Peter Hsieh - A perspective on the origin of lubricity in petroleum distillate motor fuels

Document created by Peter Hsieh on Oct 3, 2014Last modified by Peter Hsieh on Oct 3, 2014
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  Publication Details (including relevant citation   information):

  Hsieh, P.Y.; Bruno, T.J. Fuel Processing Technology   2015, 129, 52-60.


  Lubricity, or a substance's effect on friction and wear between   two surfaces in relative motion, is affected by both chemical and   physical mechanisms present at a sliding contact. The inherent   lubricity of distillate motor fuels stems from surface-active   compounds found in petroleum, principally heavy aromatic   compounds such as polycyclic aromatic hydrocarbons (PAH) and   nitrogen heterocyclic polyaromatic hydrocarbons (NPAH) containing   three or more fused rings. These compounds are less abundant in   motor gasoline and more abundant in diesel fuel due to   differences in the boiling ranges of these distillate fuels. PAH   and NPAH compounds can form chemical bonds with metal surfaces   and reduce the friction of metal surfaces in sliding contact.   Reducing the coefficient of friction lowers the peak stress   amplitude at the sliding contact, thereby mitigating the effects   of plasticity-induced wear mechanisms and delaying the transition   to abrasive wear. Hydrotreatment of distillate motor fuels to   remove sulfur also hydrogenates heavy aromatic compounds, leading   to a reduction in fuel lubricity and increased wear of fuel   injectors and pumps. The addition of linear alkyl polar compounds   can improve fuel lubricity in severely hydrotreated petroleum   distillate motor fuels. Boundary lubrication by linear alkyl   polar compounds is distinct from lubrication by native heavy   polar aromatic compounds found in petroleum. Mechanical testing   is typically employed to measure fuel lubricity due to the   complex interactions between the surface-active compounds and   wear mechanisms at work in a sliding contact, and the lack of a   single SI unit like viscosity that describes the sum of   interactions between the fluid, material, and mechanical forces   at a sliding contact.

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