Effect of fuel mixture on moderate and intense low oxygen dilution combustion

The effects of fuel mixture on the establishment of moderate and intense low oxygen dilution (MILD) combustion in a recuperative furnace were investigated. Experimental as well as computational results are presented in this paper. Data from exhaust sampling of NOx and thermocouple measurements of temperature are reported along with results from simultaneous measurement of temperature and OH using Rayleigh scattering and laser induced predissociation fluorescence, respectively. A variety of fuel mixtures using methane, ethylene, and propane were investigated. It was found that dilution of fuel with CO2 or N2 reduced the NOx emission and made the flame inside the furnace invisible. This dilution caused the stoichiometric mixture fraction to shift toward the rich side where the scalar dissipation is highest. This implies that premixing of the fuel stream with circulated exhaust gases can have beneficial effects on the establishment of MILD combustion without the need for higher fuel jet momentum. The reaction zone was found to be characteristically broad and the temperature images were patchy in the lower part of the furnace. The probability density function of the temperature exhibited a bimodal behavior with a cross over temperature of 1300 K.