Generation mechanism and emission characteristics of N2O and NO 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.