Biodiesel Blend Level Detection Using Ultraviolet Absorption Spectra

Biodiesel is often blended with regular U.S. No. 2 diesel. The blending level influences engine performance, emissions, and fuel cold‐flow properties. In this article, ultraviolet (UV) absorption spectroscopy is presented as a reliable and affordable technology for blend level detection based on the absorbance patterns of the aromatic compounds in the proposed spectrum. Blends of biodiesel from six different feedstocks and U.S. No. 2 diesels from five different sources were used to test the robustness of the method. Since the absorbance of undiluted samples was too high to measure reliably, the samples were diluted with n‐heptane. It was found that the feedstock and alcohol used (methyl or ethyl) did not make a significant difference in the absorbance of diluted biodiesel in the 245 to 305 nm range, while absorbance from 254 to 281 nm was correlated with blend level with R2 > 0.99. It was also observed that if the absorbance of the diesel source was known, then a single wavelength could be used to detect the biodiesel blend level. However, a single wavelength was inadequate when the diesel source was unknown because of variation in the level of aromatics in diesel fuel. Absorbances at 265, 273, and 280 nm were used to calculate the absorbance index, which was found to be independent of the diesel fuel used. Using three wavelengths captured the shape information of the absorbance curve and eliminated the variation from the aromatics content. The root mean square error in determining blend level with this method was estimated to be 2.88%, and the R2 for the linear model was 0.99. The method worked well with biodiesel from the different feedstocks tested in this research and was independent of the diesel fuel used.