Multispectral Mid-Infrared Camera System for Accurate Stand-Off Temperature and Column Density Measurements on Flames

Abstract

Accurate measurement of temperature in flames is a challenging problem that has been successfully addressed by hyperspectral imaging. This technique is able to provide maps of not only temperature T (K) but also of column density Q (ppm-m) of the main chemical species. Industrial applications, however, require cheaper instrumentation and faster and simpler data analysis. In this work, the feasibility and performance of multispectral imaging for the retrieval of T and QCO2 in flames are studied. Both the hyperspectral and multispectral measurement methods are described and applied to a standard flame, with known T and QCO2, and to an ordinary Bunsen flame. Hyperspectral results, based on emission spectra with 0.5 cm resolution, were found in previous works to be highly accurate, and are thus considered as the ground truth to compare with multispectral measurements of a mid-IR camera (3 to 5 mum) with a six interference filter wheel. Maps of T and Q obtained by both methods show that, for regions with T -1300 K, the average of relative errors in multispectral measurements is for T (and can be reduced to 2.5% with a correction based on a linear regression) and for Q. Results obtained with four filters are very similar; results with two filters are also similar for T but worse for Q.