Optimisation of air staging in a can-type combustor using kerosene: a way forward to ultra-low nox emissions

An experimental investigation was conducted to evaluate the influence of air-staging strategies on flameless combustion characteristics in a can-type combustor operating with jet A fuel at thermal inputs of 20 kW and 30 kW over a wide equivalence ratio range ( phi ϕ φ = 0.4–1.1). The effect of swirler air fraction on flame stabilisation, emissions, temperature distribution and acoustic behaviour was systematically studied. Increasing the swirler air fraction enhanced internal recirculation and mixing, resulting in a transition from conventional flame structures to distributed flameless combustion. Optimised air-staging configurations (S50 and S60) achieved ultra-low emissions, with CO and NOx levels below 10 ppm for equivalence ratios up to phi ϕ φ = 0.8 and minimum emissions of 3–4 ppm. The flameless regime exhibited uniform central temperatures with variations within ∼100 K, reduced acoustic emissions and stable operation at both thermal inputs. Flame visualisation confirmed spatially distributed reaction zones with visible combustor walls and no flame hot spots at the combustor exit. The results demonstrate that optimised air staging enables stable flameless combustion with ultra-low emissions and uniform thermal fields, highlighting its potential for next-generation low-emission gas turbine and propulsion systems.