Study on Effects of Methanol and Its Combustion By-products on Engine Oil Properties
A commercially available regular engine oil was selected as the research subject of the paper,and the effects of methanol and its combustion by-products on the main properties of the lubricating oil were investigated.The results of the SRV friction-wear tests in reciprocating mode show that methanol and its combustion by-products have negative effects on the friction reduction and anti-wear properties of the engine oil,leading to the increase of the average friction coefficient by 19％and of the wear rate by 54％of the friction pair.This is because methanol and its combustion by-products react with friction reduction and anti-wear additive such as zinc dialkyldithiophosphate(ZDDP)and molybdenum dialkyldithiocar-bamate(MoDTC)and separate them from the lubricating oil.Besides,the oxidation resistance test shows that adding a mixture of methanol,formaldehyde,and formic acid reduces the initial oxidation temperature of the engine oil by 7 ℃ and shortens the oxidation induction time(OIT)at 210 ℃ by 7 minutes.Moreover,crankcase simulation tests show that the methanol has the greatest influence on coking behavior,while the introduction of the ternary mixture gives a ten-grade co-king rating and increases the coking amount by 400％.Furthermore,the addition of methanol and its combustion by-prod-ucts will increase the drop rate of the base number of the lubricating oil and result in the precipitation of the viscosity index improver,thereby reducing its kinematic viscosity.
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