Experimental speed-of-sound measurements of pure fatty acids methyl ester, mineral diesel and blends in a wide range of temperature and for pressures up to 300 MPa

The variety of biofuels, which was put on the market in recent years, requires a great improvement of existing thermodynamic characterization methods and, eventually, the development of new ones. A deep understanding of the chemico-physical properties of biofuels will help to identify appropriate utilization areas, to improve the efficiency, to reduce the impact on climatic changes through greenhouse gas emission control, and to reduce the dependency on fossil energy. This work focuses on accurate experimental speed-of-sound measurements of first-generation liquid biofuels, made from renewable sources, which are commonly utilized in existing compression ignition engines, of mineral diesel, and of blends. The fluids under test were rapeseed oil methyl ester (in the following referred as B100-RME), soybean oil methyl ester (B100-SME), blends with 5% of rapeseed oil methyl ester (B5-RME) or 5% of soybean oil methyl ester (B5-SME), blends with 10% of biofuels (B10-RME and B10-SME) in mineral diesel and pure mineral diesel. Accurate speed-of-sound results were obtained by means of a double reflector pulse-echo technique, in the temperature range from 273.15 K to 353.15 K and over a wide pressure range (from atmospheric pressure up to 300 MPa). The overall uncertainty for speed-of-sound values was estimated to be less than 0.3% over the whole investigated thermodynamical range.