is sprayed into the combustion chamber by the fuel nozzles. The fuel
and air mixture is then ignited by electrical igniter plugs similar
to spark plugs. This ignition system is only in operation during the
starting sequence, and once started, combustion is continuous and
selfsustaining as long as the engine is supplied with the proper
airfuel ratio. Only about 25 percent of the air is used for
combustion. The remaining air is used for internal cooling and
pressurizing.
Figure 1.1. Otto and Brayton Cycles.
The turbine engines in the Army inventory are of the free
power turbine design, as shown in figure 1.2. In this engine, nearly
twothirds of the energy produced by combustion is extracted by the
gas producer turbine to drive the compressor rotor. The power
turbine extracts the remaining energy and converts it to shaft
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