Measurement and prediction of the speed of sound of biodiesel fuels

Speed of sound is an important fuel thermophysical property that directly characterizes the fuel injection and the NOx emissions in diesel engines especially for injectors activated with pressure. Nevertheless, the experimental data of speed of sound for biodiesel fuels are very scarce in the literature. Thereby, this work aims at measuring the speed of sound for biodiesels fuels and evaluating some predictive models to estimate the speed of sound from the composition of fatty acid methyl esters in the biodiesel. at purpose the measurement of speeds of sound for three fatty acid methyl esters and ten biodiesel fuels at atmospheric pressure and temperatures from 288.15 to 343.15 K was done. The ability of two versions of Auerbach’s relation, and the ideal mixture mixing rule to describe the speed of sound of biodiesels was evaluated. The results evinced that, with the exception to the original version of Auerbach’s relation, the other models studied provide a good estimate of the experimental data. The modified Auerbach’s relation displays an overall average relative deviation of 1.64%, and the ideal mixture mixing rules predict the biodiesel speed of sound with only 0.37% of overall deviation. Moreover, the dependency of speed of sound on pressure was also correlated with a linear equation, presenting only an overall deviation of 0.56%. These models can thus be a good tool to estimate the speeds of sound using only information about the biodiesel composition.