DESIGN AND OPTIMIZATION OF CATALYTIC CONVERTER FOR SPARK IGNITION ENGINES

By

M. Subramanian

DEPARTMENT OF MECHANICAL ENGINEERING

Submitted In fulfillment of the requirements of the degree of

DOCTOR OF PHILOSOPHY

to the

INDIAN INSTITUTE OF TECHNOLOGY, DELHI

JULY, 2001

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CERTIFICATE

This is to certify that the thesis entitled, " Design and Optimization of

Catalytic converter for Spark ignition Engines", being submitted by

M. Subramanian to the Indian Institute of Technology, Delhi, for the award

of degree of Doctor of Philosophy is a record of the bonafide research work

carried out by him. He has worked under our guidance and supervision and

has fulfilled the requirements for the submission of this thesis, which to our

knowledge has reached the requisite standard.

The results contained in the thesis have not been submitted, in part or full, to

any other university or institute for the award of any degree or diploma.

Dr. J. P. Subrahmanyam Dept. of Mech. Engineering Indian Institute of Technology, New Delhi-110 016

e,?..y7. •/'et-.$1L,-4-4,1-,-.4

Prof. M. K. Gajendra Babu Centre for Energy Studies Indian Institute of technology, New Delhi-110 016

ACKNOWLEDGEMENTS

I wish to express my sincere gratitude to Prof. M. K. Gajendra Babu and Dr. J. P.

Subramanyam for their excellent, untiring guidance, constant encouragement and

valuable suggestions towards the successful completion of this work. Their rich

knowledge in Emission Control of internal combustion engines, computations and

good reputation with automotive industries inspired me to learn many things during

this work. I am indebted to them for their concern and sincerity, which has brought

this work to a completion.

I am grateful to Dr. A. K. Bhatnager, Director Indian Oil Corporation R&D centre,

Sh. N. R. Raje, Sh. R. K. Malhotra and Sh. R. K. Dua for granting permission to

pursue the course and under take it as an on going project as part of this work. My

sincere thanks and gratitude to Sh. N. R. Raje and Sh. R. K. Malhotra for their

encouragement and support during course of this work. I indebted to them.

I am very much thankful to Prof. R. R. Gaur, Head, Mechanical Engineering

Department, Dr. Desmukh, Dr. M. R. Ravi and Dr. P.M.V. Subba Rao Faculty

members of Mechanical Engineering Department, IIT-Dethi for formal discussion

and encouragement in completion.

I am very grateful to Dr. A Ramesh, Prof. K. V. Gopala Krishnan and Prof.

B.Nagalingam, Indian Institute of Technology, Madras, for their cordial and

inspiration and encouragement, which made me to pursue the course.

Gratitude to my teacher Dr. P. Chandrasekaran for his philosophy, guidance,

inspiration and moral support which helped me to attain this position.

I thank Sh. R. M. Cursetji, Dr. D. Venkateswaran and Dr. S. Bhaduri of

Associated Cement Companies Limited, and Dr. K. Kumar, Sh. I. V. Rao,

Sh. Porusothman, Sh. R. Sivanesan, Sh. Sivakumar, Dr. Khatri and M. Saravanan of

M/s Maruti Udyog Limited, Mr. T. P. Singh and Mr. Sanjeev Dhiman, of M/s Hero

Motors limited for their help and support to bring my work to completion in spite of

their tight schedule of the work.

My sincere thanks to Prof. B. P. Pundir and Dr. Eswaran, Indian Institute of

Technology, Kanpur for their help in CFD applications.

I thank Dr. I. R. Devota, Sh. I. R. Choudhary, Dr. Alex C. Pulikotil, Sh. C. Kannan,

Dr. J. Christopher, Dr. A. Partibhan, and Sh.R.Ramanarayanan who showed interest

in the progress of the work.

I thank Shri Rama Prasad, Sh. S. S. Negi, Sh. Kuldeep Singh, Sh. P. S. Negi, IC

engines lab, and Mr. G. P. Singh CES lab for their support during the course of the

work.

I am grateful to my colleagues G. K. Acharaya, A. K. Setia, N. K. Pal, Sh. Pradeep

Patanwal, Sh. Rakesh, Sh Neeraj Kumar Sh. N. Subramanian and Kishan Chand for

their support and help in progress of the work.

I am grateful to My wife, A. V. Karthi keyani, son, S. Mohana Krishnan and parents

for their patience and kind understanding which has always been a morale booster

for me.

