Analyzing Combustion Characteristics and Stability in Free-Piston Engine Generators with Variable Stroke

A free-piston engine generator (FPEG) system offers significant advantages in multi-fuel applications and high-efficiency combustion technologies due to its unique variable stroke characteristics. Consequently, FPEGs have become a research focus in high-efficiency, low-emission internal combustion engine technologies. This study experimentally determined the effects of varying stroke lengths (۴۷ mm to ۵۵ mm) on the combustion characteristics, system performance, and operational stability of an FPEG. Reducing the stroke length significantly increased the FPEG’s operating frequency; decreasing the stroke from ۵۵ mm to ۴۷ mm raised the frequency by ۱۴.۷%. Furthermore, shortening the stroke length enhanced both the peak cylinder pressure and the peak heat release rate. Although the indicated work (Wi) decreased marginally by ۴.۳%, the indicated power (Pi) increased significantly by ۱۰%. Additionally, fuel economy improved with shortening of stroke length, as indicated by a ۱۹.۴% reduction in the indicated specific fuel consumption. In terms of system stability, the short stroke configuration significantly reduced cyclic variability in combustion and system operation. Notably, the coefficient of variation for peak pressure (COVpmax) and indicated mean effective pressure (COVIMEP) decreased by ۳۴.۵% and ۵۰.۶%, respectively, while the frequency variation (COVf) reduced to ۰.۵۹%. These findings provide empirical insights into the optimal design of FPEGs and establish a foundation for their application in high-frequency, high-power systems.

کلیدواژه ها:

Free-piston engine generator ، Variable stroke ، Combustion characteristics ، Stability ، Engine performance