Observation of detailed structure of turbulent pulverized-coal flame by optical measurement. (Part 1, Time-averaged measurement of behavior of pulverized-coal particles and flame structure)

The purpose of this study is to elucidate of the primary air combustion zone in pulverized-coal combustion by means of advanced laser-based diagnostics with high temporal and spatial resolutions. An open-type burner is fabricated to apply various optical measurement techniques. Detailed and overall evaluation is performed by applying various optical measurement techniques to the flame, such as the velocity and shape of nonspherical pulverized-coal particles, temperature, and light emissions from a local point in the flame. It is observed that the particle mean diameter increases as the distance from the burner increases, and this is found to be caused by the decrease in the diameters of small particles and the increase in the diameters of large particles, which result in the char reaction and the particle swelling due to devolatilization, respectively. The size-classified streamwise velocities of pulverized-coal particles in the central region of the jet exhibit the same magnitude, whereas those in the outer region are different depending on the particle size. The behavior is well explained in terms of the particle inertia.