In 2016, Germany launched a 3-year study of oxymethylene ethers (OME) as clean diesel fuels with €800,000 (US$894,000). (Earlier post.) OMEs are promising synthetic diesel fuels with an enormous potential for the reduction of soot and NO_x emissions. Karlsruhe Institute of Technology (KIT) is the coordinator of that project, in cooperation with TU Kaiserslautern and TU München.

Now, researchers at the Technical University of Munich (TUM) as part of a separate project—the xME-Diesel project—have tested how OMEs behave in engines and have developed an optimized combustion process.

Synthetic fuels such as OMEs burn virtually free of undesirable by-products such as soot and hydrocarbons, and thus provide an additional air-quality benefit over other long-standing designer fuels. However, they also have disadvantages: production costs are higher than those of fossil fuels and there are no production facilities available yet.

The XME Diesel project, funded by the German Federal Ministry of Economics, aims to promote the use of OMEs. The overall goal is to build two demonstrator vehicles, one operating on dimethyl ether (DME) and one on dimethoxymethane (OME).

(A separate project, Kopernikus-Projekt P2X, is exploring the production and application aspects of oxymethylenether as a fuel and polymer. The interface to the other subprojects within “Power to X” is the use of hydrogen generated by renewable energy sources as well as carbon dioxide from various sources, e.g. industrial processes or power stations. The interdisciplinary research addresses the development of novel catalysts and processes as well as the evaluation of the synthetic fuels potential, considering kinetic, single-cylinder, full-engine, and vehicle investigations. )

Scientists from TUM’s Chair of Internal Combustion Engines are involved in the project, along with DENSO Automotive Germany, IAV and Ford Research and Innovation Center.

The TUM team investigated the behavior of OMEs in engines, the adjustments required to improve combustion efficiency and the degree to which harmful emissions can be reduced in comparison to fossil fuels.

First, the researchers did computer simulations and experiments on a single-cylinder engine testbed. They determined the optimal parameters for efficient combustion.

For example, the synthetic fuel has a lower calorific value than diesel, which means more fuel must be injected into the engine to achieve the same performance. The scientists thus adapted the injectors accordingly.

Furthermore, since the synthetic fuel does not produce soot, large amounts of exhaust gas can be recirculated into the engine without contaminating the intake. This approach inhibits the formation of nitrogen oxides because the recirculated exhaust gas prevents very high temperatures during combustion.

Next, the scientists tested the parameters on a full-engine testbed comprising a six-cylinder production engine that was adapted specifically to run on synthetic fuel. The tests on the full engine confirmed the previous results.

We determined that using this fuel can significantly reduce pollutant emissions. The Euro 6 level, the currently applicable limit, is easily met when using the synthetic fuel. We are also convinced that high-performance exhaust after-treatment can even reduce emissions to almost zero.

—Dr. Martin Härtl, who coordinates the project

OME made from waste CO₂ and electricity from renewable sources would even be carbon neutral.

Particularly interesting is the use of OME in vehicles and systems in which internal combustion engines cannot be readily replaced by battery-powered electric drives, explains Härtl. Examples include long haul trucks, energy provision in remote areas and the aviation and shipping sectors.

Further research in the field of OMEs at the Institute of Internal Combustion Engines is part of the project “OME – Environmentally Friendly Diesel Fuel Additives” (funded by the Agency for Renewable Resources with funds of the German Federal Ministry of Food and Agriculture) and the project “Sub-Zero-Emissions Diesel Engine” (funded by the Bavarian Research Foundation).