Measurement of Temperature Distribution in a Low-Pressure Flat Flame

Abstract

The temperature distribution in a very lean, flat propane-air flame was measured by the thermocouple method, at a pressure of 0.0594 atmos. The temperature change occurred in a zone about 3 cm thick. Wallquenching was minimized by employing a burner tube diam of 25 cm. The thermocouple was made from 12-micron wire, coated with ceramic to avoid catalytic effects. One hundred experimental traverse points were obtained, with a standard deviation of ±0.016 cm. The burning velocity was also measured, and was found to vary with the inverse 0.30 power of pressure. This is in agreement with Egerton and Sen's result, obtained over a more limited range of pressure. The temperature pattern was analyzed mathematically to obtain the pattern of heat release rate, taking into account the variation with temperature of thermal conductivity and specific heat. It was found that the heat release began at 300°C, attained a maximum value of 1.2 cal/cm3-sec at 1100°C, was nowhere negative, and was finite over a zone about 2 cm thick. The maximum temperature of the flame was 1332°C. The result obtained for the ``ignition point'' was found to be extremely sensitive to the exponent giving the temperature dependence of the thermal conductivity. Some calculations relating to the chemical kinetics of the flame are described.