Thermodynamic,Engine Types&Overview Nezar

8/10/2019 Thermodynamic,Engine Types&Overview Nezar

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P and T sDiagrams of Power Cycles

The area under the heat addition process on a T-s

diagram is a geometric measure of the total heat

supplied during the cycle

q

in

, and the area under the

heat rejection process is a measure of the total heat

rejected q

out

. The difference between these two (the

area enclosed by the cyclic curve) is the net heat

transfer, which is also the net work produced during

the cycle.

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Reversible Heat-Engine Cycles

The second law of thermodynamics states that it is

impossible to construct a heat engine or to develop a

power cycle that has a thermal efficiency of 100%.

This means that at least part of the thermal energy

transferred to a power cycle must be transferred to a

low-temperature sink.

There are four phenomena that render anythermodynamic process irreversible. They are:

Friction

Unrestrained expansion

Mixing of different substances

Transfer of heat across a finite temperature difference

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Thermodynamic cyclescan be divided into twogeneral categories: Powercycles andrefrigeration

cycles.

Thermodynamic cycles can also be categorized asgascycles orvaporcycles, depending upon the phase

of the working fluid.

Thermodynamic cycles can be categorized yetanother way: closedandopencycles.

Heat engines are categorized asinternal or external

combustion engines.

Categorize Cycles

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Air-Standard Assumptions

To reduce the analysis of an actual gas power cycle to a

manageable level, we utilize the following

approximations, commonly know as the air-

standard assumptions:

1. The working fluid is air, which continuously circulates

in a closed loop and always behaves as an ideal gas.

2. All the processes that make up the cycle are internally

reversible.

3. The combustion process is replaced by a heat-

addition process from an external source.

4. The exhaust process is replaced by a heat rejection

process that restores the working fluid to its initial

state.

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Bore and

stroke of acylinder

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Mean Effective Pressure

Notice that the compression ratio is a

volume ratio and should not be

confused with the pressure ratio.

Mean effective pressure(MEP) is a

fictitious pressure that, if it acted

on the piston during the entire

power stroke, would produce the

same amount of net work as that

produced during the actual cycle.

The ratio of the maximum volume formed in the cylinder to

the minimum (clearance) volume is called the compression

ratio

of the engine.

TDC

BDC

min

max

V

V

V

Vr

minmax

net

VV

WMEP

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Three Ideal Power Cycles

Three ideal power cycles are completely reversiblepower cycles, called externally reversible power

cycles. These threeideal cycles are the Carnot cycle,

the Ericsson cycle, and the Stirling Cycle.

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Three Ideal Power Cycles

The Carnot cycle is an externally reversible power cycleand is sometimes referred to as the optimum power

cyclein thermodynamic textbooks. It is composed of

two reversible isothermal processes and two reversible

adiabatic (isentropic) processes.

The Ericsson power cycle is another heat-engine cyclethat is completely reversible or externally reversible. It

is composed of two reversible isothermal processes and

two reversible isobaric processes (with regenerator).

The Stirling cycle is also an externally reversible heat-

engine cycle and is the only one of the three ideal power

cycles that has seen considerable practical application.

It is composed of two reversible isothermal processes

and two reversible isometric (constant volume)

processes.

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Carnot Cycle and Its Value in Engineering

The Carnot cycle is composed

of four totally reversible

processes: isothermal heat

addition, isentropic expansion,

isothermal heat rejection, and

isentropic compression (as

shown in the

P-

diagram at

right). The Carnot cycle can be

executed in a closed system (a

piston-cylinder device) or a

steady-flow system (utilizing

two turbines and two

compressors), and either a gas

or vapor can be used as the

working fluid.

H

LCarnot,th

T

T1

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Internal-Combustion Engine Cycles

Internal-combustion(IC) engines cannot operate onan ideal reversible heat-engine cycle but they can be

approximated by internally reversible cycles in which

all the processes are reversible except the heat-

addition and heat-rejection processes.

