基于某自由活塞发动机（FPE）建立活塞动力学模型和多维燃烧模型，改变传热模型参数实现缸内的低散热，并优化活塞运动，仿真分析原机、低散热FPE以及优化运动后低散热FPE的燃烧特性。结果表明：与原机相比，低散热FPE在燃烧后缸内温度和压力较大，而优化后缸内温度和压力进一步增大，其峰值分别比原机高162.77 K和1.53 MPa；放热率峰值依次增大，且峰值相位也逐渐提前。与原机相比，低散热FPE具有相对较短的滞燃期和速燃期，缓燃期和后燃期更长；而优化后的低散热FPE滞燃期和速燃期较长，缓燃期和后燃期相对较短，燃烧放热规律更理想。原机、低散热FPE及优化低散热FPE的指示热效率分别为45.8%，48.4%，51.5%，即采用低散热技术和优化活塞运动能进一步提高FPE的热效率。
The piston dynamic model and multidimensional combustion model were established based on a freepiston diesel engine. The characteristic of incylinder low heat rejection was realized by changing the parameters of heat transfer model and the piston motion was optimized to further investigate the combustion characteristics of the original engine, low heat radiation FPE and the one after optimization. The results indicated that the incylinder temperature and pressure of FPE were higher than those of original engine after combustion and those of optimized FPE were much higher with the 162.77 K and 1.53 MPa increase of their respective peak value. The peak heat release rates of FPE under three conditions increased in turn and the corresponding crank angles advanced gradually. Compared with the original engine, low heat radiation FPE had a short ignition delay and rapid combustion period, but a much longer mixingcontrolled combustion stage and late combustion phase. The characteristics of optimized low heat radiation FPE were just the opposite of low heat FPE, which was close to the ideal heat release rule. The indicated thermal efficiency of three mentioned engines was 45.8%, 48.4% and 51.5% respectively. Accordingly, the thermal efficiency of FPE could be further improved by adopting low heat radiation and optimizing piston motion.
