Scavenging Process Optimization of a Free-Piston Engine Equipped with an Electromagnetic Valvetrain

The free-piston engine is an innovative type of internal combustion engine, which has great potential in structural flexibility and energy diversity. The power density and combustion efficiency of the free-piston engine are primarily affected by the scavenging process. The computational fluid dynamics method is used to optimize the scavenging process of a two-stroke free-piston engine, which features a dual-cylinder opposed structure and is equipped with an electromagnetic valvetrain. The valve timing and port inclination angle are optimized by utilizing the scavenging efficiency and circulation intake mass as the main evaluation indicators. The results indicate that the short-circuit loss in the loop scavenging mode is relatively severe, which leads to a low trapping efficiency of only about 40%. By modifying the valve timing, a better scavenging performance can be achieved with a higher scavenging efficiency and a larger circulation intake mass, with the scavenging efficiency reaching 86.38%. Additionally, extending the valve opening duration enhances scavenging efficiency. With the increase of the port inclination angle, the scavenging efficiency and circulation intake mass first grow and then are reduced. The scavenging efficiency of 87.62% and the circulation intake mass of 466.9 mg are obtained when the port inclination angle is 35°. A comparison with the original engine reveals an improvement of 2.29% and 32.93 mg, respectively.