Lastly, I owe an unqualified apology to those whose names do not find a place here

and out of sheer love and compassion have helped me in progress of the work.

M. Subramanian.

ii

ABSTRACT

The large increase in the number of automobiles in India during the past decade

has created a serious environmental problem especially in metropolitan cities. In

view of this, emission standards were introduced in 1991 and they were made

more stringent. The proposed one due in 2005 is expected to be more difficult to

be met without any exhaust gas after treatment devices.

Design and optimization of the catalytic converter is crucial for the automotive

industry to meet the stringent emission standards because of different raw

emission and inlet flow conditions for different type of vehicles. Moreover, the

performance of the catalytic converter depends not only on the type of catalyst

impeded but also on the operating condition of the engine.

Although optimization of a catalytic converter for a specific vehicle could be

carried out on an experimental test bed, it involves time consuming and expensive

engine testing. Hence computer simulation models are often used to minimize the

cost and narrow down the range of engine testing. Such models are found to be

of considerable use in the design and development of catalytic converters for

vehicles. Kinetic rate constants, heat and mass transfer are key parameters that

affect accuracy in the model prediction.

In view of this it was necessary to undertake the development of a computational

scheme for providing guidance in the design of catalytic converters by analyzing

the performance with respect to species conversions and wall temperature over a

iii

wide range of operating conditions. In this direction, investigations that have

been carried with respect to the following are reported in the present thesis.

A comprehensive literature survey to know about the present status of using

catalytic converters for emission control has been undertaken.

A new concept in mass transfer coefficient has been employed in the present

investigations based on Reynolds analogy.

A comprehensive computer simulation model is developed for a catalytic

converter (with Pt as catalyst on Ceramic substrate having higher density) of

monolithic type fitted in a passenger car engine. The above model has been

validated with the already published .data.

Nowadays metallic converter and binary catalyst is popular in a Three-Way

Catalytic converter applications. The above model is modified for Pt/Rh catalyst

on metallic substrate and vaildated with the published data.

Current generation catalytic converters use Pd/Rh as catalyst and ultra low

density ceramics. Rate constants have been deduced for Pd/Rh (10:1) and was

checked over a wide range of operating conditions of a passenger car.

A comprehensive experimental setup was developed for obtaining the necessary

experimental data to validate the data obtained from the above model and also to

assess the conversion efficiency of the developed catalytic converter. A

iv

A satisfactory correlation has been found between the predicted and

experimentally measured results.

An effective use of the catalyst is investigated by using Fluent CFD software to

study the flow pattern in a catalytic converter and to arrive at a better design for

an improved performance.

A radial flow type of catalytic converter has been designed and developed using

pellets as catalyst. This is an unique technique and can be used in any type of

spark ignition engine. Ideally it is suitable for two-stroke engines where

durability is of primary concern.

A comprehensive experimental investigations has been done on moped

and scooter vehicles to compare performance of radial flow pellet and monolith

converters and it was found that the radial catalytic converter is on par with

monolith catalytic converter.

Flow characteristics in the conical type of catalytic converter has been optimized

with the help of Fluent CFD software for better utilization of the catalyst and

improved performance.

