Theoretical Maximum Efficiency and Specific Impulse of the External Burning Scramjet

The aim of this work is to provide an upper estimate of the theoretical maximum efficiency and specific impulse of the external burning scramjet. Contrary to the classical Carnot and Brayton cycles for the heat and gas-turbine engine and the known ideal cycle for the ramjet, in this case there is not a reversible cycle to provide a reference. The reason for this is that the heat release to the high-speed flow is accompanied by inherent total pressure losses, and thus the process results are irreversible. Subsequently, to estimate the maximum efficiency an idealized optimization problem inevitably must be analyzed that also takes into account these inherent losses. This optimization problem was solved 1) in the linear approximation, valid for thin bodies and small amounts of applied heat, and 2) in the nonlinear formulation but in the original framework of heat release in the jet stream with a “zero mass flux” condition. The results obtained in the two cases are comparable for small heat release, but they ...