Combustion and emission characteristics in a swirling-flow single trapped vortex combustor: Fuel staging effect

Aero-engine emissions have attracted more interest in environmental pollution. The staged combustion in the developing combustors has been recognized as a potentially effective approach to achieving low emissions. The swirling-flow single trapped vortex combustor (SSTVC), integrates the superior mixing capability of swirl combustion, and the broad operational range of trapped vortex combustion. Experiments on the SSTVC demonstrate the role of fuel staging under various operating conditions. A three-dome rig is employed to obtain systematic data on flame structures, outlet temperature profiles, combustion efficiency, and emission index of carbon monoxide, unburned hydrocarbons, and nitrogen oxides. It is found that the combustion efficiency improves progressively with the cavity equivalence ratio under the Only Cavity Mode, reaching a maximum of 96.8% as the cavity equivalence ratio approaches 1.4. In the Two Stage Mode, efficiency further improves to 99.9%, while the nitrogen oxides emission index remains as low as 7.2 g/kg even at the highest fuel air ratio. Fuel staging strongly influences flame propagation and temperature uniformity, with the cavity equivalence ratio approaches 1.4 identified as the optimal value for stable combustion and low emissions. Finally, the empirical correlations for nitrogen oxides emissions in both modes are constructed. It can be used as a predictive tool for designing low-emission aero-engine combustors.