Experimental investigation of a SCRAMJET model combustor with injection through a swept ramp using laser-induced fluorescence with tunable excimer lasers

Tunable excimer lasers are used to obtain two-dimensional images to study the nonreacting and reacting flow field of a hydrogen-fueled SCRAMJET model combustor with underexpanded Ma=1.6 injection in the base of a swept ramp. The rectangular combustion chamber consists of an exchangeable injection module and a 3^o divergent expansion duct, both with optical access from all sides at different axial locations. The inlet conditions of the vitiated Ma=1.9 airflow are T=850 K static temperature at a pressure of 0.96 bar. Therefore, self-ignition of the injected hydrogen mixed with air is possible but was not reached throughout the whole flow field. As an alternate solution, shock-induced ignition by an oblique shock generated by a small wedge fixed at the upper wall of the combustor has been investigated. The spatial structure of the flow field is characterized by relative distributions of different species. Measurements of natural fluorescence of OH and laser-induced predissociative fluorescence (LIPF) of OH in axial and cross-sectional planes are presented. The averaged fluorescence distributions turned out to be highly reproducible and illustrate clearly the gasdynamical features of the flow field, as well as the highly three-dimensional mixing process by vorticity generated by the swept ramp in flow direction. Furthermore, ignition and mixing were improved significantly by the oblique shock wave generated by the additional wedge.