The Central Combustor Design And Numerical Simulation Of A Free Piston Engine

Free-piston engine（FPE）has the advantages of high power density,great energy utilization and good fuel adaptability.In recent years,it was a new kind of vehicle power device which has been researched throughout domestic and foreign scholars.This article taken the fourth generation of opposed-piston FPE developed by the research group as the research object,and completed the design and numerical simulation of a central combustor with the bore of50mm and the stroke of 72mm（36mm×2）,including following aspects:（1）According to the structural components,working cycle and performance indicators of the opposed-piston FPE,an opposed-piston type of central combustor was designed including combustor shape,the structure schemes of intake and exhaust ports,GDI system and the layout schemes of spark plug.Then the structural parameters designed and physical processing of the combustor prototype were completed.（2）The CFD simulation model of FPE was established,the establishment of 3D model and the division of calculation mesh were completed.Based on the piston displacement-time curve calculated by system zero-dimensional model,the piston motion was equivalent to the opposed-piston displacement of virtual crankshaft-angle.According to the research contents of the numerical simulation,the simulation parameters and calculation strategy of CFD simulation were determined.（3）The CFD calculation and results analysis of the FPE in-cylinder working cycle was completed,the changes of the scavenging process under different port positions and intake pressure were studied.A GDI spray model was built,the model parameters calibration and experimental verification were completed,and the formation process of the mixed gas was analyzed.The ignition and combustion model was determined,and the influence of different fuel injection angles on the combustion was studied.Finally the various performance indicators such as power,economy and emissions of FPE were predicted.The results of numerical simulation shown that the cycle indicated work of the designed combustor chamber prototype was 107.1J,the indicated power was 6.25k W,the indicated thermal efficiency was about 35.7%,the indicated fuel consumption rate was 232.4 g/k W·h,the emission mass fraction of NOx and CO were about 1.1×10^-3 and 5.9×10^-3.It provided essential data for next stage prototype design and experimental research.