In general, IC engines are more polluting thanexternal-combustion (EC) engines because of the

formation of nitrogen oxides, carbon dioxide, and

unburned hydrocarbons.

The Otto cycle is the basic thermodynamic powercycle for the spark-ignition (SI), internal-

combustion engine.

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Otto Cycle: The ideal Cycle for Spark-Ignition Engines

Figures below show the actual and ideal cycles in spark-

ignition (SI) engines and their P- diagrams.

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Ideal Otto Cycle

The thermodynamic analysis of

the actual four-stroke or two-

stroke cycles can be simplified

significantly if the air-standard

assumptions are utilized. The T-

sdiagram of the Otto cycle is

given in the figure at left.

The ideal Otto cycle consists of four internally

reversible processes:

1

2 Isentropic compression

23 Constant volume heat addition

3

4 Isentropic expansion

41 Constant volume heat rejection

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Thermal Efficiency of an Otto Cycle

The Otto cycle is executed in a closed system, and

disregarding the changes in kinetic and potential

energies, we have

1

2

1

232

141

23

14

1414

2323

111

1

11

11

k

in

out

in

netOtto,th

vout

vin

outinoutin

rT

T

T/TT

T/TT

TT

TT

q

q

q

w

TTCuuq

TTCuuq

uwwqq

2

1

2

1

3

4

1

4

3

1

1

2

2

1

V

V

V

Vr

T

T

T

T

min

max

kk

and;Where,

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Example IV-4.1: The Ideal Otto Cycle

determine a) the maximum temperature and pressure

that occur during the cycle,

b

) the net work output,

c

)

the thermal efficiency, and d) the mean effective

pressure for the cycle.

Solution:

An ideal Otto cycle has a

compression ratio of 8. At the

beginning of the compression

process, the air is at 100 kPa and

17

o

C, and 800 kJ/kg of heat is

transferred to air during the

constant-volume heat-addition

process. Accounting for the variation

of specific heats of air with

temperature,

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essdimensionlaisvolume)specific(relativepropertyThe

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,

:cycleOttoaninpressureandetemperaturMaximum

r

inin

rr

r

r

r

v:Note

MPa..

.

MPa.v

v

T

T

PPT

vP

T

vP

K.Tkg/kJ..uquuuq

kPa..

v

v

T

TPP

T

vP

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vP

kg/kJ.uK.T..

r

vv

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v

v

v

.vkg/kJ.uKT

a

345414652

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3

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32323

2

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1

11

2

22

22

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2

1

2

1

2

111

20


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s.assumptionthisutlizinginexercisedbeshouldCare

56.5%or

:sassumptionstandard-air-coldtheUnder

52.3%or

:efficiencythermalThe

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:outputworknetThe

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4

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.rr

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kg/kJ..qqqw

kg/kJ...uuquuq

kg/kJ.uK.T

..rvvrv

v

v

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b

.k

kth

in

netth

outinnetnet

outout

rrr

r

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cycle.entiretheasoutputworknetsametheproducew ould

strokepow ertheduringkPa574.4ofpressureconstantaTherefore,

Thus,

:definitionitsfromdeterminedispressureeffectivemeanThe

vp

netnet

ccNote

kPa.kJ

m.kPa

..

.

r

vv

w

vv

wmep

kgm.

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22


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Diesel Cycle: The Ideal Cycle for Compression-Ignition Engines

The diesel cycle is the ideal cycle for CI(Compression-

Ignition) reciprocating engines. The CI engine first

proposed by Rudolph Dieselin the 1890s, is very

similar to the SIengine, differing mainly in the method

of initiating combustion. In SI engines (also known as

gasoline engines), the air-fuel mixture is compressed

to a temperature that is below the autoignition

temperature of the fuel, and the combustion process is

initiated by firing a spark plug. In CI engines (also

known as diesel engines), the air is compressed to a

temperature that is above the autoignition temperature

of the fuel, and combustion starts on contact as the

fuel is injected into this hot air. Therefore, the spark

plug and carburetor are replaced by a fuel injector in

diesel engines.

