Numerical Study of the Effects of Volumetric Heat Transfer and Emissivity Coefficient and Porosity on Combustion and Pollutants Formation in a Porous Burner

Abstract

In recent years, more attention has been focused on the use of porous materials to enhance the efficiency of combustion systems and to reduce the emission of pollutants. This is because combustion in inert porous media offers an interesting and promising route towards burner with high-power density, high-power dynamic range, and very low emission of pollutants such as NOx and CO. This work reports one-dimensional combustion in a porous burner using three combustion models: GRI 3.0, GRI 2.11, skeletal mechanism. We conclude that GRI 2.11 mechanism has a good agreement with GRI 3.0 and it costs less. At first, we present a numerical study which shows the effects of these models on temperature, species and pollutant emissions. Then, we investigate the effects of volumetric heat transfer and emissivity coefficient and porosity on combustion and pollutions. It was concluded that NO and CO emission depend mainly on the volumetric and emissivity coefficient. When volumetric heat transfer increased, the difference between gas and solid temperature reduced, therewith NO formation noticeably decreased whereas CO emission didn’t change sensible. On the other hand, the flame peak temperature is increased with the reduction of the solid emissivity coefficient. This important conclusion means that NO and CO emission and velocity increases. Also gas and solid temperature increase and vice versa. The other parameter is Porosity. Increasing in porosity of burner resulted in decreasing gas and solid temperature and subsequently NO and CO emission decreased sensible. Porosity has effected on velocity, too. As porosity decreased, velocity increased. Emissivity effects on the rate of heat flux which issue from burner. As the emissivity increased the efficiency of burner arose. Also these parameters have important roles in decreasing the emission especially on No emission because it has more depend on temperature. In addition the resulted gas and solid temperatures were compared with reported measurements of center line temperature in a cylindrical porous burner. The good agreement with experimental observation upholds that the numerical model is a perfect tool to investigate combustion and pollutants formation in porous media.