Combustion optimization of a hydrogen free-piston engine with high-energy ignition

With the advantages of simple structure, high power density, and better fuel adaptability, the hydrogen FPE is one of the ideal onboard power devices for new energy vehicles in the future. The combustion system is essential for forming the in-cylinder mixture and the stable operation of the engine. This paper compares combustion, injection, and performance at different ignition energy using high-energy ignition methods and applying computational fluid dynamics simulations. In order to further optimize the combustion system, the influence of ignition timing was discussed. The results show that with the increase of ignition energy, the flame kernel size increases continuously, the speed of flame propagation increases, and the mixture participating in combustion increases simultaneously. When the ignition energy reaches 300 mJ, the fuel combustion efficiency rises to 90.22%, and the indicated thermal efficiency rises to 32.76%. Finally, a comparison was made with a gasoline FPE; the hydrogen FPE in this paper reduces the NO emission value to less than 20 ppm without any after-treatment device, while no other pollutants are