The Effect of Fuel On Automotive Lubricant Degradation

Fuel is known to mix with automotive lubricants during cold starting of the engine, leading to fuel contamination in the sump. The effect that fuel contamination has on lubricant degradation is not well understood, so is investigated for this work. The effect of selected fuel components representative of naphthalenes and bioethanol on the degradation of partially formulated and model base oils has been examined by oxidation in bench top reactors under temperature conditions representative of those found in engines with fuel dilution levels representative of those found in the field.
The ethanol treatment of squalane samples containing 1% (w/w) dispersant promoted reverse micelle formation, confirmed by laser scattering and UV-VIS analysis using nile red as a marker. The ethanol treated samples were found to be significantly more stable to oxidation in comparison to the untreated sample. It is proposed in the literature that the increased oxidative stability is due to the ability of the reverse micelle to act as an alkyl peroxide trap. This in turn reduces the bulk alkyl peroxide concentration which reduces the reaction rate of the radical chain mechanism.
A mechanism has been proposed in this work for the effect of reverse micelles on the autoxidation of branched hydrocarbons. In this work it is suggested that alkyl peroxides formed during autoxidation of the bulk hydrocarbon migrate to the reverse micelle. Once inside the alkyl peroxide can undergo decomposition in the presence of other alkyl peroxides away from the bulk hydrocarbon to form less reactive radicals. This work highlights the need to fully understand the effect of heterogeneity on the autoxidation of hydrocarbons.
1-methylnaphthalane was observed to inhibit the autoxidation of squalane at 150 oC while present in solution. A computational method has been devised to accurately calculate the carbon oxygen bond strength in the alkyl peroxyl radical.