TABLE OF CONTENTS The most important deviations from the ideal behavior described in chapter 2 result from
imperfect diffusion of the free-stream flow from flight to engine-inlet conditions,
nonisentropic compression and expansion in the compressor and turbine,
incomplete combustion and stagnation pressure loss in the burners,
variation of the gas properties through the engine due to temperature and composition changes,
incomplete expansion (or overexpansion) to ambient pressure in the nozzle, and
extraction of compressor discharge air for turbine cooling or for use by the airframe.
Nozzle losses due to under- or overexpansion can be eliminated by design for proper expansion, but many engines use simple convergent nozzles for simplicity and weight savings. This particular loss (really a penalty due to fixed geometry, and qualitatively different from the other nonidealities listed) will be included in the cycle analysis even though it would be more logical to consider it when the other ramifications of engine geometry are considered.
The aim at this point is to characterize each of these mechanisms for deviation from ideality so that their effects can be included in a more realistic cycle analysis. More detailed discussion of the sources of the losses and the means of minimizing them will follow in subsequent chapters.
As the air temperature rises in the compressor and as combustion changes the molecular composition of the gas as well as its temperature, its thermodynamic properties change. In the compressor the specific heat C v rises with increasing temperature so that
