model at higher engine speeds as predicted.

Figure 69 illustrates the brake power results of these extended simulations. As

predicted, the power of the poppet valve model is lower than that of the sleeve valve

model at higher engine speeds due to the smaller effective area of the valves causing

choked flow at lower mass flow rates. At 7500 rpm the sleeve valve engine reaches

maximum brake power. At this engine speed the mass flow rates through the

carburettor elements are 0.03306 kg/s and 0.03229 kg/s for the sleeve valve and

poppet valve models respectively. Although it is not a big difference, it amounts to

roughly a 3% difference which is observed in the respective brake power figures of

24.12 kW against 22.72 kW. This difference increases with increasing engine speeds as

observed in the figure.

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Figure 69: Brake Power of Sleeve and Poppet Valve Models

6.4 CONCLUSION

Although the different discharge coefficients used for the sleeve valve model did not

make a significant difference in the engine performance, it did make an observable

difference in the effective valve areas of the different valves. Subsequently comparing

the sleeve valve model to the poppet valve model lead to the realisation that when the

mass flow rates through the engine increases, the flow has the possibility to choke if

the effective valve areas are not sufficiently large. Therefore, the effective valve areas

becomes of high importance and hence the discharge coefficients and true valve areas

becomes of high importance.

This study has focussed largely on determining the true valve area of the arbitrary

shaped sleeve valves as well as the discharge coefficients of these valves. While it was

shown that the exact determination of these variables did not make a substantial

difference in simulating the performance of the experimental engine, it will be of high

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importance in either high speed sleeve valve engine or downsized sleeve valve engines

where correctly simulating choked flow through the valves will be of very high

importance. This is due to the possibility of choked flow in the high mass flow rate

high speed engines and small valve area in downsized engines. The small valve areas

in the downsized engines will result in higher flow velocities through the valves,

leading to choked flow and the necessity to accurately predict the choked condition.

The methods of determining the true valve areas and discharge coefficients presented

in this report can therefore serve a great purpose if sleeve valve engine technology is

to be re-evaluated.

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7. FINAL CONCLUSION AND FURTHER WORK

7.1 CONCLUSION

The use of sleeve valves in engine design pose advantages in the form of enhanced

breathing capabilities and possibly larger valve areas when downsizing the piston bore.

All this leads to possible higher performance outputs especially in downsized engines.

Subsequently, the present interest in downsizing due to emission regulations therefore

justifies the consideration and analyses of sleeve valve engines. However, the lack of

sleeve valve engine development in the computer era necessitates the need for sleeve

valve models when sleeve valve analyses are done using computer simulations.

It was initially believed that accurate sleeve valve areas and discharge coefficients are

needed in order to accurately simulate sleeve valve engine performance. This belief

was proved valid in the comparison of the sleeve valve engine model and the similar

poppet valve engine model. It was realised that very accurate valve models are

needed for high speed applications where choked flow through the valves occur. This

occurs when engines operate at very high engine speeds, and can also occur in

downsized engines where minimal space is available for valves and the consequent

small valve areas tend to produce high flow velocities leading to choked flow. It is

subsequently important to accurately predict the onset of choked flow to determine

the maximum mass flow rate which in turn determines the engine performance.

In order to obtain accurate sleeve valve models the valve areas must be determined as

a function of the engine crank angle as well as the valve discharge coefficients. This is

challenging as very random valve profiles occur. This study presents a mathematical

method to determine the sleeve valve areas accurately from engine drawings and

practical measurements from the engine. However, in the modern CAD environment

this method might be redundant as the design software will probably be able to

automatically calculate the valve areas. Nonetheless, working through this method

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still provides a proper understanding of the sleeve movement during the engine cycle

and could aid in the design of new sleeve valve configurations.

Extensive work was also done on determining the valve discharge coefficients.

Experimental coefficients were found in the open literature and employed in an initial

WAVE model. These coefficients provided very sufficient results and it is suggested

that these coefficients could be used in an initial model especially during analyses in a

conceptual design phase.

When more detailed engine analyses are done, for instance in a detail design phase, it

is however suggested that the designer determine discharge coefficients characteristic

to the specific sleeve valve profiles being design or analysed. As was done in this

report, CFD simulations could be used to determine these coefficients. It was shown

how CFD was used to obtain discharge coefficients for the respective valves of the

experimental engine. The resultant CFD coefficients compared very well with the

experimental coefficients found in the open literature, but were more detailed

especially for different valve openings.

