Hydrogen-ammonia-air flame acceleration and explosion overpressure generation in a horizontal closed obstructed duct

Applying renewable hydrogen-ammonia mixed energy, composed of green hydrogen and green ammonia, in internal combustion engine can help reduce carbon emissions from the transportation sector. It is essential to understand the fundamental combustion characteristics to support its development. Therefore, the effects of equivalence ratio, ammonia ratio, and obstacle number on hydrogen-ammonia-air flame dynamics in an obstructed duct are obtained in this work. A prediction model is established to reveal the flame acceleration and overpressure generation. The results indicated that as the obstacle number increases, the flame structure within the main flame vortex transitions from wrinkled to filamentous fragmented flame structure; the flame tip speed increases, with the maximum value occurring at the cumulative acceleration stage. As the ammonia ratio increases, both the maximum flame tip speed and the speed fluctuation amplitude decreases. Regarding the explosion overpressure, the maximum explosion overpressure increases slightly with the increasing obstacle number. When the ammonia ratio is below 52 = 20 %, the obstacle #3 significantly increases the amplitude of explosion overpressure fluctuation. The prediction model can accurately predict the pressure rise rate under different experimental conditions and suggest that the flame stretching acceleration and the turbulent acceleration are the primary factors affecting the pressure rise rate.