Experimental study of axial spark location effects on transient flame/flow dynamics during ignition in a kerosene-fueled gas turbine model combustor

Effects of axial spark location on the transient flame and flow field dynamics during successful ignition events in a kerosene-fueled gas turbine model combustor were investigated using high-speed flame OH* chemiluminescence (CL) imaging, direct photography, and planar particle image velocimetry (PIV) techniques. The combustor was operated with single nozzle and lean premixed pre-vaporized kerosene/air mixture at atmospheric pressure. Three different axial locations, which located respectively in the outer recirculation zone (ORZ), jet and close to inner recirculation zone (IRZ) regions were considered. Experimental results suggested that the axial location of the ignitor played an important role in determining the transient evolutions of the flame and flow field in phases of flame kernel initiation, flame growth and flame breakdown, while minor effects on the flame recovery and final stabilization. More specifically, during the flame kernel initiation and growth phases, when the mixture was ignited in the ORZ, the flame kernel propagated to the nozzle first and then expanded further downstream due to the recirculation flow. However, as the ignitor was in the jet and close to IRZ regions, the flame kernels were seen to travel only downstream and upstream, respectively. As for the phase of flame breakdown, images captured from both front and back views indicated that effects of the swirling flow on the flame dynamics were weakened as the ignition location was away from the nozzle. PIV measurements implied that the spark location had significant effects on the ignition evolutions of large-scale coherent flow structures, including ORZ, jet, shear layers and IRZ. Finally, temporal profiles of the flame OH* CL signals and PIV measurements demonstrated that longest time was needed for the formation of flame kernel and flame growth if the mixture was ignited close to IRZ.