Molecular mechanisms of deposit control additive inhibition by biofuels
4 affiliations
- 1Department of Mechanical Engineering, Imperial College London South Kensington Campus London SW7 2BX UK
- 2Department of Physics, King's College London Strand Campus London WC2R 2LS UK
- 3Shell Global Solutions International B.V. Grasweg 39 1031 HW Amsterdam Netherlands
- 4Shell Centre York Road London SE1 7NA UK
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.
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BibTeX
@article{corralcasas2026molecular,
title = {{Molecular mechanisms of deposit control additive inhibition by biofuels}},
author = {Carlos Corral-Casas and Chiara Gattinoni and Mark Brewer and Alastair Smith and Daniele Dini and James P. Ewen},
journal = {Physical Chemistry Chemical Physics},
year = {2026},
month = sep,
doi = {10.1039/d6cp02171a},
url = {https://doi.org/10.1039/d6cp02171a},
note = {CC BY 3.0},
}
RIS
TY - JOUR
TI - Molecular mechanisms of deposit control additive inhibition by biofuels
AU - Carlos Corral-Casas
AU - Chiara Gattinoni
AU - Mark Brewer
AU - Alastair Smith
AU - Daniele Dini
AU - James P. Ewen
PY - 2026
DA - 2026/09/28
JO - Physical Chemistry Chemical Physics
DO - 10.1039/d6cp02171a
UR - https://doi.org/10.1039/d6cp02171a
AB - 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.
SN - 1463-9076
SN - 1463-9084
ER -