XME: Alternative fuels for the diesel combustion process

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. «
Dr.-Ing. Werner Willems (Ford Research and Innovation Center Aachen)


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. «
Dipl.-Ing. Dietmar Goericke (FVV e. V.)


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. «
Dipl. Wirt.-Ing. Ralf Thee (FVV e. V.)


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.



Public Funding

3.500.000,00 EUR

Time Period
2015-06-01 to 2019-03-31

Federal Ministry for Economic Affairs and Energy (BMWi)

Scharnhorststrasse 34-37
10115 Berlin


Dr.-Ing. Werner Willems
Ford Research and Innovation Center Aachen

Dr.-Ing. Bernhard Koonen
TÜV Rheinland Consulting GmbH

Project Partner

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

RTD Performers

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

Technical University of Munich (TUM)

Institute of Internal Combustion Engines (LVK)

Arcisstrasse 21
80333 Garching

RWTH Aachen University

Chair of Thermodynamics of Mobile Energy Conversion Systems (tme)

Forckenbeckstrasse 4
52074 Aachen

Project Management

Ralf Thee

+49 (0) 69 6603 1349
+49 (0) 69 6603 2349

Research Association for Combustion Engines eV

Lyoner Strasse 18
60528 Frankfurt am Main
T +49 69 6603 1345