Investigation On Asymmetric Turbocharging Technology Of Internal Combustion Engines

Turbocharging is an important strategic measure for energy saving and emission reduction of Internal Combustion Engines(ICEs).The asymmetric turbocharging is a crucial technology to meet more stringent fuel consumption and emission regulations for ICEs.Studying and developing the asymmetric turbocharging has great significance for further energy saving and emission reduction of ICEs and the development of the next generation automotive ICEs in China.The thesis applied an approach combing theoretical analysis,numerical simulations and experiments to lucubrate the matching rules,performance characteristics,technical improvement,and cycle optimization.The thesis established and validated a numerical model of an asymmetric turbocharged ICE.The error of the simulated and experimental data is within 2%,which meets the research requirements.Based on the model,the quantitative influences of asymmetric turbine critical parameters including asymmetry,throat area and efficiency on engine performance are studied and obtained,which lays a foundation for achieving better matching between asymmetric turbochargers and ICEs.The thesis studied the performance advantages of the asymmetric turbocharging compared with the symmetric turbocharging,and indicated the selection direction among the variable geometry,two-stage and asymmetric turbocharging for different Exhaust Gas Recirculation(EGR)requirements.The asymmetric turbocharging has greater performance potential than the symmetric turbocharging.Turbocharging routes are different under different requirements for EGR rates.There is an inflection point in the relative advantages of asymmetric,variable geometry and two-stage turbocharged engines.In the study,when the EGR rate is lower than 29%,the two-stage turbocharging technology has the best performance.However,when the EGR rate is higher than 29%,the asymmetric turbocharging technology is the best choice.The thesis studied the performance deficiency of the traditional asymmetric turbocharging technology in the partial opening of the EGR valve and the high-speed range of engines,and first proposed two new technologies named the asymmetric turbocharging with two wastegates or two EGR circuits.Then,the effect laws of the critical parameters and the control laws of the EGR valves and wastegates were explored.The maximum energy saving potential of the two new technologies are proved to be about 2.9% and 2.0%,respectively.The thesis optimized the traditional asymmetric turbocharged engine cycle,and first proposed a new combined cycle of the asymmetric turbocharged engine cycle and inverse Brayton cycle.By studying the critical parameters of the inverse Brayton cycle and the combined cycle,it is proved that the combined cycle can save energy up to approximately 5.8% and 3.7% compared with the traditional asymmetric turbocharging and the power turbine technologies,respectively.The combined cycle is more suitable for the requirements of higher torque at low speeds,and energy saving and emission reduction in ICEs.