Research On The In-cylinder Combustion Process Of The Opposed-piston Free-piston Engine

In order to further improve the fuel efficiency and emissions of the opposed-piston freepiston engine(FPE),this paper takes the fourth-generation opposed-piston FPE developed by the research group as the research object,and uses the three-dimensional computational fluid dynamics(CFD)method to research the combustion process in the cylinder of the engine.The research content mainly includes the following aspects:(1)According to the specific structure of the opposed-piston FPE,the combustion organization method of the engine is designed,the spray-guided combustion organization method is designed.The evaluation indexes of the mixture formation process and combustion process are analyzed.(2)The geometric model and mesh model of the opposed-piston FPE central combustor are established,the appropriate spray model and combustion model are compared and determined,and the spray model is tested and verified.Finally,the calculation conditions and calculation strategies are determined.(3)The effects of initial fuel-air equivalence ratio,spray angle and fuel injection rate on the mixture formation process are studied,the movement of the in-cylinder airflow and the distribution of residual exhaust gas are analyzed,and different spray parameter research programs are set up.The influence of each spray parameter on the evaporation rate of fuel,the sauter mean diameter of droplets and the distribution of the mixture in the cylinder at the moment of ignition are discussed.(4)The effects of initial fuel-air equivalence ratio,spray angle,and fuel injection rate on the combustion process and emissions in the cylinder are analyzed.The effects of different spray parameters on the heat release rate,average pressure,unburned fuel distribution,CO emissions and temperature are analyzed,and finally the economic performance and power performance of the engine are predicted.The research results show that when the initial fuel-air equivalence ratio is 0.85,the spray cone angle is 40°,and the fuel injection rate is 20 mg/ms,the engine has the best comprehensive performanc.The fuel combustion efficiency can reach 98.5%,the thermal efficiency reaches40.5%,and the CO content in the cylinder is the lowest when the exhaust is open,accounting for 0.2% of the in-cylinder working condition quality.