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Specific Gravity and API Gravity of Biodiesel and Ultra-Low-Sulfur Diesel (ULSD) Blends

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Biodiesel is an alternative fuel made from vegetable oils and animal fats. In 2006, the U.S. Environmental Protection Agency mandated a maximum sulfur content of 15 ppm in on-road diesel fuels. Processing to produce the new ultra-low-sulfur petrodiesel (ULSD) alters the specific gravity (SG) and other fuel properties. Accurate determination of SG (or density) of fuels is necessary for conversion of measured volume to volume or mass at standard temperature. Furthermore, SG is generally correlated against performance indicators such as cetane number and heating value. The present study addresses the need to develop a better understanding of how blending biodiesel with ULSD affects SG. The effects of biodiesel volumetric blend ratio (VBD) on SG were evaluated for blends of fatty acid methyl esters (FAME) from soybean oil (SME) from three different fuel producers and FAME from used cooking oil (UCOME) in ULSD. Regression analysis of results at 15.6°C and 40°C indicated that SG increased linearly with respect to increasing VBD . Average differences between predicted and measured values were less than 0.001. Results for blends of the three SMEs in ULSD were pooled to yield a combined linear correlation for SME/ULSD blends (R2 = 0.999 for SG at 15.6°C). The API gravities of blends were determined from SG data at 15.6°C. Two methods were proposed to calculate API gravity of a given blend with VBD = BX (X vol% biodiesel). Method I was to determine SG from the appropriate linear correlation reported in this work and calculate API gravity accordingly. The accuracy of this method depended on the precision in calculating SG (noted above). Method II involved determining API gravities of the unblended components and taking a volumetric average at VBD = BX. Accuracy of method II was <or= 0.11° based on predicted and measured values. It was concluded that both methods were capable of very precise determination of the API gravity of biodiesel/ULSD blends.
Dunn, R.O.
biodiesel , sulfur , gravity , diesel fuel , regression analysis , fatty acid esters , soybean oil , cooking fats and oils
p. 571-579.
Includes references
Transactions of the ASABE 2011 Mar-Apr, v. 54, no. 2
Journal Articles, USDA Authors, Peer-Reviewed
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