Numerical Study on MILD Combustion of a Premixed NH ₃ /Air Versus CH ₄ /Air Flame in a Lab-Scale Furnace

Ammonia (NH3) is a sustainable, carbon-free fuel that has received worldwide attention as a potential alternative to fossil fuels. This study numerically investigates the MILD combustion characteristics of a premixed ammonia flame in a laboratory-scale furnace. The influence of inlet conditions on the combustion is systematically examined and compared with methane (CH4) combustion. The investigated inlet parameters include the nozzle-exit diameter, input power, global equivalence ratio, and global oxygen concentration. The results show that the combustion temperature of NH3 is significantly lower than that of CH4, accompanied by a longer ignition delay and reduced flammability. Furthermore, the jet momentum rate is identified as a hybrid parameter that influences the MILD combustion characteristics of ammonia and methane very differently. For CH4 combustion, increasing the jet momentum lowers the peak temperature and distributes heat more uniformly, thereby enhancing the MILD combustion regime. In contrast, for NH3 combustion, typical MILD combustion is readily achieved at lower momentum rates, whereas excessively high momentum leads to reduced combustion efficiency. These divergent combustion behaviors between the two fuels cannot be attributed solely to their difference in calorific value. This paper provides a detailed analysis and discussion on the premixed MILD combustion of NH3/air versus CH4/air.