Experimental and numerical investigation of combustion, performance and emission characteristics of a GDI engine using hydrogen-water complementary regulation

In this paper, the coupling effect of water injection and hydrogen enrichment on combustion, performance and emission characteristics of a GDI engine was experimentally and numerically investigated. The engine speed is maintained at 1300 rpm with an excess air/fuel ratio of 1.0. The hydrogen energy substitution ratio is set to 15%. Water/fuel ratio is set to 0.2 and 0.4. The spark timing is kept fixed at −25 °CA ATDC. Results indicated that there exists competing effect between water injection and hydrogen enrichment. Water injection works as a reactivity suppressor, which slows down the overall flame propagation and deteriorates combustion. Whereas, hydrogen enrichment works as a combustion enhancer, which accelerates the combustion and improves the mixing of air-fuel mixture. The overall combustion speed, which is slowed down by water injection, can be largely recovered by hydrogen enrichment. In addition, a reasonable balance between the competing effects of water injection and hydrogen enrichment can make the combustion similar, meanwhile exhibits different emissions performance. Furthermore, the competing effect vanishes when the liquid water is completely vaporized. To some extent, hydrogen enrichment has a more lasting effect on combustion. •Water injection and hydrogen enrichment can be used to regulate combustion.•Water injection works as a reactivity suppressor, which slows down the overall flame propagation and deteriorates combustion.•Hydrogen enrichment works as a combustion enhancer, which accelerates the combustion and promotes combustion.•Water injection can simultaneously reduce NO, HC and CO emissions however at the expense of engine performance.•A balance between water injection and hydrogen enrichment is beneficial for emission control.