Journal of the Korean Society of Combustion ISSN:1226-0959(Print) 2466-2089(Online) 한국연소학회지

Experiments were carried out to study the flame liftoff height(FLH) and flame stabilization at the fuel-lean region in CH4/Air premixed flames of a low-swirl combustor. The burner used in this study had a nozzle diameter of 28 mm, a combustion chamber with an expansion area ratio of 7.0, a swirler with a swirl angle of 37°, and a turbulence generator with a porosity of 28.7%. The experiments were performed for equivalence ratios ranging from 0.53 to 0.8 and inlet velocities from 2.3 to 4.6 m/s. The CH* chemiluminescence images were acquired using ICCD camera to measure the FLH. As a result, at the equivalent ratios ranging from 0.8 to 0.6, the FLH increased as the equivalence ratio decreased, which is reasonable as the laminar flame speed decreases along with the decreasing equivalence ratio. At equivalence ratios smaller than 0.6, however, the FLH was reduced despite the reduction in equivalent ratio. At the same equivalent ratio, the FLH decreased at elevated inlet velocities, which was again counterintuitive. According to the results with the absence of a chamber wall, the flame stabilization was observed to be highly dependent on the existence of the outer recirculation zone.