What is the potential of oxygenated methyl ether-based synthetic fuels for replacing fossil-based diesel in an compression-ignition combustion process? In the “XME Diesel” research project supported by FVV, funded as part of the “Neue Fahrzeug- und Systemtechnologien” [New Vehicle and System Technologies] specialist programme of the German Federal Ministry for Economic Affairs and Energy (BMWi), research institutes at RWTH Aachen University and the Technical University of Munich investigated the suitability of DME (dimethyl ether) and OME-1 (mono-oxymethylene ether) in collaboration with Denso, Ford and IAV. The main goal of the project was to adapt the combustion process to the physical and chemical properties of the new fuels in such a way that raw pollutant emissions are reduced significantly while the efficiency of the engine improves.
» DME is manufactured from methanol. In turn, methanol can be produced from solar or wind energy in many parts of the world, transported to Central Europe by ship and processed here – using plant engineering that already exists today. We would then have large quantities of a synthetic fuel available immediately. «
The collaborative research project "XME Diesel" looked into the question of whether synthetic fuels based on methyl ether are suitable as diesel substitutes. The result: If the right molecule is selected, CO2 emissions and pollutants will be reduced significantly.
Emission improvement of DME relative to diesel in WLTC
In terms of driving experience, the test vehicle - a Ford Mondeo with a 1.5-litre diesel engine - does not sound any different from a normal diesel vehicle.
DME is a liquid gas with a vapour pressure curve comparable to LPG. Therefore LPG-like tanks and components can be used for fuel supply.
The 1.5 l diesel engine had to be adapted for the DME injection components.
The DME injection system is operated by a control unit in the trunk. Engine and injection control communicate with each other via a specific CAN interface.
The literature quotes numerous individual investigations into low-emission or even soot-free combustion of methyl ether-based fuels. When used in a vehicle, however, carburation and combustion must be adapted to the properties of new fuels. If this is successful, synthetically produced fuels can not only contribute towards air pollution control, but also make road traffic climate-friendly.
» Sector coupling via the use of electricity-based fuels is extremely important for future mobility concepts, as it links innovative energy and transport topics in a targeted manner. The XME diesel project was funded as part of the ‘Neue Fahrzeug- und Systemtechnologien’ project, which focuses on the research and development of internal combustion engine powertrains fuelled by alternative energy sources and also offers a CO2-neutral perspective for existing vehicles in the medium term. «
The first task was to develop an injection system capable of handling the physical properties of DME and OME-1, which are very different to those of fossil diesel. The subsequent tests on a single-cylinder engine were primarily aimed at designing a suitable combustion process. Alongside these basic investigations, test series were conducted on fully assembled engines – these confirmed the benefits of the fuels in terms of soot emissions. Following this, two demonstrator vehicles were modified to run on DME and were subjected to an emission test as per the WLTP.
» The excellent results were mainly thanks to the broad support we received from the consortium partners and the research group. Everyone who worked on this project was highly motivated. «
Even the tests on the single-cylinder engine illustrated that soot-free combustion is possible with the two fuels; furthermore, it was possible to match the power density of the combustion engine run on fossil fuels using DME. Tests on the fully assembled car engine confirmed the predicted emissions behaviour of the single-cylinder engine while producing the same CO2 emissions as the corresponding diesel engine. A further reduction in CO2 (up to approximately 10%) can be achieved when the combustion process and the air and exhaust gas path are adapted for operation with DME. A commercial vehicle engine was built for the test with OME-1; using this, significant emission benefits were also demonstrated for application-specific load points. Finally, two cars were equipped with the optimised engine concept developed on the test bench and a liquid gas tank system derived from a conventional LPG system. In the WLTC test cycle, these demonstrator vehicles (with unlimited driveability) achieved completely soot-free operation while reducing nitrogen oxides by a third at the same time. Despite the air path and combustion process not being adapted in the vehicle, CO2 emissions remained almost constant. Final tests on the single-cylinder engine showed that the engine efficiency can still be raised considerably – and that emergency operation with conventional diesel fuel is possible with a minimised worsening of emissions.
XME Diesel | (Bio) methyl ethers as alternative fuels in bivalent diesel combustion processes | Project No. 1005 | Collaborative research | Funding No. 19U15007 A-D
We would like to thank Oberon Fuels and Prins Westport for providing dimethyl ether and DME tank systems.
2015-06-01 to 2019-03-31
Dr.-Ing. Werner Willems
Ford Research and Innovation Center Aachen
Dr.-Ing. Bernhard Koonen
TÜV Rheinland Consulting GmbH
1 | IAV GmbH Ingenieurgesellschaft Auto und Verkehr
Head of research:
Dipl.-Ing. Thorsten Tietze
2 | DENSO AUTOMOTIVE Deutschland GmbH
Head of research:
Dr.-Ing. Jost Weber
1 | Institute for Combustion Engines (vka) - RWTH Aachen University
Head of research:
Univ.-Prof. Dr.-Ing. Stefan Pischinger
2 | Institute of Internal Combustion Engines (LVK), Department of Mechanical Engineering - Technical University of Munich (TUM)
Head of research:
Prof. Dr.-Ing. Georg Wachtmeister
Research Association for Combustion Engines eV
Lyoner Strasse 18
60528 Frankfurt am Main
T +49 69 6603 1345