The effect of temperature and pressure on thermodynamic properties of diesel and biodiesel fuels

The current work focuses on the study of the influence of pressure and temperature on three important thermodynamic properties: speed of sound, compressibility and density of common diesel fuels. The sample fuels studied were conventional diesel (Repsol Elite), Rape Methyl Ester (typical bio-diesel used in Spain) and a fuel used especially for winter season (Arctic). Speed of sound and densities has been determined experimentally. The third property, bulk modulus, has been calculated from the other two. Speed of sound measurements have been carried out in wide range of temperatures (298 < T/K < 343) and pressures (15 < p/MPa < 180), which represent the typical values used in injection systems for diesel engines. Hence, a particular configuration was coupled to the high-pressure injection system, obtaining accurate measurements at these extreme conditions. A detailed description of the method is presented; also, the obtained results are listed, with an uncertainty of ∼0.3%. Density measurements have been performed over a broad range of temperatures (298 < T/K < 343), using two commercial devices, obtaining an overall uncertainty of ∼0.6%.