Drop-In Performance of Propyl- and Butyl-Terminated Oxymethylene Ethers in a Compression Ignition Engine

Oxymethylene ethers (OMEs) have been proposed for use in diesel engines as a high-reactivity fuel with reduced soot emission. Historically, the focus on methyl-terminated OMEs has limited drop-in applicability. In this work, a set of extended-alkyl OMEs with methyl, propyl, and butyl terminations are tested in an unmodified 4.5L Deere diesel engine, neat and in various blends with ultra-low-sulfur diesel (ULSD). Engine operability and emissions data are collected for the various fuel blends. External laboratory testing against the ASTM D975 standard demonstrates that a blend of 30% butyl-terminated OMEs with ULSD meets all ASTM standard requirements except lubricity. It is shown that the OMEs and OME–diesel blends demonstrate shorter combustion durations, as defined by the 10%–90% heat release timing, than the ULSD control. Engine brake efficiency is unaffected by OME usage, while specific fuel consumption increases in proportion to the reduced heating values of OMEs. Particulate emissions are reduced to a greater extent for all OMEs and OME blends than the blend ratio would suggest when using the yield sooting index as an estimator. NO_x emissions from the OMEs and OME blends are increased with respect to ULSD; however, the increase in NO_x is much lower than the decrease in particulates, indicating a possible improvement in the soot/NO_x tradeoff seen in combustion engines. Two observed downsides are increases in unburned hydrocarbon and formaldehyde emissions. Overall, butyl-terminated OMEs are recommended for future study as the ideal diesel blendstock studied in this work, with good balance of matching properties and improved emissions performance.