Optically determined temperatures, sizes, and velocities of individual carbon particles under typical combustion conditions

Abstract

This study utilizes an in situ optical method to determine the temperature, size, and velocity of individual particles of burning pulverized fuels. Temperature-size and velocity-size correlations were determined for both nonreacting and ignited suspensions of a spherical, nonvolatile, molecular sieve carbon flowing in one dimension. The measurements at three axial positions when no oxygen was present illustrate the strong sensitivity to particle size in the transient temperatures. A comparison with predictions from a heat transfer model with no adjustable parameters assesses the experimental errors. Sizes were determined to within 10 μm (120 < d p, μm < 240), temperatures to within 50K (1150 < T p, K < 1950), and velocities to within 5% (150 < ν p, cm/s < 300). Four temperature-size correlations for suspensions burning in 24% excess oxygen show that heterogeneous reaction steepens the correlations beyond their levels for conduction heating alone. For a 75 μm size range, the observed ranges of temperature during heatup and ignition span several hundred degrees, which raises serious doubts about the utility of using average temperatures and sizes to assign kinetic parameters throughout the first 100–150 ms of this process.