Spray combustion characteristics in a highly pressurized swirl-stabilized combustor

Abstract

Flame structure and droplet behavior in a swirl-stabilized gas turbine combustor at elevated pressure were investigated. The combustion chamber was specially designed and optimized for laser diagnostics, such as phase Doppler anemometry and laser-sheet visualization. Direct observation and CH* chemiluminescence measurements were used to investigate the flame structure and its dependence on ambient pressure. The setup parameters of phase Doppler anemometer were optimized for high-pressure flow field measurements and this considered the thickness of the optical windows and the refractive index of the ambient air in the combustor were taken into account, respectively. The parameter to be discussed in the study is the pressure dependence of droplet velocity, slip velocity, size distribution, and mass flux. This study concentrated on a spray pilot flame burner in order to have stable flame holding but reduce soot and NOx at elevated pressure, then we focused on flame shape, spray droplet size, and velocity, which were measured directly using a high-speed camera and phase Doppler anemometer (PDA). The pressure dependencies of these characteristics are discussed. Image analysis of flame shape indicated that the spray angle narrowed and the flame lengthened as ambient pressure increased. The same tendency was observed with the PDA measurements. The axial velocity difference was not very large, although the fuel flow rate was increased in the high-pressure condition. These results are due to centrifugal force and the variation in the size of the recirculation region within the hollow cone.