Generation mechanism and emission characteristics of N2O and NOx in ammonia-diesel dual-fuel engine

Ammonia, as a hydrogen-derived fuel, primarily emits N₂O and NOₓ when burned in an engine. The emissions originate from ammonia fuel and nitrogen in the air. In this paper, the N of N₂ was labeled by isotope labeling method, so that the nitrogen element in the formation path of the thermal N₂O and NOₓ was labeled, and the chemical reaction path of the formation and evolution of the fuel and thermal nitrogen oxide was defined. In addition, the spatiotemporal distribution characteristics, generation and evolution rules of fuel and thermal nitrogen oxide in ammonia-diesel dual-fuel engine, as well as the influence of different ammonia energy ratios on the generation ratio of two types of N₂O and NOₓ were studied by combining experiment and simulation. The ammonia energy ratio is defined as the proportion of energy provided by ammonia in a constant total lower calorific value. The results showed that when the ammonia energy ratio increased from 20 % to 60 %, the emissions of NO and NO₂ decreased, but the proportion of fuel NO and NO₂ increased. The proportion of N₂O in nitrogen oxide emission increased from 7.3 % to 20 %. Fuel N₂O accounts for about 90 % of N₂O emission. Fuel N₂O and NOₓ were mainly generated in ammonia-rich, low-temperature regions and thermal N₂O and NOₓ were mainly generated in the high-temperature regions. Temperature significantly affected N₂O generation.