Investigation of Turbojet Engine Performance at Speeds and Gas Temperatures Above Rated Using Turbine-Blade External Water-Spray Cooling from Stationary Injection Orifices Page: 3 of 33
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SNACA RM E54G30
Substantial thrust increases over the rated thrust condition were
realized. At 107 percent rated speed and 20000 F inlet-gas temperature,
the engine thrust obtained was 20 percent above rated. At the same op-
erating point the specific fuel consumption was 21 percent above rated.
Introduction of water into the gas stream at the turbine rotor inlet up
to a coolant-to-gas flow ratio of 0.029 and overspeed, overtemperature
operation apparently did not adversely affect turbine performance for
Water-spray cooling of turbine rotor blades is being investigated
at the NACA Lewis laboratory as a means of externally cooling the blade
surfaces to permit turbine operation at elevated stress and temperature
levels in order to provide increases in thrust for brief intervals. In
the spray cooling process, a liquid is injected into the hot gas stream
upstream of the turbine rotor and the liquid droplets are transferred by
the gas stream onto the rotor blade surfaces where boiling occurs. The
process thus utilizes the latent heat of vaporization of the liquid to
cool the blades.
Several factors must be taken into consideration before spray cool-
ing may be applied to an aircraft turbine engine installation. These
1. If spray cooling is to be of value, the turbine must be operated
at gas temperatures and speeds above rated so that thrust increases may
be realized (ref. 1).
2. Turbine operation over a range of gas temperatures above rated
at a specific overspeed point requires a substantial operating margin
between the compressor operating.point and the compressor surge region,
a design .factor which determines whether a particular engine should be
considered for a spray cooling application.
3. Turbine operation at speeds above design also requires that the
turbine disk and compressor can safely withstand the elevated stress
4. Since the coolant is expended in the gas stream, spray cooling
is restricted to periods of short duration, such as take-off, climb, or
5. The rotor blade material must be able to withstand thermal shock
and stresses induced by the sudden impingement of water sprays upon
heated rotor blade surfaces.
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Freche, John & McKinnon, Roy A. Investigation of Turbojet Engine Performance at Speeds and Gas Temperatures Above Rated Using Turbine-Blade External Water-Spray Cooling from Stationary Injection Orifices, report, October 11, 1954; (digital.library.unt.edu/ark:/67531/metadc62727/m1/3/: accessed December 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.