Unlike the conventional two-stroke engine, a two-stroke free piston linear engine can change compression ratio due to free motion of a piston in a cylinder. The free motion of the piston directly affects the gas exchange process or scavenging process of the free piston engine which is key to improving the engine performance. In this study, a numerical simulation using computational fluid dynamics (CFD) is conducted to examine the scavenging process taking place in a two-stroke free piston linear engine. The motion of the free piston is built first based on a dynamic model to define the motion profiles of the piston, and afterward, the piston's motion profiles are imported into a commercial CFD software (Ansys Fluent v.14) to simulate the scavenging process. The simulation results in piston motion and in-cylinder pressure are compared with experimental results to validate the presented simulation. To provide information for this study, some key parameters such as operating frequency of the piston, exhaust port distance, and inlet pressure are changed to find out their effects on the trapping efficiency. The simulation results show that the trapping efficiency has a maximum value of 83% at optimal operating frequency f=33Hz. Besides, by increasing exhaust port distance and reducing inlet pressure, the trapping efficiency is increased.
Hung, N. B., Jaewon, S., & Lim, O. (2017). A Study of the Scavenging Process in a Two-stroke Free Piston Linear Engine using CFD. In Energy Procedia (Vol. 142, pp. 1353–1360). Elsevier Ltd. https://doi.org/10.1016/j.egypro.2017.12.519