Applied Energy, Vol.239, 1242-1249, 2019
Potential of long-chain oxymethylene ether and oxymethylene ether-diesel blends for ultra-low emission engines
Oxymethylene ether (OMEn) has recently drawn high attention due to its high pollutant emission reduction potential and the sustainable synthesis pathways involving carbon capture and renewable hydrogen. In this work, five blends of OMEn in diesel fuel in addition to pure OME3.5 and diesel fuel as reference were investigated in a single cylinder engine. Each OMEn-Diesel blend was prepared with a different chain length, ranging from OME1 to OME5. The blending ratio of OMEn in fossil diesel fuel was set to 35 vol%, corresponding to a similar to 23.5% diesel fuel substitution on a heating value basis. We find that OMEn contributes to improved oxidation conditions, resulting in a more complete combustion compared to conventional diesel fuel operation. This is reflected by reduced emissions of unburned hydrocarbons and carbon monoxide (up to 90%), higher burned mass fractions after the main combustion phase, higher indicated efficiencies (up to +3%) and lower exhaust gas temperatures (up to -70 degrees C). Furthermore, while pure OMEn burns soot-free, a significant soot reduction was measured for the OMEn-Diesel blends. Based on the findings of this work, it is concluded that from a combustion and emission point of view, the OMEn chain length is of minor importance for applications where OMEn is blended with diesel fuel up to a ratio of 35 vol%. Thus, the main considerations for an optimal OMEn chain length range should focus on aspects like fuel properties and OMEn synthesis. In this regard, a simple and efficient synthesis process (e.g. synthesis of OME1) must be weighed up against favorable fuel properties of the synthesis product (e.g. OME3-5). Hence, bearing in mind that OMEn is not a drop-in fuel and will always demand a dedicated engine, the preference of long chain OMEn over OME1 is not straight forward and strongly depends on the application.