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The I deal Air Standard Diesel Cycle

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Ideal Cycle for CI Engines continued)

In diesel engines, ONLYair is compressed during the

compression stroke, eliminating the possibility of

autoignition. Therefore, diesel engines can be designed

to operate at much higher compression ratios, typically

between 12 and 24.

The fuel injection process in diesel engines starts when

the piston approaches TDC and continues during the

first part of the power stroke. Therefore, the

combustion process in these engines takes place over a

longer interval. Because of this longer duration, the

combustion process in the ideal Diesel cycle is

approximated as a constant-pressure heat-addition

process. In fact, this is the ONLYprocess where the

Otto and the Diesel cycles differ.

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Ideal Cycle for CI Engines continued)

1

11111

123

14

1414

232323

c

kc

kin

out

in

netDiesel,th

vout

pinout,bin

rk

r

rTTk

TT

q

q

q

wTTCuuq

TTChhquuwq

2

3

2

1

cr

r

and

Where,

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Thermal efficiency of Ideal Diesel Cycle

Under the cold-air-standard assumptions, the

efficiency of a Diesel cycle differs from the efficiency of

Otto cycle by the quantity in the brackets. (See Slide

26)

The quantity in the

brackets is always greater

than 1. Therefore,

th,Otto

>

th, Diesel

whenboth

cycles operate on the

same compression ratio.

Also the

cuttoff ratio, r

c

decreases, the efficiency

of the Diesel cycle

increases. (See figure at

right)

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Cylinder Arrangements for Reciprocating Engines

Figure below shows schematic diagrams of some of the

different cylinder arrangements for reciprocating

engines.

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Verticalin-line engine is commonly used today infour- and six-cylinder automobile engines.

TheV-engineis commonly employed in eight-cylinder (V-8) and some six-cylinder (V-6) automobile

engines.

Thehorizontalengine is essentially a V-engine with

180

o

between the opposed cylinders. This system was

used as the four-cylinder, air-cooled engine that

powered the Volkswagon bug.

Theopposed-pistonengine consists of two pistons,

two crankshafts, and one cylinder. The two crankshafts

are geared together to assure synchronization. These

opposed-piston systems are often employed in large

diesel engines.

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Thedelta engine is composed of three opposed-piston cylinders connected in a delta arrangement.

These systems have found application in the petroleum

industry.

Theradialengine is composed of a ring of cylindersin one plane. One piston rod the master rod is

connected to the single crank on the crankshaft and all

the other piston rods are connected to the master rod.

Radial engines have a high power-to-weight ratio and

were commonly employed in large aircraft before the

advent of the turbojet engine.

When the term rotary engine is used today itimplies something other than a radial engine with a

stationary crank.

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Engine Performance

There are several performance factors that are common

to all engines and prime movers. One of the main

operating parameters of interest is the actual output of

the engine. The brake horsepower(Bhp) is the power

delivered to the driveshaft dynamometer.

The brake horsepower is usually measured by

determining the reaction force on the dynamometer

and using the following equation:

00033

2

,

FRNBhp d

Where

F

is the net reaction force of the dynamometer,

in lbf, Ris the radius arm, in ft, andN

d

is the angular

velocity of the dynamometer, in rpm.

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Horsepower

For a particular engine, the relationship between the

mean effective pressure (mep) and the power is:

minute.perstrokespowerofnumbertheisand

w here

ep

dis

minmax

net

pdis

CNN

strokeboreV

VV

Wmep

,

NVmepBhp

4

00033

2

Where Cis the number of cylinders in the engine,N

e

is

the rpm of the engine, and is equal to 1 for a two-

stroke-cycle engine and 2 for a four-stroke-cycle

engine.

