Measurement of Soot Temperature and Volume Fraction of Axisymmetric Ethylene Laminar Flames Using Hyperspectral Tomography

Three kinds of atmospheres, namely, air, oxygen-enriched air, and oxygen/carbon dioxide atmospheres, and a total of ten axisymmetric coflow ethylene laminar flames are experimentally studied using a hyperspectral imaging device. 2-D distributions of the local emission source term in the visible and near-infrared ranges are reconstructed using the least-squares method. Then the distributions of temperature and absorption coefficient are calculated using the Newton-type iterative method, while the wavelength dependence of the absorption coefficient is fitted by polynomials. For the nonoptically thin flame, an iterative algorithm is adopted by substituting the absorption coefficients back into the reconstruction. The experimental results show that there exists a local temperature peak near the flame edge and the flame root. Additionally, for an oxygen-enriched atmosphere, there also exists another local temperature peak in upper center part of the flame in an air/oxygen atmosphere or in the upper edge part in an oxygen/carbon dioxide atmosphere. The results also reveal that the reduction in the flow of ethylene will result in the decrease in the highest soot volume fraction, and a higher oxygen content will generate a higher temperature peak and a lower soot volume fraction peak in an oxygen-enriched air atmosphere, but a higher soot volume fraction peak in an oxygen-enriched oxygen/carbon dioxide atmosphere. In addition, in an air atmosphere or an atmosphere with a large quantity of carbon dioxide, there will be another local peak of the soot volume fraction in the upper center part of the flame, which may be aggravated by the reduction in the amount of ethylene.