Decarbonizing hydrogen rotary engines: suppressing knock and NOX via premixed ammonia

Premixed ammonia is an effective strategy for regulating mixture reactivity, suppressing knock, and improving combustion stability in hydrogen direct injection rotary engines. This study investigates the effects of ammonia fraction on rotary engine under lean burn conditions. Compared with pure hydrogen direct injection, a small amount of premixed ammonia alters the hydrogen injection duration, produces different fuel distributions, and reduces the extent of locally rich fuel regions near the front of the combustion chamber, thereby slowing flame propagation. At ammonia mole fractions is 1.0%, the maximum knock index decreases to 0.26 MPa, which is below the knock threshold. Increasing the ammonia fraction reduces mixture reactivity, delays the formation of rich OH regions, lowers peak heat release rate and peak pressure, and shifts their peaks to later phases. Premixed ammonia alters the formation mechanisms by suppressing NO and NO 2 production, slightly increasing N 2 O emissions, and reducing total NO x emissions. It also changes the engine energy balance by decreasing indicated power, cooling loss, and exhaust loss, while increasing unburned loss mainly because of unburned ammonia.