Exergy Analysis as a Tool for Decision Making in Aircraft Systems Design

Abstract

Airplanes are designed to attend the customer needs with minimum fuel consumption by reducing the inefficiencies. The aeronautical industry has evolved to design extremely complex aircrafts, with highly integrated systems. The current methods to design and later optimize are based on trade-off studies. However, this type of analysis for new systems evaluation may present non-conclusive results and, due to the high level of integration between aircraft systems, the optimization of a single system may lead to sub- optimized solutions for the whole aircraft. Therefore, the search for an optimized aircraft becomes a search for commitment solutions for different systems. There is a need to develop a general methodology that allows a complete vehicle design as a system that contains sub-systems in the same basis. It is important to define aircraft design parameters (ex.: weight, fuel consumption, drag) as energy objective functions so that the problem may be classified as an optimization with objective defined by the customer. In this way, the design is committed to the maximum efficiency and minimum waste of useful energy (exergy destruction), if adequate constraints are considered. The concept of exergy analysis has already been successfully applied to evaluate, compare and optimize thermal systems and chemical processes in other industrial fields. This work shows a revision of several papers related to the exergy method on the design of aircrafts, and includes the different approaches and applications of design optimization. Also, a case study is included to illustrate the potential of the exergy tool. Nomenclature drag d E _ & = destroyed exergy rate due to drag, kW cabin d E _ & = destroyed exergy rate in the cabin, kW ECU d E _ & = destroyed exergy rate in the environmental control unit, kW engine d E _ & = destroyed exergy rate in the engine, kW