Propulsion Efficiency Considerations for Combined Cycle Propulsion Systems

摘要

In the conventional derivation of the propulsion efficiency, two separate propulsion efficiency equations are developed: one for airbreathing engines, and one for rockets. However, for combined cycle propulsion systems in which the respective reaction-mass flowrates of air and on-board propellants may be of a similar order of magnitude, neither of these equations is suitable. In this paper, a more general equation for the propulsion efficiency is formulated which is suitable for all reaction-mass propulsion systems: combined cycle engines, airbreathers, and rockets. Furthermore, this reformulated propulsion efficiency equation can be reduced to the separate, conventional propulsion efficiency equations for airbreathers and rockets, respectively, when the standard simplifying assumptions are applied. The more general equation for the propulsion efficiency provides some additional insight into combined cycle, airbreathing, and rocket propulsion systems.