Development of Controller for the Post-Catalyst Oxygen Sensor on EcoCAR Vehicle Undergraduate Honors Thesis Presented in Partial Fulfillment of the Requirements for Graduation with Distinction at The Ohio State University By Katherine M. Bovee * * * * * The Ohio State University 2010 Defense Committee: Professor Giorgio Rizzoni, Advisor Dr. Shawn Midlam-Mohler, Advisor Professor Yann Guezennec Copyrighted by Katherine M. Bovee 2010 ii iii ABSTRACT Increasingly stringent regulations on emissions require automobile manufacturers to find new ways to reduce the emissions produced by their vehicles. Competitions like EcoCAR challenge engineering students to modify a production vehicle to reduce the vehicle’s energy consumption and tailpipe emissions, while maintaining standard vehicle performance. The purpose of this project is to develop a strategy to reduce the emissions produced by the EcoCAR vehicle, using the catalytic converter and post-catalyst oxygen sensor in the vehicle’s exhaust system. A proportional-integral controller is used with the post-catalyst oxygen sensor, to keep the engine operating as close to stoichiometry as possible. The following research describes how a phenomenological model of a catalytic converter was developed and validated. The model of the catalytic converter was then used in a simulation of the post-catalyst oxygen sensor controller, to determine the most effective proportional and integral gains for the controller. The post-catalyst oxygen sensor controller was then integrated into the EcoCAR’s overall engine controller, so emissions testing could be performed. The results of the emissions test showed the EcoCAR vehicle should meet the Environmental Protection Agencies Tier 2, Bin 5 emission regulations, when the EcoCAR vehicle is operating in series mode. iv ACKNOWLEDGMENTS I would like to thank Dr. Giorgio Rizzoni for the chance to participate in this undergraduate research project. I would especially like to thank Dr. Shawn Midlam- Mohler, for all the guidance he has given me during this research project. I would like to thank Beth Bezaire for all her help learning about catalytic converters and the EcoCAR team in general. I would also like to thank Brad Cooley, Josh Supplee and Ryan Everett for helping me learn how to run the EcoCAR engine and figure out the engine controller code. Finally, I would like to acknowledge the financial support I received from the National Science Foundation, under the grant CMMI0928518, “A System Dynamics Modeling Methodology to Predict Transient Phenomena in Compressible Fluid Flow Systems.” v TABLE OF CONTENTS Page ABSTRACT ....................................................................................................................... iv ACKNOWLEDGMENTS .................................................................................................. v TABLE OF CONTENTS ................................................................................................... vi LIST OF FIGURES ......................................................................................................... viii LIST OF TABLES ............................................................................................................ xii Chapter 1: Introduction ....................................................................................................... 1 1.1 Introduction ......................................................................................................... 1 1.2 Motivation ........................................................................................................... 3 1.3 Project Objective ................................................................................................. 3 Chapter 2: Literature Review .............................................................................................. 5 2.1 Engine Operating Conditions .............................................................................. 5 2.2 Background on Catalytic Converters .................................................................. 6 2.3 Oxygen Sensors ................................................................................................ 11 2.4 Catalyst Models ................................................................................................ 14 2.5 Oxygen Sensor Controllers ............................................................................... 18 Chapter 3: Experimental Description................................................................................ 21 3.1 Honda Engine.................................................................................................... 21 3.2 Emitec Catalytic Converter ............................................................................... 24 3.3 Engine Instrumentation ..................................................................................... 25 3.4 Data Acquisition System................................................................................... 29 Chapter 4: Model of Three-Way Catalyst Oxygen Storage Characteristics ..................... 31 4.1 Model Structure ................................................................................................ 31 4.2 Data Processing ................................................................................................. 35 4.3 Oxygen Storage Capacity ................................................................................. 41 4.4 Oxygen Release Rate Curve ............................................................................. 47 vi 4.4.1 Mass Based Oxygen Release Rate Curve ..................................................... 50 4.4.2 Normalized Oxygen Release Rate Curve ..................................................... 53 4.5 Oxygen Absorption Rate Curve ........................................................................ 54 4.6 Transport Delay ................................................................................................ 56 4.7 Filtering the Simulated Post-Catalyst EQR ...................................................... 57 4.8 Hydrogen Effects Acting on the Sensor ............................................................ 60 4.9 Validation of Catalyst Model ............................................................................ 61 Chapter 5: Software VAlidation of the Control ................................................................ 65 5.1 Post-Catalyst EGO Sensor PI Controller .......................................................... 65 5.1.1 Structure in Overall Engine Controller Code................................................ 65 5.1.2 Structure in Model ........................................................................................ 67 5.2 Calibration Curve for Post-Catalyst EGO Sensor ............................................. 69 5.3 Determination of Post-Catalyst EGO Sensor Set Point .................................... 70 5.4 Catalyst Efficiency Curves ............................................................................... 72 5.5 Results of Controller Model in Simulation ....................................................... 73 Chapter 6: Emissions Testing ........................................................................................... 80 6.1 Emissions Testing Procedure and Data............................................................. 80 6.2 Estimate of the EcoCAR’s Emissions in Series Mode ..................................... 85 6.3 Emissions Testing Summary............................................................................. 88 Chapter 7: Future Work and Conclusion .......................................................................... 89 Chapter 8: Bibliography .................................................................................................... 91 Appendix A ....................................................................................................................... 93 vii LIST OF FIGURES Figure Page Figure 2.1: Structure of Three-Way Catalyst (Selamet, 2009) ........................................... 7 Figure 2.2: Catalyst Conversion Efficiency as a Function of Air/Fuel Ratio in Gasoline Engines (Heywood, 1988) .......................................................................................... 8 Figure 2.3: Oxygen Storage Characteristics of Catalysts ................................................. 10 Figure 2.4: Catalyst Efficiency as a Function of Temperature (Heywood, 1988) ............ 11 Figure 2.5: Structure of Oxygen Sensors (ME 631 Lecture 7, Winter 2010) ................... 12 Figure 2.6: Schematic of Relative Diffusion Rates of Exhaust Gas Components (Buglass, Morgan and Grauper, 1998) ...................................................................................... 13 Figure 2.7: Lean Relative Air/Fuel Ratio Shift due to Particles in the Exhaust Gases (Buglass, Morgan and Grauper, 1998) ...................................................................... 14 Figure 2.8: Rich Relative Air/Fuel Ratio Shift due to Particles in the Exhaust Gases (Buglass, Morgan and Grauper, 1998) ...................................................................... 14 Figure 2.9: Structure of Three-Way Catalyst Model (Brandtl, Wang and Grizzle) ......... 15 Figure 2.10: Structure of Oxygen Storage Model (Brandtl, Wang and Grizzle) .............. 16 Figure 2.11: Relative Oxygen Absorption and Release Rates as a Function of Relative Oxygen Level (Brandtl, Wang and Grizzle) ............................................................