A fibre-optic probe has been developed for measuring the gas temperatu
re in flames. The principal feature of the method is that the probabil
ity distribution function of the gas temperature can be obtained local
ly in a particle-loaded gas flow. Instant gas temperatures are determi
ned from infrared emission spectra obtained from the interior of a 1.3
MW pulverized coal flame. Thermal radiation from different positions
in the furnace is collected with the infrared fibre-optic probe and th
e emission spectra are measured with a Fourier transform infrared spec
trometer. The experiments show that the instant local gas temperature
can be extracted from the brightness temperature spectrum at the 2350
cm(-1) fundamental band of CO2, at which self-absorption is minimized.
The brightness temperature spectrum is very useful for evaluation of
the measurement, in that the measuring conditions for applying the met
hod are fulfilled. Good agreement is observed between the temperatures
measured with the infrared probe and those measured with a suction py
rometer. The performance and characteristics of the infrared relative
to the suction pyrometer method as well as laser methods in flames are
compared and discussed. The gas temperature profile and probability d
istribution functions can be obtained even faster with the infrared pr
obe than can the mean gas temperature with a conventional suction pyro
meter.