The nature of lubricant-derived ash-related emissions and their impact on diesel aftertreatment system performance

Diesel particulate filters (DPF) have seen widespread use in onand off-road applications as an effective means for meeting increasingly stringent particle emissions regulations. Over time, incombustible material or ash, primarily derived from metallic additives in the engine lubricant, accumulates in the DPF. Ash accumulation leads to increased flow restriction and an associated increase in pressure drop across the particulate filter, negatively impacting engine performance and fuel economy, and eventually requiring filter removal for ash cleaning. While the adverse effects of ash accumulation on DPF performance are well known, the fundamental underlying mechanisms controlling these effects are not. This work explores the parameters influencing key ash properties such as porosity and permeability, and factors controlling the soot deposition ash formation/accumulation process, which ultimately determines the magnitude of the ash effect on DPF pressure drop. In addition to the ash properties, the location of ash deposit accumulation inside the DPF channels, whether in a cake layer along the filter walls or packed in a plug at the rear of the channels, also plays a major role in influencing DPF pressure drop. Through a combined approach employing targeted experiments and theoretical models, explanations for the key factors and processes controlling ash properties and their effects on DPF pressure drop were developed. These results, among few fundamental data of this kind, correlate changes in diesel particulate filter performance with lubricant chemistry, exhaust conditions, and ash morphological characteristics. Results are useful in optimizing the design of the combined engine-aftertreatment-lubricant system for future diesel engines, balancing the requirements of additives for adequate engine protection with the requirements for robust aftertreatment systems. Thesis Supervisor: Victor W. Wong Title: Principal Research Scientist and Lecturer in Mechanical Engineering (This page intentionally left blank) ACKNOWLEDGEMENTS A number of people have contributed to making my time at MIT a memorable, always interesting, and extremely rewarding experience. My time at the Institute has afforded me a multitude of opportunities to grow and develop on a number of levels, and for that I am extremely grateful. I would like to extend my sincerest thanks to my thesis advisor, Dr. Victor Wong, for encouraging me to stay on for the Ph.D., and allowing me the opportunity to spend my time here working on a project that I truly enjoy. Aside from learning to conduct scientific research, Dr. Wong has helped me to develop the ability to critically evaluate experimental results. My experience at MIT would not have been nearly as rewarding without the opportunity to work independently and publish and present my work at conferences around the world, and for that I wish to thank Dr. Wong as well. Additionally, I would also like to acknowledge Profs. Wai K. Cheng, John Heywood, and Bill Green for their advice as members of my thesis committee. This project would not have been possible without the support of the MIT Consortium to Optimize Lubricant and Diesel Engines for Robust Emission Aftertreatment Systems. I would like to thank all of the current and past consortium members for not only funding this work, but for providing stimulating discussions and for their helpful advice during our consortium meetings. Many thanks also go to Michael Blanz and the staff at Cummins Technical Center for their technical support, and the staff of the MIT Center for Materials Science and Engineering for their contributions to the soot and ash analysis. The contributions of Thane DeWitt and Raymond Phan to the successful completion of this project were immeasurable. Both Thane and Raymond's cheerful demeanor always brightened my day and made working in the lab that much more enjoyable. I would also like to thank all of my friends and colleagues at the Sloan Automotive Laboratory for the opportunity to develop many lasting friendships. In particular, I would like to thank Eric Senzer and Steve Przesmitzki for their help and support in preparing for my qualifying exams, and Themistocles Resvanis for his contributions to reviewing the theoretical work in this thesis. Additionally, I would like to thank RJ Scaringe, Jeff Jocsak, Devon Manz, Jim Cuseo, Ferran Ayala, Walter Hoffman, and countless others at the Sloan lab who provided many memorable moments and made the lab such an enjoyable place to work. Lastly, I am grateful for the opportunity to have supervised many undergraduate students including Tomas Vianna, Dan Beauboeuf, Yassir Hassan, Bala Mohanamurugan, and Michael Santiago whose work contributed greatly to the completion of this project. Most of all I would like to thank my family for all of their support and the inspiration they have provided me with every step of the way. I am especially grateful to my parents for the example they set each and every day, and many thanks go to my father for his commission-free technical advice. I am also extremely blessed to have the loving support of my girlfriend, Heidi, whose patience, encouragement, and support has made my time here at MIT that much happier. (This page intentionally left blank)