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National Advisory Committee for Aeronautics, Research Memorandum - Experimental Investigation of Thrust Augmentation of Axial Flow Type 4000 Pound Thrust Turbojet Engine by Water and Alcohol Injection at Compressor Inlet

An experimental investigation of thrust augmentation of an axial—
flow-type turbojet engine with a 4000-pound-thrust rating by means
of water-alcohol injection at the compressor inlet has been conducted
at sea- -level conditions and zero ram. Three injection systems were
investigated in an effort to obtain satisfactory atomization and
distribution of the injected liquids. The engine was equipped with
an adjustable-area exhaust nozzle during these investigations in
order to provide control of the exhaust-gas temperature independent
of injection rate and rotor speed. The engine performance was
determined at constant rotor speed and exhaust-gas temperature for
various mixtures and flow rates of injected water and alcohol up to
4.5 pounds per second of water and 2.25 pounds per second of alcohol.

The thrust augmentation by injection of water and alcohol at
the compressor inlet was limited by centrifugal separation of the
injected liquid and air in the compressor. A thrust augmentation
of 15. 4 percent was obtained by injecting 5. 0 pounds per second of
water at a rotor speed of 7635 rpm, an exhaust-gas temperature
of 16650 R, and an inlet-air temperature of 548° R. Small reduc-
tions of inlet-air temperature (8° to 25° F) appeared to cause large
decreases in the thrust augmentation produced. Although three
different injection systems were used, differences in the inlet-air
temperature for each system prevented any determination of the
importance of form of injection on the thrust augmentation produced.

The limited thrust output of turbojet engines at take-off and
during climb has instigated considerable study and experimentation
on the thrust augmentation of these engines. Several methods of
providing additional thrust have been investigated at the NACA
Cleveland laboratory. One simple method of thrust augmentation is
the injection of refrigerants at the compressor inlet, and the
results of an experimental investigation of this method for
centrifugal-flow-type turbojet engines with 1600- and 4000-pound
thrust ratings are presented in references 1 and 2, respectively.
Investigations have also been conducted to determine the application
of this method of augmentation to axial-flow-type turbojet engines.