An evaluation of the implementation possibilities of power-to-fuel (PTF) technologies by a team from Forschungszentrum Jülich GmbH in Germany recommends the PTF products DME, OME3-5 and n-alkanes as suitable diesel alternatives for the transportation sector. PTF processes essentially use renewable energy, CO2 and water to produce fuel, as in Audi’s targeted e-fuels projects. (Earlier post.) A paper on the Jülich study is published in the journal Fuel.
The simplest implementation strategy for such electrofuels would be a gradual market penetration by means of blending with conventional diesel, the authors suggested. Potential blending combinations highlighted in the paper include: fossil diesel + n-alkane cut; fossil diesel + OME3–5; Fossil diesel + n-alkane cut + 3-5; and n-alkane cut + OME3–5. The last blend—a suitable n-alkane cut mixed with OME3-5—has the greatest potential for increasing engine efficiency and reducing pollutant emissions. In addition, fossil diesel would no longer be required.
|Power-to-fuel, interlinking the energy and transport sectors. Schemme et al. Click to enlarge.|
The investigations reveal that the lower heating value of fuels containing O has no negative impacts on engine efficiency, not even in existing engines. The electrofuels examined have a significantly higher cetane number than fossil diesel, which usually promises potential for improved engine performance. Exhaust gas values were also greatly improved by the use of electrofuels. Since the tests of engine efficiency and exhaust gas values of all sources reviewed were conducted in test engines that had not been optimized for the used fuel, further potentials regarding emission reduction and the optimization of engine efficiency are expected. With regard to a conceivable implementation strategy, the critical aspects are, above all, viscosity as well as boiling, flash and melting temperatures. Suitable additives can mitigate any connected problems. The n-alkanes and OMEn used are usually not pure substances, but instead mixtures of molecules with different chain lengths. Their composition depends on the production process. Analyzing the potential of various OMEn as diesel fuels identifies OME3–5 as the most promising mixture.—Schemme et al.
The researchers reviewed liquid fuel alternatives that could be used in existing vehicles in the transportation sector. Blend capability was a requirement—pushing methane aside for the purposed of their evaluation. The researchers subdivided their candidate fuels into three main groups:
- Hydrocarbons (olefins, paraffins, aromatics)
- Alcohols (methanol, ethanol,…)
- Ethers (DME, OMEn)
In addition to the properties in DIN EIN 590 (fossil diesel), the team considered:
- Mixture formation with fossil diesel
- Molecular structure
- Heating value and air demand
- Vaporization characteristics
- Combustion characteristics, emissions
- Social acceptance
Steffen Schemme, Remzi Can Samsun, Ralf Peters, Detlef Stolten (2017) “Power-to-fuel as a key to sustainable transport systems – An analysis of diesel fuels produced from CO and renewable electricity,” Fuel, Volume 205, 2017, Pages 198-221 doi: 10.1016/j.fuel.2017.05.061