Combustion of Preheated Hydrocarbon Fuel in a Scramjet Model Combustor

This work investigates the impact of fuel preheating on combustion in a cavity-based scramjet. A Mach 2.2 vitiated crossflow ([Formula: see text], [Formula: see text]) was used to emulate Mach 5 flight at 21 km. Results from unheated and superheated n-dodecane experiments were compared for wall-normal injection with and without strut assistance. Combustion was studied with pressure and chemiluminescence measurements; mixing was assessed with shadowgraphy and infrared imaging. The overall effect of fuel state was minor for the evaluated strategies. Wall-based injection was characterized by excessive entrainment, rich blowout at globally lean conditions for both cases. In the strut-assisted scheme, both fuel states produced similar behavior: stable choking at [Formula: see text] and intermittent oscillation at [Formula: see text], between strut-wake location and the cavity shear-layer. Preheating the fuel notably affected flame dynamics, reducing the oscillation interval between the stabilization modes. The unheated case exhibited lower flame intensity over the cavity and stronger high-frequency oscillations that could be linked to jet-induced instabilities. Modal and spectral analyses revealed overlap between nonreacting plume dynamics and flame oscillations. These findings emphasize that while fuel preheating can suppress vaporization-driven instabilities, injector configuration remains the dominant factor governing combustion efficiency and flame stability.