Analysis and Design of a Hypersonic Scramjet Engine with a Transition Mach Number of 4.00

When pressures and temperatures become so high in supersonic flight that it is no longer efficient to slow the oncoming flow to subsonic speeds for combustion, a scramjet (supersonic combustion ramjet) is used in place of a ramjet. Currently, the transition to supersonic combustion generally occurs at a freestream Mach number around 5.0 to 6.0. This research details analysis completed towards extending scramjet operability to lower Mach numbers, while maintaining performance at higher Mach numbers within the same flowpath as detailed in the Air Force solicitation AF073-058. The specific goal was to determine whether the scramjet starting Mach number could be lowered to Mach 3.50 and, if not, what the constraints are that prohibit it and what the lowest possible starting Mach number for a scramjet is with today’s technology. This analysis has produced many significant insights into the current and required capabilities for both fuel and overall engine design in lowering the starting Mach number; these results are presented here. The analysis has shown that a scramjet with a starting Mach number of 3.50 is not currently possible with the fuels researched unless fuel additives or other modifications to the system are used. However, a scramjet with a starting Mach number of 4.00 is possible with today’s existing technology. This paper has designed the engine flowpath for this case; its specifications and resulting performance are also detailed here.