Distinct combustion characteristics of a one-dimensional premixed laminar flame of ammonia under various combustion regimes

The present study numerically investigates the distinct combustion characteristics of a one-dimensional premixed laminar flame of gaseous ammonia under traditional, MILD, and high-temperature combustion regimes. Specifically, we examine the flames diluted by N2 and H2O, respectively, analyzing the flame structure, heat release rate, temperature, main species concentrations, and NOx emissions. The fictitious gaseous diluents of FH2O and FN2 are applied to quantitatively distinguish physical and chemical effects. Results show that the chemical effect of dilution by N2 is negligible while both physical and chemical effects by H2O dilution significantly increase the flame thickness and hence reduce the heat release rate and temperature. Furthermore, both effects of H2O dilution diminish as the burning regime transitions from MILD to traditional or high-temperature combustion. In particular, the H2O dilution physically reduces the concentrations of the main species. On the other hand, the chemical effect raises the concentrations of H2, OH, and NO in the traditional and high-temperature combustion, contrasting to that under the MILD regime. As for NOx emissions, the H2O dilution reduces NO emission in the MILD and high-temperature combustion but influences negligibly in traditional combustion. Additionally, the chemical effect of H2O shows a contrasting influence on the NO emission under the MILD and high-temperature regimes. Comprehensive explanations are provided for the observed phenomena, shedding light on the intricate interplay of dilution and combustion.