Design and Fabrication of Heat Exchanger for EGR System

Submitted in partial fulfillment of the requirements for the award of degree of

BACHELOR OF TECHNOLOGYIN

MECHANICAL ENGINEERING

Submitted by:

Grampurohit Chaitanya V (06BME016) Parikh Aradhya A (06BME030)

Patil Alpesh S (06BME039)

Guided by:

Prof. N K ShahCo-Guide: Dr. R N Patel

MECHANICAL ENGINEERING DEPARTMENTINSTITUTE OF TECHNOLOGY

NIRMA UNIVERSITY OF SCIENCE AND TECHNOLOGY

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CERTIFICATE

This is to certify that, Mr./ Ms. Grampurohit Chaitanya V, student of Mechanical engineering, 7th / 8th Semester of Institute of Technology, Nirma University, has satisfactorily completed the project report titled Design and Fabrication of Heat Exchanger for EGR System.

Date:

Guide (s): Head of the Department

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CERTIFICATE

This is to certify that, Mr./ Ms. Parikh Aradhya A, student of Mechanical engineering, 7th / 8th Semester of Institute of Technology, Nirma University, has satisfactorily completed the project report titled Design and Fabrication of Heat Exchanger for EGR System.

Date:

Guide (s): Head of the Department

-

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CERTIFICATE

This is to certify that, Mr./ Ms. Patil Alpesh S, student of Mechanical engineering, 7th / 8th Semester of Institute of Technology, Nirma University, has satisfactorily completed the project report titled Design and Fabrication of Heat Exchanger for EGR System.

Date:

Guide (s): Head of the Department

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ACKNOWLEDGMENT

A work of this caliber calls months of hard work and commitment which is only possible by the constant efforts put by the guide. We thank our guide Prof. N.K.Shah, Asst Professor of Mechanical Engineering Department for providing a better platform to complete our project. We thank him for taking out his time for the project in-spite of his busy schedule. . We would like to thank Dr. R.N.Patel for bringing satisfactory solution to our queries and doubts related to the project. We would also like to thank Nirav Patel, for his guidance on the topic.

We would be failing in our duties if we do not acknowledge the invaluable contribution of the faculties of Mechanical Engineering Department for the successful completion of the project. It would have been very difficult to prepare this project without the enthusiastic support, advice and inspiration given to us by staff of Mechanical Engineering Department. We also thank Mr. V. R. Iyer, Head of the Mechanical Department for giving us such a great opportunity.

Grampurohit Chaitanya V Parikh Aradhya APatil Alpesh S

Date:Place:

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ABSTRACT

To meet stringent vehicular exhaust emission norms worldwide, several exhaust pre-treatment and post-treatment techniques have been employed in modern spark Ignition and Compression Ignition engines. Exhaust Gas Recirculation (EGR) is a technique, which is being used widely to reduce and control the NOx emission mainly from diesel engine. This technique is mainly concerned with the reduction in the amount of NOx generated and which can be achieved by either reducing the amount of oxygen in the combustion chamber or by reducing the excessive amount of heat generation in the combustion chamber during the ignition stroke. The method adopted by the EGR device is, adequate amount of exhaust is deviated back to the combustion chamber with the help of an EGR valve to the intake manifold. This will reduce the excessive amount of heat generation in combustion chamber and hence reduce NOx generated per cycle.

We have undertaken the project to design a Heat Exchanger for the purpose of Exhaust Gas Recirculation. The design should be economical and simple in construction. It should also be light in weight. Based on available data and the actual engine parameters, we have designed the heat exchanger. This heat exchanger would be used afterwards for observing the effects of Exhaust Gas Recirculation.

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INDEXChap No. Contents Page No.

-- Certificate 2-- Acknowledgement 5-- Abstract 6-- List of Figures 8-- List of Tables 8-- Symbols used in Project Calcuation 9

1 Introduction Aim of the Project 11 Introduction to Project Parameters 11 Introduction to Project 12

2 Pollutants Introduction to Pollutants 13 Mechanism of NOx Formation 13

3 Emission standards Emission Norms 15 Evolution of BIS Standards 15 Euro Standards 16

4 Exhaust Gas Recirculation Introduction 17 Classification 18 EGR Components 19 Theory of Operation 20 EGR Percentage 21 EGR Malfunction 21

5 Calculation Rating of Heat Exchanger 22 Reynolds Number Calculation 24 Overall Heat Transfer Coefficient 25 Pressure Drop 27 Power Requirements 28

-- Conclusion 30-- References 31

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LIST OF FIGURES

Fig No. Title Page No.

