Generalized Thermodynamic Assessment of Concepts for Increasing the Efficiency of Civil Aircraft Propulsion Systems

Abstract

It is known from thermodynamics that intercooling, recuperation, sequential combustion and constant-volume combustion increase the efficiency of thermal engines. Although these concepts are already analyzed at a high level of detail, no comparative and structured assessment of the theoretic and realistic efficiency increase for long-range turbofan engines is given. In light of this a generalized thermodynamic assessment of the mentioned technologies is conducted. First, current technological limits are ignored and the propulsive power is completely utilized. Theoretic efficiency improvements of over 24% are obtained. Second, the modelling is refined to include a ducted fan, turbine blade cooling and account for minimum blade height and maximum temperature at HPC outlet. Realistic efficiency improvements of still over 10% are identified. It is shown that significant increases in efficiency necessitate new engine architectures, outlining the restrictions of the current engine architecture. Intercooling is identified as the driving technology for high efficiency.