@article{xiong_roberts_2002, title={Observations on the interaction between a premixed flame kernel and a vortex of different equivalence ratio}, volume={29}, ISSN={["1873-2704"]}, DOI={10.1016/S1540-7489(02)80207-3}, abstractNote={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.}, journal={PROCEEDINGS OF THE COMBUSTION INSTITUTE}, author={Xiong, Y and Roberts, WL}, year={2002}, pages={1687–1693} }
 @article{xiong_roberts_drake_fansler_2001, title={Investigation of pre-mixed flame-kernel/vortex interactions via high-speed imaging}, volume={126}, ISSN={["1556-2921"]}, DOI={10.1016/S0010-2180(01)00293-0}, abstractNote={To reduce cycle-to-cycle variations in SI-IC engines, knowledge of early flame kernel growth in a turbulent flow field is required. Understanding the interaction between a flame kernel and a vortex is an important fundamental step toward this goal. This paper presents high-speed movies of combustion luminosity during the interaction of a laminar vortex with a spark-generated pre-mixed flame kernel in a quiescent combustion chamber. The resulting time evolution of the perturbed flame kernel shows that laminar vortices of various sizes and vortex strengths can increase the kernel growth rate by at least a factor of 3 and significantly increase combustion reaction rates by involving additional highly curved and stretched flame fronts.}, number={4}, journal={COMBUSTION AND FLAME}, author={Xiong, Y and Roberts, WL and Drake, MC and Fansler, TD}, year={2001}, month={Sep}, pages={1827–1844} }