Effect of unsteady stretch on spark-ignited flame kernel survival

The chemistry-turbulence interaction remains one of the most important topi cs in combustion research. The ignition of premixed reactants in a highly t urbulent environment is fundamentally coupled to this chemistry-turbulence interaction. The spark-ignition (SI) internal combustion (IC) engine relies on the ability of the flame kernel to survive the high-strain-rate, unstea dy environment of a turbulent flowfield and successfully transition into a fully developed flame to operate cleanly and efficiently. If certain length and velocity scales within the turbulence spectrum are found to promote fl ame kernel growth, then by tailoring the flow passages and aerodynamics of the intake valves, piston, and combustion chamber, it may be possible to in crease the efficiency and reduce the emissions of SI IC engines. This paper describes a novel experimental investigation of a spark-generated flame ke rnel interacting with a single vortex toroid with well-defined length and v elocity scales. This experiment measured the ability of a vortex to quench a growing kernel in a very lean methane-air mixture at atmospheric pressure . The absence of superequilibrium OH concentrations, qualitatively determin ed by planar laser-induced fluorescence (PLIF), was used as in indicator of quenching. It was found that larger eddies are more effective at globally quenching the flamefront, requiring a lower strength, when compared to vort ices with a smaller characteristic length. At the globally quenching condit ion, the maturity of the kernel was then increased incrementally until the vortex was no longer able to completely strain out the kernel. The result o f this was surprising in that the larger vortices had a much narrower range of kernel maturity for which the vortex could still quench the growing ker nel. (C) 1999 by The Combustion Institute.