THE EFFECT OF OXYGEN-ENRICHED AIR ON THE PERFORMANCE AND EXHAUST EMISSIONS OF INTERNAL COMBUSTION ENGINES by VARADARAJA SETTY, B.E. A THESIS IN MECHANICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN MECHANICAL ENGINEERING Approved Accepted May, 1993 ACKNOWLEDGEMENTS I am deeply indebted to my advisors Dr. Timothy T. Maxwell and Mr. Jesse C. Jones for their superb technical advice, understanding, and patience in helping me to solve \'arious problems during the course of this work. I am equally indebted to Dr. Raghu Narayan for his support and active involvement in this project. I would like to thank Mr. Don Boone whose selfless effort and past experience helped me to expedite the completion of this work. I thank Mr. Patrick Nixon, Mr.Christopher Boyce, and Mrs. Carmen Hernandez for their ideas and timely assistance. I also thank Mr. Norman L. Jackson, Mr. Lloyd Lacy, and Mr. John P. Bridge for their help during the experimental work. I am highly grateful to my parents Mr. Narayan Setty and Mrs. Gangamma Narayan Setty for their loving support and constant exhortation as well as other family members who provided encouragement and prayer. Finally, I would like to thank my roommates and friends for their help and support during this project. 11 TABLE OF CONTENTS ACKNOWLEDGEMENTS 11 ABSTRACT v LIST OF TABLES Vl LIST OF FIGURES Vlll CHAPTER 1 I. INTRODUCTION 1 The Future of Automobile 1 Factors Influencing the Formation of Exhaust Emissions 4 The Importance of Oxygen Enrichment 7 II. LITERATURE SURVEY 13 ill. OBJECTIVES 16 Project Objectives 16 Thesis Objectives 16 IV. TEST EQUIPMENT 17 General Plan 17 Modified Test Engine 18 Fuel Injection System 22 The Injector 22 Injector Control Mechanism 22 Water Dynamometer 26 Air Flowmeter 27 111 Mass Flowmeter for Compressed Natural Gas 27 Oxygen Sensor 30 Exhaust Gas Analyzer 32 Data Acquisition System 32 V. TEST PROCEDURE 33 Calibration 33 Preliminary Tests 39 Gasoline Tests 39 Compressed Natural Gas Tests 41 VI. TEST RESULTS 42 Brake-horsepower 42 Exhaust Gas Temperatures 46 Brake Specific Fuel Consumption and Fuel Conversion Efficiency 46 Volumetric Efficiency 57 Exhaust Emissions 60 Tests Results with Gas Separator 60 VII. CONCLUSIONS 71 Conclusions 71 Suggestions for Future Research 72 REFERENCES 73 APPENDIX A. BASIC COMPUTATIONS 75 B. THEORETICAL AIR CALCULATION 77 IV ABSTRACT Automobiles and trucks consume a major portion of the energy used for transportation in the US. They generate a significant amount of the emissions that contribute to air pollution. During the past few years, research on cleaner burning alternate fuels has been aimed at improving engine efficiencies and decreasing emissions that pollute the environment. Methanol, LPG, and natural gas have emerged as the leading alternative fuels; however, several problems must be solved before these fuels can be considered as true replacements for gasoline. This research was devoted to the study of the performance of I. C. engines with enriched oxygen air fueled by gasoline and natural gas and to study the feasibility of gas separator to supply oxygen enriched air for vehicle applications. A single cylinder, 4-stroke, spark-ignition engine was used in the program to evaluate the effect of enriched oxygen air on engine performance and exhaust emissions. The oxygen content in the intake air was varied between 21% and 25%. The effects of oxygen enrichment are reviewed in terms of volumetric efficiency, power output, specific fuel consumption, fuel conversion efficiency, exhaust gas temperature, and exhaust emissions (carbon monoxide and hydrocarbons). Test results indicate that the use of oxygen enriched air results essentially in a significant increase in power output, improved thermal conversion efficiency, a substantial reduction in carbon monoxide and hydrocarbons and a decrease in volumetric efficiency. v LIST OF TABLES 1.1 Total Annual U.S. Emissions from Artificial Sources 2 1.2 Total Exhaust Emissions per kg. Fuel Burned in S.I. Engines 2 1..3 Hydrocarbon Composition of S.I. Engine Exhaust, Percent of Total HC 9 .f.1 Test Engine Specification 20 5.1 Test Conditions 40 6.1 Percentage Increase in Power with Oxygen Enrichment for Gasoline 45 6.2 Percentage Increase in Power with Oxygen Enrichment for CNG 45 6 ..3 Increase in Exhaust Temperatures with Oxygen Enrichment 49 for Gasoline 6.4 Increase in Exhaust Temperature with Oxygen Enrichment for CNG 49 6.5 Brake Specific Fuel Consumption with Oxygen Enrichment for Gasoline 56 6.6 Brake Specific Fuel Consumption with Oxygen Enrichment For CNG 56 6.7 Percentage Reduction in CO with Oxygen Enrichment