Soot formation in diffusion oxygen-enhanced biodiesel flames

The focus of this work is the experimental investigation of soot formation in coflow flames formed of two fatty acid methyl esters (FAMEs) by employing the light extinction/scattering technique. Three different sets of experiments were conducted in this study. In the first set, radial soot volume fraction (f(v)) profiles of flames of vaporized neat canola methyl ester (B100CME) and neat soy methyl ester (B100SME) fuels both using air as the oxidizer were obtained. In the second set of experiments, the effect of oxygen content in the oxidizer stream on soot formation was studied in both FAME formed flames by increasing the oxygen content in the oxidizer stream from 21% to 35%, 50% and 80%. In the third set of experiments, the effect of fuel blending on the formation of soot particulates was studied in flames formed using CME blended with No. 2 diesel. The blends consisted of 80% biodiesel/20% diesel (B80) and 50% biodiesel/50% diesel (B50). The flames were scanned in the radial direction at various heights above the burner (HAB). For the B100CME-air flame the measured soot volume fraction f(v) peak was 4.04 ppm and was located at the symmetry axis at a HAB of 16.25 mm. For B100SME-air, the f(v) peak was measured to be 4.22 ppm at approximately the same flame height as in the CME-air flame. For the B100CME oxygen enriched-air flames the peak values at 35%, 50% and 80% were 6.50, 5.82 and 3.22 ppm, respectively. It was observed that by increasing the oxygen content in the B100CME flame from 21% to 35% oxygen, the f(v) peak increases by approximately 61%. However, a further increase in oxygen content in the oxidizer stream suppressed soot formation. A similar trend in the f(v) was observed for B100SME oxygen-enhanced flames. Furthermore, the increase of diesel fuel in the blending of B50CME resulted in significantly higher f(v) values compared to the B80CME. The addition of oxygen content in the oxidizer stream in these blended fuel flames (from air to 35%) resulted in an increase in the f(v) peak of approximately 47% and 71%, respectively. Centerline temperatures were measured at various HAB for selected flames. (C) 2015 Elsevier Ltd. All rights reserved.