Physico-chemical properties and fuel characteristics of oxymethylene dialkyl ethers

Oligomeric oxymethylene dimethyl ethers (OMDMEs, CH3O–(CH2O)n–CH3) are promising diesel fuel additives, which can reduce soot formation as well as NOx emissions. Due to the poor availability of high purity OMDMEs a comprehensive characterization of diesel standards was not feasible until now. Two types of oxymethylene dialkylethers (OMDMEs and oxymethylene diethyl ethers, OMDEEs) were synthesized, purified and characterized with respect to their physico-chemical and fuel properties. Density, melting point, flash point, auto ignition point as well as lubricity, kinematic viscosity and surface tension of OMDMEs and OMDEEs were measured and compared to the corresponding n-alkanes. Fuel requirements such as boiling points, flash points and surface tensions can be fulfilled by OMDMEs and OMDEEs. Furthermore, OMDMEs (n = 3–5) and OMDEEs (n = 2–4) are, due to their high cetane numbers of 124–180 and 64–103, particularly promising since cetane numbers in this range can lead to improved motor efficiency and smoother fuel combustion. Additionally, the heat of combustion as well as the standard enthalpy of formation and reaction were determined. Apart from somewhat lower heating values, OMDMEs exhibit fuel properties similar to conventional diesel complying the required fuel standards without the need of changing engines or fuel infrastructures.