Performance Research Of Automotive Gasoline Engine Based On Variable Compression Ratio Technology

Based on the patent of a variable compression ratio(VCR)mechanism applied for my team project,A gasoline engine is equipped with VCR mechanism in this paper.In this paper,Taking a 1.5L gasoline engine as an example,and it is equipped with VCR mechanism,Then studied the motion of VCR structure,Its principle is to adjust the phase angle beta by adjusting mechanism,This can change the position of auxiliary piston,Namely changed the combustion chamber volume,so as to change the engine compression ratio.The dimensions of the auxiliary piston and other parts are designed,and the variation range of the compression ratio is 9 ～ 18.The experimental data of the prototype are obtained through the bench test,And the performance of the prototype is described,Based on GT power software,a onedimensional simulation model of the test pro totype is built,And calibrated with experimental data,the error is not more than 5%,On this basis,VCR module is added to realize the transformation to variable compression ratio model.Taking 2000 r/min and 8.16 bar as an example,10 simulation cases was designed,The simulation results show that with the increase of CR,the in-cylinder pressure during combustion is increased and the phase of PCP is advanced,meanwhile,the peak HRR is increased and its combustion phase is advanced,so that the piston will have enough expansion to do work.When the CR increased from 10 to 18,the EER and EEE is increased by8.1% and 9.6%.when the CR is increased from 10 to 14.5,the BSFC and ISFC of VCR engine are decreased by 10.5% and 12.8%.It can be seen that the application of VCR significantly improves the power performance and fuel economy of the engine.However,NOX and knock index increase with the increase of CR.Therefore,this paper intends to use EGR to reduce NOX emission and knock tendency.After EGR module is added,the matrix scanning of EGR rate and CR is carried out.Taking 2000r/min,intake pressure 2bar,4bar,6bar and 8bar as examples,the simulation results show that in the presence of EGR,the change rule of engine performance with compression ratio is consistent with that without EGR,When the compression ratio is fixed,the effective thermal efficiency increases slightly with the increase of EGR rate,the PMEP and BSFC is decreased,This shows EGR can effectively improve the fuel economy and power performance of the engine.Taking the compression ratio of 10 as an example,The calculation shows that the effective thermal efficiency is increased by 1.5%,the PMEP reduced by nearly 47%,and the BSFC is reduced by 5.1%.With the increase of EGR rate,the knocking index(KI)decreases obviously,which proves that EGR can effectively relieve the knocking tendency.