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National Advisory Committee for Aeronautics, Technical Notes - Determination of RamJet 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 ramrjet engine may be determined
from the loss in total pressure measured across the combustion 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-chamber inlet may be deter-
mined from the measured loss of total pressure across the combustion
chamber and the known values of air flow, total pressure, and total temr
perature at the combustion-chamber inlet.

Values of total-temperature ratio across the combustion chamber of
a 20-inch ram jet were Obtained in the NACA Lewis altitude wind tunnel
over a range of pressure altitude from 6000 to 15,000 feet. The differ-
ence between the temperature ratio across the combustion chamber deter-
mined 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-propulsion engine and
its combustion chamber requires a knowledge of the temperature of the
combustion-chamber outlet gases. The temperatures in a ramrjet 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 known.values of total
temperature, total pressure, and air flow at the combustionrchamber
inlet and of the ratio of total temperature of the exit gas to total
temperature of the inlet gas. This chart 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.