Theoretical Modeling and Energy Conversion Process of Free Piston Internal Combustion Power System

A numerical model for energy flow calculation of the free piston internal combustion power system (FPICPS) was established, which was compared with the traditional internal combustion engine (IC engine) with the same structure and input conditions. The piston motion characteristics and energy transfer process of FPICPS are studied by numerical simulation method. The results show that the changes of cylinder pressure, temperature and piston motion characteristics of free piston engine (FP engine) lag behind those of IC engine, and the piston peak acceleration of the FP engine is approximately 2.8 times that of IC engine. The proportion of compression stroke and expansion stroke of IC engine is basically the same, while the expansion stroke of FP engine only accounts for 41.6% of the whole operating cycle. FP engine have obvious advantages in heat transfer and air leakage loss, their percentages are 11.82% and 0.83%, respectively. The percentage of indicated power in FP engine and IC engine are 27.44% and 25.98%, respectively. And 79.64% of FP engine indicated power is converted into the motor electromagnetic energy.