Combustion and emissions of an ammonia heavy-duty engine with a hydrogen-fueled active pre-chamber ignition system

Combustion and emission characteristics of a heavy-duty single-cylinder ammonia engine with a hydrogen-fueled active pre-chamber ignition system are investigated experimentally at the condition of IMEP 10 bar, 1000 rpm, where effects of spark timing, excess air ratio (lambda), and hydrogen energy ratio are tested. Three distinguishable combustion phases are observed, including pre-chamber combustion, turbulent-jet-controlled combustion, and ammonia-chemical-kinetics-controlled combustion. Advancing spark timing makes combustion phases earlier, increasing pressure rise rate, combustion pressure, and NOx emissions. The optimal spark timing for the highest indicated thermal efficiency (ITE) is -12 degrees CA ATDC in the experiment. lambda range for stable combustion is 1.1-1.5 and ITE peaks at lambda = 1.3. The hydrogen energy ratio, 7.9%similar to 10.5%, has little influence on the engine performance. However, a low hydrogen energy ratio could increase the risk of misfire. The optimal hydrogen energy ratio is about 9 similar to 10%.