Towards predictive molecular simulations of normal and branched alkane adsorption in carbonaceous engine deposits

Engine deposits are complex carbonaceous materials that tend to accumulate on the inner surfaces of the car engine. The presence of these deposits leads to adverse engine performance through a variety of mechanisms that strongly depend on the porous nature of the deposits. The two objectives of this study are to characterize these materials and elucidate their interactions with representative components of the fuel at various conditions. Previously, we used experimental data from a single ethane adsorption isotherm at 278 K to develop a model of engine deposits, based on simple slit pore geometry, and obtained representative pore size distributions for two samples of the deposits. Here we extend this approach to another type of engine deposit, compare simulation predictions to experimental results for ethane adsorption at various conditions, and explore adsorption of more complex species such as n-butane and isobutane. Finally, we provide predictions for the adsorption of n-heptane and isooctane and demonstrate that substantial amounts of these species would be adsorbed in engine deposits in the equilibrium limit under typical engine conditions. Although the simulation predictions most likely overestimate the amount adsorbed, it is clear that the adsorption processes can not be ignored in the engine operation optimization.

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► A model of carbonaceous engine deposits is developed and validated using computer simulations and physical adsorption experiments for ethane, n-butane and isobutane at several temperatures.
► Using this model predictions for adsorption of fuel components are made in various deposits under engine operating conditions.
► Substantial amount of fuel components is adsorbed in equilibrium limit
► Isooctane is adsorbed preferentially over n-heptane.
► These findings highlight the importance of adsorption as a mechanism of engine performance deterioration in the presence of engine deposits.