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National Advisory Committee for Aeronautics, Technical Notes - Theoretical Augmentation of Turbine Propeller Engine by Compressor Inlet Water Injection, Tail Pipe Burning, and Their Combination

The theoretical performance of the turbine-propeller engine with
augmentation by means of compressor-inlet water injection, tail-pipe
burning, and a cambination of the two methods was evaluated. The inves-
tigation covered altitudes and Mach numbers representing the most prob-
able range of application for each of the augmentation methods. The
effects on augmentation of variations in compressor and turbine effi-
ciency, compressor pressure ratio, turbine—inlet temperature, and
propeller-plus-gear efficiency were investigated. The effects of ambi-
ent humidity and temperature and of the degree of evaporation during
compression were also investigated.

The augmentation from either compressor—inlet water injection or
tail-pipe burning varied directly as the compressor pressure ratio and
inversely as the turbine—inlet temperature, compressor efficiency, or
turbine efficiency.

For an engine having an unaugmented pressure ratio of 8, a turbine-
inlet temperature of 20000 R, and normal compressor and turbine poly—
tropic efficiencies of 0.88, augmentations as great as 95 percent with
water injection and 58 percent with tail—pipe burning were obtained.
Greater augmentation was obtained from water injection than from tail-
pipe burning under all conditions except for transonic speeds at an
altitude of about 55,000 feet; at this altitude the augmentations were
comparable but the liquid consumption with tail-pipe burning was con-
s‘iderably lower. In the transonic speed range at an altitude of
35,000 feet, augmentations from the individual methods were more than
additive when the methods were used in combination. Liquid consumptions
for the different augmentation methods were from 5. 5 to 9. 6 times the
unaugmented consumption.

A large part of the maximum augmentation with water injection at the
compressor inlet would result even if no evaporation occurred during
compression.

variations of ambient relative humidity had slight effect on the
degree of augmentation with water injection.

Compressor-inlet water injection maintained standard take-off power
with temperatures as high as 580° R at pressure altitudes up to 7500 feet.

Up to the present time little interest has been shown in the aug-
mentation of Whine-propeller engines because this engine type has been
considered less desirable than the turbojet engine for high-speed appli-
cations, and because the take-off performance of unaugmsnted turbine-
propeller-powered aircraft is generally satisfactory. Consequently, the
augmented performance of turbine-propeller engines has not been thoroughly
investigated even though extensive studies of turbojet augmentation have
been made (references 1 to 3).