Combustion characteristics and thermal efficiency for premixed porous-media types of burners

This research was conducted to experimentally compare the emission characteristics and thermal efficiency of porous-media types of burners and to determine which types to use with a condensing boiler to be developed later. Three types of porous-media burners; metal fiber (MF), ceramic (CM) and stainless steel fin (SF) were used with a commercial heat exchanger and tested for various equivalence ratios and burner capacities. The MF burner had the lowest CO emissions of the three burner types, and the SF burner had the highest CO emissions. However, The MF burner had the highest NO_x emission and thermal efficiency, and the SF burner had the lowest NO_x emissions and thermal efficiency. In other words, the smaller the burner porosity was (porosity: SF < CM < MF), the higher the CO emission was and the lower the thermal efficiency was. Based on the thermal efficiency, turn-down ratio and NO_x and CO emissions with respect to the Korean industrial standard and European norms, the most appropriate burner type for the condensing boiler is the MF burner. The optimal operating equivalence ratio was 0.80 for the range of experimental factors considered in this research.