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 NO_x 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 NO_x 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.