4.1 EGR Components 19

4.2 EGR Flow 20

5.1 Design of Heat Exchanger 33

LIST OF TABLES

Table No. Title Page No.

1.1 Introduction to Project Parameters 113.1 Euro Standards 165.1 Properties of Fluid at Bulk Mean Temperature 235.2 Dimensions of Pipe 245.3 Cross-sectional Area 245.4 LMTD Calculations 255.5 Reynolds Number Calculations 255.6 Convective Heat Transfer Coefficients 265.7 Fouling Factor 275.8 Overall Heat Transfer Coefficient 275.9 Surface Area 285.1 Parametric Study 29

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Symbols used in Project Calculationd, bore diameter (m)l, length of stroke (m)

Vd, engine swept volume (m3)

N, speed of the engine (rpm)

ρi, density of air (kg/m3)

maideal , ideal mass flow rate of air(kg/hr)

ηv, Volumetric efficiency of engine

maactual , actual mass flow rate of air(kg/hr)

Bp, Brake power (kw)Bsfc, brake fuel specific consumption (kg/kw-hr)mfuel, mass flow rate of fuel(kg/hr)

mexhaust, mass flow rate of exhaust gas(kg/hr)

mgas, mass flow rate in EGR (kg/hr)

NPD, nominal pipe diameter (inch)Di, outer pipe inner diameter (mm)Do, outer pipe outer diameter (mm)Dh, outer pipe hydraulic diameter (mm)De, outer pipe equivalent diameter (mm)

Ao, cross-sectional area for flow (mm2)

di, do, dh, de, Ai respective terms for inner tubeLmtd, log mean temperature differenceCpg, specific heat of exhuast gas (kj/kg -°C)Mwater , mass flow rate of cooling water (kg/s)Cpw, specific heat of water(kj/kg °C)

T1, Exhaust gas temperature from engine (°C)T2, Exhaust gas outlet temperature from EGR (°C)ΔTg , temperature drop of exhaust gas in EGR (°C)

T3, cooling water inlet temperature (°C)T4, cooling water outlet temperature from EGR (°C)ΔTw , temperature drop of water in EGR (°C)

Tbg, bulk mean temperature of exhaust gas (°C)

μg, dynamic viscosity (kg / m s)Prg, prandlt number for exhaust gas Reg Reynolds number for exhaust gasK, Thermal Conductivity of exhaust gas (W/ m K)

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f, friction factor for exhaust gasNug, Nussselt Number for exhuast gas

Ho, heat transfer coefficient for outer tube (W/m2 k)

Rfo , fouling factor for outer tube (m2 K/W)

Uo , overall heat transfer coefficient (W/m2 K)

Afo, Surface area required for heat transfer (m2)

Similarly the terms for cooling water and inner tube

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INTRODUCTION

1.1 AIM OF THE PROJECT

As a part of syllabus of final year, we are supposed to prepare a project on a existing or theme model present in the industry. Our aim was to study a device which is helpful to society as being an engineer we were and also to implement our design and heat exchanger knowledge, heat transfer being a area of interest of ours. Pollution in recent times, has been a real problem in almost every part of the world, so we decided to do our project on some measures which are helpful in reducing pollution. The major source of pollution in today’s day to day life is an automobile engine. 27% of total pollution is created by daily use of automobile and this is only an analytical data, the actual data maybe higher or beyond. The chief pollutant from automobile engine is NOx and other toxic acidic gas

1.2 INTRODUCTION TO PROJECT PARAMETERS [2]

ENGINE SPECIFICATIONSFuel : Diesel oilNo of cylinders : 1No of strokes : 4Bore : 92mmStroke length : 110mmEngine R.P.M : 1500 rpmB.H.P : 5 hp at 1500 rpmBsfc : 0.3 kg/kW-hrCalorific value : 43000 Kcal/kgCooling type : Water cooled