CONTENTS

Page

Certificate

Acknowledgements

Abstract iii

List of Figures xxi

List of tables xxxi

List of Plates xxxiii

Nomenclature xxxiv

CHAPTER — 1 INTRODUCTION 1

CHAPTER — 2 LITERATURE REVIEW ON CATALYTIC

CONVERTERS 4

2. 1 Types of Catalytic Converter Used in Automobiles 5

2. 1. 1 Pellet Types of Catalytic Converters 6

2. 1. 2 Monoliths 9

2. 1. 2. 1 Ceramic Monolith 10

2. 1. 2. 2 Metallic Monolith 13

2. 1. 2. 3 Pinfixed Metal Foil Catalytic converter 14

2. 1. 2. 4 Soldered Metal Foil Catalytic converter 15

vi

2. 2 Substrate 15

2. 3 Wash Coat 19

2. 4 Engine Emission Control System 21

2. 4. 1 Closed Loop 21

2. 4. 2 Open Loop 23

2. 5. Catalyst Type 23

2. 5.1 Oxidation Catalysts 23

2. 5.2 Reduction Catalysts 25

2. 5.3 Three-Way Catalyst(TWC) 25

2. 6 TWC mechanism on Cerium oxide 27

2. 7 Different Arrangement of Catalytic converter used in practice with

air injection 28

2. 7. 1 Single Bed Process with Oxidation Catalyst 28

2. 7. 2 Double Bed Reactor 29

2. 7. 3 Single Bed Multifunctional Catalyst 30

2. 8 Lean Catalyst 31

2. 9 Closed Coupled Catalyst 32

2. 10 Catalysts 33

2.10.1 Base Metal Catalyst 35

vii

•

2.10.2 Noble Catalyst Used in the Automotive catalytic converter 36

2. 10. 2. 1 Platinum(Pt) 36

2. 10. 2. 2 Palladium(Pd) 36

2. 10. 2. 3 Rhodium(Rh) 37

2. 10. 2. 4 Binary Catalyst For Three-Way Catalysts 38

2. 10. 2. 5 Trimetallic Three-Way Catalyst 39

2. 11 Alternative Materials 40

2. 12 Recent Trends in Emission Control Technology 42

2. 12. 1 Development of Automobile Manufacturer 42

2. 12. 2 Development of Catalyst Device Manufacturer 43

2. 12. 3 Several Technique are Being Developed to Achieve

Lower Tail Pipe Emissions these are 43

2. 12. 4 Proposal for Change to Fuel Composition 44

2. 13. Cold Start Emission Control 44

2. 13. 1 Position of the Catalyst in the Exhaust System 45

2. 13. 2 Temperature and Heat Transfer in the Exhaust System 46

2. 13. 3 Electrically Heated Catalytic Converters (EHCS) 47

2. 13. 4 Hydrocarbon Trap used with Catalytic Converter 48

2. 13. 5 Air Injection into the Exhaust System 51

2. 13. 6 Exhaust Gas Ignition 52

2. 14 Exhaust Manifold Material and Structure 53

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2. 15 Durability of the Catalytic Converter 53

