Numerical study on combustion characteristics of ammonia mixture under different combustion modes

Ammonia, an emerging carbon-free fuel, exhibits promising potential within the energy field. Nevertheless, it faces challenges such as unstable combustion and high NOx emissions that necessitate resolution. In this paper, numerical simulation methods are used to compare the combustion characteristics under different modes. Furthermore, the numerical research is carried out by adding ammonia gas in different combustion modes. The results indicated that regardless of the combustion mode, induction of ammonia elicits a significant surge in NOx emissions, but the combustion characteristics of different combustion modes are different. When ammonia is introduced into conventional combustion mode, ignition is significantly delayed. It is proved that the excess enthalpy combustion technology is effective in facilitating the combustion of ammonia mixtures. However, excess enthalpy combustion temperature will lead to elevate NO emissions. In contrast, MILD combustion and oxy-fuel MILD combustion technologies effectively suppress NO formation within ammonia mixtures. This is because in MILD combustion mode, the reaction rate becomes slow, which inhibits the formation of NO.