OTHER PARAMETERSType of Heat exchanger : Tube-in-Tube Heat exchanger% exhaust gas circulated : 18 %Density of exhaust gas : 1.15 kg/ m3

Density of water : 995.9 kg/ m3

Volumetric efficiency : 85%Inlet temperature of gas in EGR : 250 °COulet temperature of gas in EGR : 80 °CWater inlet temperature : 30°CSpecific heat of gas : 2.23 kJ/kgKSpecific heat of water : 4.179 kJ/kgKInter fouling for water : 0.000176 m2K/WOuter fouling for gas : 0.001761 m2K/WInner and Outer tube material : Stainless steelPump efficiency : 80%

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1.3 INTRODUCTION TO PROJECT

The function of an Exhaust Gas Recirculation (EGR) system is to re-circulate some calculated amount of exhaust gas back into the inlet manifold in order to reduce the excessive heat generated inside the engine. The actual system consists of an EGR valve, an actuator for the valve, EGR flow pipes, some gaskets and the total installation costs of this system is around 15000 to 18000 Rupees.

We were required to design and fabricate a heat exchanger that can be used as an EGR. The constraints were the simplicity in design, light weight and economical. The NOx emissions should also reduce by a satisfactory result.

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POLLUTANTS

2.1INTRODUCTION TO POLLUTANTS [3]

Motor vehicles produce many different pollutants. The principle pollutants of concern those that have been demonstrated to have significant effects on human, animal, plant, and environmental health and welfare include:

• Hydrocarbons: This class is made up of unburned or partially burned fuel, and is a major contributor to urban smog, as well as being toxic. They can cause liver damage and even cancer. Technology for one application (to meet a non-methane hydrocarbon standard) may not be suitable for use in an application that has to meet a total hydrocarbon standard. Methane is not toxic, but is more difficult to break down in a catalytic converter, so in effect a "non-methane hydrocarbon" standard can be considered to be looser. Since methane is a greenhouse gas, interest is rising in how to eliminate emissions of it.• Carbon monoxide (CO): a product of incomplete combustion, carbon monoxide reduces the blood's ability to carry oxygen and is dangerous to people with heart disease.• Nitrogen oxides (NOx): These are generated when nitrogen in the air reacts with oxygen at the high temperature and pressure inside the engine. NOx is a precursor to smog and acid rain.• Carbon dioxide (CO2): CO2 is not a pollutant per se, but is a greenhouse gas and so plays a role in global warming. The only way to reduce CO2 emission is to burn less fuel.• Particulates — soot or smoke made up of particles in the micrometer size range. Particulate matter causes respiratory health effects in humans and animals.• Sulphur oxide (SOx): is a general term for oxides of sulphur, which is emitted from motor vehicles. Burning fuel contains a high concentration of sulphur.

2.2 MECHANICS OF NOx FORMATION [2]

A major hurdle in understanding the mechanism of formation and controlling its emission is that combustion is highly heterogeneous and transient in diesel engines. While NO and NO2 are lumped together as NOx, there are some distinctive differences between these two pollutants. NO is a colorless and odorless gas, while NO2 is a reddish brown gas with pungent odor. Both gases are considered toxic; butNO2 has a level of toxicity 5 times greater than that of NO. Although NO2 is largely formed from oxidation of NO, attention has been given on how NO can be controlled before and after combustion (Levendis et al 1994). NO is formed during the post flame combustion process in a high temperature region. The most widely accepted mechanism was suggested by Zeldovich (Heywood 1988). The principal source of NO formation is the oxidation of the nitrogen present in atmospheric air. The nitric oxide formation chain reactions are initiated by atomic oxygen, which forms from the dissociation of oxygen molecules at the high temperatures reached during the combustion process. The principle reactions governing the formation of NO from molecular nitrogen are,

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N2 + O NO + N;N + O2 NO + O;N + OH NO + H:

