Rational Objective Functions for Vehicles

Although energy is the key resource for achieving vehicle performance desiderata, it is not necessary, nor is it necessarily desirable, to assess the desiderata in terms of energy alone. Yet, because the energy conversion systems in vehicles may use or supply energy in several forms (thrust, power, heat, cooling, etc.), exergy must be used to account for energy-based interactions between systems and for the costing of various "streams" (mass, power, etc.). Exergy is the key to the decomposition of energy systems and allows concurrent engineering of the several devices that may make up an overall system. One proposed method for creating an overall objective function is presented. Then, the methods of thermoeconomics will be combined with it to allow decomposition and detailed design of subsystems and devices. As an example, objective functions and weighting factors will be developed for a light experimental aircraft. Decomposition will be illustrated with the selection of an alternator and engine.