Double Compression Expansion Engine: Evaluation of Thermodynamic Cycle and Combustion Concepts Dissertation by Vijai Shankar Bhavani Shankar In Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy King Abdullah University of Science and Technology, Thuwal, Kingdom of Saudi Arabia © November, 2019 Vijai Shankar Bhavani Shankar All rights reserved EXAMINATION COMMITTEE PAGE This dissertation of Vijai Shankar Bhavani Shankar is approved by the examination committee. Committee Chairperson: Dr. Mani Sarathy Committee Members: Dr. Bengt Johansson, Dr. Himanshu Mishra, Dr. Jamie Turner 2 ABSTRACT Double Compression Expansion Engine: Evaluation of Thermodynamic Cycle and Combustion Concepts Vijai Shankar Bhavani Shankar The efficiency of an internal combustion (IC) engine is governed by the thermodynamic cycle underpinning its operation. The thermodynamic efficiency of these devices is primarily determined by the temperature gradient created during the compression process. The final conversion efficiency also known as brake thermal efficiency (BTE) of IC engines, however, also depend on other processes associated with its operation. BTE is a product of the combustion, thermodynamic, gas-exchange, and mechanical efficiencies. The improvement of BTE through maximation of any one of the four efficiencies is reduced by its implication of the other three. Split-cycle engine provides an alternative method of improving the engine efficiency through over- expansion of combustion gases by transferring it to a cylinder of greater volume. The operation of split-cycle engines is based on either the Brayton or the Atkinson Cycles. Atkinson Cycle has been demonstrated in IC engines without the split-cycle architecture but is limited by the reduced energy density. Double Compression Expansion Engine (DCEE) provides a method of accomplishing the Atkinson Cycle without the constraints faced in conventional engine architectures. DCEE splits the compression and expansion processes in a vertical manner that enables the use of larger cylinder volumes for over-expansion as well as first-stage compression without much friction penalties. 3 The present thesis explores the thermodynamic cycle of this novel engine architecture using well- validated 1-dimensional engine models solving for gas-exchange, real gas properties, and heat transfer provided in the GT-Power software tool. The effect of compression ratio, rate of heat addition, sensitivity to design and modeling parameters was assessed and contrasted against conventional engine architecture. The synergies of combining low-temperature combustion (LTC) concepts with DCEE was investigated using simulation and experimental data. DCEE relaxes many constraints placed the operation of an engine in Homogenous Charge Compression Ignition (HCCI) mode. The limitations of adopting Partially Premixed Combustion (PPC) concept is also alleviated by the DCEE concept. BTE improvement of above 10% points is achievable through the DCEE concept along with possibility to achieve very low emissions through use of LTC concepts and new after-treatment methods uniquely available to the DCEE. 4 ACKNOWLEDGEMENTS “Standing on the shoulders of giants” – Bernard of Chartres The work while credited to this author is really the result of the cooperation of many souls who have overwhelmed me with their kindness. Prof. Bengt Johansson, Prof. Mani Sarathy, and Mr. Arne Andersson played a pivotal in shaping my thought process and attitude towards research. They have been terrific role models for a young researcher with their dedication towards the science of combustion and their relentless pursuit of excellence. I am very fortunate to be blessed with the endless love and adoration of my parents, Mr. Bhavani Shankar and Mrs. Lakshmi Shankar who have supported and provided for me. I hope their best efforts at molding me into a good human being is reflected by my actions in professional and personal life. I would also like to thank my grandmother, Mrs. Kalyani who has exemplified love, sacrifice, and humility before God. I am indebted to the late King Abdullah for his vision and perseverance of creating an extraordinary institution that has nurtured and developed me. I am forever grateful to the great man and his memory. I am thankful for the excellent faculty of the Clean Combustion Research Center. Prof. Robert Dibble has taken the role of the wise sage in my life. The width and depth of his experience, his ability to communicate, and hold an audience captive, his endless curiosity for science and technology. I consider his a life to cherish and emulate. I am in awe of Prof. William Roberts and Prof. Suk Ho Chung for their audacity to envision and materialize such a top center for combustion research. 5 I like to send my warmest hugs to – Major. Puli Pandian, Captain. Arun, Mr. Suraj Tiwari, Mr. Ahkilesh Krishnan, Mr. Yashwanth Narayanan, Mr. Raghavendran Pala, and Dr. Ehson Fawad Nasir for being the most magnificent buds. Finally, I like to thank my peers and friends at CCRC, especially Dr. Samah Mohamed, Dr. Nour Elsagan, Dr. Adamu Alfazazi, Dr. Ahfaz Ahmed, Dr. Eshan Singh, Dr. Mariam El Rachidi, Prof. Zhandong Wang, Mr. Ariff Magdoom, Dr. Yang Li, and Ms. Can Shao for being inspirational with your outstanding research and for extending your friendship to me. 6 TABLE OF CONTENTS EXAMINATION COMMITTEE PAGE………………………………………. 2 ABSTRACT……………………………………………………………………… 3 ACKNOWLEDGEMENTS……………………………………………………... 5 TABLE OF CONTENTS………………………………………………………... 7 LIST OF FIGURES……………………………………………………………… 9 LIST OF TABLES……………………………………………………………… 11 1 Introduction .............................................................................................................................. 13 1.1 Objectives and Limitations ................................................................................................. 14 1.1 Thesis Contribution ............................................................................................................. 14 1.2 Outline................................................................................................................................. 16 2 Literature .................................................................................................................................. 18 2.1 Evolution of Class 8 Vehicle Engine .................................................................................. 19 2.2 SuperTruck .......................................................................................................................... 20 2.3 Split-Cycle Engines ............................................................................................................ 22 3 Thermodynamic Cycles ........................................................................................................... 26 3.1 Otto and Diesel Cycles........................................................................................................ 26 3.2 Over-Expanded Cycles ....................................................................................................... 29 3.3 Real Cycles - Heat Transfer, Gas-Exchange, and Friction ................................................. 33 3.3.1 Quantifying Losses in Real Cycles. ............................................................................. 35 3.4 Conclusions ......................................................................................................................... 54 4 Double Piston Compression Expansion Engine .................................................................... 55 4.1 Implementing the Atkinson Cycle ...................................................................................... 55 4.2 Efficiencies and Losses in DCEE ....................................................................................... 59 4.2.1 Engine Model ............................................................................................................... 59 4.2.2 Results .......................................................................................................................... 60 4.3 Conclusions ......................................................................................................................... 66 5 Optimum Heat Addition Process for DCEE ......................................................................... 68 5.1 Influence of Heat Addition Process on Efficiency and Losses ........................................... 68 5.1.1 Wiebe Function ............................................................................................................ 69 7 5.1.2 Results .......................................................................................................................... 72 5.2 Conclusions ......................................................................................................................... 83 6 Parametric Study and Optimization of DCEE Configuration ............................................ 84 6.1 Sensitivity of System Efficiency to Heat Transfer Losses .................................................. 84 6.1.1 Influence of Heat Transfer Coefficient Scaling Factor ................................................ 84 6.1.2 Influence of Charge Air Cooling Temperature ............................................................ 87 6.2 Compressor and Expander Geometry ................................................................................. 95 6.2.1 Compressor Compression Ratio .................................................................................