Exergetic analysis of a turbojet engine in off design conditions

The exergetic analysis of the behavior of industrial systems and plants is employed quite frequently in enter to uncover critical points of the system itself. In the field of aircraft propulsion the applications are still very few and usually confined to analyses in design conditions. This even if the recourse to the exergetic analysis allows, also in the field of aircraft propulsion, to achieve a deeper analysis of the behavior of each component, together with its interactions. The present paper deals with an analysis applied to the exergetic behavior of a simple turbojet, outside its design conditions. First of all, some parameters to be employed are discussed in order to define the exergetic efficiency for each component and for the turbojet as a whole, with reference also to the classic definition for the efficiency usually adopted in conventional analyses. It is then accomplished, in order to make available a situation to be used as a reference, die exergetic analysis of a turbojet at design conditions. A study is now performed, still from an exergetic point of view, of the turbojet behavior in some typical situations of off design (change of: Mach number, flight conditions, altitude, cycle max temperature, etc). Both global and single component behaviors are taken into consideration, to emphasize the critical points in different operative conditions. This allows to make an evaluation about the optimization of the available exergy with reference also to the assigned kind of mission. The analysis presented allows however to emphasize how moving from design to off design conditions some consistent differentiations emerge for the behavior of many components. With reference to this result, it becomes therefore possible to conduct a much deeper evaluation of the off design behavior of the turbojet, in order also to make a full optimization of its performances.