Could dimethyl ether power trucks in the future?

truck

Trucks have special requirements for their fuels. (Image: Kesu01 / iStock)

Research has been going on for a long time to make trucks more environmentally friendly – for example by using electric drives and hydrogen instead of fossil diesel. Another alternative fuel could be dimethyl ether, as researchers are now reporting. Accordingly, slightly modified diesel engines could be operated with the fuel. Tests on long-distance journeys are already under way.

Diesel vehicles have fallen into disrepute due to their high emissions of nitrogen oxides and fine dust. Alternatives to fossil diesel are therefore in demand. Electric drives are hardly suitable for long-distance commercial vehicles, however, because the batteries are too heavy, the charging times too long and the required charging capacities too high for competitive use. In contrast, hydrogen could be a future solution, as suggested under initial tests. And the first natural gas trucks will also be refueled on a trial basis with synthetic natural gas from excess green electricity from 2021.

Dimethyl ether – also a possible alternative?

But so-called dimethyl ether (DME) could also be suitable as an alternative fuel for trucks. This chemical is found in spray cans as a propellant, is a component of refrigerants in cooling systems and is widely used as an intermediate in the chemical industry – so that tens of thousands of tons of it are already being produced annually. The advantage: It can be produced inexpensively and with almost no loss from methanol, which can be obtained cheaply with electricity from solar and wind energy. In addition, dimethyl ether has similar properties to liquid gas and can therefore – unlike hydrogen – be transported and stored in liquid form in tanks under low pressure. And the technology for tank systems is also inexpensive and has been in use worldwide for decades. In addition, dimethyl ether burns cleanly and with little soot formation.

In order to find out whether dimethyl ether is also suitable as an environmentally friendly fuel for long-distance truck journeys, scientists led by Patrik Soltic from the Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa) are currently testing the chemical on a test engine. Volvo Trucks has been carrying out practical tests with experimental trucks in Sweden and the USA since 2013. A research project at the Ford Research and Innovation Center Aachen has also been running in Germany since 2016, in which an engine powered by DME was installed and tested in a Ford Mondeo. Building on this, Soltic and his colleagues have now set themselves the goal of driving vehicles with pure dimethyl ether – without lubricating additives.

Tests are running with converted diesel engines

The problem: an ordinary diesel engine is not completely suitable for a drive with dimethyl ether. It has to be converted in some points. On the one hand, unlike diesel fuel, the volatile dimethyl ether has practically no lubricating properties. Above all, this can damage the injection pump, which is usually installed and supplies the engine with the correct amount of fuel at a certain pressure. On the other hand, some materials and the combustion chamber in the diesel engine cannot simply be adopted. For this reason, the researchers have now developed a test engine with a new, oil-lubricated common rail pump and also converted the valves and valve seat inserts to a suitable material. In addition, the scientists used an electrically operated compressor for precise exhaust gas recirculation and also adjusted the combustion chambers and the compression ratio of the former diesel engine.

“Now we want to get to know the machine with the new fuel,” says Soltic. To do this, the researchers are initially testing the engine in the medium-load range that is typical for motorway operation, in which the engine has to deliver 100 kilowatts of power. “Then we modify the timing and pressure of the injection, among other things, and look at the exhaust gas values ​​and fuel consumption,” explains Soltic. During the test phase, the research team also repeatedly takes samples of the motor oil to examine chemical changes. The results are used to develop a specially adapted engine oil.

First results are promising

In an initial test phase it was already shown that the dimethyl ether operation could actually be a more environmentally friendly alternative to the diesel engine in the future – even for trucks on long journeys, according to the researchers. In addition to the emission-free production of the substance, there are even more advantages: “The big advantage is the opportunity to transfer a very high proportion of exhaust gas to the next filling of the cylinder in almost all operating conditions, using what is known as exhaust gas recirculation,” explains Soltic. “This technology makes it possible to save a lot of nitrogen oxides, which relieves the burden on exhaust gas cleaning downstream of the engine and allows future, stricter limit values ​​to be safely met.”

At the moment, however, further research is necessary to optimize the drive with dimethyl ether and to use it for everyday use. In addition, the scientists are still working on chemical processes with which dimethyl ether can be manufactured as efficiently as possible and on special production facilities.

Source: Federal Materials Testing and Research Institute

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