Structure and stabilization mechanism of a stratified premixed low swirl flame

Abstract

This paper presents numerical and experimental investigations of the structure and stabilization of a low swirl turbulent stratified lean premixed methane/air flame. Large-eddy simulations are performed using a two-scalar flamelet model based on mixture fraction for predicting the stratification in the fuel/air mixture and a level-set G-function for tracking the flame. Measurements are carried out with LDV for velocity field and simultaneous PLIF of OH radicals and fuel tracer acetone to identify the structures of the flame. The leading edge flame front is observed to exhibit large-scale flame front wrinkling with a particular W-shaped front frequently occurring. This structure is formed due to the interaction of flame front with the large-scale flow motion in the inner low speed zone and the outer high-speed shear-layer of the burner. The W-structures are formed and destroyed periodically at 15Hz. The flame stabilization is shown to be dictated by the large-scale vortex rings in the shear-layer. This flame stabilization mechanism is rather different from that found in typical bluff-body stabilized flames and high-swirl flames.