Application of Spontaneous Raman Scattering to the Flowfield in a Scramjet Combustor

The weight of the oxidizer dominates the take-off weight of rocket based propulsion systems. Therefore, airbreathing engines that consume the oxygen from the atmosphere offer a promising alternative. At flight conditions with Mach numbers above 6 SCramjet propulsion systems represent a better suited concept than ramjet systems, as the high static temperature resulting from the deceleration to subsonic speed in ramjet combustors leads to the dissociation of the air and to thermal problems in the engine. For the investigation of the ignition and reaction of fuel injected into the combustor of a SCramjet at a flight Mach number of 8 high temperature test air at supersonic speed is required. One economic possibility to simulate these inlet conditions experimentally is the use of vitiators, which preheat the air by the burning of hydrogen. Downstream of the precombustor the flow is accelerated in a Laval nozzle to a Mach number of 2.15 and enters the combustor. For the numerical simulation of a supersonic reacting flow precise information concerning the physical properties during ignition and reaction are required. Optical measurements are best suited for delivering this information as they do not disturb the supersonic flow like probes and as their application is not limited by thermal stress. Raman scattering offers the possibility of measuring the static temperature and the concentration of majority species.