Free piston engine linear generator (FPELG) is a novel and promising engine for the next generation of hybrid engines. It has several benefits over conventional engines, including minimal friction, a multi-fuel engine, fewer parts, minimal emissions, and excellent thermal efficiency. FPELG is an engine that lacks a crankshaft, and cycle-to-cycle variation (CCV) is viewed as the critical challenge affecting its stability and performance. Therefore, in the present research, the simulation model of FPELG including two sub-models was developed. The CCV and ignition timing (IG) were proposed as sub-models. The FPELG model was demonstrated and run via MATLAB/Simulink. The experimental data were used to validate the model. The validation results indicate that the error was about 5 for the most of cycles, which is within an acceptable range, indicating that the model is valid for accurately predicting future outcomes. Analysis of the simulation model's result showed that the CCV occurs when certain parameters vary during engine running, one of which is the IG variation. Two scenarios were executed for the IG variation in order that CCV variation could be generated using IG variation. In the first scenario where IG occurs after top dead centre (TDC), the modeling results indicated the formation of two peaks and low in-cylinder pressure. While in the second scenario which involves IG occurring early before TDC, the single peak shape and high in-cylinder pressure were produced. Therefore, the IG significantly impacts on combustion characteristics, which is reflecting on the stability and performance of the FPELG. Therefore, further investigation into the effect of the ignition timing on the combustion characteristics is required. In addition, the optimal IG and control of IG are required for achieving high engine performance with stability, this could be achieved in our next work. © Institute of Technology PETRONAS Sdn Bhd (Universiti Teknologi PETRONAS) 2024.