The sleeve valve models described in this study could therefore be used to accurately

simulate the performance of a sleeve valve engine. It was done using standard

software that does not even provide the use of sleeve valve models. These models will

be sufficient for analysing sleeve valve engine performance.

7.2 RECOMMENDATIONS FOR FURTHER WORK

As with any project there is always more work that could be done on this project. A

first and obvious extension of this project would be to acquire experimental sleeve

valve engine results and to calibrate the engine model presented in this report.

Chapter 5, which describes the experimental setup, could provide an excellent starting

point should this task is undertaken.

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A second recommendation for further work would be to redo the CFD analyses of the

discharge coefficients. In this study the detail geometry of the valve openings were

considered, but the surrounding element geometries were simplified to a simple

orifice type setup. Therefore it is suggested that the CFD analyses be updated with the

detail geometries of these adjacent elements as well. Although it is believed that the

current CFD results are a very good representation of the coefficients (as it compares

well with the experimental results) it is suggested that for more detail analyses of the

sleeve valve engine, the CFD models be updated. It is also suggested that the CFD

simulations for the exhaust valves be updated with a temperature boundary condition

representing the high temperature exhaust gasses, instead of the simplified 300K

simulations done in this study.

There are certainly always improvements that could also be done to the projects, for

instance including the sleeve material in the heat transfer coefficient of the cylinder

liner, but it is believed that the above mentioned issues are that major issues that

needs to be addressed before more conclusions can be drawn after which more work

could be identified.

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8. REFERENCES

Anton, H. (1995). Calculus (5th ed.). New York: John Wiley & Sons, Inc.

Bosch. (2004). Automotive Handbook (6th ed.). London: Professional Engineering

Publishing.

Chabert, L. (2007). Developing the Direct Injection on a 4 Stroke Sleeve Valve Engine.

School of Engineering. Cranfield, UK: Cranfield University.

Cole, A. (2006). Lecture Notes, Powertrain. UK: Cranfield University, School of

Engineering.

Dardalis, D. (2004). Rotating Liner Engine A New Approach to Reduce Engine Friction

and Increase Fuel Economy in Heavy Duty Engines. Austin, Texas: RLE Technologies, Inc.

Farrugia, M. (2004). FSAE: Engine Simulation with WAVE. Oakland: Oakland University.

Franco Sumariva, J. A. (2007). CFD Study of a 4 Stroke Sleeve Valve Engine. School of

Engineering. Cranfield, UK: Cranfield University.

Greenhalgh, D. (2006). Lecture Notes, Powertrain. UK: Cranfield University, School of

Engineering.

Hendrickson, S. P. (1999). A Miniature Powerplant for Very Small, Very Long Range

Autonomous Aircraft. Bingen WA, USA: The Insitu Group.

Incropera, F. P., & De Witt, D. P. (1996). Fundamentals of Heat and Mass Transfer (4th

ed.). New York: John Wiley & Sons, Inc.

Lowi, A. J. (2003). Designing a Miniature Engine for Large-Engine Performance. SAE .

Lumley, J. L. (2001). Early Work on Fluid Mechanics in the IC Engine. Annu. Rev. Fluid

Mech. , 33, 319-338.

Ricardo and Company. (1947). Investigation of Induction Swirl on Single-Cylinder

Sleeve-Valve Engines. HMSO.

Ricardo, H. R. (1931). The High-Speed Internal-Combustion Engine. London: Blackie &

Son Limited.

Rousseau, P. G. (2002). Advanced Thermal-FLuid Systems Course Notes.

Potchefstroom, South Africa: Potchefstroom University for Christian Higher Education.

Shames, I. H. (1992). Mechanics of Fluids (3rd ed.). Singapore: McGraw-Hill.

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Vasudevan, N. (2007). A Study of Coating Technologies for Minimal Lubrication

Operation for Sleeve Valve Engine. School of Engineering. Cranfield, UK: Cranfield

University.

Waldron, C. D. (1940). Flow Coefficients of Monosleeve Valves. National Advisory

Committee for Aeronautics , Report No 717, 227-239.

Wells, J. (n.d.). The 120 HP Argyll. Retrieved May 9, 2007, from

www.enginehistory.org/pioneering_sleeve_valve.htm

Yagi, S., Ishizuya, A., & Fujii, I. (1970). Research and Development of High-Speed, High-

Performance, Small Displacement Honda Engines. Honda R&D Co., Ltd. SAE Report No.

700122.