多点点火对高强化液压自由活塞发动机燃烧过程影响的仿真研究

利用CONVERGE仿真平台建立点燃式液压自由活塞发动机(hydraulic free piston engine,HFPE)三维仿真模型,并实时求解作用在活塞顶表面的压力,从而使缸内燃烧气体力和液压力耦合。在此基础上研究了增压多点点火HFPE的指示热效率情况。研究结果表明:采用多点点火能改善增压HFPE的指示热效率。采用多点点火之后,最佳指示热效率对应的压缩比变小。多点点火使增压比较大时的工况也呈现较高的指示热效率。采用多点点火后,高效区能够扩大到增压比为4以上。适当增加活塞组质量能够延长活塞在上止点附近停留时间,从而进一步提高指示热效率。

Simulation Study on the Influence of Multi-Point Ignition on Combustion Process of an Intensified Hydraulic Free Piston Engine

A three-dimensional simulation model of an ignited hydraulic free piston engine(HFPE) was established by using a CONVERGE simulation platform. The pressure acting on the top surface of piston was solved in real time to promote the coupling of the combustion gas force in the cylinder with the hydraulic pressure. On this basis, the indicated thermal efficiency and knocking conditions of the pressurized multi-point ignition HFPE were also studied. Results show that the use of multi-point ignition improves the indicated thermal efficiency of the pressurized HFPE, which results in a smaller compression ratio for the best indicated thermal efficiency and a higher indicated thermal efficiency at a higher boost ratio. Use of multi-point ignition also expands the boost ratio in the high efficiency zone to over 4. Moreover, an appropriate increase in the mass of piston assembly can extend the residence time of the piston near the top dead center, thus further improving the indicated thermal efficiency.