Performance Investigation Of Miller Cycle Engine Applied On The APU Of The Series Hybrid Electric Vehicle

Energy crisis and environment problem challenge the development of conventional Internal Combustion Engine(ICE)based vehicle.The electrification of the vehicle becomes an important trend of development in automobile industry.However the overall range of pure electric vehicle at present is limited compared to an equivalent gasoline or diesel fuelled due to the capabilities of battery.Thereby,the hybrid electric vehicle is a good interim solution for the aforementioned limitation.The series hybrid electric vehicle attracts attentions from automobile industry due to its simple and reliable structure of powertrain,and the Series Plug-in Hybrid Electric Vehicle(SPHEV)becomes focus in this area.The SPHEV is confronted with the low energy efficiency when the engine works.In order to solve the aforementioned problem,Miller cycle was adopted to improve the efficiency of the engine and increase the overall efficiency of the SPHEV.The performance of the Miller cycle engine and its effects on the SPHEV were investigated in this thesis.The SPHEV was investigated based on a conventional vehicle of Class A.The design requirement of SPEHV was set according to the power performance of the base vehicle.The selection and match of the key components in powertrain were performed in this thesis,providing the performance analysis of the Miller cycle engine and Millerized SPHEV with parameter basis.According to the result of powertrain matching,a 1.1 L gasoline engine was selected as the base engine.A full-factorial design of experiment was applied to investigate the effects of geometrical compression ratio,intake valve closing retardation angle,and engine speed on the fuel consumption performance and power performance of the Miller cycle engine based on a quasi-dimensional simulation model.The design parameter interacts with the performance parameter,and the relationship of the both makes it difficult to analyze the performance of the Miller cycle engine.In this thesis,a target-oriented analysis was adopted.The simulation results were analyzed with the aid of the intermediate parameter,which bridges the gap between the design parameter and performance parameter.Results show that the fuel economy of the engine is improved by adopting the Miller cycle only when the geometrical compression ratio and intake valve closing retardation angle are reasonably increased.The further improvement of brake specific fuel consumption is mainly limited by four factors,i.e.,the back flow loss,the exergy loss,the incomplete expansion loss,and the combustion loss.The improvement of fuel consumption performance is at a cost of power performance,and the trade-off between the both essentially results from the knock constraint.Aiming to evaluate the series hybrid electric technology combined with Miller cycle,the energy efficiency and emission of a Miller cycle engine based SPHEV were investigated compared with conventional SPHEV equipped with Otto engine and ICE-based vehicle in the same baseline under different driving cycles.Results show that the series hybrid electric technology improves the fuel economy of the vehicle under urban and rural driving conditions;however it harms the fuel economy of the vehicle under the driving condition of motor way.The Millerization draws the fuel consumption of SPHEV back to the same level of ICE-based vehicle under the driving condition of motor way,and further improves the fuel economy of SPHEV under urban and rural driving conditions.The series hybrid electric technology increases the emission of HC,CO,and NOx,resulting from the increased proportion of the warming condition.Furthermore,emission behaviors of the SPHEVs are different when equipped with different types of engine.Compared with the SPHEV equipped with Otto cycle engine,the Miller cycle engine based SPHEV has lower emission of CO and NOx,and higher emission of HC.