Chemical equilibrium consideration indicates that for burnt gases at typical flame temperatures, NO2/NO ratios should be negligibly small. While experimental data show that this is true for spark ignition engines, in diesels, NO2 can be 10 to 30% of total exhaust emissions of oxides of nitrogen. A plausible mechanism for the persistence of NO2 is as follows. NO formed in the flame zone can be rapidly converted to NO2 via reactions such as

NO + HO2 NO2 + OH:Subsequently, conversion of this NO2 to NO occurs viaNO2 + O NO + O2;

Unless the NO2 formed in the flame is quenched by mixing with cooler fluid. This explanation is consistent with the highest NO2/NO ratio occurring at high load in diesels, when cooler regions which could quench the conversion back to NO is widespread wood 1988).

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EMISSION STANDARDS

3.1 EMISSION NORMS

Emission norms are prescribed CO (Carbon Monoxide), HC (Hydrocarbons) and NOX (Nitrous oxide) levels set by the government which a vehicle would emit when running on roads. All the manufacturers need to implement the same for vehicles being manufactured from the date of implementation. The stages are typically referred to as Euro 1, Euro 2, Euro 3, Euro 4 and Euro 5 fuels for Light Duty Vehicle standards. The corresponding series of standards for Heavy Duty Vehicles is represented by using Roman letters rather than using Arabic numerals (Euro I, Euro II, etc.)

Emission standards for passenger cars and light commercial vehicles are summarized in the tables 1 and 2. Since the Euro 2 stage, EU regulations introduce different emission limits for diesel and gasoline vehicles. Diesels have more stringent CO standards but are allowed higher NOx emissions. Gasoline-powered vehicles are exempted from particulate matter (PM) standards through to the Euro 4 stage, but vehicles with direct injection engines will be subject to a limit of 0.005 g/km for Euro 5 and Euro 6

3.1 EVOLUTION OF BIS STANDARD [3]

1991 - Idle CO Limits for Gasoline Vehicles and Free Acceleration Smoke for Diesel Vehicles, Mass Emission Norms for Gasoline Vehicles.

1992 - Mass Emission Norms for Diesel Vehicles.

1996 - Revision of Mass Emission Norms for Gasoline and Diesel Vehicles, mandatory fitment of Catalytic Converter for Cars in Metros on Unleaded Gasoline.

1998 - Cold Start Norms Introduced.

2000 - India 2000 (Eq. to Euro I) Norms, Modified IDC (Indian Driving Cycle), Bharat Stage II Norms for Delhi.

2001 - Bharat Stage II (Eq. to Euro II) Norms for All Metros, Emission Norms for CNG & LPG Vehicles.

2003 - Bharat Stage II (Eq. to Euro II) Norms for 11 major cities.

2005 - From 1 April Bharat Stage III (Eq. to Euro III) Norms for 11 major cities.

2010 - Bharat Stage III Emission Norms for 4-wheelers for entire country whereas Bharat Stage - IV (Eq. to Euro IV) for 11 major cities. Bharat Stage IV also has norms on OBD (simalar to Euro III but diluted)

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3.1 EURO STANDARDS [3]

The following table indicates the reforms suggested in euro standards over the years. From the table we can see that each time the permissible limits for emission goes on decreasing.

Tier Date CO THC NMHC NOx HC+NOx PM

Diesel

Euro 1† July 1992 2.72 (3.16) - - - 0.97 (1.13) 0.14 (0.18)

Euro 2 January 1996 1.0 - - - 0.7 0.08

Euro 3 January 2000 0.64 - - 0.50 0.56 0.05

Euro 4 January 2005 0.50 - - 0.25 0.30 0.025

Euro 5 September 2009 0.500 - - 0.180 0.230 0.005

Euro 6 (future) September 2014 0.500 - - 0.080 0.170 0.005

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EXHAUST GAS RECIRCULATION SYSTEM

4.1 INTRODUCTION

Over recent past years, stringent emission legislations have been imposed on NOx, smoke and particulate emissions emitted from automotive diesel engines worldwide. Diesel engines are typically characterized by low fuel consumption and very low CO emissions. However, the NOx emissions from diesel engines still remain high. Hence, in order tomeet the environmental legislations, it is highly desirable to reduce the amount of NOx in the exhaust gas. Diesel engines are predominantly used to drive tractors, heavy Lorries and trucks. Owing to their low fuel consumption, they have become increasingly attractive for smaller Lorries and passenger cars also. But higher NOx emissions from diesel arises major problem in the pollution aspect. For reducing vehicular emissions, baseline technologies are being used which include direct injection, turbointer-cooling, combustion optimization with and without swirl support, cylinder head, advanced high pressure injection system i.e. split injection or rate shaping, electronic management system, lube oil consumption control etc.

