Study On The Effect Of Valve Timing On The Economy Of Atkinson Cycle Gasoline Engine

Atkinson cycle solves the problems of the low compression ratio and pumping loss in part load of conventional Otto cycle gasoline engine and improves the fuel economy of engine.The reconstruction of valve timing is the key to design Atkinson cycle on the conventional Otto cycle gasoline engine.Understanding energy saving mechanism and effect of valve timing on Atkinson cycle is the basis of applying Atkinson cycle to improve the fuel economy.This paper studies a 1.0 liter displacement conventional Otto cycle gasoline engine,establishes a one-dimensional thermodynamic model and a three-dimensional computational fluid dynamics?CFD?model,which have been verified by experiments.These models are used for the follow-up simulation research of Atkinson cycle.This paper designs two sets of valve timing strategy for Atkinson cycle,Early Intake-Valve Closure?EIVC?strategy and Late Intake-Valve Closure?LIVC?.The intake duration of EIVC reduced by 30°CA and the intake duration of LIVC increased by 30°CA,compared with 230°CA of the Otto cycle engine.Simultaneously,this paper applies high mechanical compression ratio and matches high-tumble port.The above work transforms the conventional Otto cycle gasoline engine into high-efficiency Atkinson cycle gasoline engine.The influence of different valve timing strategies on pumping loss is explored on the one-dimensional thermodynamic model and the influence of different valve timing strategies on in-cylinder tumble and turbulence motion,combustion process is researched on the three-dimensional CFD model.Based on the above rules,the fuel economy of the 1.0 liter gasoline engine with Atkinson cycle is evaluated and the contribution weight of the energy saving benefits on thermal efficiency is evaluated.The main conclusions of this paper are as follows:1.At low load?2000·8?8)8)^-1,₈8))=0.2),EIVC strategy can reduce the pumping loss more obviously than LIVC strategy.EIVC strategy decreases part of the upward compression work by using the downward expansion work by advancing Intake-Valve closure.When Intake-Valve late Closure angle at-60°CA ABDC,the pumping loss reduced by 56.58%compared with the Otto cycle engine.LIVC strategy can make part of gas backflow,increase intake pressure and decrease pumping loss.When Intake-Valve late Closure angle at 105°CA ABDC,the pumping loss reduced by 7.39%compared with the Otto cycle engine.2.At low load?2000·8?8)8)^-1,₈8))=0.2),LIVC strategy can better enhance in-cylinder tumble and turbulence motion and optimize combustion phasing than EIVC strategy.EIVC strategy limits in-cylinder tumble motion by low valve lift,supples less energy at the end of intake stroke.Calculation results show that the maximum of tumble ratio in the intake stroke reaches 1.73 and that in the compression stroke reaches 1.52,the maximum of turbulent kinetic energy near the top dead center reaches 46.29 m²·s^-2,the maximum of heat release rate reaches 14.61 J·deg^-1 by applying LIVC strategy,while under EIVC strategy the maximum of tumble ratio in the intake stroke reaches 1.16 and that in the compression stroke reaches 0.68,the maximum of turbulent kinetic energy near the top dead center reaches 25.39 m²·s^-2,the maximum of heat release rate reaches 12.20 J·deg^-1.3.At low load?2000·8?8)8)^-1,₈8))=0.2),EIVC strategy can better improve fuel economy,in which the reduction of pumping loss contributes more to the fuel economy.Calculation results show that the lowest brake specific fuel consumption is 308.28 g/?kW·h?under the EIVC strategy and reduces by 18.33%compared with the Otto cycle engine,while the lowest brake specific fuel consumption is 336.74 g/?kW·h?under the LIVC strategy and reduces by 9.75%compared with the Otto cycle engine.The LIVC strategy can better optimize the combustion phase and make its total indicator thermal efficiency up to 43.98%.However,the pumping loss is also large under the LIVC strategy.Considering pumping loss and mechanical loss,the maximum effective thermal efficiency under the EIVC strategy is 26.78%.The energy saving mechanism of valve timing on the 1.0 liter gasoline engine with Atkinson cycle is analyzed in detail by the research above,which establishes foundation for improving the fuel economy of the 1.0L gasoline engine.