Molecular mechanisms of deposit control additive inhibition by biofuels
Year: 2026
Type: article
Abstract: Blending biofuels into gasoline can have several environmental and performance benefits. However, high ethanol concentrations are known to reduce the effectiveness of deposit control additives (DCAs) that operate by adsorption onto deposit surfaces. The fundamental physicochemical difference between fossil fuels and biofuels is that the former are mostly non-polar hydrocarbons, while the latter are predominantly oxygen-containing polar species. Here, we use molecular modelling to reveal how the presence of ethanol molecules affects the binding strength of three DCAs with markedly different chemistries to a model carbonaceous deposit from surrogate fuel blends. For a zwitterionic DCA, ethanol forms a structured solvation shell around the charged head-group, which reduces its adsorption free energy on the model deposits by around 75%. The local ethanol density at the ionic DCA head-groups saturates at low (5% volume) ethanol concentration, where most of its loss in adsorption free energy has already occurred. For a Mannich base DCA, no solvation shell forms around the DCA, even at high concentrations (85% volume). Ethanol molecules interact with the non-ionic head-group over timescales that are indistinguishable from the bulk self-network. The adsorption free energy is insensitive to ethanol concentration, even though its enthalpic and entropic components change markedly: enthalpy-driven binding opposed by entropy in iso-octane rich blends becomes weak binding with small enthalpic and entropic contributions in ethanol rich ones. Polyisobutylene succinimide DCAs are an intermediate case between the Mannich base and zwitterionic DCAs, with their adsorption free energy decreasing only at high ethanol concentrations. Our simulation results agree qualitatively with engine test results and offer a molecular-level explanation for why DCAs designed for ethanol-free gasoline are less efficient in ethanol-containing formulations. These findings provide atomistic insights to guide the rational design of DCAs for ethanol-containing fuels, which will continue to be important in the mobility landscape to enable a smoother transition towards net-zero.
DOI: 10.1039/d6cp02171a
Language: English
Subfield: Fluid Flow and Transfer Processes
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W7214673769