A study on the effect of spark plug micro-hole hydrogen injection on the spray and combustion processes of a gasoline engine with intake port water injection

This study examined the impact of hydrogen direct injected through an aperture on edge of the spark plug (SHDI) on the spray and combustion processes of a gasoline engine operating with high water injection rates. The results demonstrated that SHDI effectively mitigated the negative effects of water injection, enhancing the combustion process. SHDI-generated jets significantly increased in-cylinder turbulence—by up to 40 m2/s2—and redirected large-scale vortex motion, enriching the fuel mixture around the spark plug. The equivalence ratio near the spark plug rose from 0.5 to 0.8, promoting the formation of a stable flame kernel up to 7° crank angle (CA) earlier, which accelerated overall combustion. Additionally, the heightened turbulence and increased in-cylinder temperatures induced by SHDI reduced water droplet size, promoting faster evaporation and minimizing the flame-extinguishing effects of residual water mist under high-load, high-water injection conditions. This also leaded to a more uniform air-fuel ratio distribution. Furthermore, hydrogen injection generates abundant H radicals, which enhance the formation of reactive species, accelerating low-temperature fuel decomposition and flame propagation. This counteracts the dilution effect of water injection, ensuring stable and efficient combustion even in challenging conditions. When the hydrogen injection ratio is 15 %, carbon emissions are reduced by 16 %.