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National Advisory Committee for Aeronautics, Technical Notes - Studies of OH, CO, CH, and C2 Radiation from Laminar and Turbulent Propane Air and Ethylene Air Flames

0H, CO, CH, and 02 radiations from propane-air and ethylene-air
flames were isolated with a monochromator, and the OH, CH, and Cg emitters
were purified by subtracting the unwanted 00 background. The changes in
intensity with changing equivalence ratio were determined for each emitter.
The ratio of the CZ and the 9H radiation intensities was found to be a
good index of the equivalence ratio of the flame, but the Cg—CH ratio was
good only for the fuel for which it was calibrated.

Radiation ratios were measured in different regions of laminar and
turbulent ethylene—air flames. No changes were found in laminar flames.
Turbulent open flames burning on tubes were found to become leaner near
the base, but in the turbulent brush they appeared to be burning at the
metered equivalence ratio. No appreciable mixing with secondary air was
detected in the turbulent brush, even at 125 feet per second, the maxi—
mum average gas-flow velocity obtainable.

The amount of radiation given off by the flame per unit rate of fuel
consumption decreased with increasing average gas-flow velocities and
Reynolds numbers. This decrease could not be accounted for by admixing
of the secondary air with the turbulent flame brush.

In recent years attention has been focused on theories of turbulent—
flame structure and reaction mechanism. Experimental verification of
these theories has been difficult to obtain because of the high tempera-
tures, high gas velocities, and rapid reaction rates existing in turbu—
lent flames. Prdbing techniques have been tried, but they are fraught
with experimental pitfalls. Because of the generally unsatisfactory
nature of the probing techniques in their current state of development,
other methods of studying flame structure and reaction mechanism have
been considered. One of the most promising of these is the study of the
radiation emitted by a flame.