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Brake Thermal Efficiency

The brake thermal efficiency of an engine,

th

, unlike

power plants, is usually based on the lower heating

value (LHV) of the fuel. The relationship between

efficiency and the brake specific fuel consumption

(Bsfc) is:

Bhp

Bsfc

LHVBsfcth

lbm/hrate,fuel

w here

2545

Note that the brake specific fuel consumption (Bsfc) of

an engine is a measure of the fuel economy and is

normally expressed in units of mass of fuel consumed

per unit energy output.

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External-Combustion Systems

External-combustion power systems have several

advantages

over internal-combustion systems. In

general, they are less polluting. The primary pollutants

from internal-combustion engines are unburned

hydrocarbons, carbon monoxide, and oxides of

nitrogen.

In external-combustion engines, the CH

x

and CO can

be drastically reduced by carrying out the combustion

with excess air and the NO

x

production can be

markedly reduced by lowering the combustion

temperature. By burning the fuel with excess air, more

energy is released per pound of fuel.

There are three general ideal external-combustion

engine cycles, the Stirling and Brayton are ideal gas-

power, and vapor power cycles.

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The

Brayton

cycle was first proposed by George Brayton

for use in the reciprocating oil-burning engine that he

developed around 1870.

Brayton Cycle:

The Ideal Cycle for Gas-Turbine Engines

Fresh air at ambient conditions is drawn into the compressor,

where its temperature and pressure are raised. The high-

pressure air proceeds into the

combustion chamber, where

the fuel is burned at constant

pressure. The resulting high-

temperature gases then enter

the turbine, where they

expand to the atmospheric

pressure, thus producing

power. (An open cycle.)

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Brayton Cycle continued)

The open gas-turbine cycle can be modeledas a closed

cycle, as shown in the figure below, by utilizing the air-

standard assumptions.

The ideal cycle that the working

fluid undergoes in this closed

loop is the Brayton cycle, which

is made up of four internally

reversible processes:

1

2 Isentropic compression (in a

compressor)

2

3 Constant pressure heat addition

3

4 Isentropic expansion (in a

turbine)

4

1 Constant pressure heat rejection

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T sDiagram of Ideal Brayton Cycle

Notice that all four processes

of the Brayton cycle are

executed in steady-flow

devices (as shown in the

figure on the previous slide,

T-sdiagram at the right), and

the energy balance for the

ideal Brayton cycle can be

expressed, on a unit-mass

basis, as

1414

2323

TTChhq

TTChhqhhwwqq

pout

pin

inletexitoutinoutin

and

w here

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P Diagram and

th

of Ideal Brayton Cycle

Then the thermal efficiency of

the ideal Brayton cycle under

the cold-air-standard

assumptions becomes

k/kp

p

p

in

out

in

netBrayton,th

r

T/TT

T/TT

TTC

TTC

q

q

q

w

1

232

141

23

14

11

1

111

1

ratio.pressuretheisand,w here1

2

4

3

1

4

3

1

1

2

1

2

P

Pr

T

T

P

P

P

P

T

Tp

k/kk/k

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Thermal Efficiency of the Ideal Brayton Cycle

Under the cold-air-standard

assumptions, the thermal

efficiency of an ideal Brayton

cycle increases with both the

specific heat ratio of the

working fluid (if different from

air) and its

pressure ratio

(as

shown in the figure at right) of

the isentropic compression

process.

The highest temperature in the cycle occurs at the end

of the combustion process, and it is limited by the

maximum temperaturethat the turbine blades can

withstand. This also

limits the pressure ratios

that can

be used in the cycle.

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With the demise of the steam powered tractor in thelate 1800s, most modern tractors are equipped withinternal combustion engines.

Internal combustion engines are identified by thenumber of strokes in the cycle and by the fuel that is used to run them.