2. 15. 1 Thermal Phenomenon 54

2. 15. 2 Chemical Poisoning 55

2. 15. 2. 1 Selective Poisoning on the Catalyst 55

2. 15. 3 Run-Away of Catalyst 57

2. 16. Fuels and Catalytic Conversion 57

2. 17. Effect of Lubricating Oil consumption on Catalytic Conversion 58

2. 18 Effect of Temperature and Space Velocity 59

2. 19 Cell density 59

2. 20 Flow Model 59

2. 21 Mathematical Modelling of Catalytic Converters 60

2. 22 Summary of the Literature Review 70

2. 23 Present work 72

CHAPTER - 3 Mathematical Modelling of Catalytic Converter 75

3. 1 General Processes Which Occur in a Catalytic Converter 75

3. 2 Design of Monolithic Catalytic Converter 80

3. 2. 1 Support Design 80

ix

3. 2. 2 Basis of Cell Structure 81

3. 2. 3 Pressure Drop Model for the Support 83

3. 2. 4 Cellular Flow Resistance 87

3. 2. 5 Design of Converter Length 88

3. 2. 6 Reactor Volume 89

3. 3 Model Formulation 90

3. 3. 1 Chemical Reactions and Kinetics 92

3. 3. 2 Basic Equations and Assumptions 95

3. 4 Packed Bed Catalytic Converter 100

3..4. 1 Transport Properties in Packed Bed 102

3. 4. 2 Fluid/Solid Mass Heat Transfer Coefficients in Packed Beds 103

3. 4. 3 Thermal Conductivities in Packed Beds 104

3. 4. 4 Bed to Wall Heat Transfer Coefficient in Packed Beds 107

3. 4. 5 Overall Heat Transfer Coefficient for the Reactor 108

3. 4. 6 Pressure Drop Model for Paced Bed 108

3. 5 Calculation of the Active Shell Volume of a Catalyst 110

3. 6 Grid Design 112

3. 6. 1 Front Plate 112

3. 6. 2 Grid Design on Cones 114

x

CHAPTER - 4 NUMERICAL SOLUTION 116

4. 1 Method Used to Solve Linear Equation 116

4. 1. 1 Tridiagonal Problem 116

4. 2 Iterative Method 117

4. 3 Finite Difference Numerical Solution 118

4. 3. 1 The Finite Difference Method for Marching Problems 121

4. 3. 2 The Newton Method for Non-Linear Problems 123

4. 4 Numerical Method of Solution 124

4. 4. 1 Numerical Descretization 125

4. 4. 2 Gas Phase Mass Conservation 127

4. 4. 3 Gas Phase Energy Conservation 127

4. 4. 4 Solid Phase Mass Conservation 127

4. 4. 5 Solid Phase Energy Conservation Equation 128

4. 4. 6 Total Gas Mass Conservation 129

4. 4. 7 Non-Dimensionalisation 129

4. 4. 8 Brief Description of the Discretized Equations 132

4. 5 Numerical Method of Solution 134

4.5. 1 Accuracy 137

4. 6 Computer Program 137

4. 6. 1 Brief of Subroutines 138

xi

CHAPTER - 5 EXPERIMENTAL INVESTIGATIONS 147

5. 1. 1 Experimental Setup 147

5. 1. 2 Test Vehicle 148

5. 1. 3 Chassis Dynamometer 148

5. 1. 4 Automotive Emission Analysis System MEXA-9400D 148

5. 1. 4. 1 Measurement of CO/CO2 153

5. 1. 4. 2 Measurement of THC 156

5. 1.4. 3 Measurement of NOx 157

5. 1. 4. 4 Measurement of Oxygen (02) 158

5. 1. 5 Exhaust Gas Sampler Unit 159

5. 1. 5. 1 Critical Flow Venturi (CFV) 159

5. 1. 6 Basic Instrumentation 160

5. 1. 6. 1 Temperature Measurement 160

5. 1. 6. 2 Pressure Measurement 160

5. 1. 6. 3 Engine Speed measurement (RPM) 161

5. 1. 6. 4 Fuel Consumption Measurement 161

5. 1. 7 Air/Fuel Ratio Measurement (A/F) 161

5. 1. 8 Printer 162

5. 2 Catalyst Preparation and Characterization 163

5. 2. 1 Monolith Catalyst 163

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5. 2.2 Brief of Pellet Catalyst Preparation 164

5. 2. 2. 1 Substrate 164

5. 2. 2. 2 Wash Coating 164

5. 2. 2. 3 Metal Doping 167

5. 2. 2. 4 Canning 167

5. 3 Measurement of Pellet Diameter 168

5. 4 Properties of the Pellet Type Catalyst 168

5. 5 Characterization of Catalyst

173

5. 5. 1 Catalyst Samples 175

5. 5. 2 Elemental Analysis 9 175

5. 5. 2. 1 Scanning Electron Microscope (SEM) 175

5. 5. 2. 2 Inductive Coupled Argon Plasma (ICAP) 176

5. 5. 3 Pore Size, Volume and Distribution 181

5. 5. 3. 1 Measurement of Pore Volume 182

5. 5. 3 .2 Measurement of Surface Area 183

CHAPTER 6 TEST PROCEDURE 182

6. 1 Vehicle Test on Chassis Dynamometer 182

6. 2 Driving Cycle Data 183

6. 3 Steady Speed Data 186

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6. 4 Back Pressure Measurement 189

