Ammonia-hydrogen engine with reactivity-controlled turbulent jet ignition (RCTJI)

Ammonia (NH3) is a promising fuel for engine carbon neutrality. However, the terrible combustion characteristics substantially restrain the application of NH3 in internal combustion engines (ICE). Hydrogen addition and pre-chamber turbulent jet ignition (TJI) show outstanding abilities to solve the difficult ignition and low flame velocity for ammonia combustion. At present work, a concept of reactivity-controlled TJI (RCTJI) with hydrogen fuel is proposed, and the combustion characteristics of the ammonia-hydrogen engine are investigated. The present study proposes two operating modes of the RCTJI ammonia-hydrogen engine. The controllable prechamber reactivity is achieved by varying the hydrogen concentration and/or adjusting the quantity of the pre-chamber mixture. Then, the effects of the pre-chamber properties regarding the pre-chamber nozzle diameter, per-chamber operating mode, and pre-chamber mixture reactivity on the engine performance are analyzed. The results show that adjusting the mixture reactivity in the pre-chamber can effectivity control the ignition ability and engine performance. The better performance of the RCTJI ammonia-hydrogen engine is obtained under the conditions of per-chamber with a 4 mm hole size and hydrogen fuel, and it can further be optimized by operating the pre-chamber in Mode 2 with an extra scavenging process. An operation strategy of the pre-chamber for the RCTJI ammonia-hydrogen engine is proposed: the RCTJI pre-chamber is suggested to operate under Mode 2 and achieve the first scavenging process by stoichiometric hydrogen/air mixture, and the injection quantity of scavenging gas in the pre-chamber should be controlled in the range of 1.0 Mt-2.5 Mt. At the boosting conditions, the power performance and fuel economy of the RCTJI ammonia-hydrogen engine are optimized effectively. The indicated mean effective pressure (IMEP) increases from 6.3 bar to 10.0 bar at lambda = 1.0 as the intake pressure increases from 1.0 bar to 1.4 bar. The optimum fuel consumption rate is obtained at the lean condition of lambda = 1.4, achieving a 13.3% reduction of the indicated specific fuel consumption (ISFC).