Observations on the interaction between a premixed flame kernel and a vortex of different equivalence ratio

Abstract

Charge stratification by direct local injection has been actively studied as a technology for spark-ignitedlean-burn engines. Local mixture enrichment by direct injection in the vicinity of the spark plug at the time of ignition can significantly affect flame kernel development and extend the lean flammability limit of a given fuel/air mixture. The interaction between a lean premixed spark-ignited flame kernel and a laminar vortex toroid containing a different fuel/air mixture was experimentally investigated to gain an understanding of the effect of “turbulent” bulk transport of material into the growing flame kernel. In this study, flame kernels were ignited in a lean premixed methane/air mixture with equivalence ratio of 0.6, while the equivalence ratio of the vortex core fluid was varied between zero and infinity. Chemiluminescence images from CH* of the kernel-vortex interaction were captured using either a single-shot ICCD camera or a high-speed intensified camera. Results of the flame kernel-vortex interactions for six test cases are presented and discussed. It was observed that vortices composed of fluid outside the traditional flammability limits were completely consumed inside the growing flame kernel. Due to entrainment of ambient fluid as the vortex propagates toward the kernel, the equivalence ratio of the vortex is not constant. The Lewis number of the vortex mixture determines if the vortex is consumed as a single pocket or breaks up into multiple pockets before being consumed. Pure fuel vortices were observed to have both a very diffuse reaction zone as well as a region at the upper rim of the kernel-vortex interface of intense chemiluminescence.