Composite combustion behaviors of tubular flame and central jet flame in a reduced-diameter vortex combustor

Abstract

The characteristics of the tubular flame and the flow field mixing mechanism in a reduced-diameter vortex combustor are investigated by varying the fuel flow rate and equivalence ratio through experiments and numerical simulations. Single-layer tubular flame and double-layer composite tubular flame are found in the combustor under the coupling effect of the cyclone and the central jet. The composite tubular flame will be formed when the air in the combustor is more abundant (Ф>1.00), and the center flame frequency is linearly and positively correlated with the Reynolds number of the central jet air. When the Reynolds number exceeds 2000, the double-layer composite flame tends to stabilize, with the center flame frequency higher than 9 Hz. The turbulence of the central jet air promotes the mixing of reactants by enhancing the recirculation near the nozzle, guaranteeing the central flame's stable combustion. Through analysis of the burn rate of methane at the outlet and the emission species of CO and CO2, it is evident that the double-layer flame achieves the methane burn rate exceeding 95 %, while also exhibiting lower CO emissions compared to the single-layer flame.