A Work Availability Perspective of Turbofan Engine Performance

Abstract

This paper presents a work availability perspective on the thermodynamic performance of the turbofan engine and contrasts this with the classic presentation, which describes performance based primarily on cycle efficiency. It is shown that the availability perspective leads to a more fundamental understanding of the basic problem, this being to maximize the conversion of work potential stored in the fuel into useful work output. The discussion specifically addresses the impact of primary turbofan cycle parameters on usage and loss of work potential. It is shown that cycle pressure ratio governs exhaust heat losses, turbine inlet temperature governs non-equilibrium combustion losses, and fan pressure ratio governs loss due to residual exhaust kinetic energy. Finally, simplified loss calculation methods applicable to any turbofan engine are presented and the method is applied to the analysis of cycle losses in the Northrop F-5E propulsion system.