Experimental investigation of inlet-injection radical-farming scramjet combustion

Abstract

The flow/chemistry coupling inside a nominally twodimensional inlet-fuelled scramjet configuration has been studied using a combination of experimental surface pressure measurements, optical diagnostics and 2-D premixed CFD simulations. The experiments were conducted at a flow total enthalpy of 4.6MJ/kg which corresponds to a Mach 10 equivalent flight condition, and a flight dynamic pressure of 58 kPa, corresponding to an altitude of 32 km. Radical-farming behaviour was investigated employing two-dimensional chemiluminescence imaging of excited OH (OH*) within the scramjet combustor. The streamwise location of the onset of combustion inferred from the OH* measurements correlates well with the start of the measured combustion-induced pressure rise along the combustor. 2-D premixed CFD results confirm the experimental observations where the ignition process is seen to be initiated downstream of the first shock reflection causing the production of highly reactive radicals, which then travel with the flow and enhance the combustion process further downstream at subsequent shock reflections. The intensity of the OH* signal was found to increase with increasing fuel equivalence ratio indicating mixing limited combustion kinetics