Predicting biodiesel densities over a wide temperature range up to 523Â K

Density is an important parameter for liquid fuel to correlate the cetane number, heating value and viscosity, and directly influences the fuel injection process. Densities of biodiesel over a wide temperature range up to high temperatures are required for accurate spray and combustion modeling. In this study, densities were predicted for three methyl ester biodiesels from room temperature to 523 K at atmospheric pressure by validating against the experimental data. Three versions of the group contribution model (GCVOL) and four versions of the modified Rackett equation based methods were evaluated with special emphasis on the evaluation of the predictive ability for biodiesel densities over the high temperature range beyond 373 K. The Rackett-Soave method and the proposed Rackett-Revised method were used to predict temperature-dependent biodiesel densities for the first time, to the best of our knowledge. The computational results show that, the Rackett-Revised method is the most accurate method in predicting high-temperature biodiesel densities with the compressibility factor determined by the proposed linear regression method. Among the GCVOL group contribution methods, the revised version by updating the parameters of the double-bond gives more accurate biodiesel densities when no experimental data are available. Moreover, the modified Rackett equation based methods can present the correct temperature dependency of biodiesel densities at temperatures beyond 373 K, while the GCVOL group contribution methods fail to reproduce the fast decreasing trend.