Thermal expansion coefficient and algebraic models to correct values of specific mass as a function of temperature for corn biodiesel

Abstract

Values of thermal expansion coefficients (b) were experimentally determined for three samples: a mineral diesel and two biodiesels constituted by either fatty acid ethyl esters (FAEE) or fatty acid methyl esters (FAME), from transesterification reactions using raw corn oil and ethyl or methyl alcohol. Values of b were found to be 8.36(±0.06)10−4°C−1, 8.43(±0.09)×10−4°C−1 and 8.39(±0.03)×10−4°C−1, respectively, within 95% of statistical confidence. The thermal expansion coefficients for biodiesels from corn are higher than that for the mineral diesel. The expansion coefficient is also a key parameter in modeling fuel injection system of internal combustion engines. Comparing the two sets of data, for fossil diesel and biodiesel provides essential information to support the design and optimization of more efficient engines. A higher value for the cubic expansion coefficient implies that less specific mass of fuel is injected at higher temperatures, which can cause a loss in engine power. This is a fundamental parameter, reinforcing further the interest to establish an algebraic model to estimate the specific mass for a biofuel as a function of temperature, which is thought to be significantly different from that more commonly used for the fossil diesel. Polynomial models for such a correction were determined in this work; resulting rates for diesel and for corn oil biodiesels, based on either fatty acid methyl esters (FAME) or fatty acid ethyl esters (FAEE), were respectively −0.7089kgm−3T−1, −0.7323kgm−3T−1 and −0.7313kgm−3T−1. From the linear correlation between these data and those from standard EN14214, values for the sensitivity (slope term) are seemingly small, or roughly 0.723, but are high enough to cause relatively large impacts, in financial terms, for cases involving considerably big volumes of biodiesel, in commercial transactions.