Effect of hot-gas bleedback ice prevention on performance of a turbojet engine with fixed-area tail-pipe nozzle Page: 4 of 28
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NACA RM No. E9B23
A. The additionof sufficient heattothe inlet air to main-
tain the temperature of the boundary-layer air and the
compressor-inlet turning-vane wall above freezing
(Tw = 320 F)
B. The addition of sufficient heat to the Inlet air to raise
the temperature of the boundary-layer air in the
compressor-inlet turning vanes to the dew point (Tw =
C. The addition of sufficient heat to the inlet air to main-
tain the static temperature of the air stream in the
compressor-inlet turning vanes at the dew point (ts
Sources of heat for ice prevention. - Hot gases extracted
from various locations in the turbojet engine and bled back into
the engine inlet serve as a source of heat, mixing with the inlet
air and preventing ice accretions. Two bleedoff locations were
investigated in the analysis: (1) combustion-chamber bleedoff
upstream of the turbine nozzle, and (2) tail-pipe bleedoff down-
stream of the turbine outlet. The hot gases were assumed to be
ducted from these two bleedoff locations to the front of the engine,
where they were mixed with the inlet air through high-velocity jets.
The efficacy of such a method of mixing hot and cold gases is illus-
trated in reference 2.
The experimental data for a typical turbojet engine (fig. 1)
show the pressure ratio available to force the hot gases into the
inlet air. At the combustion chamber the pressure is sufficient
over a wide range of engine speeds to provide penetrating jets;
whereas, sonic jet velocities, necessary for good mixing, cannot
be obtained at any engine speed from tail-pipe bleedback. Cases
bled from the turbine inlet have a higher heat content than those
bled from-the tail pipe. In order to supply a given amount of
heat to the inlet air, less gas would therefore be needed from
combustion-chamber beeaback thanfrom tail-pipe bleedback.
Flight and engine operating conditions. - Flight conditions
'corresponding to sea-level pressure and zero ram-pressure ratio
were chosen for this analysis. Air temperatures from -400 to
380 F with two liquid-water contents of 1.0 and 2.5 grams per
cubic meter at the compressor-inlet guide vanes were considered.
The flight conditions approximated flight attitudes in which icing
is a serious problem, that is, take-off, climb, and letdown. The
two liquid-water contents chosen are those listed by Lewis (ref-
erence 3) as maximums for long and short flight conditions, respec-
tively, increased by 25 percent to cover the effect of scooping at
the engine inlet.
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Dietz, Robert O., Jr. & Krebs, Richard P. Effect of hot-gas bleedback ice prevention on performance of a turbojet engine with fixed-area tail-pipe nozzle, report, May 16, 1949; (https://digital.library.unt.edu/ark:/67531/metadc58308/m1/4/: accessed April 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.