FGM-LES study of premixed H2/CH4/air flame flashback in a bluff-body swirl burner: The impact of preferential diffusion

One of the major difficulties to adapt H2-enriched fuels in industrial combustors is the high tendency of flashback. Given the challenge of transient flashback diagnostics in experiment, large eddy simulation (LES) becomes an effective approach to study it. In this study, the flamelet generated manifold (FGM) coupled with LES is applied to simulate the flashback of premixed CH4/air and (95% H2/5% CH4)/air flames in a bluff- body swirl burner established by University of Texas. A revised tabulation method to include the preferential diffusion of H2 was proposed, which is special to also efficiently cover the heat loss and stretch effects. Good agreement between experimental and numerical results is attained as to the flashback mode and speed. It is found that the preferential diffusion of H2 significantly promotes the flashback, which causes increased H2 concentration near the flame front, and leads to higher flame temperature and lower tip-wall distance. The flame front area is also increased with preferential diffusion thus expected to promote the flashback speed. Novelty and Significance Statement A revised FGM method including preferential diffusion of hydrogen in the multi-dimension tabulation is proposed and applied to improve hydrogen-enriched flashback prediction. Especially, the varied mixture fraction in the FGM table is attained by varying the inlet mixture components instead of modifying the inlet equivalence ratio as traditionally conducted, which can capture the species and element variation better and cover the heat loss and stretch effects more efficiently. For both flames with or without hydrogen enrichment, the simulated flashback mode and flashback speed correspond well to the experimental results. The flashback behaviors were examined and major reasons for the improved flashback prediction due to the inclusion of hydrogen preferential diffusion were revealed.