Experimental study of swirl-stabilized turbulent premixed and stratified LPG/air flames using optical diagnostics

Abstract

Experiments are carried out to investigate the effects of mixture stratification, velocity ratio, and swirl on the LPG/air flame structures using a swirl-stabilized axisymmetric burner. Stereo Particle Image Velocimetry (SPIV) technique is used to measure the velocity field of non-reacting and reacting flows. Chemiluminescence imaging technique is used to measure the OH*/CH* signals of premixed and stratified flames. The mixture stratification ratio at the burner exit is varied from 1 to 5 by changing the equivalence ratios of the inner and outer streams between 0.32 and 1.60. The swirl intensity of the inner and outer streams is varied independently by using two different sets of axial swirlers. The ratio of velocities between the inner and outer streams ranged from two to three. Examination of the non-reacting flow field showed that the combination of axial swirlers plays a crucial role in the formation of the streamlines which would help to sustain the flames. Analysis of reacting flow fields of different cases revealed the robustness of the flame structure to the stratification of the mixture. Further investigation on the Abel-inverted chemiluminescence images showed that the transition from premixed to stratified condition makes the flame more compact and closer to the exit of the burner. The flame structure is similar among stratified conditions with the increasing stratification ratios confirming the robustness of the flame structure to the stratification of the mixture. Under the operating conditions studied, the flame structure is more sensitive to changes in the velocity ratio or swirler combination relative to the stratification ratio.