A research consortium led by Ford Research and Innovation Center Aachen is currently investigating the technical conditions under which diesel vehicles can run on dimethyl ether (DME) as an alternative fuel. DME is a gas that has similar physical properties to the liquid gases propane and butane and is also liquid at an atmospheric pressure of 5 to 6 bar.
Like its sister molecule methanol, DME can be produced particularly efficiently and cost-effectively as a climate-neutral energy source and is characterized by emission-reducing properties in diesel engine combustion (virtually soot-free when used as a pure fuel with simultaneous reduction of nitrogen oxides). This is of interest, for example, in freight transport, where more than 95% of medium- to heavy-duty commercial vehicles still use diesel engines.
Hardware-in-the-loop test bench for the qualification of the liquefied gas dimethyl ether as a fuel. Photo: TEC4FUELS
Technical adaptations are required to enable existing and new vehicles to run on dimethyl ether. Previous studies have shown that it is possible to operate diesel engines with 100% DME, but that this requires significant effort (injection components, combustion process, exhaust gas aftertreatment, tank system) in terms of conversion.
The research consortium is therefore investigating new DME-based fuel blends as solutions for existing vehicles that require minimal retrofitting effort and are therefore cost-effective. Ideally, the conventional system components already installed in the vehicle are retained.
Another advantage of this solution is that, with DME/diesel blends, both the lubricating properties and the energy content are virtually retained at the appropriate blending rate. On the one hand, the fuel blends under investigation can be refueled premixed (static blending), but would also allow both components to be blended upstream of the high-pressure fuel pump (potentially dynamic blending). With dynamic blending, even flex-fuel operation (diesel or DME/diesel) would be possible while retaining the original diesel system.
In addition to the technical development of such a retrofit solution, the project also focuses on determining possible fuel blends.
Tec4Fuels GmbH, a competence center for conventional and alternative fuels, fuels and lubricants and their application in existing and new technologies, is testing dimethyl ether in blends with liquid fossil or renewable fuel components such as mineral oil-based diesel, paraffinic fuels in accordance with EN15940 and biodiesel for use in diesel engines.
This suitability testing relates both to the compatibility of the fuels in varying blends with each other and their impact on the materials of fuel-carrying components, such as high-pressure pumps, fuel filters, seals and injectors. Initial studies indicate that a blend of 80% petroleum-based diesel and 20% DME meets compatibility requirements. Other DME blends, such as with fatty acid methyl ester (biodiesel) or gas-to-liquid products (paraffinic diesel), will be investigated as the project progresses.
The selection of suitable efficient and sustainable propulsion technologies for future mobility requirements is complex and is determined not only by the need for environmental compatibility (CO2 and pollutants), safety and feasibility, but above all by affordability at the consumer end. Dimethyl ether offers advantages such as sufficient energy density and ignition and combustion properties comparable to diesel fuel, with significantly low soot formation, which enables the increase of the compression ratio and thus an increase in thermodynamic efficiency and more efficient fuel consumption. In addition, when DME is produced as eFuel, it is possible to reduce well-to-wheel emissions of CO2 by more than 90%.
The research project is funded by the German Federal Ministry for Economic Affairs and Energy based on a resolution of the German Bundestag.