Experimental and numerical assessment on co-combustion of hydrogen with ammonia in passive pre-chamber engines

This paper explores the combustion and emission characteristics of TJI ammonia/hydrogen (NH₃/H₂) dual-fuel engines through experiments and numerical simulations. The NH₃/H₂ engine operates at 1600 rpm with a manifold absolute pressure of 60 kPa. Two independent hydrogen supply systems enable hydrogen port injection (HPI) and hydrogen direct injection (HDI). The results indicate that HDI yields higher power output compared to HPI. The strong injection ignition ability of the pre-chamber (PC) realizes the stable combustion of the NH₃/H₂ engine under different ammonia volume share (AVS) conditions. With the increase of AVS, the mixture of HDI in PC is stratified and the jet velocity is significantly reduced. Power output under HDI conditions decreases with increasing AVS. At an AVS of 10 %, the brake mean effective pressure (BMEP) and brake thermal efficiency (BTE) reach maximum values of 3.67 bar and 30.25 %, respectively. The BMEP and BTE increase and then decrease with increasing AVS under HPI conditions. An AVS of 40 % achieves peak power and efficiency. The CA10-90 is always shorter than CA0-10 in the combustion process. At an AVS of 20 %, NO emissions peak and then decrease with increasing AVS, but higher AVS increases unburned NH₃ and N₂O. Experimental results show that spark timing (ST) has relatively low sensitivity to H₂-dominated TJI NH₃/H₂ combustion. With the increase of AVS to 60 %, the delayed ST will lead to a rapid decrease in power output and a sharp deterioration in combustion stability. When the ST is postponed from 12 °CA BTDC to 4 °CA ATDC, and AVS is 60 %, the COV_Pmax of the TJI engine increases rapidly from 1.9 % to 13.9 %.