A quantum chemical study of the processes during the evaporation of real-life Diesel fuel droplets

Abstract

Evaporation rate (γ) of molecules from Diesel fuel molecular clusters and nanodrops is analysed using the solvation model SMD within quantum chemistry, the kinetic gas theory, and experimental or extrapolation data on temperature dependence of the enthalpy of evaporation and liquid density. The SMD/HF or SMD/DFT with the same 6-31G(d,p) basis set is used to estimate changes in the Gibbs free energy during the transfer of a molecule from a liquid medium into a gas phase (using the Gibbs free energy of solvation, ΔGs). The kinetic gas theory is used to estimate the collision rate of molecules/clusters/nanodrops in the gas phase. This rate depends on partial pressures, temperature, sizes and masses of molecules and clusters/nanodrops. Such solvents as n-dodecane, tetraline, benzene, and isopropyltoluene are used to analyse the effects of surroundings on the evaporation rate of the components of Diesel fuel: normal, iso and cyclic alkanes, 1–3 ring aromatics, tetralines and indanes (in the C12–C20 range). Compounds C14–C16 give the main contribution to Diesel fuel under consideration, and all cyclic organics have the C1–C6 aliphatic side groups. An increase in the molecular size of alkanes from n-octane to n-heptacosane or in the aromaticity of compounds results in a strong decrease in the γ values.