Component and over-all performance evaluation of an axial-flow turbojet engine over a range of engine-inlet Reynolds numbers Page: 8 of 44
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NACA RM E52B08 S 7
engine speeds investigated, the total-pressure-loss ratio decreased with
increasing corrected engine speed with no apparent effects of Reynolds
number index. Combustion efficiency (fig. 8(b)) was found to generalize
with the parameter p42/Wa,3 which is proportional to a combustion
parameter derived in reference 5. At a combustion parameter value above
300,000, the correlation was within 0.025 and a constant combustion
efficiency of about 0.94 was indicated. At lower values of the combus-
tion parameter, combustion efficiency dropped rapidly and the data
scatter was approximately doubled. From these data, it is concluded
that for the Reynolds number indices and the corrected engine speeds of
this investigation, the effects of fuel-air ratio and. fuel-spray pattern
were secondary. The dashed curve in figure 8(b) shows the results of a
subsequent investigation (reference 6) in which modified combustor liners
had been installed and indicates an improvement in combustion efficiency
of about 0.03 over a large part of the operable range. These modified
liners are designated "smokeless" liners by the manufacturer and are
standard on the production models of the engine.
In order to use figure 8(b) for predicting combustion efficiency
under altitude operating conditions, the variation of the term p42/Wa,3
with corrected engine speed and Reynolds number index must be evaluated.
In order to facilitate this evaluation, a generalized plot of
p42 a,38/ against corrected engine speed for the various Reynolds
number indices is presented in figure 8(c).
Turbine total-pressure ratio (fig. 9(a)) generalized for all condi-
tions at the high corrected engine speeds but the data scattered at the
lower engine speeds investigated. Turbine efficiency (fig. 9(b)) remained
nearly constant at about 0.81 over the engine-speed range investigated at
Reynolds number indices above 0.4. Reducing the Reynolds number index
to 0.3 and 0.2 lowered the efficiency by 0.01 and 0.03, respectively.
The corrected turbine gas flow (fig. 9(c)) was constant over the range of
corrected engine speeds investigated and no Reynolds number effect was
obtained. The constant corrected gas flow resulted from the turbine noz-
zle being choked over this range of engine speeds and indicates that
within the accuracy of the data there was no apparent reduction in effec-
tive turbine-nozzle area due to a Reynolds number effect. The decrease
in turbine efficiency at the low Reynolds number indices is believed to
have been the result of a shift in the turbine operating point and a
Reynolds number effect.
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Walker, Curtis L.; Huntley, S. C. & Braithwaite, W. M. Component and over-all performance evaluation of an axial-flow turbojet engine over a range of engine-inlet Reynolds numbers, report, July 10, 1952; (https://digital.library.unt.edu/ark:/67531/metadc59177/m1/8/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.