Effects of fuel-air unmixedness on NO(x) emissions

Abstract

Unmixedness effects of lean fuel-air mixtures on emissions of nitrogen oxides (NOV) are experimentally studied. The objective is to study the relative influence of temporal fuel concentration fluctuations and spatial nonuniformities of mean concentration profiles on NO V emissions from lean premixed combustion. The NO2 laserinduced fluorescence (LIF) technique is used to quantify Unmixedness levels at the flameholder. Unmixedness data are related to NOr emissions measurements from downstream of the flames. The results show that temporal unmixedness contributes significantly to higher NOX emissions. It is not sufficient to eliminate only spatial nonuniformities of mean concentration in order to minimize NO_V emissions from lean premixed combustion. Nomenclature c = volumetric fuel concentration c' = rms fluctuation component of c c - time-mean fuel concentration Dc = combustor diameter Z)cf = coflow diameter Dj = jet diameter Recf = coflow Reynolds number Rej - jet Reynolds number U = unmixedness parameter Xj - distance from jet to flameholder z - vertical coordinate; origin at combustor centerline = fuel-air equivalence ratio