Combustion chamber injection system:

Injecting a water or water/methanol mixture into the combustion chambers increases the mass flow through the turbine and the high volumetric expansion as the water becomes steam increases the thrust. The pressure and temperature drop across the turbine is reduced and this further increases the thrust. The reduction in turbine inlet temperature due to water injection enables the fuel system to provide an increased fuel flow to restore the maximum speed of the engine, thus providing further additional thrust without exceeding the safe turbine gas temperature limits. When methanol is used with the water the turbine inlet temperature is partially restored without extra fuel from the fuel system.

Water flows from an aircraft-mounted tank to an air turbine driven water pump and is delivered to a water flow sensing unit. From the water sensing unit the mixture is distributed to the burner feed arms where two jets at the base of each arm spray the mixture on to the upstream side of the swirl vanes to cool the air entering the combustion zone. The water pressure between the sensing unit and the discharge jets, is sensed by the fuel system control, which automatically resets the engine speed governor to give a higher maximum engine speed.

The water system is brought into operation when the throttle lever is moved into the take-off position where it closes micro-switches to provide an air supply for the air turbine-powered water pump. The water flow sensing valve opens when a correct pressure difference exists between water pressure and compressor delivery air pressure. The valve in the water flow sensing unit also acts as a non-return valve to prevent air pressure feeding back from the water discharge jets and provides for the operation of an indicator to show when water/methanol is flowing.