Improvement of flameholding characteristics by incident shock waves in supersonic flow

The objective of this study is to investigate the effect of incident shock waves on flameholding behind a fuel injection strut in low temperature supersonic flow, and to elucidate the structure of the flameholding region. A non-premixed hydrogen flame was established behind a fuel injection strut in Mach 2.5 supersonic airflows with total temperature between 400 K and 900 K. The shock waves interacted with the wake behind the fuel injection strut, which improved the flameholding characteristics remarkably by enlarging the recirculation flow and enhancement of mixing. The incident position and the strength of the shock waves control the size of the recirculation flow and flameholding limit. As the strength increases, the upper limit of fuel flow rate for flameholding increases. As the incident points of the shock waves move downstream from the strut base, the upper limit decreases and finally the flame is not stabilized for any fuel flow rate. Instantaneous OH distribution in the flameholding region was observed by laser induced fluorescence. The main reaction occurs near the base at the small fuel flow rate. As the flow rate increases, OH distribution moves downstream and varies between the front and the middle section of the wake. On the other hand, homogeneous OH distribution is observed around the rear throat region of the wake until the blow-off. This suggests that the upper flameholding limit is largely determined by the stability of flame base in the throat region.