Oxymethylene Ethers: Evaluating the Optimum Fuel Composition from an Engine Standpoint with Respect to Emissions and Combustion Performance

The mobility landscape changes drastically. Ever-stricter regulation limits lead to extensive efforts in reducing emissions and fuel consumption. While diesel engines are the superior device in on-road transportation in terms of practicality and fuel consumption, they suffer from a distinct trade-off in particulate matter (PM) and nitrogen oxides (NO_X) to the nature of the diffusive combustion process. The oxygenated fuel oxymethylene ether (OME) displays great potential to resolve this trade-off in multiple ways. With respect to engine-out emissions, the near soot-free combustion provides great leverage to drastically reduce NO_X with little to no penalty in terms of particle emissions. Apart from its benefits in engine applications, OME displays high potential to reduce well-to-tank carbon dioxide (CO₂) emissions. With an increasing fraction of CO₂-neutral fuel production, the significance of engine-out CO₂ decreases, since it would be embedded and locked into a closed circuit of OME production and usage, and therefore effectively counteracts the ever-stricter CO₂ emission regulation limits.

In this investigation, the authors provide a detailed analysis on the impact of OME’s fuel chain length on combustion performance with high exhaust gas recirculation (EGR) rates and specific mixture compositions. This ultimately allows for a sophisticated discussion on possible OME mixtures from an engine standpoint. First, neat OME are investigated at swept EGR rates in order to evaluate the impact of the fuel chain length on the combustion process and emissions. Second, it will be evaluated whether emissions and thermodynamic combustion properties of any arbitrary OME mixture can be derived solely based on the data obtained with neat OME, i.e., approximating the behavior of mixtures from neat OME combustion. Third, these findings will be put into perspective by discussing requirements to the OME market introduction from an engine standpoint. Key fuel features will be evaluated with respect to their significance to market introduction and future, large-scale OME production.