Common Tractor Classifications:4 stroke cycle

- gasoline- diesel

- LP

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IntakeExhaust

Lubricating

Electrical

Cooling

Fuel

Hydraulic

Drive Train

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Parts:1. Crankcase Oil Reservoir (Oil

Pan)

2. Oil Pump

3. Oil Filter

4. Oil Passages

5. Pressure Regulating Valve

Oil goes to:1. Camshaft Bearings

2. Crankshaft Main Bearings

3. Piston Pin Bearing

4. Valve Tappet Shaft 47


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Parts:

1. Battery

2. Ground Cable

3. Key Switch

4. Ammeter5. Voltage Regulator

6. Starter Solenoid

7. Starter

8. Distributor * Gasoline

Only

9. Coil

10. Alternator

11. Spark Plug

12. Power Cable48


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Cooling System

Liquid & Air

Parts:

1. Radiator

2. Pressure Cap

3. Fan4. Fan Belt

5. Water Pump

6. Engine Water Jacket

7. Thermostat8. Connecting Hoses

9. Liquid or Coolant

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P T i i


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Power Transmission

Mechanical & Hydraulic

Parts:

1. Clutch Pedal

2. Clutch

3. Shift Controls

4. Transmission

5. Differential

6. Differential Lock Pedal

7. Final Drives

8. Power Take Off (PTO)

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TWO STROKE ENGINES

Two-stroke engines do not have valves,

which simplifies their construction and

lowers their weight.

Two-stroke engines fire once every

revolution, while four-stroke engines fire

once every other revolution. This givestwo-stroke engines a significant power

boost.

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TWO STROKE ENGINES

Two-stroke engines don't last nearly as

long as four-stroke engines. The lack ofa dedicated lubrication system means

that the parts of a two-stroke engine

wear a lot faster.

Two-stroke oil is expensive, and you

need about 4 ounces of it per gallon ofgas. You would burn about a gallon of

oil every 1,000 miles if you used a two-

stroke engine in a car.

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COMPRESSION

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FOUR CYCLE ENGINES

conventional Otto engines

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Unusual Four stroke engines

applications

ROTARY CYLINDER VALVE ENGINE RCV ENGINE

ROTARY ENGINES WANKEL ENGINE

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The heart of a rotary engine is the rotor.This is roughly the

equivalent of the pistons in a piston engine. The rotor is

mounted on a large circular lobe on the output shaft. This

lobe is offset from the centerline of the shaft and acts like thecrank handle on a winch, giving the rotor the leverage it

needs to turn the output shaft. As the rotor orbits inside the

housing, it pushes the lobe around in tight circles, turning

three timesfor every one revolution of the rotor. 69


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How Rotary Engines Work


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How Rotary Engines Work

If you watch carefully, you'll see the offsetlobe on the output shaft spinning three times

for every complete revolution of the rotor.

As the rotor moves through the

housing, the three chambers

created by the rotor change size.

This size change produces apumping action. Let's go through

each of the four stokes of the

engine looking at one face of therotor.

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Thi t t t th


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This starts at thehighest pointknown as topdead center andends at bottomdead center

The intake strokeallows the pistonto suck fuel andair into thecombustionchamber through

the intake valve 74

Compression stroke


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Second stroke

The piston moves from BDC to TDC

Intake and exhaust valves stay closed

Air and fuel mixture is compressed8:1 to 12:1

The pressure in the cylinder is raised

75

Compression startsat bottom dead


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at bottom deadcenter and ends attop dead center.

The second motion ofthe stroke takes allthe fuel and air that

was stored andcompresses it intoone tenth its originalsizes. Making theair/fuel mixtureincrease intemperaturepreparing it for thenext stage in its

combustion cycle. 76


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The power stroke starts as


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The power stroke starts as

soon as the piston reaches

top dead center allowing the

spark plug to ignite.

This electric current created

by the spark plug ignites the

fuel and air mixture sending

the piston back down the

cylinder with a pressure

reaching high as 600 PSI.

