Bad air in town (Part III)
The new through station has commenced operations. Local traffic flows more smoothly as a result; many commuters leave their cars sitting in the garage. The city railways have expanded their capacities accordingly. But there is more: part of the bus fleet now runs on electricity from renewable sources – with noticeable consequences for the city residents, as the noise level on the streets has fallen correspondingly. The types of engines used in cars have also become more diverse: electric vehicles with batteries or fuel cells are on the road, but also a rising number of cars powered by natural gas or synthetic fuels.
Researchers are already working towards more environmentally friendly fuel. “If you want to make diesel propulsion cleaner, you can start at the engine. Alternative fuels are another possibility”, explains Prof. Ralf Peters from the Institute of Energy and Climate Research (IEK-3). “We are focusing on these and looking for substitute compounds that are customized, synthetic and that burn much cleaner than, for example, diesel: they generate significantly fewer soot particles, i.e. particulate matter. One can then fully concentrate on reducing the amount of nitrogen oxides in the exhaust gas through the engine settings.”
According to Ralf Peters, anyone who wants to reduce the pollutant emissions of diesel vehicles via the engine settings alone will be on the horns of a dilemma: “If the particulate matter goes down, the nitrogen oxides go up – and vice versa.” The nitrogen oxides result from the the diesel engine’s usually high combustion temperatures. If the temperature is lowered through partial exhaust gas recirculation, for example, less nitrogen oxides are formed, but the amount of soot particles increases.
Possible clean designer fuels for diesel engines are primarily of substances such as alcohols and ethers, which themselves already contain oxygen. Oxygen prevents carbon from accumulating to form solid soot particles inside the fuel droplets. Methanol, the simplest of all alcohols, is considered promising – either directly as fuel or as a precursor for other synthetic fuels such as dimethyl ether (DME), oxymethylene ether (OME) or Fischer-Tropsch products.
“However, there is as of yet no optimum fuel. It is difficult to predict which candidate will win the race. On the one hand, the production processes and costs play a major role; on the other hand, so do the carbon footprints of the various fuels. Even with synthetic fuels, CO2 is released during combustion,” Peters points out. Comparing the production processes of various fuels is what primarily occupies him and his team.
Therefore, the synthesis should be as sustainable as possible, starting with the basic substances and including the various process steps to the necessary energy. Peters summarizes: “Not only air quality benefits from clean combustion in the diesel engine then, but also the climate.” For example, one possibility is to break water down into its components hydrogen and oxygen – with excess electricity from wind and solar power plants. The energy carrier, hydrogen, obtained in this way can be converted into fuel with CO2 from industrial waste gases or power plants.
Measures to improve air quality in cities
Regulation of traffic flows
Retrofitting of commercial vehicles
New tyre materials
It is precisely this approach that Jülich researchers and partners of science and industry pursue in the Copernicus project “Power-to-X” (P2X): electricity from renewable energies that is not demanded at times – “Power” – is to be used to produce various products – “X” – such as hydrogen as an energy carrier, chemical raw materials or alternative fuels. Specifically, the project partners are developing a way to produce OME sustainably. OME is already produced in small quantities today from a mixture of carbon monoxide and hydrogen, the synthesis gas. In the “P2X” project, several Jülich institutes are working with industrial partners to produce this synthesis gas sustainably in just one process step. Partners from Karlsruhe Institute of Technology, RWTH Aachen University, and from the industry will then convert the synthesis gas into OME or improved petrol and diesel fuels as well as kerosene.
Prof. Dr. Rüdiger-A. Eichel from the Institute of Energy and Climate Research (IEK-9), one of the three coordinators of “P2X”, is convinced: “Power-to-X will play a role in all areas of life in the future, including mobility. In the same way that petrol and diesel engines coexist, future mobility will be diverse and depend on batteries, fuel cells and sustainably produced alternative fuels.”
ILLUSTRATIONs: BERND STRUCKMEYER