Coupling optimization of ammonia-hydrogen reactivity boundary and passive pre-combustion chamber structure: A numerical study

Ammonia-hydrogen (NH 3 -H 2 ) co-firing is an important technological path for achieving clean combustion, and passive pre-combustion chamber (PPC) has received widespread attention as a low-cost and easy to implement optimization method. However, research on PPC mainly focuses on the discussion of fuel supply strategies, with relatively little research on chemical reactions and structural boundaries, which undoubtedly limits the structural updates of PPC and the development of clean combustion technologies. Based on experiments, this study constructed a simulation model of NH 3 -H 2 engine and then proposed a multivariate structural study by changing the inclination angle (α), swirl angle (β), and nozzle numbers, combined with the nitrogen (N 2 ) labeling method. In the study, thermal pollutants are distinguished by labeling nitrogen that comes from air as N* 2 , and the results showed that Thermal N*O accounted for 50% of the total generated NO, mainly generated in the temperature range of 2400 K-2800 K. The study further clarified the N 2 O generation process, which consists of three stages: high temperature, medium-to-low temperature, and low temperature, and is dominated by Thermal N* 2 O (increased by 83.39%), Fuel N 2 O (increased by 50.75%), and Thermal N* 2 O (increased by 40.37%), respectively. Finally, it is confirmed that the structure with 4-nozzle α of 20° and β of 5° possesses the optimal thermodynamic properties, which can increase the indicated thermal efficiency (ITE) to 40.92%. This study provides new optimization ideas for the efficient utilization and pollutant control of NH 3 -H 2 engines and provides mathematical support and empirical reference for achieving clean combustion.