Disturbances in N_{2}-CARS Gas Temperature Measurements in Pulverised Coal-Air-CH_{4} Flames

Authors: D. BRADLEY, M. LAWES, M. J. SCOTT, NAZIM USTA

Abstract: The application of nitrogen vibrational and rotational CARS thermometry to flat, premixed, laminar, methane-air and coal-methane-air flames has been investigated using a Nd:YAG and dye laser system at a low pressure of 30.4 kPa. Although the CARS technique previously has been easily applied to lean and stoichometric methane-air flames, it was found that, in rich methane-air and coal-methane-air flames, C_{2} radicals produced by the laser and flame strongly absorbed part of the fundamental band of the CARS spectrum. This imposed severe interference on the N_{2}-CARS signal. A quantitative investigation of the errors in temperature measurements caused by the C_{2} absorption is presented. It is suggested that the effect of C_{2} on the CARS signal must be taken into consideration before reliable temperature information can be obtained from rich gas-air flames and coal-air flames. In this study, a modified experimental and data analysis technique has been applied successfully to eliminate the influences of C_{2} on the CARS temperature measurements.

Keywords: Laser diagnostics, CARS, C_{2} interference, Temperature measurement.

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