Density, Speed of Sound, and Viscosity Measurements of Reference Materials for Biofuels

Abstract

Measurements of density, speed of sound, and viscosity have been carried out on liquid certified reference materials for biofuels as a function of temperature at ambient pressure. The samples included anhydrous and hydrated bioethanol and two biodiesel fuels from different feedstocks, soy and animal fat. The ethanol samples were measured from a maximum temperature of 60 to 5 °C (speed of sound) and to −10 °C (density and viscosity), respectively. The biodiesel samples were characterized from 100 °C (density and viscosity) and from 70 °C (speed of sound) to 10 °C (animal fat-based) and 5 °C (soy-based). Densities were measured with two vibrating-tube instruments of different accuracy. The speeds of sound were measured with a propagation-time method in an acoustic cell that was combined with one of the densimeters. Viscosities were measured with an open gravitational capillary viscometer and with a rotating concentric cylinder viscometer, according to Stabinger. The measurement results are reported with detailed uncertainty analyses.

Advanced calibration, adjustment, and operation of a density and sound speed analyzer

“…Water is the commonly used reference fluid because it is particularly well characterized. However, as shown in figure 11, the temperature dependence of its speed of sound is opposite of that observed for many sample liquids that we have measured [28][29][30]; the speed of sound of water increases with temperature from 278 K to 343 K, while that of other liquids decreases with temperature. Furthermore, as was the case with density, the speeds of sound of water [23] and air [47] are drastically different in magnitude from those of our typical sample liquids.…”

“…However, as can be seen in figure 8, many of the liquids that we have measured with this instrument [28][29][30] have densities that are lower than water [23] and significantly higher than air [31]. This is a concern because it is preferable to calibrate the instrument with a reference standard whose properties are similar to those of the measurement sample of interest.…”

“…[23], air ( ) [31], toluene ( ) [32], and isooctane ( ) [34]. Symbols represent the averaged results of measurements made with the present instrument: d, water; j, toluene; N, isooctane; Ç, animal biodiesel [28]; , anhydrous ethanol [28]; ., methylcyclohexane [29]; , jet fuel [30].…”

“…We present here an approach to a comprehensive uncertainty assessment for the density and sound speed analyzer as a guideline for other users of similar commercial instruments. A similar approach is described in Laesecke et al [28], and additional details can be found therein.…”

High-Sensitivity Measurement of Density by Magnetic Levitation

“…39 and coupled MagLev with smartphones for automated analysis of density. 40 Although we have previously demonstrated a measurement accuracy up to ±0.0002 g/cm 3 for narrow ranges of densities 29 , many applications-such as evaluating cerebrospinal fluid and high purity fuels 16,[41][42][43] , or detecting small changes in density (e.g. binding of proteins on a surface)-require even higher resolution in density to measure small changes in composition or impurities.…”