Sensitivity and effect of key operational parameters on performance of a dual-cylinder free-piston engine generator

The free-piston engine generator (FPEG) is regarded as the next generation of energy conversion system which may replace traditional engines in the future. The effect of key operational parameters like excess air ratio of input mixture and ignition position on the engine performance of a dual-cylinder FPEG was investigated, and their sensitivity was analyzed in this paper. The operating compression ratio of the system is susceptible to changes in excess air ratio and ignition position. At the same time, it decreases from 15.8 to 6.6 when excess air ratio increases from 0.85 to 1.15, but it increases from 6.1 to 13.3 as ignition position increases from 15 mm to 20 mm. The operating frequency and indicated power are more sensitive to changes in excess air ratio than ignition position. But it is the opposite for the indicated thermal efficiency and friction loss. Excess air ratio and ignition position have a quite similar influence on heat transfer. Therefore, from the perspective of system operation and performance, it is preferable to keep excess air coefficient slightly below 1.0. In contrast, when selecting ignition position, it is of great importance to comprehensively consider the risk of structural damage caused by the increase in the compression ratio and in-cylinder gas pressure.