Determination of optimal spacing between transverse jets in a SCRAMJET engine

Abstract

A SCRAMJET engine typically has multiple transverse fuel injectors with a flame holder. In this study, we consider a two-jet SCRAMJET engine design configuration that uses the low speed recirculation region created by a backward facing step as a flame holder. The effect of spacing between the transverse fuel injectors on the performance of a SCRAMJET engine has been studied using cold-flow simulations. The position of the leading jet is kept fixed at the end of the recirculation zone as suggested by previous studies and the second jet is placed at various locations downstream in the distinct flow regions formed behind the leading jet. It is assumed that the two jets are identical in dimensions and flow. The spacing between the jets is expected to play a significant role in determine the performance of the SCRAMJET engine. Three-dimensional simulations have been performed, using Menter's SST model in our in-house parallel 3-D RANS unstructured grid CFD solver. The mixing of inlet air and the injected air-fuel in such a SCRAMJET configuration is augmented by the interaction of the transverse under-expanded jet with the incoming supersonic cross-flow through the generation of strong streamwise vorticity. The performance and mixing of the combustor have been quantified for each of the distinct configurations. It is observed that they are indeed affected by the spacing between the jets. From the results presented in this paper, the optimal location for the second jet is at the end of the zone over which the lateral momentum of the first jet is dominant in affecting the jet penetration into the streamwise flow.