Cause of Hysteresis in Flame Stabilization in a Hydrogen Fueled Strut-Stabilized Supersonic Combustor

Hysteresis in flame stabilization in a strut-stabilized hydrogen-fueled supersonic combustor for varying Equivalence Ratio (ER) was experimentally studied. The three different combustion modes observed are divergent flame (CM1), strut-stabilized flame (CM2), and fuel jet stabilized flame (CM3). Two hysteresis loops are observed between the flame stabilization modes. The first hysteresis is observed between CM1 and CM2 for lower ERs. For higher ERs, hysteresis is observed between CM2 and CM3. 10 Hz Hydroxyl Planar Laser-Induced Fluorescence (OH PLIF) imaging is used to study the two hysteresis loops. The hysteresis between CM1 and CM2 is due to the retention of hot combustion products in the recirculation zone formed at the wake of the strut. A large concentration of OH radicals is observed within the recirculation zone. When reducing the ER, the recirculation zone supplies the existing OH radicals and high temperature to the combustible mixture sustaining CM2. The absence of the free OH radicals, when approached from a lower ER causes the CM2 to start at higher ERs. Similarly, when reducing the ER, the OH radicals in the wake of the fuel jet supply sufficient preheat and free radicals sustaining CM3. The absence of OH radicals in the wake of the fuel jet, when approached from a lower ER, causes the CM3 to occur at higher ERs. Hence, two combustion modes for flame stabilization modes were observed depending on the history of ER. This paper explains one of the fundamental mechanisms of hysteresis in flame stabilization modes occurring in a strut-equipped hydrogen-fueled supersonic combustor.