Temperature effects on the flame and emission characteristics of partially ammonia cracked combustion

Stable ammonia combustion is essential for sustainable power. Non-premixed swirl combustion integrated with catalytic cracking was evaluated across ϕ=0.4-1.2 and cracking ratios of 0–30%. Cracking triggers thermal-chemical synergy and increases total mole fractions from 1.0 to 1.3. Resulting volumetric expansion drives fluid dynamic shifts. A 30% cracking ratio increases fuel velocity from 5.84 to 7.59 m/s and raises the momentum ratio (J) from 1.89 to 2.45. Higher jet stiffness (+30.0%) promotes radial penetration against swirl shear (S=0.73), shifting reaction zones toward the outer shear layer and expanding the flame structure. Reactant preheating T_air=543 K, T_fuel=705 K enhances air flow by 79% and fuel velocity by 106%. Thermal elevation improves efficiency and reduces NH₃ slip despite localized NO increases. Multi-objective optimization identifies 30% cracking and ϕ=0.9 as the superior condition. Efficiency reaches 98.87%, with NH₃ and NO emissions at 2217 ppm and 158 ppm. Oxygen competition between H₂ and NH _i radicals governs emission trends. Insights guide the design of high efficiency, low-NO _x ammonia turbines.