Thermodynamics of fuels with different CeO2 sizes and addition amount based on thermogravimetric analysis

Abstract: By the combination of physical dispersion and chemical dispersion methods, various types of nano-fuel blend containing 20 and 50 nm CeO2 with the dosing levels of 50 and 100 mg/L (20nmCe50, 20nmCe100, 50nmCe50 and 50nmCe100) were prepared, in which the pure tetradecane (C14) served as the base fuel to surrogate diesel and the CTAB worked as the surface active agent to prevent agglomeration by altering the surface properties of suspended nanoparticles. The evaporation characteristics of various nano-fuel blend and C14 were investigated using isothermogravimetrical analysis. According to the boiling point of C14, the evaporation experiments were performed at different constant temperatures ranging from 100 to 140 ℃ with an interval of 5 ℃, and each isothermal section was held for 10 min. The principles to determine the activation energy, vapor pressure and vaporization enthalpy of nano-fuel were also briefly described. Based on isothermal thermogravimetry experimental data, the activation energy needed for fuel evaporation was figured out by the Arrhenius equation, the vapor pressure at various temperatures was calculated according to the Antoine and Langmuir equations, and the vaporization enthalpy was solved by correlating the Clausius-Clapeyron equation with the vapor pressure. It is revealed that owing to the lower specific heat capacity of nanoparticles, during the fuel evaporation the heat transfer from the outside to the inside was accelerated, which delayed the volatilization of fuel molecules located at gas-liquid surface. As a result, for nano-fuels, the activation energy needed for vaporization increases with the decrease in nanoparticle size or the increase in nanoparticle mass fraction. The 20nmCe50, 20nmCe100, 50nmCe50 and 50nmCe100 nano-fuel are increased by 5.6%, 9.3%, 3.2% and 6.8% respectively compared with that of the base C14. Moreover, the presence of nanoparticles in fuel leads to an increase of the surface tension, and the postponing of the diffusion of fuel molecules into gas. Therefore, the nano-fuel has a lower vapor pressure than the base fuel. For instance, the vapor pressure of the 20 nm CeO2-fuel with a dosing level of 100 mg/L was declined by 18.1% compared with that of the base C14 at 373.15 K. With the decrease of nanoparticle size or the increase of nanoparticle mass fraction, the vapor pressure of the nano-fuel declined. In addition, the vaporization enthalpy of 20 nm CeO2-fuel with a dosing level of 100 mg/L at 383.15 K was increased by 16.7% compared with that of C14, due to the enhanced interactions, like van der Waals force and the hydrogen bond between fuel molecules and nanoparticles. With the decrease of nanoparticle size or the increase of nanoparticle mass fraction, more enthalpy was needed for the vaporization of nano-fuels. Furthermore, the errors of the calculation are little compared with other references. Therefore, the isothermogravimetry can be used for the calculation of the thermodynamic physical parameters of nano-fuel. In summary, for nano-fuels, the nanoparticle size and its mass fraction have coherent and self-consistent effects on the activation energy, vapor pressure and vaporization enthalpy. The study on thermodynamic physical parameters of nano-fuel can provide important basic data for its application.