Premixed and stratified ammonia/air combustion in an optical chamber using hydrogen pre-chamber jet ignition

This study presents premixed and stratified lean ammonia combustion ignited by a hydrogen pre-chamber jet at an 8% hydrogen energy share and a global equivalence ratio of 0.6. Ammonia is directly injected into an optical chamber at 165 (premixed) and 40 (stratified) crank angle degrees before top dead centre. High-speed natural flame luminosity imaging, OH*/NH* chemiluminescence imaging, and exhaust measurements were employed. Premixed operation shows simultaneous emergence of the six jets and a lower coefficient of variation of indicated mean effective pressure of 2.9% against 4.0%. Stratified operation raises peak pressure from 76.6 to 84.8 bar and IMEP from 5.4 to 6.9 bar, with stronger but spatially concentrated OH* emission. Stratification reduces unburned ammonia from 20,037 to 4734 ppm and N 2 O from 108 to 80 ppm, but increases NO from 289 to 656 ppm and total NOx from 355 to 738 ppm, showing a trade-off between ammonia slip and NOx.