Study Of Flow Field On The Transfer Channel Of Five Stroke Engine And Optimization On The Performance

Due to the advantages of long range and energy saving,E-REV has played an important role in the transformation of the automotive industry.An important part of improving the performance of E-REV is to improve the thermal efficiency of the engine.Five stroke engine is a special type of engine,which adds additional expansion cylinder for secondary work to improve thermal efficiency.Its high thermal efficiency in narrow range is suitable for the special engine of E-REV.The combustion cylinder and additional expansion cylinder in five stroke engine are connected through transfer channel,which has a big influence in the performance of the five stroke engine.In this paper,a comparison between 1D-simulation and co-simulation is executed to find whether the geometry of transfer channel has influence on the simulation result of five stroke engine,and using the CFD to explain the reason.In order to improve the performance of the five stroke engine,after determining the compression ratio,a bionic multi-objective optimization algorithm is used to carry out multi-objective optimization with the objectives of power,fuel economy and NO_xemission.(1)The one-dimensional model of a four stroke engine is built in GT power based on the data of an enterprise,and the five stroke engine established in this paper is improved on it with the method of foreign scholars building five stroke engine.Comparing the performance of the two engines,it can be found the five stroke engine can reach the performance level of the four stroke engine with the thermal efficiency increasing.(2)The co-simulation is carried out by coupling STAR-CCM+and GT-Power after established the 3D model of transfer channel,and the obtained results are compared with the 1D simulation.The differences get in the comparison is below 5%at all speeds,showing a little difference.So that he geometric structure of transfer channel has little impact on the performance of five stroke engine,and 1D simulation can simulate the five stroke engine well.(3)A multi-objective bionic algorithm,improved multi-objective whale optimization algorithm(ENSWOA),is introduced.It adds TENT chaotic map,nonlinear convergence factor and inertia weight to the multi-objective whale optimization algorithm(NSWOA)to avoid the local optimal and speed up convergence,and comparing it with NSGA-Ⅱand NSWOA shows that the improved algorithm perform a better optimization.Using the two-steps optimization method,after determining the compression ratio of high pressure cylinder and low pressure cylinder of the five stroke engine,select three working condition of an ranged extender vehicle,and use ENSWOA to optimize the valve timing and air-fuel ratio of five stroke engine with the objectives of power,BSFC and NO_xemission.The results show that the three objectives have improved by 3.85%,1.5%and12.13%respectively at 2000 rpm,and 1.53%,0.57%and 11.11%respectively at 2500 rpm,but a poor optimization performed in 3000 rpm.The comparison between 1D simulation and co-simulation shows that the 1D model of five stroke engine can achieve a good simulation on the performance of five stroke engine,and on this basis,an improved multi-objective optimization method is applied to achieve better optimization results.