Influence of the Burnout in Vitiators on Ignition Limits in Scramjet Combustors

The influence of radicals emitted by a vitiator into a model of a hydrogen-fueled scramjet combustor was investigated. The effect of the preheater combustion was analyzed by varying between a flame mode with high radical formation and a flame mode in which the concentration of the OH radicals was reduced below the detection limit of the optical system. The ignition performances of two fuel injectors were compared to estimate the influence of radicals and water molecules from the preheater on the different types of flame stabilization. The shock wave system, the hydrogen air mixing, and the flame stabilization were studied with optical methods and computational fluid dynamics. It was observed that the two injectors react differently with increasing radical content in the incoming air. The injector with high total pressure loss is insensitive to the burnout in the preheater, whereas the injector that achieves low losses is considerably influenced by the quality of the air preheating. Thus, the cases of higher technical interest with a low pressure loss are more difficult to investigate using test rigs with vitiated air. A technical solution for improving the vitiator burnout, which allows the use of vitiators even in these critical cases, is presented.