Boundary-Layer Flashback Control in Premixed Hydrogen Flames via Gradient Magnetic Fields

Hydrogen is increasingly recognized as a key energy carrier in the transition toward carbon neutrality due to its high specific energy and zero direct carbon emissions. However, its distinct combustion properties, especially the high laminar burning velocity, make premixed hydrogen flames highly susceptible to flashback, which threatens the safety of practical burners. This study investigates the mechanisms of flashback suppression and promotion under gradient magnetic fields using a two-dimensional multislit burner model that incorporates detailed chemistry, conjugate heat transfer, nonunity Lewis numbers, and the Soret effect. Baseline simulations show that reducing inlet velocity or increasing equivalence ratio intensifies near-wall preheating and hydrogen enrichment, reorganizing the flame into a boundary-layer-anchored structure where the flame root dominates propagation behavior, thereby lowering the flashback limit. When a gradient magnetic field is applied, the Kelvin force─strongest in the oxygen-rich, cooler core flow─redistributes momentum and steepens the near-wall velocity gradient. With upstream placement, the core flow is decelerated while boundary-layer velocity increases, enhancing convective wall cooling and displacing the flame base downstream, which reduces near-wall heat-release density and lowers the flashback propensity. In contrast, downstream fields accelerate the core flow, reduce near-wall cooling, elevate wall temperature, and promote upstream flame propagation, which facilitates flashback. Strong fields can also activate a core-flashback mode distinct from boundary-layer mechanisms. Therefore, appropriate placement and strength of gradient magnetic fields offer a nonintrusive strategy to suppress boundary-layer flashback via Kelvin-force-driven momentum redistribution, supporting safer, more efficient hydrogen combustion.