Disturbances in N2-CARS gas temperature measurements in pulverised coal-air-CH4 flames

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, C2 radicals produced by the laser and flame strongly absorbed part of the fundamental band of the CARS spectrum. This imposed severe interference on the N2-CARS signal. A quantitative investigation of the errors in temperature measurements caused by the C2 absorption is presented. It is suggested that the effect of C2 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 C2 on the CARS temperature measurements.