Shock Tunnel Experiments on Oxygen Enrichment in a Hydrogen Fuelled Scramjet

Abstract

Oxygen enrichment is proposed as a thrust augmentation technique for scramjet engines flown at high Mach numbers and altitudes where there is little freestream oxygen available and mixing is poor. It is defined here as the premixing of oxidiser and fuel prior to injection into the mainstream flow. Shock tunnel experiments were conducted to investigate the effectiveness of oxygen enrichment in improving engine operation at two simulated flight conditions; a standard altitude condition with M∞ = 12.3 and q∞ = 41.3 kPa, and a high altitude condition with M∞ = 11.5 and q∞ = 11.0 kPa. A constant area rectangular combustor (followed by a generic nozzle) was supplied with hydrogen fuel through parallel slot injection into the centre of the flow. At the standard altitude condition, experiments without enrichment showed a linear increase in specific thrust with equivalence ratio. On the contrary, at the high altitude condition , increasing equivalence ratio had virtually no effect on specific thrust. When enrichment was employed at the standard altitude condition a similar linear trend existed however the magnitude of specific thrust did increase slightly. At the high altitude condition the use of oxygen enrichment vastly improve d the specific thrust trend such that, for similar enrichment percentages an increase in equivalence ratio resulted in a linear increase in specific thrust comparable to that at the standard altitude condition. At both altitude conditions, oxygen enrichment decreased ignitio n length significantly by providing a head start to the overall mixing by premixing a portion of fuel with oxidiser. The experimental results presented in this paper are quite promising and suggest that oxygen enrichment may be a viable means by which to combat the poor mixing and combustion experienced by scramjets travelling at high speeds and high altitudes.