Using Ammonia as an Alternative Fuel: Effects of Ammonia Substitution on Methane/Air Counterflow Premixed Flames

Abstract

As a promising green fuel, ammonia can be used as an alternative to traditional fossil fuels. In this study, the effect of ammonia substitution on methane/air counterflow premixed flames was evaluated numerically at standard temperature and pressure conditions. The methane-ammonia-air counterflow flames were modelled within a wide range of ammonia mole fractions, equivalence ratio conditions and flame stretch rates. Extinction limits calculation has quantified the stable burning range and determined the reduction of combustible range of different ammonia-substituted methane fuel blends. With increasing ammonia mole fractions in the methane/ammonia fuel blends, combustion stability limits of the flames tend to decrease. Flame structure analysis reveals the detailed development of the stretched premixed flames. It showed no remarkable reduction of temperature in the methane/ammonia flames. Emission analysis of ammonia-substituted methane/air flames showed considerable reduction of CO₂ emissions compared with the methane/air flames, while moderate reduction of combustible range is found. It was also found that nitrogen oxides emissions tend to increase with ammonia substitution. Finally, sensitivity analyses help to gain a deep insight into the NOx chemistry of different methane/ammonia fuel blends.