The quest for efficient oxygenated fuels: Examining interactions between lubricant components and oxygenates

Abstract

This work empirically evaluated oxygenated blendstock - lubricant compatibility using a novel but simple method. The reactivity or compatibility was evaluated via gas chromatograph equipped with a flame ionization detector (GC-FID) before and after heating for 2 h at 150 °C, which would roughly mimic conditions encountered in the crankcase of a Spark Ignition (SI) or Compression-Ignition (CI) engine. Although 150 °C does not mimic combustion chamber temperatures, it may provide an insight of potential in-cylinder interactions. Five oxygenate blendstocks spanning several functional groups and chain lengths (prenol, isoprenol, butyl acetate, isohexanol, polyoxymethylene dimethyl ethers) were evaluated in a base fuel with nine variations of lubricant components of controlled concentrations, including fully formulated commercial lubricants. Baseline comparative examples were also generated, to decouple the effect of the oxygenate on the mixture, by heating only the base fuel with the lubricant component. Results demonstrate the relative compatibility between noted lubricants and oxygenates in base fuel upon heating. This was illustrated by minimal to no changes in the GC-FID traces. However, reactions of several of the chosen lubricants, especially Molybdenum di(2-ethylhexyl) phosphorodithioate (Molyvan L) and zinc dialkyldithiophosphate (ZDDP), with prenol and polyoxymethylene dimethyl ethers blendstocks showed substantial side reactions compared to corresponding baseline examples. Control experiments without oxygenates but comprising the same lubricant components showed no change in the mixture with heating. We concluded the reactivity is due to the oxygenate and not the components of the base fuel. This preliminary work is valuable in establishing trends as well as providing useful information when a new component is introduced in the fuel.