Measurement of Particle and Gas Temperatures in a Slightly Luminous Premixed Flame

Abstract

Particle and gas temperatures were independently measured above a 7.0-cm-diam flat, premixed ethylene-air flame. The mixture ratio (F/A = 0.144) and gas velocity (10 cm/sec NTP) were chosen to yield a faintly luminous flame in which soot deposition occurred far from chemical equilibrium. Thus, heat input to the particles due to surface chemical reaction was as large as possible consistent with accurate measurement. Soot cloud emission was measured relative to a tungsten lamp between 4138 and 10 000 A. The soot cloud extinction was similarly measured for an approximate flame path of 50 cm. Soot particles, sucked through a small quartz probe, were caught in vacuum on a cool electron microscope target. The particles were about 100 A across at the 6-mm level, growing to 400 A at 12 mm above the burner. The particle temperature, derived from the spectral distribution of the soot cloud emission, was found to be 1714 ± 60°K at the 12-mm level. The gas temperature, measured by the Na D-line reversal method, was 1775 ± 20°K. Chemiluminescent effects were absent. It is concluded that even in this case where the particle size was one-tenth the mean free path, and where the particles were being heated by surface reaction, the particle temperature equals the gas temperature within the quoted limits of uncertainty.