The effects of premixed pilot-stage on combustion instabilities in stratified swirling flames: A large eddy simulation study

Abstract

Large Eddy Simulation (LES) is conducted for the combustion instabilities of the stratified swirling flames. Two different pilot-stage equivalence ratios (Φp), 0 (lifted flame) and 1 (pilot-stage flashback), are investigated in a same global equivalence ratio. The main aspects of the combustion instabilities focused in the present work are the flow field structure, flame anchoring position, velocity and heat release rate (HRR) fluctuation modes. The results show that the variation of Φp leads to the transforms in the location and intensity of the chemical reaction, which affects the swirling intensity of the pilot-stage fluid through the changing of fluid temperature and volume flow rate, ultimately influences the coupling of the pilot-stage and the main-stage swirling flow, and leads to significant changes in the combustion field structure. The variation of Φp affects the excitation and suppression of the precessing vortex core (PVC), which leads to the change of HRR fluctuation and the transition of the HRR mode, and influence the distribution range of amplitude and energy of HRR oscillation over the frequency domain.