Exploring the thermophysical properties of biodiesel: high-pressure density and speed of sound prediction with PC-SAFT and ester composition models

• Speed of sound was measured in three biodiesels at high pressure (up to 200 MPa). • Density was determined in three biodiesels up to 200 MPa. • Derivative volumetric and acoustic properties were determined up to 200 MPa. • The data were used to evaluate the applicability of PC SAFT and two correlations. This paper presents comprehensive experimental data on the density ( ρ ) , the speed of sound ( c ) , the isentropic compressibility κ s , and the acoustic impedance Z for three methyl biodiesels derived from coconut, sucupira, and canola oils. Measurements were carried out over a broad range of pressure (0.1 to 200 MPa) and temperature (293.15 to 373.15 K ), providing valuable insights into the thermophysical properties of biodiesel under extreme conditions. Speed of sound was measured via the pulse-echo technique in the full p,T range. Density was measured using a U-shaped vibrating tube densimeter and up to 100 M P a and extended to 200 MPa by integrating the speed of sound data. The experimental data were compared to PC-SAFT equation of state calculations, and to the predictions of two specific models developed to calculate the thermophysical properties (density, speed of sound, isentropic compressibility, and acoustic impedance) of methyl biodiesel up to 200 MPa, based solely on the fatty acid methyl ester composition. Both the experimental and modeling results contribute to a deeper understanding of biodiesel’s behavior under high-pressure conditions at varied temperatures, enhancing its practical application in advanced fuel injection systems and supporting its potential as a sustainable alternative fuel.