Relight imaging at low temperature, low pressure conditions

High-altitude relight inside a lean, direct-injection, gas turbine combustor is investigated experimentally by high-speed imaging. Ignition testing is conducted at two operating conditions: a 'safe' point at which relight is possible, and an 'unsafe' condition where ignition is precluded by the large air mass flow rate. Image processing software has been developed to analyze the motion and breakup of the imaged flame. At the safe condition, the developing flame kernels are typically swept downstream and towards the fuel-injector center-line, before moving upstream. The comparatively large gas-phase velocity at the unsafe condition causes rapid disintegration of the ignition kernel. At neither condition does the size of the spark kernel determine ignition outcome. Good agreement is demonstrated between the measured spark-centroid velocity and CFD predictions of gas-phase velocity below the igniter tip.