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National Advisory Committee for Aeronautics, Research Memorandum - Determination of Ram-Jet Combustion Chamber Temperatures by Means of Total Pressure Surveys

A method is‘described by which the total temperature of the
gases at the combustion-chamber outlet of a ram-Jet engine may be
determined frOm the 'loss in total pressure measured across the com—
bustion chamber; A working chart is presented by means of which the
ratio of the total temperature of the gases at the combustion—chamber
outlet to the total temperature of the'gases at the combustion-
chambe'r inlet may be determined from the measured loss of total pres-
sure across the combustion chamber and the known values of air flow,
total pressure, and total temperature at the combustion—chamber inlet.

Values of total-temperature ratio across the combustion chamber
of a 20-inch ram Jet were obtained in the Cleveland altitude wind
tunnel over a range of pressure altitudes from 6000 to 15,000 feet.
The difference between the temperature ratio across the combustion
chamber determined from the chart and that obtained from thermocouple
measurement was within 6.2 percent of- the thermocouple-temperature
ratio and was within the accuracy of the thermocouple measurements.

The evaluation of the performance of a Jet —propu_lsion engine and
its combustion chamber requires a knowledge of the temperature of the
combustion—chamber outlet gases. The temperatures in a ram-Jet com-
bustion chamber, however, are often too high for thermocouple measure-
ment and must be determined by other means. Because the total-pressure
loss across the combustion chamber- -is dependent on the ratio of the
total temperature of the outlet gases to the total temperature of the
inlet gases (reference 1), the temperature ratio can be determined
from the total-pressure measurements.

A chart- is presented in reference 1 to estimate the pressure
losses in Jet-propulsion combustion chambers from the .lmown values of
total temperature, total pressure, and air flow at the combustion-
chamber inlet and of the ratio of total temperature of the exit gas
to total temperature of th.e'inlet gas. it is based on the assumption
that the pressure losses in a given combustion chamber can be matched
by those of an equivalent combustion chamber_ of uniform cross—sectional
area.