Temporally and spectrally resolved images of single burning pulverized wheat straw particles

Abstract

This work focuses into the combustion behaviour of single wheat straw particles with the aim of providing a quantitative description of the particle burning process from ignition to the early stages of the char oxidation. The single particles, in the size range 224–250 µm, were injected upward into a confined region with hot combustion products, produced by a flat flame McKenna burner, with a mean temperature of 1550 K and a mean dry O2 concentration of 6.5 vol%. Spectral emission data and temporally resolved images of the single burning particles were obtained with a spectrometer and an ICCD camera, respectively. To obtain spectrally resolved images the camera was equipped with different band-pass filters. Overall, the results demonstrate the ability of the present experimental setup and associated optical diagnostics to gather quantitative information of the combustion process of single pulverized solid fuel particles. The emission spectra from the burning wheat straw particles showed that the emission was mainly originated from CH∗, C2∗, Na∗ and K∗ chemiluminescence, and thermal radiation from soot and char burning particles. The ICCD images show that the emission from excited CH, C2, Na and K is initially detected almost at the same time, the burning of the soot particles initiates soon after the ignition, and the char particles experience ignition after the extinction of the homogeneous combustion. During the volatiles combustion stage, the temporal evolution of the normalized emission intensity of the excited CH, C2, atomic sodium and atomic potassium is quite similar; during the char oxidation stage, however, the decrease of the emission intensity of the excited atomic sodium and potassium is delayed in relation to the decrease in the emission intensity of CH and C2 because of the continuous release of atomic sodium and potassium from the burning char particles.