| An exergy analysis is applied to a turbojet engine for a range of altitudes from 0 to 15,000 m (∼50.000 ft) and for a 3,500 km flight to examine the effects of using different reference-environment models. The results of tins analysis using a variable reference environment (equal to the operating environment at all times) are compared to the results obtained using two constant reference environments (0 and 15,000 m). The rational efficiency of a turbojet was observed to decrease with increasing altitude, due mainly to an increase in exhaust exergy emissions. The accuracy of exergy results was found to be dependent on the choice of reference environment, where the use of a constant reference environment can lead to errors as large as 52%. For most atmospheric applications, the use of a variable reference environment does not add great complexity to the exergy analysis while yielding the most accurate results. |
