NOx emission from high-temperature air/methane counterflow diffusion flame

The objectives of the present study are to measure NO_x emission of counterflow diffusion flame, to compare the findings with numerical results, and finally to demonstrate efficacious effect of high-temperature air with low concentration of oxygen on NO_x emission. Recently, high-temperature air with low concentration of oxygen is used for various industrial furnaces, resulting high efficiency and low emission of pollutants. Since high-temperature air increases NO_x emission and air with low concentration of oxygen decreases it, these effects are competitive. Measurement and computation were conducted to clarify these two effects by use of counterflow diffusion flame. Since it is difficult to employ very high temperature over 1100 K in a laboratory-scale apparatus, a quantitative agreement between experimental and numerical results was confirmed first, and then a numerical approach was used to obtain a larger effect of low oxygen to reduce NO_x emission. In the experiments, the methane concentration is changed from 10 to 30 vol% diluted by nitrogen, oxygen from 10 to 21 vol%, and air temperature from room temperature to 1100 K. The total amount of NO_x sufficiently agreed between experimental and numerical results, although NO and NO₂ could not be separated. By the numerical method, it was found that NO_x emission from the counterflow diffusion flame of high-temperature low-oxygen air of 1500 K and 5% oxygen is comparable with that of room-temperature air of 21% oxygen.