The Study Of Performance And Matching Of An Atkinson Cycle Gasoline Engine Applied On Hybrid Electric Vehicle

In response to the fourth-stage fuel consumption regulation for passenger vehicles,many automobile enterprises propel the development of new energy and fuel-efficient vehicle.The hybrid electric vehicle is one of the major research focuses.However,most of self-owned brand hybrid electric vehicles apply Otto cycle engines in their powertrains,whose thermal efficiency is lower compared with the powertrain system with Atkinson cycle engine like Toyota’s system.In order to solve the problem,performance research and applied matching research of Atkinson cycle engine with high-compression ratio are carried out to obtain higher thermal efficiency and lower vehicle fuel consumption based on a development platform of a Class B vehicle’s hybrid electric system in this thesis.First,compression ratio is increased from 10 to 13 by reducing the clearance volume by the means of raising piston crown on a 2.0L naturally aspirated gasoline engine.The selection and analysis of intake valve lift are done,and the influence of late intake valve closing(LIVC)on engine performance and flow situation is deeply studied with one and three dimensional simulation,Atkinson ratio is introduced to clear the relationship between LIVC and theoretical thermal efficiency.Results show that extending intake valve open duration can decrease the brake specific fuel consumption(BSFC).On the one hand,LIVC can decrease pump loss and increase combustion constant volume degree.On the other hand,it can decrease the theoretical thermal efficiency.Consequently,setting LIVC angle reasonably is important to achieve high thermal efficiency.Then,genetic algorithm method is used to optimize the design parameters to achieve Atkinson cycle.Results show that the engine fuel consumption of most of operating points is improved.At WOT,minimum BSFC of the Atkinson cycle engine decreases by 12.4 g/(kW?h)compared and the maximum decrease of BSFC is up to 13.5% compared with the baseline engine while the torque higher than 80% of that of baseline engine.Among all operating conditions,minimum BSFC decreases by 10.4g/(kW?h)and the low-fuel consumption region extends toward low-load and low-speed area compared with the baseline engine,which is beneficial to make the engine operate in the high efficiency area.Finally,to take full advantage of Atkinson cycle’s high thermal efficiency in the hybrid electric vehicle,the hybrid mode switching and energy-split strategies centering on the Atkinson cycle engine are established,which guarantees the engine operating in high efficiency area.A facing-forward simulation model is established to do a simulation research about the powertrain in the Class B vehicle.Results show that the powertrain system based on the Atkinson cycle engine can make the engine operating points gather in the engine’s low fuel consumption region,the fuel consumption of powertrain with Atkinson cycle engine is lower 0.52L/100 km than that of the powertrain with Otto cycle engine at NEDC.