Study on premixed hydrogen-ammonia-air flame evolution in a horizontal rectangular duct

The hydrogen-ammonia mixture exhibits significant potential as a carbon-free fuel for internal combustion engines. To gain a deeper understanding of the combustion characteristics of hydrogen-ammonia-air flames in internal combustion, the flame evolution and pressure dynamics are systematically investigated in a closed duct by varying ammonia mixing ratio and equivalence ratio. Concerning flame dynamics, the distorted tulip flame disappears and the inclined flame is formed as the ammonia mixing ratio increases. Additionally, the depression and protrusion structure distributed on flame front is diminished. For pressure dynamics, as the equivalence ratio increases, both the maximum explosion overpressure and maximum pressure rise rate initially increase and then decrease. As the ammonia mixing ratio increases, both of them continue to decrease, and the equivalence ratio corresponding to the peak value transfers from phi = 1.2 to phi = 1.0. In terms of detailed chemistry analysis, the H and OH radical dominate when the ammonia mixing ratio is lower than Omega = 40%. NH2 and OH radical dominate at ammonia mixing ratio higher than Omega = 80% on the lean and stoichiometric side, but NH2 and H radical dominate at ammonia mixing ratio higher than Omega = 40% on the rich side.