Effect of flash-boiling spray on ignition and flame-holding characteristics under sub-atmospheric pressure

To prevent the performance degradation and flameout of an afterburner/ramjet combustor under sub-atmospheric pressure, the flash-boiling spray by twin-orifice nozzle is attempted to incorporate with the pilot flameholder for reliable ignition and flame stability. Herein, the effects of flash boiling spray by twin-orifice nozzle on the ignition and flame-holding characteristics of evaporating V-gutter flameholder under sub-atmospheric pressure are investigated. According to the analysis of flow patterns and fuel concentrate distribution, the flame stabilization mechanisms of evaporating V-gutter flameholder under lean-state and rich-state are concluded. Compared with subcooled spray, the significant improvement of flash boiling spray on fuel atomization and evaporation under sub-atmospheric pressure can effectively broaden the maximum ignitable velocity of the evaporating V-gutter flameholder, and the lean ignition and blowout fuel-to-air ratios can be reduced by 68.2% and 71.3%, respectively. Furthermore, the flash-boiling spray can promote the establishment of initial flame kernel and accelerate the flame-front propagation, and make the flame stabilization mechanism transform from the rich-flame stabilization mechanism under subcooled spray to the lean-flame stabilization mechanism, resulting in a better performance of flame stability. The results provide a theoretical and technical basis for the practical application of flash-boiling spray in engineering afterburner/ramjet combustors under extreme conditions.