A Quasi-One-Dimensional Investigation Into the Effect of Combustion Processes on Scramjet Performance

Abstract

Scramjet engines can decrease the cost of access-to-space systems. One-dimensional solvers can be used to rapidly analyse many scramjet engine configurations to maximise performance. This paper uses an inviscid, quasi-one-dimensional, chemical equilibrium solver to examine the effects of combusting using constant area, constant pressure, constant Mach number or constant temperature processes. Constant area combustion typically produces the highest specific impulse for given combustor entrance conditions. When a maximum engine pressure constraint is imposed the constant pressure process becomes more effective. This work shows that if combustion occurs at constant area until the maximum pressure is reached, then continued using a constant pressure process, the required intake compression and contraction ratios can be decreased by 53% and 35% respectively from the constant pressure case. This decrease results in improved starting characteristics for a negligible cost to performance. The effect of maximum engine pressure on performance is examined and it is shown that there is little benefit from increasing intake compression ratios above 60, or maximum engine pressure over a factor of 150 above the freestream pressure.