Analysis of techniques for measuring temperature variations at the exit of a coal-fired MHD combustor

The performance of an MHD coal-fired combustion system is critically dependent on achieving and maintaining a high level of plasma electrical conductivity. Also, spatial or temporal conductivity nonuniformities can degrade the generator performance. Hence by Saha's equation, which establishes the relationship between electron number density (hence conductivity) and temperature, the performance of the MHD generator is also critically dependent on maintaining a high level, uniform plasma temperature profile entering the generator.

An MHD combustion plasma is a high temperature, corrosive and erosive environment which creates extreme difficulties in obtaining temperature measurements. The method used for measuring plasma temperatures must take into consideration not only the character of possible temperature variations and spatial inhomogeneities in the gas stream but also the probable degradation of conventional contact temperature meaning devices by exposure to the severe MHD environment.

A literature search was conducted to provide an overview of available diagnostic techniques which could be implemented to obtain temperature measurements in combustion MHD flows. Several optical and spectroscopic techniques were evaluated, including spontaneous Raman spec-spectroscopy, near-resonant Raman spectroscopy, laser-induced resonance fluorescence, line reversal, and luminosity sensor techniques. In addition, the Abel integral numerical inversion technique was investigated, in conjunction with emission-absorption methods such as line reversal, as a technique for decoupling line-of-sight average measurements to provide spatially defined temperature distributions.

Diagnostic techniques are recommended for possible implementation at the UTSI Coal-Fired Flow Facility. Additionally, recommendations are offered in regard to preliminary tests which should be performed in order to experimentally examine those plasma conditions required for successful application of recommended diagnostic techniques.