High-fidelity LES of ammonia spray evaporation and mixing under high-temperature and high-pressure conditions

Abstract

This study addresses the challenge of accurately predicting ammonia spray primary atomization, evaporation, and mixing under high-temperature and high-pressure conditions. The objectives are to improve modeling fidelity and to clarify the governing mechanisms of ammonia evaporating sprays. High-fidelity large-eddy simulations (LES) were performed using a Blob injection model coupled with a Kelvin–Helmholtz (KH) breakup model to represent primary breakup. The performance and grid sensitivity of this approach were systematically compared against a random model. Differences between ammonia and diesel sprays were quantified. A parametric analysis was conducted, and the resulting effects on local equivalence ratio and temperature of ammonia spray were summarized for the first time. The results show that the Blob–KH model provides more accurate predictions and is less sensitive to grid resolution than the random model. Ammonia spray exhibits a substantially higher evaporation rate than diesel spray, especially in the near-nozzle region, followed by a rapid decrease in the equivalence ratio in both axial and radial directions. Ammonia spray tends to fall below the stoichiometric ratio, resulting in a much larger lean region compared to diesel spray. Higher ambient temperatures markedly accelerate evaporation yet have limited impact on mixing extent; increased injection pressure intensifies turbulence and expands the lean region; larger nozzle diameters enrich the equivalence ratio and enhance spray cooling; and higher ambient pressures promote a leaner mixture while reducing spray cooling. These findings offer key insights into evaporating ammonia spray behavior, supporting the advancement of ammonia-fueled engine technologies.