Thermal compression effects within a fundamental, hydrogen-fuelled scramjet

Abstract The impact of thermal compression on combustion has been studied experimentally in a hydrogen-fuelled, non-uniform scramjet flowpath. The experimental model consisted of a three-dimensional inlet, a constant area rectangular combustor, and a single-ramp expansion nozzle, all having a constant width, and was tested at an equivalent Mach 10 flight condition with 58 kPa dynamic pressure. Combustion was suppressed in different regions of the combustor by injecting helium as a replacement for hydrogen fuel in either spanwise half of the engine. Thermal compression effects increased the combustion-induced pressure rise by ( 11.9 ± 5.8 ) % across the majority of the combustor for an equivalence ratio of 0.8, however a shock-related artefact dominated similar measurements for a case with an equivalence ratio of 1.0. Over a smaller region at the end of the combustor, the combustion-induced pressure rise was increased by ( 9.4 ± 9.2 ) % and ( 6.7 ± 6.8 ) % for equivalence ratios of 0.8 and 1.0, respectively. Time-integrated OH emission signals increased by 19% and 31%, whilst time-resolved signals increased by 54% and 35%, for equivalence ratios of 0.8 and 1.0, respectively. This study presents the first experimental evidence of thermal compression directly increasing combustion-induced pressure rise in a scramjet engine.