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The final stage of the


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The final stage of the

stroke releases all the

burned fuel through the

exhaust valve.

As the piston moves

from bottom dead center

to top dead center it

takes all the burned fuel

and pushes it out of thecylinder, preparing it for

the next cycle of strokes.

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Inlet Valve : Valve Timing Diagram


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PcylPatm

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When expressed as a percentage, the thermal efficiency must bebetween 0% and 100%. Due to inefficiencies such as friction,

heat loss, and other factors, thermal engines' efficiencies aretypically much less than 100%. For example, a typical gasolineautomobile engine operates at around 25% efficiency. The largestdiesel engine in the world peaks at 51.7%.

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The term indicated work is used to define the net work doneon the piston per cycle

the indicated mean effective pressure (imep),can be defined

by;

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The imep is a hypothetical pressure that would produce the

same indicated work if it were to act on the piston throughoutthe expansion stroke. The concept of imep is useful because itdescribes the thermodynamic performance of an engine, in away that is independent of engine size and speed and frictionallosses.

Unfortunately, not all the work done by the gas on the piston isavailable as shaft work because there are frictional losses inthe engine. These losses can be quantified by the brake meaneffective pressure (bmep,), a hypothetical pressure that acts onthe piston during the expansion stroke and would lead to thesame brake work output in a frictionless engine.

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Mechanical Efficiency contd


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Mechanical efficiency depends on pumping losses

(throttle position) andfrictional losses (engine design and engine speed).

Typical values for automobile engines at WOT are:90% @2000 RPM and 75% @ max

speed.

Throttling increases pumping power and thus themechanical efficiency

decreases, at idle the mechanical efficiencyapproaches zero.

93

Brake Specific Fuel Consumption (BSFC) is a measure of fuel

efficiency within a shaft reciprocating engine It is the rate


93/120

efficiency within a shaft reciprocating engine. It is the rate

of fuel consumption divided by the power produced. Specific

fuel consumption is based on the torque delivered by the

engine in respect to the fuel mass flow delivered to the engine.

Measured after all parasitic engine losses is brake specific fuel

consumption [BSFC] and measuring specific fuel consumption

based on the in-cylinder pressures (ability of the pressure to do

work) is indicated specific fuel consumption [ISFC].

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Volumetric Efficiency


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Volumetric efficiency a measure of overall effectiveness ofengine and its intake and exhaust system as a natural

breathing system. It is defined as:

If the air density ra,0is evaluated at inlet manifold conditions, thevolumetric efficiency is a measure of breathing performance of the

cylinder, inlet port and valve.

If the air density ra,0is evaluated at ambient conditions, the volumetricefficiency is a measure of overall intake and exhaust system and other

engine features. The full load value of volumetric efficiency is a design feature of entire

engine system.

NV

m

da

a

v

0,

2

r

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Ignition and Combustion in Spark Ignition


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and Diesel Engines

Spark ignition (SI) engines usually have pre-mixed combustion, in which aflame front initiated by a spark propagates across the combustion chamberthrough the unburned mixture. Compression ignition (CI) engines normallyinject their fuel toward the end of the compression stroke, and thecombustion is controlled primarily by diffusion.

Whether combustion is pre-mixed (as in SI engines) or diffusion controlled

(as in CI engines) has a major influence on the range of air-fuel ratios(AFRs) that will burn.

In pre-mixed combustion, the AFR must be close to stoichiometric-the AFRvalue that is chemically correct for complete combustion. In practice,dissociation and the limited time available for combustion will mean thateven with the stoichiometric AFR, complete combustion will not occur.

In diffusion combustion, much weaker AFRs can be used (i.e., an excess ofair) because around each fuel droplet will be a range of flammable AFRs.

Typical ranges for the (gravimetric) air-fuel ratio are as follows:

10

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Diesel engines have a higher maximum

efficiency than spark ignition engines for threereasons:

The compression ratio is higher.

During the initial part of compression, only airis present.

