Profiling of Redox Index During Combustion to Monitor C/C Composite Degradation in Flames

Abstract

It is often important to know if the local area in a flame is in reducing or oxidizing environmental conditions during combustion. In this study, a new reducing/oxidizing (redox) index parameter has been introduced. The value of this parameter has been determined experimentally by a chemical seeding technique. A solution of chromium was sprayed into a premixed acetylene-air flame supported on a slot burner. The flame temperature was determined as an excitation temperature by comparing the spectral intensities of two triplet lines emitted from chromium atoms. The redox index is defined as the ratio of experimentally determined and theoretically calculated degrees of atomization. The degree of atomization for the reaction CrO→Cr+O has been determined by comparing the spectral intensity of CrO band emission with the Cr triplet lines. Theoretically, the degree of atomization was calculated by assuming that a simple thermal dissociation takes place in the reaction. Two-dimensional distributions or profiles of the excitation temperature have been determined experimentally. The degree of atomization and redox index has been measured using a charge-coupled device camera fitted with an optical bandpass filter. The output from the camera was coupled to a personal computer for data acquisition and data processing. This diagnostic tool has been successfully used to determine the degradation processes of high-temperature materials, such as carbon/carbon composites, using an air-acetylene flame.