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Addressing flashback represents a pivotal challenge in the advancement ofinnovative perforated burners intended to substitute natural gas with hydrogenin household appliances. Current numerical models, employing 2D configurationsto estimate flashback velocities in the slits of such burners, offer valuableinsights with reasonable computational costs. However, the inherent complexityof the phenomena suggests that a 2D model may inadequately capture flashbackdynamics, resulting in inaccurate estimations of flashback limits. In thisstudy, 3D simulations are employed for the first time to explore the impact ofthe three-dimensional shape of slits on the flashback limits ofhydrogen-premixed flames. Steady-state simulations are conducted to computeflashback limits for different equivalence ratios, investigating slits withfixed width and varying lengths up to 8 mm. Additionally, transient simulationsare performed to investigate the flashback dynamics. The results are comparedwith those from 2D configurations to assess the reliability of the infiniteslit approximation. Notably, 2D simulations significantly underestimateflashback limits as the critical initiation region is consistently located atthe slit extremities, which are neglected in 2D configurations. For the samereason, the flashback velocity exhibits weak dependence on slit length, sincethe flashback is consistently initiated at the slit far ends regardless oflength. The physical mechanisms driving the initiation of flashback in thatzone are identified as preferential diffusion effects, which cause theenrichment of the mixture at the slit extremities, and enhanced heat transferpromoted by the enclosed geometry, which increases the pre-heating of the freshgases in that regions.

Effects of three-dimensional slit geometry on flashback of premixed hydrogen flames in perforated burners