Oscillations in ducted swirl-stabilised flames

Abstract

The characteristics of naturally-occuring oscillations in ducted swirl-stabilised LPG flames simulating the latest type of industrial burner for gas turbine were examined with various geometric parameters, flow boundary conditions, and a function of the temperature of an air supply. It was observed that oscillations were dominated with a quarter-wave of the entire duct and as conventional findings, increased with its length. The onset of oscillations were with equivalence ratios greater than 0.75 and they were greater with the degree of unpremixedness and maximum at 4 kPa. Oscillations were decreased with the addition of exit nozzle due to the transition to bulk-mode and attenuated to smooth combustion as the combustor length was reduced to less than five times of duct diameter. The preheating of an air supply increased the reaction rate and had two different consequences, one that improved the uniformity of temperature close to the upstream flow where antinode positioned and the other could increase the maximum temperature in that area. The former was more influencial so that the oscillations were attenuated, and at stoichiometry they were reduced by a factor of 1.8 or from 3.5 to 1.9 kPa.