Structural Heat-Transfer Characteristics of Free Piston Engine

The thermodynamic state in the cylinder of free piston engine is different from the traditional crank engine. To study the influence of the structural heat-transfer differences, a multi-discipline coupling simulation model was established based on the piston dynamics, in-cylinder thermodynamics and structural heat transfer. The simulation model was then verified by the experimental results of the prototype. Furthermore, the differences of thermal load, heat-transfer loss and structural temperature between the free piston engine and the crank engine were also analyzed by the comparison of simulation results. Results show that, compared with the crank engine, the peak value and the action time of explosion heat load is less and the energy conversion efficiency of the free piston engine is higher with less heat loss in the free piston engine. Under the influence of free piston motion, the proportion of the structural heat transfer loss between combustion air and cylinder liner is higher. In addition, the structural temperature and the temperature fluctuation amplitude in the free piston engine are lower than those in the crank engine. Since heat load is lower, the free piston engine has greater potential for performance.