Experimental study on flameless combustion and NO emission with hydrogen-containing fuels

Flameless combustion is a good alternative for a combustion technology that can simultaneously reduce CO and NOx, which generally have a trade-off relationship with each other. The most important feature of flameless combustion is its ability to control the radical and intense combustion atmosphere and suppress the formation of flame hot spots. Existing flameless combustion technology requires an additional diluent or preheating of reactants; but in this study, flameless combustion was achieved by controlling the flow through a bluff-body burner and inducing internal recirculation of the flue gas. In addition, the characteristics of flameless combustion using various fuels (CH4/CO/H-2) were analyzed in detail. Consequently, in the flameless combustion atmosphere, the formation of hot zones was suppressed, and the amount of thermal NO was significantly reduced (>85% NO reduction). In the case of CO, most of the combustion characteristics were almost the same as those of methane, whereas when hydrogen was added, the amount of thermal NO generated was relatively large (<15% NO reduction) due to the influence of the hydrogen fuel in the chemical reaction. The effect of hydrogen on NO generation was found to be mainly a chemical reaction such as NNH and N2O intermediate route, which is especially noticeable in a flameless combustion atmosphere where the formation of a localized high-temperature region is suppressed. In addition, stable complete combustion was achieved even at a very low excess air ratio in a flameless combustion atmosphere. These characteristics of flameless combustion can have positive influence in terms of low pollutant emission and fuel diversification.