Analysis of flame characteristics in a scramjet combustor with staged fuel injection using common path focusing schlieren and flame visualization

We conducted a comprehensive set of combustion experiments in a connected tube test facility to investigate the interface between supersonic and dual-mode combustion in a scramjet combustor. This is achieved using a staged injection scheme consisting of a strut as first stage and wall ramps as second stage. Wall pressure measurements, flame visualization and focusing schlieren imaging are applied simultaneously to gain information on the flow field and the reaction zone. These combined data sets allow the analysis of the interaction of the supersonic main flow with the combustion zone. Stable and distinct flame states are identified at this interface, which are generally described rather unspecific in literature. These states differ in terms of flame structure and local shock pattern in the reaction zone, but cannot be distinguished solely by evaluating the static wall pressure distribution. Therefore, the present study also shows the limits of wall pressure measurements as only criterion for the classification of scramjet combustion phenomena.