Transactions on Machine Design Nguyen Huynh Thi, Nguyen Van Trang, Huynh Thanh Cong, Dao Huu Huy, Huynh Van Loc, Truong Hoa Hiep 13 2 2025 https://doi.org/10.6025/tmd/2025/13/2/68-79 https://www.dline.info/tmd/fulltext/v13n2/tmdv13n2_3.pdf The Free-Piston Engine (FPE) offers a flexible alternative to conventional Internal Combustion Engines (ICE) by allowing variable compression ratio control and eliminating the crankshaft. The advantages of FPEs lie in their simple design with fewer moving parts, resulting in a compact engine with lower maintenance costs, reduced friction losses, and improved fuel efficiency. However, the main technical challenges to adopting this technology are engine startup and stable operation. This study proposes a dual two-stroke FPE model using gasoline fuel and spark ignition. An independent starting mechanism for the FPE was developed, which does not utilize an integrated linear motor as in previous studies. The simulation results show that with a starting speed of 0.7 m/s, a starting compression ratio of 3.3, fuel injection of 3 mg, and a combustion duration of 2 ms to 5 ms, the FPE can ignite with pressures ranging from 9 bar to 11 bar. The mechanical resonance starting method was experimentally validated, achieving the desired compression ratio of 3.3, a fixed electric motor pull force of approximately 400 N over 1.4 seconds, and a piston displacement speed of about 0.7 m/s. The pressure during the startup process was around 4 bar, and the ignition process produced a peak pressure of 13 bar. The FPE model then transitioned to continuous operation over several cycles with peak cylinder pressures reaching 12 bar.