Laser and Spark-Plug Ignitions in High-Speed Flows

Laser ignition and spark-plug ignition were compared in high-speed ethylene-oxygen mixture flows of up to approximately 100 m/s. In the experiments, an Nd:YAG laser of 12-ns pulse duration and a semi-surface-discharge-type spark plug of 1.8-ms discharge duration were used, where the deposited energy was approximately 24 mJ in both cases. Observing the self-emission using a high-speed camera, the flame-spread behavior and ignition ability were examined in lean-fuel conditions. The laser ignition was superior to the spark-plug ignition in the aspect of rapid flame spread, although the probability of successful ignition for the laser ignition was a little lower than that for the spark-plug ignition near the lean ignitable limit.