for Gasoline 65 6.8 Percentage Reduction in HC with Oxygen Enrichment for Gasoline 65 6.9 Percentage Reduction in CO with Oxygen Enrichment for CNG 66 6.10 Percentage Reduction in HC with Oxygen Enrichment for CNG 66 6.11 Power Output with 0 2 Enriched Air Supplied by Separator for Gasoline 68 Vl 6.12 Power output with 0 2 Enriched Air Supplied by Separator for CNG 68 6.13 Reduction in CO with 0 2 Enriched Air Supplied by Separator 69 for Gasoline 6.1-+ Reduction in HC with 0 2 Enriched Air Supplied by Separator for Gasoline 69 6.15 Reduction in CO with 0 2 Enriched Air Supplied by Separator for CNG 70 6.16 Reduction in HC with 0 2 Enriched Air Supplied by Separator for CNG 70 Vll LIST OF FIGURES 1.1. Summary of HC, CO, and NO Pollutant Formation Mechanism in a Spark -Ignition Engines 3 1.2. Schematic of Complete SI Engine HC Formation and Oxidation Mechanism within the Cylinder and Exhaust System 8 1.3. Schematic Drawing of a Membrane Gas Separator 12 4.1. Overall Experimental Set-up 19 4.2. Sectional View of an Injector 23 4.3. Fuel Injection and Control Mechanism For Gasoline 24 4.4. Fuel Injection and Control Mechanism for CNG 25 4.5. Sectional View of the Typical Water Dynamometer 28 4.6. The General Construction of Laminar Flowmeter 29 4.7. A Cross-Section Drawing of an Oxygen Sensor 31 5.1. Calibration Curve for Water Dynamometer 34 5.2. Calibration Curve For an Air Flowmeter 35 5.3. Calibration Curve for GM Map Sensor 36 5.4. Calibration Curve for Honda Gasoline Injector 37 5.5. Calibration Curve for Servojet Injector 38 6.1. Engine Speed versus Power Output for Gasoline 41 6.2. Engine Speed versus Power Output for CNG 44 6.3. Engine Speed versus Exhaust Temperature For Gasoline 47 6.4. Engine Speed versus Exhaust Temperature For CNG 48 Vlll 6.5. Engine Speed versus Fuel Consumption In Lb/hr for Gasoline 50 6.6. Engine Speed versus Fuel Consumption In Lb/hr for CNG 51 6.7. Engine Speed versus BSFC for Gasoline 52 6.8. Engine Speed versus BSFC for CNG 53 6.9. Engine Speed versus Thermal Conversion Efficiency for Gasoline 54 6.10. Engine Speed versus Thermal Conversion Efficiency for CNG 55 6.11. Engine Speed versus Volumetric Efficiency for Gasoline 58 6.12. Engine Speed versus Volumetric Efficiency for CNG 59 6.13. Engine Speed versus Percentage of CO for Gasoline 61 6.14. Engine Speed versus Percentage of CO for CNG 62 6.15. Engine Speed versus Percentage of HC for Gasoline 63 6.16. Engine Speed versus Percentage of HC for CNG 64 IX CHAPTER I INTRODUCTION The Future of the Automobile The future of the automobile, which accounts for over half of all energy[1] used for transportation in developed countries, is of great concern since automobiles generate a significant amount of the emissions that contribute to air pollution. During the last ten years significant changes have occurred in automobile design due to energy and air pollution concerns. The result of these changes has been a move to lighter, cleaner fuel burning cars with improved aerodynamics, and smaller and more fuel efficient engines that provide higher specific output. Studies continue to be aimed at improving engine efficiencies and decreasing vehicle emissions. The principal vehicle exhaust gas pollutants are hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), which contribute to the formation of smog as well as to acid rain. Although auto tailpipe emissions have decreased by approximately 95% in CO and HC, and 60-70% in NOx since 1970, total vehicle emissions have increased because of an increase in the number of vehicles on the road and, the number of miles driven. The future of the automotive industry depends heavily on the satisfactory reduction of exhaust emissions. Table 1.1 [2] gives the total percentage of annual US emissions from transportation and highway vehicles. 1 Table 1.1 Total Annual U.S. Emissions from Artificial Sources [2] co HC SOx NOx Particulates Total. Terra grams/yr 85.4 21.8 23.7 20.7 7.8 All Transportation,% 81 36 3.8 44 18 Highway Vehicles, o/c 72 29 1.7 32 14 Table 1.2 Total Exhaust Emissions per kg Fuel Burned in S.I. Engine [3] PPM/% GMS./KG-FUEL Hydrocarbon 300-500 PPM 25 Carbon monoxide 1%-2% 200 Oxides of Nitrogen 500-1000 PPM 25 2 CO present at high temperature and if fuel · h Oil layers A arne source of absor C HC if combustion incomplete (a) Compression (b) Combustion As burned gases cool, flrst NO chemistry, then CO chemistry freezes wall into bulk gas tflow of HC from Piston crevices; scrapes some HC HC off burns walls (c) Expansion (d) Exhaust Figure 1.1 Summary of HC, CO, and NO Pollutant Formation Mechanisms in a Spark-Ignition Engine.