Flame Structures and Emissions of Premixed Partially Cracked Ammonia/Air Swirl Flames

Waste-heat-assisted catalytic cracking offers a practical route to improve the reactivity of ammonia for gas turbine applications. This study experimentally examines the effects of cracking ratio on flame structure, stability, and nitrogen oxide emissions in a model gas turbine combustor. As the cracking ratio increases from 0 to 0.4, the lean blowout limit decreases from approximately [Formula: see text] to [Formula: see text], while the rich blowout limit increases from approximately [Formula: see text] over the bulk velocities of [Formula: see text], corresponding to an approximately 4–8-fold expansion of the stable operating window. However, this is accompanied by increased emissions, with the peak [Formula: see text] emission increasing from approximately [Formula: see text] at [Formula: see text] to above [Formula: see text] at [Formula: see text]. Moreover, [Formula: see text], [Formula: see text], and [Formula: see text] chemiluminescence intensities rise nonlinearly with cracking ratio, indicating enhanced formation of reactive intermediates and stronger coupling between oxidation and fuel-nitrogen conversion. OH-PLIF and NH-PLIF further show a transition from elongated, weakly anchored flames to compact, highly wrinkled structures. These results clarify the tradeoff between flame stabilization and emission control in partially cracked ammonia combustion.