Auto-ignition of near-ambient temperature H2/air mixtures during flame-vortex interaction

This paper demonstrates auto-ignition in reactants at approximately 350 K, upstream of curved H2/air flame surfaces during flame/vortex interaction. Temperature fields were measured using laser Rayleigh scattering during head-on interactions of toroidal-vortices with stagnation flames. Repeatable ignition occurred along the ring of the vortex – slightly towards the center – when it was approximately 1 mm upstream of the wrinkled flame surface. The resultant outwardly propagating toroidal flame led to approximately twice the volumetric heat release rate over the duration of the interaction. The ignition occurred in a region of low kinetic energy dissipation rate that was farther from the flame than the region of maximum vorticity. This region was upstream of positively curved flame segments. The advective time over which the vortex transports flame-generated products to the ignition site corresponded well to the time between the beginning of the flame/vortex interaction and ignition. It therefore is hypothesized that the vortex transports HO2 and H2O2 to the low-temperature, low-dissipation region wherein ignition is promoted by preferential diffusion of H due to the positively curved flame. Evidence of additional ignition pockets was found upstream of other flame wrinkles, preferentially near the highest magnitude flame curvatures. These results provide a novel test case for validating diffusion and low-temperature kinetic models, and also have potential implications for reaction rate closure models.