A good starting point for considering theoretical performance and performance optimization is theoretical cycle diagrams (see Chapter 3, Gas Turbine Configurations and Heat Cycles). From that chapter, it was noted that

1. Intercooling during compression,

2. Adding (exhaust waste) heat to the compressed gases prior to combustion (recuperation),

3. Adding heat at an interim stage of the turbine (reheat),

all add to the efficiency of the gas turbine cycle. Further cycle efficiency improvements can be made by

1. Cooling inlet air (cooler air is denser and provides more power per unit volume of inlet air).

2. Other waste heat recovery and cogeneration, such as waste heat being used in a HRSG (heat recovery steam generator) to run a steam turbine with the gas turbine (a combined cycle).

3. A variation in principle of an aircraft engine afterburner in land-based applications injects a fuel source downstream of the gas turbine exhaust and ignites the exhaust air/supplementary fuel mix for additional power.

In addition to these basic cycle adaptations and variations on a theme thereof, gas turbine users now also use inlet air fogging (for cooling inlet air) and steam and/or water injection for power augmentation. The latter means, sometimes used for NO _x reduction or cooling (for instance, to take turbine discs out of heat damage range, such as a premature hot section component crack zone), can result in 20 25% additional power developed.

There are a myriad of other performance retention and optimization technologies. They include the science of performance recovery with (online or otherwise)...