Effects of hydrogen volume fraction, air fuel ratio, and compression ratio on combustion and emission characteristics of an SI ammonia-hydrogen engine

An effective approach to reducing greenhouse gas emissions is to utilize low/zero carbon fuels. This study simulated the combustion of a marine spark ignition (SI) ammonia-hydrogen engine, focusing on the effects of hydrogen volume fraction (XH2), air fuel ratio (λ), and compression ratio (CR) on the combustion and emission characteristics. The pathways of nitrogen-based pollutants such as NH3, NO, and N2O were explained. The results show that increasing XH2 improves Pmax, heat release rate, thermal efficiency, and power. Regarding emission characteristics, when XH2 rises, NH3 emissions drop; NOx emissions remain almost constant at λ ≤ 1 (2100 ppm at λ = 1) and considerably increase at λ > 1, peaking at 5245 ppm. Moreover, as CR rises, the engine power and thermal efficiency increase, NOx emissions decrease by 10%, and N2O emissions are below 20 ppm. Furthermore, chemical kinetic analysis shows that NO comes from N and N2, diffuses from the flame front toward the center in the cylinder under λ = 1.2. And NO comes from HNO and is generated in the flame front and the center under λ = 0.9, respectively. N2O is produced by NH and NH2 and is only generated in the flame front. •The effects of XH2, λ, CR on an SI ammonia-hydrogen engine were investigated.•At λ = 1.0 and XH2 = 20 %, NH3 and NOx are roughly equal, easier for after-treatment.•Increasing CR reduces NOx emissions by 10 % under stoichiometric condition.•The pathway and distribution of NO are clearly different under λ = 0.9 and λ = 1.2.