6. 5 Tests on Two Wheelers 189

6. 5. 1 Power Measurement under Constant Speed 189

6. 5. 2 Temperature Measurement Under Constant Speeds 190

6. 5. 3 Back Pressure Measurement 190

6. 5. 4 Fuel Consumption 190

6. 5. 5 Conversion Efficiency Using IDC 190

6. 5. 6 Durability of the Converter 191

6. 6 Calculation of Exhaust Gas Mass Flow 191

6. 6. 1 Measurement of Exhaust Gas Mass Flow 191

Through Constant Volume Sampler

6. 6. 2 Mass Flow Calculation of the Exhaust Flow by Fuel

Consumption and A/F Ratio Measurement Method 193

CHAPTER 7 DESIGN OF CATALYTIC CONVERTER

USING CFD 194

7. 1 Flow Simulation Using Commercial CFD Codes 195

7.2 CFD FLUENT 5.4 197

7. 2. 1 General Problem Solving Procedure 199

7. 3 Application of CFD for Optimizing Pellet Type Catalytic Converter 201

xiv

7. 4 Application of CFD for Optimizing Monolith Type Catalytic Converter 204

CHAPTER - 8 RESULTS AND DISCUSSION

8. 1 SIMULATION OF OXIDATION CATALYTIC CONVERTER 206

8. 1. 1 Effect of Step Increase on Gas Temperature 207

8. 1. 2 Effect of CO Concentration on the Converter Performance 211

8. 1. 3 Conversion of CO and C3H6 with and without

Hydrogen on the Converter Performance 211

8. 1. 4 Effect of Gas flow rate on the Converter performance 212

8. 1. 5 Effect of Cell density on the Converter Performance 219

8. 1. 6 Effect of Monolith Length on the Converter Performance 220

8. 1. 7 Effect of Platinum loading on Conversions 224

8. 1. 8 Effect of Thermal Conductivity of Solid Phase on the

Converter Performance 225

8. 1. 9 Step Decrease in Gas temperature on the

Converter Performance 226

8. 2 DISCUSSION OF 3-WAY CATALYTIC CONVERTER FOR Pt/Rh

CATALYST ON METALLIC SUBSTRATE 235

8. 2. 1 General Performance of Metallic Converter 235

8. 2. 2 Effect of H2 on CO and C3H6 Conversion 237

8. 2. 3 Effect of Pt/Rh Loading on CO and C3H6 Conversion 238

8. 2. 4 Effect of Pt/Rh Loading on Solid Temperature 238

8. 2. 5 Effect of Thermal Conductivity on CO and C3H6 Conversion 243

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8. 2. 6 Effect of Inlet Gas temperature on Conversions 243

8. 2. 7 Effect of mass flow rate on Conversions 244

8. 2. 8 Pattern of Pt/Rh loading Metal Saving Calculation 251

8.2.8.1 Type-1: Metal dispersion in L/2 + L/2 type of Pattern

Loading 257

8.2.8.2 Type -2: Metal Dispersion in 0.75L + 0.25L type of

Pattern loading 257

8. 2. 3 Type -3 Metal Dispersion in 0.9L +0.1L type 258

8. 3 DISCUSSION OF 3-WAY CATALYST IN CURRENT GENERATION

CATALYTIC CONVERTER (Pd/RH ) (10:1) 258

8. 3. 1 For Air/Fuel Ratio of 14.9 and Mass Flow Rate of 7.5 g/s 263

8. 3. 2 Warm-Up Characteristics Solid 263

8. 3. 3 Conversion Efficiency Species 263

8. 3. 4 Effect of Mass Flow Rate on Conversions 265

8. 3. 5 Effect of Pd/Rh loading on Conversions 265

8. 3. 6 Effect of Monolith Length on conversions 266

8. 3. 7 Effect of cell Densities on Conversions 275

8. 3. 8 Effect of Inlet Gas Temperature on Conversions 276

8. 3. 9 Metal Loading Pattern on Conversions 281

8. 4 Effect of Mass Flow Rate on Back Pressure 286

8. 5 Effect of Inlet Gas Temperature on Back Pressure 286

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8. 6 Performance of Pd/Rh In Air Fuel Ratio of 14.8 and

Mass Flow Rate of 5.6 g/s 286

8. 6. 1 Effect of Mass Flow Rate on Conversions

Effect of Mass Flow Rate 290

8. 6. 2 Effect of Inlet Gas temperature on Conversions 290

8. 7 Performance of Pd/Rh In Air fuel Ratio of 14.6 and

Mass Flow Rate of 9.8 g/s 290

8. 8 Effect of Mass Flow rate on Conversions in A/F of 14.6 and Mass Flow

Rate of 9.8 g/s 295

8. 8 1 Effect of Inlet Gas temperature on Conversions 295

8. 9 Experimental Investigation on Radial Flow Catalytic Converter 296

8. 9. 1 Description of Conical Radial Flow Catalytic Converter 296

8. 10 CFD Analysis of Flow Through the Catalytic Converter 306

8. 10.1 Original Configuration 310

8.10.2 Modification-1 310

8.10.3 Modification-2 316

8.10.4 CFD Study on Monolith 316

8. 10. 4. 1 Original Configuration 316

8. 10. 4. 2 Modification-1 316

8. 11 Experimental Investigations and Validation of the

Model on Passenger Car 319

xvii

8. 12 Validation of the Pd/Rh Model 320

CHAPTER — 9 CONCLUSIONS 329

9. 1 Oxidation model 329

9. 2 Three-way Converter on Metallic Substrate 330

9. 3 Current generation Catalytic Converter 332

9. 4 Development of Radial Flow Catalytic Converter 334

9. 5 CFD Model 335

9. 6 Suggestion for Future Work 335

REFERENCES 336

APPENDICES 348

LIST OF PAPER PUBLISHED FROM THIS THESIS 371

BRIEF BIO-DATA 372

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