Recently developed methodology that provides the direct assessment of traditional thrust-based performance of aerospace vehicles in terms of entropy generation (or equivalently exergy destruction) is modified for stand-alone jet engines. This methodology is applied to a specific single-spool turbojet engine configuration. A generic compressor performance map along with simplified component performance characterizations are first utilized in order to provide comprehensive traditional engine performance results (engine thrust, mass capture, and RPM), for on and off-design engine operation. Details of exergy destruction in engine components, across the entire engine, and in the engine wake are then provided and the performance losses associated with this entropy generation are discussed. Results are provided across the engine operating envelope defined by operational ranges of flight Mach number, altitude, and fuel throttle setting. The wake losses occurring in the engine wake and their impact on the correct quantitative characterization of actual performance losses associated with the operation of a turbojet engine are shown to be dominant with respect to other losses, including all losses occurring inside the engine. Specifically, the ratio of the exergy destruction rate in the wake to the exergy destruction rate inside the engine itself ranges from 1 to 2.5 across the operational envelope of the engine.