Thermodynamics, Dynamics, and Rheology of Fuel Surrogates: Application of the Time-Temperature Superposition Principle in Molecular Dynamics Simulations
A Perego and F Khabaz, ENERGY & FUELS, 34, 10631-10640 (2020).
All-atom molecular dynamics (MD) simulation is used to determine the thermodynamics and rheological properties of fuel surrogates, which are modeled as a mixture of n-hexadecane and methyl laurate. The volumetric properties of the studied systems, namely, density and coefficient of thermal expansion, show an excellent agreement with experiments. The temperature dependence of translational and rotational diffusion of the molecules follows an Arrhenius-type behavior, which is consistent with the temperature dependence of the zero shear viscosity obtained from nonequilibrium simulations. At high shear rates, the molecules align in the flow direction that gives rise to the shear-thinning behavior for these fuel surrogates. The time-temperature superposition (TTS) principle is then successfully applied to collapse the shear viscosity and translational/rotational motion data in all systems. The application of TTS on the dynamics data obtained in equilibrium, which are readily accessible in the all-atom MD simulations, allows one to reduce the time scale gap between experiments and simulations and predict the rheological response of complex fluids, especially mixtures of short alkanes and fatty acid esters, which are of interest in fuel surrogates.
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