Effects of Upstream Injection on Scramjet Performance Using an Entropy-Based Method

Upstream injection has the potential for increasing the overall performance of a scramjet by reducing the overall length required to complete combustion and, thereby, reducing overall vehicle frictional drug. However, high flow losses will be incurred by injecting a fuel on the inlet where the Mach number is high. A simple overall approach based on entropy generation was used to investigate the effect or flow losses oil overall performance. This showed that the injection flow losses can he quite high for upstream injection when compared with conventional combustor injection. An inviseid analysis of a two-dimensional scramjet at a Mach 10 flight condition found that a significant loss In overall performance of the engine occurs if the bulk of injection is undertaken on the intake. Estimates of viscous effects in a scramjet combustor showed that depending on the reduction of the mixing length achieved in the combustor, the upstream injection flow losses could he substantially recovered, making it an advantageous design option. The analysis technique developed, like similar simple analysis methodologies, provides a useful understanding of the physical processes that influence thrust production and can also be used to quickly evaluate and optimize potential configurations before starting detailed flow-field simulations