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| Fig. 17-1 Turbo-jet thrust restoration |
1. The maximum power output of a gas turbine engine depends to a large extent upon the density or weight of the airflow passing through the engine. There is, therefore, a reduction in thrust or shaft horsepower as the atmospheric pressure decreases with altitude, and/or the ambient air temperature increases. Under these conditions, the power output can be restored or, in some instances, boosted for take-off by cooling the airflow with water or water/methanol mixture (coolant). When methanol is added to the water it gives anti-freezing properties and also provides an additional source of fuel. A typical turbo-jet engine thrust restoration curve isshown in fig. 17-1 and a turbo-propeller engine power restoration and boost curve is shown in fig. 17-2.
2. There are two basic methods of injecting the coolant into the airflow. Some engines have the coolant sprayed directly into the compressor inlet, but the injection of coolant into the combustion chamber inlet is usually more suitable for axial flow compressor engines. This is because a more eve distribution can be obtained and a greater quantity of coolant can be satisfactorily injected.
