Effects of Oxygen Enrichment on Supersonic Combustion in a Mach 10 Scramjet

Scramjet engines are a suitable replacement for rockets in access-to-space systems, but, being air-breathing engines, their operational envelope is limited to altitudes where enough oxygen is available for combustion. Oxygen enrichment, in which fuel is premixed with oxygen, is a promising technique to overcome constraints in altitude due to low oxygen availability, and the difficulty to generate positive thrust at high Mach numbers. Large-eddy simulations of an inlet-fueled Mach 10 scramjet engine are performed to investigate the effect of oxygen enrichment on the flowfield and to characterize the turbulent combustion regimes. It is shown that combustion levels increase substantially with the addition of premixed oxygen, which leads to a considerable increase in combustion efficiency. It is shown that the mixing process is altered by oxygen enrichment in such a way that the observed increase in mixing efficiency is higher than the increase caused by premixing alone. Finally, the combustion regimes in the simulated engine are analyzed. This shows that combustion is mostly nonpremixed, and oxygen enrichment leads to an increase in premixed combustion, but without significantly altering turbulent combustion overall, which is distributed over a large range of regimes.