EXHAUST AND IN-SITU MEASUREMENTS OF NITRIC-OXIDE FOR LAMINAR PARTIALLY PREMIXED C2H6-AIR FLAMES - EFFECT OF PREMIXING LEVEL AT CONSTANT FUEL FLOW-RATE

NO formation in laminar partially premixed ethane-air flames is invest igated as a function of the amount of air introduced into the central fuel tube of an annular co-flow burner. The NO emission index at the e xhaust is determined by chemiluminescent detection while the local NO number density is measured by laser-saturated fluorescence. The measur ements are taken in flames with an overall equivalence ratio of 0.5, f uel-tube equivalence ratios varying from 1.1 - 10, and a fixed fuel fl owrate of 0.15 slpm. Local NO number densities are measured as a funct ion of both radial position and height above the burner. An intermedia te dual-flame pattern is identified which minimizes the NO emission in dex. NO production is found to occur primarily between an inner premix ed and an outer nonpremixed flame front, which constitutes the dual-fl ame structure. These results suggest that the optimum burner-tube equi valence ratio occurs because of a compromise between prompt and therma l formation of NO in the predominantly premixed and nonpremixed fame r egions, respectively.