The fluctuation of gas exchange is easy to induce the free piston linear engine (FPLE) to run unsteadily, because the gas exchange, piston motion and combustion of FPLE are intimately coupled with each other. This work presents a simulation to investigate the effect of combustion variation on the gas exchange stability of a FPLE. A full-cycle zero-dimensional dynamic model and a geometric model for FPLE are built separately, while a coupled three-dimensional combustion and gas exchange is carried out based on the piston motion profile and the geometric model. Subsequently, the effect of combustion variation (including ignition position and combustion duration) on FPLE gas exchange stability is analyzed and discussed. It is clarified that combustion variation has a significant effect on the piston motion and initial conditions of gas exchange, resulting in a variation of gas exchange stability. Specifically, the retarded ignition and extended combustion duration allow FPLE to a longer piston travel distance, providing gas exchange process with sufficient intake duration, thereby resulting in the increase of intake flow mass and fresh charge in cylinder, which improves the scavenging efficiency to 96.82% at the highest, and promotes the reduction of the residual exhaust gas in cylinder, but also inevitably causes the trapping efficiency to drop to 44.06%.

气体交换的波动很容易导致自由活塞式线性发动机（FPLE）不稳定地运行，因为FPLE的气体交换，活塞运动和燃烧紧密地联系在一起。这项工作提出了一个模拟，以研究燃烧变化对FPLE气体交换稳定性的影响。分别建立了FPLE的全周期零维动态模型和几何模型，同时基于活塞运动轮廓和几何模型进行了三维燃烧和气体交换耦合。随后，分析和讨论了燃烧变化（包括点火位置和燃烧持续时间）对FPLE气体交换稳定性的影响。需要说明的是，燃烧变化对活塞运动和气体交换的初始条件有重大影响，导致气体交换稳定性的变化。具体而言，延迟点火和延长的燃烧持续时间使FPLE可以具有更长的活塞行进距离，为气体交换过程提供了足够的进气持续时间，从而导致进气流质量增加和气缸中的新鲜充气增加，从而将扫气效率提高至96.82％最高时，促进了气缸中残留废气的减少，但也不可避免地使捕集效率下降到44.06％。