Experimental investigation of low-frequency instabilities of dual-swirl pressure-atomization spray flames

The present study is concerned with the low-frequency self-excited instabilities frequently occurring in aero-engine combustors operated with Jet A-1 fuel under pilot-mode non-premixed conditions. Here we perform extensive measurements of pressure oscillations and high-speed flame visualization to investigate several key aspects of non-premixed spray combustion dynamics associated with a dual-swirl pressure atomization nozzle. Our measurements show that the low-frequency instabilities in non-premixed combustion are intense at near-stoichiometric mixture ratios, with a strong negative correlation with inlet air temperature. The development of low-frequency instabilities is attributable to the interaction between several distinctive reaction regions with different characteristic timescales, involving periodically emerging partially-premixed flames near the injector face and downstream propagating non-premixed reaction regions.