EGR systems introduce a portion of the engine exhaust gas back into the cylinder, mixing the exhaust gas with fresh intake air. This process leads to reduced in concentration and thus modified combustion and reduced combustion temperature, which results in reduced [NOx] combustion chamber get too hot. At 2500 degrees Fahrenheit or hotter, the nitrogen and oxygen in the combustion chamber can chemically combine to form nitrous oxides, which, when combined with hydrocarbons (HCs) and the presence of sunlight, produce an ugly haze in our skies known commonly as smog. There are several types of EGR systems being used and explored and while most effectively reduce emissions, it is often done at the cost of reduced engine efficiency and higher fuel consumption. Recently, Hino Motors of Japan has announced the development of an EGR system that is intended to reduce engine emissions without a significant loss of engine efficiency. Conventional EGR systems take a part of the exhaust gas out of the exhaust manifold then lead it back into the intake manifold which are produced by combustion at high temperature and at high engine loads. Recirculation of a proportion of the exhaust gases at high loads lowers the combustion temperature and, as a result, reduces the NOx level which mixed then introduced into the cylinder. Parameters such as the mixing ratio of the EGR gas to fresh air are controlled by a microprocessor that adjusts an EGR valve and/or throttlevalve.EGR system has already been used to mass at the low and medium load of engine operating condition, resulting in effective NOx reduction. In order to meet future emission standards, EGR must be done over wider range of engine operation, and heavier EGR rate for EGR to be done in a high engine load range since the amount of NOx is larger than the other engine operation conditions.

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4.2 CLASSIFICATION [5]

4.2.1 Classification Based On Temperature

(i) Hot EGR: Exhaust gas is recirculated without being cooled, resulting in increased intake charge temperature.(ii) Fully cooled EGR: Exhaust gas is fully cooled before mixing with fresh in take air using a water-cooled heat exchanger. In this case, the moisture present in the exhaust gas may condense and the resulting water droplets may cause undesirable effects inside the engine cylinder.(iii) Partly cooled EGR: To avoid water condensation, the temperature of the exhaust gas is kept just above its dew point temperature.

4.2.2 Classification Based On Configuration

(i) Long route system (LR): In an LR system the pressure drop across the air intake and the stagnation pressure in the exhaust gas stream make the EGR possible. The exhaust gas velocity creates a small stagnation pressure, which in combination with low pressure after the intake air, gives rise to a pressure difference to accomplish EGR across the entire torque/speed envelop of the engine.(ii) Short route system (SR): These systems differed mainly in the method used to set up a positive pressure difference across the EGR circuit. Another way of controlling the EGR-rate is to use variable nozzle turbine (VNT). Most of the VNT systems have single entrance, which reduce the efficiency of the system by exhaust pulse separation. Cooled EGR should be supplied effectively. Lundquist and others used a variable venturi, in which EGR-injector was allowed to move axially, thus varying the critical area was used (Lundquist et al 2000).

4.2.3 Classification Based On Pressure

Two different routes for EGR, namely low-pressure and high-pressure route systems may be used(i) Low pressure route system: The passage for EGR is provided from downstream of the turbine to the upstream side of the compressor. It is found that by using the low pressure route method, EGR is possible up to a high load region, with significant reduction in NOx. However, some problems occur, which influence durability, prohibitionary high compressor outlet temperature and intercooler clogging.(ii) High pressure route system: The EGR is passed from upstream of the turbine to downstream of the compressor. In the high pressure route EGR method, although EGR is possible in the high load regions, the excess air ratio decreases and fuel consumption increases remarkably.

