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National Advisory Committee for Aeronautics, Report - Theoretical Analysis of Various Thrust Augmentation Cycles for Turbojet Engines

The results of analytical studies of tailpipe-burning, water-
injection, and bleedqpT methods of thrust augmentation are
presented that provide an insight into the ope-rating character-
istics of these augmentation methods and summarize the per-
formance that may be obtained when applied to a typical
turbojet engine. A brief description of the principles of oper—
ation qf each augmentation method is given, together with
curves that illustrate the ejects of the principal design and
operating variables of the augmentation system on the thrust
and the liquid consumption of the engine.

The necessity of designing tail—pipe burners with a low
burner—inlet velocity, a low burner drag, and a high difluser
efliciency in order to obtain a- high thrust augmentation and to
minimize the loss in engine performance during nonburning
operation is illustrated. The ratio of augmented to normal
thrust produced by a typical tail-pipe burner at sea-level
altitude increased with flight JIach number from a value of
nearly 1.5 at a llach number of 0 to over 3.0 at a Mach number
of 2.0 and decreased with increasing altitude for supersonic
flight JIach numbers.

Water injection is considered for injection into the com-
pressor inlet and for injection into the engine combustion
chambers. ’ith sufiicient water injection into the compressor
inlet to saturate the air at the compressor outlet, the ratio of
augmented to normal thrust at sea level increased from 1.4 at
a- .‘lfach number of 0 to nearly 2.6 at a JIach number of 2.0.
The injection of water into the combustion chambers of an
engine having compressor characteristics typical of an axial—
flow compressor provided slightly less thrust augmentation than
the compressor—inlet—injection method and the specific liquid
consumption was about twice as great.

The thrust augmentation provided by the bleedofl method was
the highest of the three methods studied for engines with com—
pressor characteristics typical of either centrifugal— or axial-
flow compressors. The maximum augmented thrust at a flight
hIach number of 0 and sea—lerel altitude for the centrifugal-
flow-type engine, which was somewhat higher than for the axial-
flow—type engine, was about 9.3 times the normal thrust of the
engine. This thrust augmentation was, however, obtained at
the expense of a high rate of liquid consumption and required
that stoichiometric combustion be maintained in the engine
combustion chambers.