Combustion Feedback Control Strategy Of An Opposed-Piston Free-Piston Engine

Free-piston engine generator(FPEG)often occurs knock,collision and misfire due to poor combustion process,so combustion control has become a technical difficulty that hinders its commercialization.To solve the such problems,this paper takes the fourth-generation opposedpiston FPEG prototype developed by the research group as the research object,and carries out modeling and simulation research on the combustion feedback control strategy during cold start and stable operation,including the following aspects:(1)The system composition and working principle of the FPEG were analyzed.A 3D CFD model was used to analyze the combustion characteristics of GDI SI.According to the engine features during cold start and stable operation,the respective combustion control goals were determined,and a phased control strategy based on cylinder wall temperature and a dual closedloop control strategy based on combustion state were designed respectively.(2)The heat release rate of 36 operating points was obtained by CFD simulation,and the dynamic prediction model of heat release rate was built by combining triple Wiebe function and artificial neural network.A control-oriented FPEG system co-simulation model was established in Matlab/Simulink and Magnet,and the model was calibrated by CFD data.(3)Based on the simulation model,the dynamic change of the heat release rate in the cold start phase was predicted;the combustion control strategy of three operating stages including cold,warm and heat engine was verified.The results show that: the best fuel injection quantity and ignition timing at the cold stage are 8.23 mg and 7mm BITC;the Pmax at the warm stage gradually increases to around the target value of 70bar;the IMEP and HR50 at the heat stage can quickly recover to the target value under a random interference.(4)Based on the simulation model,the effect of injection ignition parameters on the cyclic fluctuation in steady was analyzed;the single and double closed-loop control strategies of state parameters in transient process were verified.The results show that: more fuel injection only increases the fluctuation of IMEP,while the pre-ignition increases the fluctuation of IMEP and HR50;the dual closed-loop control of IMEP and HR50 in the transient can better improve fuel economy and combustion stability,with a volatility of 5% and 0.2mm,respectively.