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4.3 EGR COMPONENTS [6], [7]

4.3.1 EGR Valve:

An EGR (Exhaust Gas Recirculation) valve is an emission control device that sits between the exhaust and intake manifolds on a vehicle engine and regulates the amount of spent exhaust gas that is mixed into the intake stream. Its purpose is to cool combust chamber temperatures to the threshold that reduces the formation of nitrogen oxides(NOx). The higher the combustion temps, the higher the formation of NOx.

The EGR valve controls the flow of gas from the exhaust manifold to the intake manifold. The valve is controlled by the vacuum in the line connected to the EGR controller. The EGR valve is located underneath the intake manifold.

4.3.2 EGR Controller

The EGR valve is supplied with a vacuum control signal from one compartment in the controller. Vacuum from the intake manifold is supplied to another compartment. The controller stabilizes the intake manifold signal and converts the ICM signal into a modified vacuum signal for operation of the EGR valve. The controller is mounted on the underside of the relay shelf, above the engine cooling fan.

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4.3.3 EGR Pipe

The EGR pipe conveys the recirculated gases from the EGR valve to the intake manifold.

4.4 THEORY OF OPERATION [3], [7]

A part of the exhaust gas is to be recirculated and put back to the combustion chamber along with the intake air. The quantity of this EGR is to be measured and controlled accurately; hence a by-pass for the exhaust gas is provided along with the manually controlled EGR valve. The exhaust gas comes out of the engine during the exhaust stroke at high pressure. It is pulsating in nature. It is desirable to remove these pulses in order to make the volumetric flow rate measurements of the recirculating gas possible. For this purpose, another smaller air box with a diaphragm is installed in the EGR route. An orifice meter is designed and installed to measure the volumetric flow rate of the EGR. Suitable instrumentation is provided to acquire useful data from various locations.

Thermocouples are provided at the intake manifold, exhaust manifold and various points along the EGR route. An AVL smoke-meter is used to measure the smoke opacity of the exhaust gas. The pressure difference across the orifice is used to calculate the EGR rate. A matrix of test conditions is used to investigate the effect of EGR on exhaust gas temperature and exhaust smoke opacity. The EGR valve recirculates exhaust into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. These gases displace some of the normal intake charge. This chemically slows and cools the combustion process by several hundred degrees, thus reducing NOx formation.

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If too little EGR flows, the engine may knock and will not meet strict emissions standards. If there isn't enough EGR, NOx emissions increase, but the only drivability problems is a surging at cruise, a complaint of spark knock or a failed enhanced emissions inspection due to a high NOx reading. If there is too much EGR or EGR at the wrong time, your clues will be poor engine performance. The symptoms include:

· poor idle· stalling, especially when starting after cold soak· hesitation, stumble and rough running during warm· tip-in hesitation or stumble· surge at cruise, even with warm engine· poor acceleration· Low engine vacuum

4.5 CALCULATION OF EGR PERCENTAGE

EGR = (volume of EGR/total intake charge into the cylinder) (4.1)%EGR = EGR X 100 (4.2)EGR ratio = ([CO2] intake - [CO2] ambient)

([CO2] exhaust - [CO2] ambient) (4.3)

4.6 SYMPTOMS OF EGR MALFUNCTION [5]

The EGR system is often misdiagnosed or blamed for problems that may not be its fault including hard starting, stalling and hesitation during warm-up, rough idle, missing, spark knock, backfiring and loss of power. Sure, the EGR system can cause these symptoms, but so can other components and systems. Don't jump to any conclusions until you have checked the basics. Don't overlook carbon buildup in the combustion chamber for spark knock, for instance. Also, don't overlook vacuum leaks for hard starting and hesitation. Don't overlook the ignition or fuel systems as the cause of missing. The EGR system can malfunction in four ways:

* Problems with the passages* Problems with the EGR valve* Problems with the vacuum control system* Problems with the computer control system.

The exhaust is full of moisture, carbon, and other stuff that can plug up the passages or the valve itself. The two most common problems with EGR systems are stuck valves or plugged passages.

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CALCULATIONS

The following is the basic design procedure for calculating the final surface area of the Heat Exchanger, required for Exhaust Gas cooling.

