Effects of Dual Pulse Laser Ignition in Swirl Flames for Successful Ignition

This paper compares the efficacy of dual pulse laser ignition (DPLI) and single pulse laser ignition (SPLI) for premixed methane/air swirl flames. Approximately constant total incident laser energy was used for both dual-pulse and single-pulse ignition to compare the ignition characteristics. Five different distances between the plasmas were selected to study the effect of the distance on the ignition process. Ignition kernel behaviors were investigated through schlieren images and CH* chemiluminescence, and the statistical ignition probabilities compared. The ignition probabilities for DPLI were slightly higher than those for SPLI at moderate plasma separation distances of around 3-4 mm. At these separation distances between the plasmas, the two plasmas developed into a single ignition kernel and formation of lobes was suppressed. At larger distances, two separate, relatively weak kernels were formed, and lobes were observed. Hence, DPLI contributes to an increase in the ignition probability because of increased heat release and reduced heat dissipation by the lobes. However, the enhancement of the ignition with DPLI was not significant compared to SPLI.