System Simulation of Partially Premixed Combustion in Heavy-Duty Engines Gas Exchange, Fuels and In-cylinder Analysis Svensson, Erik 2019 Document Version: Publisher's PDF, also known as Version of record Link to publication Citation for published version (APA): Svensson, E. (2019). System Simulation of Partially Premixed Combustion in Heavy-Duty Engines: Gas Exchange, Fuels and In-cylinder Analysis. Energy Sciences, Lund University. 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LUND UNIVERSITY PO Box 117 221 00 Lund +46 46-222 00 00 System Simulation of Partially Premixed Combustion in Heavy-Duty Engines Gas Exchange, Fuels and In-cylinder Analysis System Simulation of Partially Premixed Combustion in Heavy-Duty Engines Gas Exchange, Fuels and In-cylinder Analysis by Erik Svensson Thesis for the degree of Doctor of Philosophy in Engineering Thesis advisor: Associate Professor Sebastian Verhelst Thesis co-advisor: Professor Martin Tunér Faculty opponent: Dr. Andrew Smallbone To be presented, with the permission of the Faculty of Engineering of Lund University, for public criticism in the M:B lecture hall at the Department of Energy Sciences on Thursday, the th of June at :. Organization Document name LUND UNIVERSITY DOCTORAL DISSERTATION Department of Energy Sciences Date of disputation Box -- SE– LUND Sponsoring organization Sweden Swedish Energy Agency KCFP Engine Research Center Author(s) Erik Svensson Title and subtitle System Simulation of Partially Premixed Combustion in Heavy-Duty Engines: Gas Exchange, Fuels and In- cylinder Analysis Abstract The concept of partially premixed combustion (PPC), applied to conventional diesel engines, has showntoyield high gross efficiencies and low emissions of oxides of nitrogen and soot. PPC emerged from the knowledge gained from homogeneous charge compression ignition (HCCI) research. To extend the load range and thus reduce cylinder pressure rise rates, the fuel is directly injected during the compression stroke, instead of in the intake port as is common with HCCI. In contrast to conventional diesel combustion, there is a separation between the fuel injection event and the start of combustion in PPC. Furthermore, the PPC concept relies on a high degree of dilution with exhaust gas recirculation (EGR) and air. This dilution and premixedness lead to a lower global temperature, which reduces NOx emissions and wall heat transfer which therefore results in a high thermodynamic efficiency. However, a high level of dilution reduces the exhaust temperature and thus leads to a lower gas exchange efficiency because the turbine needs to compensate by generating a higher exhaust back pressure. This thesis therefore focuses on expanding the system boundary of PPC, to facilitate a commercial application. This has been conducted in several studies which targeted the brake efficiency, instead of the gross. The work was conducted with a combination of engine modeling and simulations. Moreover, the in-cylinder combustion was taken from experimental measurements or predicted using a stochastic reactor model. The first part of the work investigated the influence of dilution on the gas exchange performance. The gas exchange efficiency was seen to decrease exponentially at high levels of dilution. In addition, a low inlet temperature led to an increase in both brake and gross efficiencies. Furthermore, an evaluation of turbocharger configurations revealed that, although a two- stage turbocharger only negligibly increased the brake efficiency, it enabled a substantially higher engine load than the two single-stage turbochargers. Finally, the gas exchange efficiency was increased with %pt. by using a combined low and high-pressure EGR system. The second part focused on optimizing the engine boundary conditions, choice of fuels, and injection strategy. The results showed that by using methanol, an increase inbrake efficiency of . %pt. was possible compared to gasoline. The reason was a higher gross efficiency which resulted DOKUMENTDATABLAD enl SIS 61 41 21 from an improved compromise between combustion duration, heat transfer, and NOx emissions, as well as lower compression work and favorable ratio of specific heats. Increasing the engine’s compression ratio, facilitated a lower inlet temperature with methanol and this led to a . %pt. further increase in brake efficiency. Key words Partially premixed combustion, Compression ignition, Direct injection, Methanol, Engine optimization, Stochas- tic reactor model, Gas exchange, T − ϕ-diagrams Classification system and/or index terms (if any) Supplementary bibliographical information Language English ISSN and key title ISBN - ---- (print) ---- (pdf) Recipient’s notes Number of pages Price Security classification I, the undersigned, being the copyright owner of the abstract of the above-mentioned dissertation, hereby grant to all reference sources the permission to publish and disseminate the abstract of the above-mentioned dissertation. Signature Date May , System Simulation of Partially Premixed Combustion in Heavy-Duty Engines Gas Exchange, Fuels and In-cylinder Analysis by Erik Svensson Thesis for the degree of Doctor of Philosophy in Engineering Thesis advisors: Associate Professor Sebastian Verhelst Thesis co-advisor: Professor Martin Tunér Faculty opponent: Dr. Andrew Smallbone To be presented, with the permission of the Faculty of Engineering of Lund University, for public criticism in the M:B lecture hall at the Department of Energy Sciences on Thursday, the th of June at :. A doctoral thesis at a university in Sweden takes either the form of a single, cohesive research study (monograph) or a summary of research papers (compilation thesis), which the doctoral student has written alone or together with one or several other author(s). In the latter case the thesis consists of two parts. An introductory text puts the research work into context and summarizes the main points of the papers. Then, the research publications themselves are reproduced, together with a description of the individ- ual contributions of the authors. The research papers may either have been already published or are manuscripts at various stages (in press, submitted, or in draft). Funding information: The thesis work was financially supported by the Swedish Energy Agency, grant numbers P- and P-, and the KCFP Engine Research Center. © Erik Svensson Faculty of Engineering, Department of Energy Sciences isbn: ---- (print) isbn: ---- (pdf) isrn: LUTMDN/TMHP-/-SE issn: <-> Printed in Sweden by Tryckeriet i E-huset, Lund University, Lund Till Katja Contents List of publications ............................. iii Acknowledgments ............................. v Abstract .................................. vii Populärvetenskaplig sammanfattning på svenska . viii Abbreviations & Symbols ......................... x Introduction . Motivation and Scope ........................ . Thesis Contributions ......................... . Thesis Outline ............................ Partially Premixed Combustion in Heavy Duty Engines . Distinction between Combustion Modes .............. . Mechanisms for Reducing NOx and Soot . . Means to achieve Partially Premixed Combustion . . Alternative Fuels ........................... . Engine Energy Flows and Efficiency Definitions . Models and Validation . Gas Dynamic Multi Cylinder Engine Model ............. . Gas Dynamic Single Cylinder Engine Model . . Stochastic Reactor Model ...................... . Full Engine Cycle Simulation .................... Gas Exchange Analysis . Influence of Engine Parameters on Gas Exchange Efficiency . . Evaluation of Turbochargers for Partially Premixed Combustion . . Application of Dual Loop EGR ................... . Summary .............................. Re-Optimization of the Engine Settings to achieve Maximum Engine Brake Efficiency . Operating Points ........................... . Optimization Strategy ........................ . Optimization Results ........................ . Limitations of the Approach ..................... . Influence of Optimization Constraints ................ . Summary .............................. Emission Formation and Ignition Location on the T − ϕ Plane . T − ϕ Map Methodology ...................... SRM Particle Trajectories during Optimal Combustion . . Sensitivity of Start of Injection on Ignition Timing . . The Effect of Thermal Stratification . . Summary .............................. Summary and Conclusions . Contributions ............................ . Outlook ............................... Appendix A Bibliography Summary of Papers ii List of publications