Page 193 - The Jet Engine

Water injection

Fig. 17-3 A typical compressor inlet injection system.

inlet air is reduced and consequently the air density an increase in the maximum rotational speed of the
and thrust are increased. If water only was injected, engine, thus providing further additional thrust,
it would reduce the turbine inlet temperature, but with Where methanol is used with the water, the turbine
the addition of methanol the turbine inlet temperature inlet temperature is restored, or partially restored, by
is restored by the burning of methanol in the the burning of the methanol in the combustion
combustion chamber. Thus the power is restored chamber.
without having to adjust the fuel flow.
COMPRESSOR INLET INJECTION
4. The injection of coolant into the combustion 5. The compressor inlet injection system shown in
chamber inlet increases the mass flow through the fig. 17-3 is a typical system for a turbo-propeller
turbine, relative to that through the compressor. The engine. When the injection system is switched on,
pressure and temperature drop across the turbine is water/methanol mixture is pumped from an aircraft-
thus reduced, and this results in an increased jet pipe mounted tank to a control unit. The control unit
pressure, which in turn gives additional thrust. The meters the flow of mixture to the compressor inlet
consequent reduction in turbine inlet temperature, through a metering valve that is operated by a servo
due to water injection, enables the fuel system to piston. The servo system uses engine oil as an
schedule an increase of fuel flow to a value that gives operating medium, and a servo valve regulates the

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