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 diverge as the applied heat increases, mainly for the additional total pressure losses in the generated shock waves. It is shown that the maximum efficiency monotonically grows with the velocity, with an upper limit, whereas the specific impulse initially grows, then reaches a maximum, and finally reduces asymptotically to zero at very large Mach numbers during flight.
Theoretical Maximum Efficiency and Specific Impulse of the External Burning Scramjet
Journal of Propulsion and Power ; 29 , 5 ; 1031-1040
2013-07-17
10 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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