Experimental investigation of screeching combustion in full-scale afterburner Page: 3 of 64
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2 NACA RM E53I01
The present investigation was originally initiated in the NACA Lewis
altitude wind tunnel in ''order to evaluate and improve the performance
and stability of a specific afterburner at low burner-inlet pressures
while maintaining good performance and operational characteristics at
high burner-inlet pressures. During the early portion of the program,
configuration changes were made to improve the afterburner performance
and stability at low pressures; however, screeching combustion was
encountered with several of these configurations at higher burner-inlet
pressures. At the same time it was found that the variable-area exhaust
nozzle was too small to permit operation over the desired range of fuel-
air ratio and exhaust-gas temperature; consequently, a larger exhaust .
nozzle was installed. With the higher fuel-air ratios thus obtainable,
screeching combustion and its attendant destructiveness became problems
of such severity that the objective of the investigation was altered to
that of seeking to determine those factors that influence screeching
Because an adequate theory explaining the nature or origin of-.
screeching combustion did not exist and because adequate instrumentation
to explore the details of the process was not available, the investiga-
tion was carried on by altering internal afterburner components and
observing the effects of such alterations on screeching combustion.
These alterations included changes in diffuser innerbody design,
afterburner-inlet flow distribution, flame-holder design, and fuel
injector design. For about half the investigation the presence of
screech was observed by the characteristic screeching sound. During
the course of the investigation special instrumentation became available
for the detection of screeching combustion and the recording of some
screech characteristics. The observations reported herein were obtained
with the aforementioned afterburner configurations over a range of after-
burner fuel-air ratio and flight conditions. The flight conditions
simulated correspond to afterburner-inlet total pressures from 2200 to
4200 pounds per square foot absolute.
APPARATUS AND INSTRUMENTATION
The engine used in the investigation was an axial-flow turbojet
engine and afterburner combination equipped with a variable-area iris-type
exhaust nozzle. With the afterburner in operation, the manufacturer's
military-rated turbine-outlet temperature, as indicated by 12 parallel
control thermocouples, is 16700 R.
The over-all length of the afterburner (fig. 1), including diffuser,
combustion chamber, and exhaust nozzle, is 101 inches; the maximum
diameter of the afterburner combustion chamber is 36 inches. A cooling-
air passage, designed at the NACA for the present investigation, surrounded
the rear portion of the afterburner (fig. 1).
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Usow, Karl H.; Meyer, Carl L. & Schulze, Frederick W. Experimental investigation of screeching combustion in full-scale afterburner, report, December 4, 1953; (https://digital.library.unt.edu/ark:/67531/metadc62147/m1/3/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.