Abstract

An experimental study of the effect of oxygen index (OI) on soot formation in laminar coflow propane diffusion flames is presented. The OI was defined as the oxygen volumetric concentration in the oxidizer flow, O-2/(O-2+N-2), which was varied from 21% to 37%. The influence of the OI was quantified by means of three variables: the flame height, the soot volume fraction, and the vertical distribution of radiative heat flux. The flame height was based on CH* spontaneous emission and found to vary inversely with the OI, following the classical theory of Roper. As the OI increases, the rates of soot growth and soot oxidation are enhanced, and the maximum soot volume fraction and the peak of integrated soot volume fraction also increase. Moreover, the evolution of the peak of radiative heat flux and the maximum soot volume fraction are found to follow the same evolution with the OI.