Speed of sound measurements of binary n-octane+ ethylcyclohexane mixture at liquid-gas phase transition curve

Bio-jet fuel is a key element in the aviation industry to reduce operating costs and environmental impacts. Bio-jet fuel is a complex mixture of four hydrocarbons (n-alkanes, isoalkanes, cycloalkanes and aromatics). In the present work, the speed of sound in pure n-octane, ethylcyclohexane, and their mixtures with six selected compositions of (0.3004, 0.4191, 0.4999, 0.5538, 0.6991, and 0.7852 mole fraction of ethylcyclohexane) has been measured along the l-G saturation curve in the temperature ranges from (286 to 443) K using the pulse method with a constant (acoustic) sounding base. The combined expanded absolute and relative uncertainties (0.95 level of confidence, k = 2) of the temperature, concentration, and speed of sound measurements are estimated to be 20 mK, 0.0006 mole fraction, and 0.2 %, respectively. The measured speed of sound data together with our previous reported density data for the pure component (ethylcyclohexane) and the mixture were used to calculate derived thermodynamic properties, such as isentropic compressibility $k_S$ and heat capacity ratios $\frac{C_P}{C_V}$ as a function of temperature along the l-G saturation curve for the pure components and the mixture for selected concentration of x = 0.8 mole fraction of ethylcyclohexane. The deviation of the measured speed of sound data for the mixture from the linear additive rule has been determined using the pure component data.