5.1 ENGINE SPECIFICATIONS [2]

5.2 RATING OF HEAT EXCHANGER:

5.2.1 Mass Flow Rate of Gas:

• Volume Flow Rate of Gas:

Vsweptπ dia_engine 2⋅ stroke_length⋅

4

: =

• Swept Volume = 7.314E-04

• Mass Flow Rate = ρ × Swept Volume = 0.011

kg/sec

• Volumetric Efficiency = 85 %

• BSFC = 0.3

• Brake Power = 5 kW

• Mass Flow Rate of Fuel = BSFC × Brake Power

= 4.167 × 10-4

Mass Flow Rate of gas = Mass flow rate of fuel + Mass Flow

= 9.351×10-3

• Mass Flow Rate of Gas (Mg ) through EGR = 18 % of Actual Flow

=1.87 × 10-3

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Engine Speed Stroke Diameter

Stroke Length BSFC Brake Power

Volumetric Efficiency

1500 0.092 0.11 0.3 5 85 %

5.2.2 Heat Load Calculation

Gas

• Inlet Temperature = 250°C

• Outlet Temperature = 80 °C

Water

• Inlet Temperature = 30°C

Heat Load

Q = mass flow rate of gas × cp × ΔT

= 638.13 W

5.3 REYNOLDS NUMBER CALCULATION:

5.3.1 Properties of The Fluids At Bulk Mean Temperature [1]

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5.3.2 Dimensions of Pipe [8]

Gas Water

5.3.3 Area

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5.3.4 Calculation of T2 And LMTD

5.3.5 Reynolds Number Calculation

GAS WATER

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5.4CALCULATION OF OVERALL HEAT TRANSFER CO-EFFICIENT

5.4.1 Convective Heat Transfer Coefficient [1]

Gas Water

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5.4.2 Fouling Factor [1]

(INNER FOULING FACTOR) (OUTER FOULING FACTOR)

Thermal Conductitvity of Steel Tube ksteel = 30 W/m2 K

5.4.3 Overall Heat Transfer Coefficient

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5.5 SURFACE AREA CALCULATIONS (AREA)

5.6 PRESSURE DROP CALCULATIONS FOR FLOW WATER [1]

Friction Factor for water is fw

Equivalent Length of Straight part of the pipe

Therefore Pressure Drop is,

Pressure Drop due to 180deg bend (2 nos)

Number of 180deg bends=n

Equivalent Length of bends=75

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5.7 POWER

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CONCLUSION

• PARAMETRIC STUDY OF HEAT EXCHANGER

Gas Water

Iteration noNPD (inch) di (mm) do (mm) NPD (inch) Di (mm) Do (mm)

Uo

(W/m2 K)

Lengthof

tube (m)1 1.0 27.86 33.4 1.5 40.89 48.26 8.896735 5.9659282 1.5 42.72 48.26 2.0 54.79 60.32 10.10989 3.630513 2.0 54.79 60.32 2.5 66.93 73.02 9.976936 2.9426614 2.5 66.93 73.02 3.0 77.92 88.9 13.20082 1.8369775 3.0 82.8 88.9 3.5 95.5 101.6 9.917533 2.0081866 3.5 95.5 101.6 4.0 108.2 114.3 9.879861 1.763793

From the above table it is seen that the iteration no.1, 2 and 3 give very high values of the length of heat exchanger which is unacceptable. It makes the project too costly. Though the values of iteration no 5 and 6 give very lesser values of length, we did not select them in keeping in mind the practical conditions. The shape of tubular heat exchanger is shown.

The value of iteration 4 is the optimum design value as the length is within the limits of cost.

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REFERENCES

[1] Heat Exchangers: by Sadik Kakac[2] Internal Combustion Engines: by V Ganesan

[3] Exhaust gas recirculation - Wikipedia[4] www.detroitdiesel.com[5] http://www.asashop.org/autoinc/dec97/egr.htm

[6] Effect of EGR on NOx Reduction – Project undertaken by Arpit, Dishan and Krutin[7] Volvo and Toyota – EGR Manual[8] Nominal Pipe Diameter Tables – www.allsteelpipe.com

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