Numerical Study of NOx and Soot Formations in Hydrocarbon Diffusion Flames

Pollutant emission is becoming a serious environmental issue nowadays. Stringent legislations were introduced in several countries to limit the permissible levels of pollutant particle emission in major combustion systems such as burners and furnaces that have been widely used in industrial application. In this study, a numerical study of laminar coflow diffusion flame was performed in a model combustor using the commercial software ANSYS Fluent 19.1. The main focus of this study is to understand the effect of the variation of flow characteristics in the coflow diffusion flame on the prediction of NOx and soot emissions. A comparison study of the pollutant formation was performed with different hydrocarbon gaseous fuels (methane, ethylene, ethane, propane, and n-butane) with detailed high-temperature reaction mechanisms. In addition, the Moss-Brookes model was adopted to obtain the soot emission data. Variation of the flow characteristics on the pollutant formation was performed by examining the change in fuel inlet velocity, i.e., 0.5 (u) over bar (0), (u) over bar (0), 1.5 (u) over bar (0), 2 (u) over bar (0) with (u) over bar (0) the mean fuel inlet velocity of baseline condition, and the effect of nozzle heating condition, i.e., 298 and 403 K. The results showed that ethylene flame produced higher NOx and soot compared to other hydrocarbon fuels. It was observed that the increase of the fuel inlet velocity promoted the formations of NOx and soot. Besides that, the nozzle heating condition increased the overall adiabatic temperature of the flame, where the relative effect was more pronounced on the alkane fuels, especially the lighter fuel compared to alkene fuel (ethylene).