Experimental and simulation studies on combustion and emission characteristics of heavy-duty engines with different ammonia/hydrogen mass ratios and equivalence ratios under low load conditions

In long-distance freight transport, where decarbonization targets are difficult to achieve through electrification, the adoption of cleaner fuels is more applicable to heavy-duty engines. This study explores the effects of ammonia–hydrogen mass ratio and equivalence ratio on the combustion and emissions of heavy-duty engines under low-load conditions. The results show that the indicated thermal efficiency of the engine increased and then decreased as the hydrogen mass ratio increased. Between hydrogen mass ratios of 3.5% and 20%, the blended fuels exhibited higher thermal efficiency during rarefied combustion. As the hydrogen mass ratio increases, NO x emissions increase and N 2 O emissions decrease. As the equivalence ratio increases, NO x emissions first increase and then decrease, and N 2 O emissions decrease. Under the low-load conditions of heavy-duty engines, considering performance and emissions, it is recommended to choose an equivalence ratio between 0.6 and 0.7, with a hydrogen mass ratio of 7.5%, can achieve an indicated thermal efficiency of 37.3% or higher, with NO x emission of less than 21.12 g/kwh and N 2 O emission of less than 0.74 g/kwh.