Topology of turbulent premixed and stratified LPG/air flames

Abstract

Premixed and stratified Liquefied Petroleum Gas (LPG)/air flames realized on a bluff body swirl-stabilized burner are studied in a confined environment. A laboratory-scale burner is designed in such a way that it can independently investigate the effects of mixture stratification, swirl number, swirl direction, and Reynolds number on a broad range of test conditions. A total of 80 different test cases are investigated, with four different swirl number combinations, two different swirl direction combinations, two velocity ratios, and five different mixture stratification ratios. The flame topology is investigated using the simultaneous acquisition of hydroxyl radical (OH*) and methylidyne radical (CH*) chemiluminescence and direct imaging. A series of premixed and stratified flame topologies are compared using mean Abel-deconvoluted chemiluminescence images and direct mean images. Premixed flames appear to be lifted V-flames influenced primarily by swirl number combinations rather than swirl direction or velocity ratio variations. For the same swirler combinations and velocity ratios, stratified flames are more compact than premixed flames, and higher stratified flames are similar in shape. A counter-rotating coaxial swirler arrangement is less likely to affect the flame structure than a change in swirl number. According to the study, the outer swirl angle determines the flame shape, whereas the inner swirl angle influences mixing, which aids in flame stabilization.