Water injection - COMBUSTION CHAMBER INJECTION

COMBUSTION CHAMBER INJECTION

Fig. 17-4 A typical combustion chamber injection system.

7. The  combustion  chamber  injection  systemshown in fig. 17-4 is a typical system for a turbo-jet engine. The coolant flows from an aircraft-mounted tank to an air-driven turbine pump that delivers it to a water flow sensing unit. The water passes from the sensing unit to each fuel spray nozzle and is sprayed from two jets onto the flame tube swirl vanes, thus cooling the air passing into the combustion zone. The water pressure between the sensing unit and the discharge jets is sensed by the fuel control system, which  automatically  resets  the  engine  speed governor to give a higher maximum engine speed.

Water injection - COMPRESSOR INLET INJECTION

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

5. The compressor inlet injection system shown in fig. 17-3 is a typical system for a turbo-propeller engine. When the injection system is switched on, water/methanol mixture is pumped from an aircraft- mounted tank to a control unit.  The control unit meters the flow of mixture to the compressor inlet through a metering valve that is operated by a servo piston.  The servo system uses engine oil as an operating medium, and a servo valve regulates the supply of oil. The degree of servo valve opening is set by a control system that is sensitive to propeller shaft torque oil pressure and to atmospheric air pressure acting on a capsule assembly.

Water injection - INTRODUCTION

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.