3D numerical study of NH3/H2 MILD combustion in a reversed flow MILD combustion furnace

Combustion of fuels to generate energy is essential for numerous residential and industrial human endeavors. In contrast to fossil fuels, the demand for carbon-free fuels such as ammonia and hydrogen to meet climate commitments is rapidly growing. This study conducts a numerical investigation of NH3/H2 MILD combustion. A three-dimensional CFD simulation model of a 90-degree sector of a reversed flow MILD combustion furnace is presented. The SAGE detailed chemical kinetics solver featuring the CEU-NH3 mechanism is employed with dynamic mechanism reduction for computational efficiency. The effects of varying the hydrogen mole fraction in the inlet fuel mixture from 0 to 50 % on the thermal characteristics, reaction zone, and emissions are investigated. The findings show that temperature homogeneity, assessed through temperature uniformity parameters and standard deviation, reveals a diminishing trend in temperature homogeneity with increased hydrogen concentration. The boundaries of the reaction zone are determined according to the NNH and N mole fractions, and both criteria are approximately identical. All the investigated cases match the MILD combustion definition; however, the cases with H2 concentrations ranging from 10 to 40 % fall under the MILD-like combustion regime. Emissions analysis shows that for all investigated cases, the ammonia slip emissions and the exhaust N2O emissions are below 1 and 0.5 ppm, respectively. The NOx emissions are found to increase abruptly with increasing hydrogen concentration from 0 to 35 % and subsequently undergo minor fluctuations.