The air-fuel mixture is always weak of

stoichiometric.

10

2

Simple Combustion Equilibrium


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p q

For a given combustion device, say a piston engine, howmuch fuel and air should be injected in order to completely

burn both? This question can be answered by balancing the

combustion reaction equation for a particular fuel. A

stoichiometric mixture contains the exact amount of fueland oxidizer such that after combustion is completed, all the

fuel and oxidizer are consumed to form products.

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Combustion stoichiometry for a general hydrocarbon fuel, withair can be expressed as;

The amount of air required for combusting a stoichiometricmixture is called stoichiometric or theoretical air.

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Methods of Quantifying Fuel and Air Content


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of Combustible Mixtures

In practice, fuels are often combusted with an amount of air

different from the stoichiometric ratio. If less air than the

stoichiometric amount is used, the mixture is described as fuel

rich. If excess air is used, the mixture is described as fuel lean.

For this reason, it is convenient to quantify the combustible

mixture using one of the following commonly used methods:

Fuel-Air Ratio (FAR): The fuel-air ratio, f, is given by

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Fuel Requirements


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q

Gasoline is a mixture of hydrocarbons (with 4 toapproximately 12 carbon atoms) and a boiling point range of

approximately 30-200C. Diesel fuel is a mixture of higher

molarmass hydrocarbons (typically 12 to 22 carbon atoms),

with a boiling point range of approximately180-380C. Fuelsfor spark ignition engines should vaporize readily and be

resistant to self-ignition, as indicated by a high octane rating.

In contrast, fuels for compression ignition engines should self-ignite readily, as indicated by a high cetane number.

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Octane number is a standard measure of the anti-knock


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properties (i.e. the performance) of a motor or aviation fuel.

The higher the octane number, the more compression the fuel

can withstand before detonating. In broad terms, fuels with ahigher octane rating are used in high-compression engines that

generally have higher performance.

Knocking (also called knock, detonation, spark knock, pinging

or pinking) in spark-ignition internal combustion enginesoccurs when combustion of the air/fuel mixture in the cylinder

starts off correctly in response to ignition by the spark plug,

Effects of engine knocking range from inconsequential to

completely destructive.

.

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The octane or cetane rating of a fuel is established by

i i i i i li i h f f l i


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comparing its ignition quality with respect to reference fuels in

CFR (Co-operative Fuel Research) engines, according to

internationally agreed standards. The most common type ofoctane rating worldwide is the Research Octane Number

(RON). RON is determined by running the fuel in a test engine

with a variable compression ratio under controlled conditions,

and comparing the results with those for mixtures of iso-octane and n-heptane.

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Engine Knockand thermal Efficiency of an Engine


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The thermal efficiency of the ideal Otto cycle increases

with both the compression ratio and the specific heat

ratio.

When highcompression ratios

are used, the temperature of the

air-fuel mixture rises above the

autoignition temperature

produces an audible noise,

which is called engine knock.

(antiknock, tetraethyl lead?

unleaded gas)

For a given compression ratio, an ideal Otto cycle using

a monatomic gas (such as argon or helium,

k

= 1.667) as

the working fluid will have the highest thermal efficiency.

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Combustion Chamber Designs


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Combustion Chamber Design


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Combustion Chamber Design


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A turbocharger or turbo is a centrifugal compressor

Turbocharging


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A turbocharger, or turbo, is a centrifugal compressorpowered by a turbine that is driven by an engine's exhaustgases. Its benefit lies with the compressor increasing the

mass of air entering the engine (forced induction), therebyresulting in greater performance (for either, or both, powerand efficiency). They are popularly used with internalcombustion engines (e.g., four-stroke engines like Ottocycles and Diesel cycles).

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Engine Artificial Respiratory System: An Inclusion ofCV


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CV

Turbo-Charged Engine 120

Turbo -Charger


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g

Thermodynamic,Engine Types&Overview Nezar

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