Diesel engines emitting less carbon
Engineers from ETH Zurich have created a platform that determines how the CO2 emissions of diesel engines can be reduced based on engine measurements and tests with various fuels. We talked to project manager Dr. Christophe Barro.
Dr. Christophe Barro is senior research associate at the Aerothermochemistry and Combustion Systems Laboratory LAV lead, by Prof. Konstantinos Boulouchos.
Where do we start if diesel engines are to emit less CO2?
In principle, you can start with the fuel, or optimise the engine. With the ReVerDi platform, we combine both approaches, which leads to higher CO2 reductions overall.
The platform consists, to put it simply, of a test engine and software. We first developed a model that recognises different fuels. In the course of the project, we identified four different fuels and fuel blends and created something like “fuel fingerprints”. To do this, we studied the different stages of the combustion process in the engine for each fuel in more detail.
Eventually, the platform should be able to automatically detect the fuel composition in the engine and optimise the engine’s operating parameters accordingly.
What alternative fuels can be used in diesel engines?
We tested neat GTL (Gas To Liquid), a synthetic diesel that is currently mostly produced from natural gas. However, GTL can also be produced from carbon monoxide and hydrogen (both extracted from the air). GTL has the additional advantage that it does not contain any aromatic compounds which produce soot when combusted. We then used a mixture of 20 percent GTL and 80 percent diesel. We also tested mixtures of OME (oxymethylene dimethyl ether) with diesel in the ratios 7/93%, and 15/85 % respectively. OME can be produced from air or biomass, and would therefore be CO2 neutral. Furthermore, we tested HVO (Hydrogenated Vegetable Oil, a sustainable fuel) and a mixture of HVO, OME plus a stabiliser. The latter is potentially 100% renewable and we named it R100.
For the purpose of comparison, we used neat diesel.
How is the engine optimised? Can this be done while the engine is running?
State of the art diesel engines contain software that enables different operating modes. We used a single-cylinder heavy-duty 4-stroke diesel engine for our measurements. Apart from the engine, turbochargers and exhaust fume treatment are key parts of the system. The operating temperature again is very important for all three parts.
We tried to find out to what degree the different fuels would change the high-pressure processes in the engine, and how the engine strategy could be optimised accordingly in a second step. For example, the engine can be run differently, if less soot is produced upon combustion. For combustion, the most important parameters are boost- and injection pressure, injection rate, and exhaust gas recirculation.
Currently, only diesel is available at petrol stations. However, this could change soon.
Yes, several of the blends and alternative fuels mentioned above are compliant with the regulatory requirements for diesel. The diesel blend with 7 percent OME, diesel containing 20 percent GTL or HVO, as well as R100, would in principle be marketable already and could be sold at any petrol station.
Among the blends currently approved as diesel-like, R100, the mixture of HVO, OME with a stabiliser, stands out.
Yes, with this blend of about 15 percent OME in HVO plus stabiliser, soot emissions have been reduced substantially, even more than by using neat GTL as a fuel.
Oxymethylene dimethyl ethers such as OME exist in different variations; all variations are compounds containing oxygen, so-called oxygenates. The oxygen content improves the combustion process and leads to significant reduction of soot. However, depending on the oxygenate used and on its ratio in diesel, certain blends can lead to higher emissions of nitrogen oxides, which is also undesirable. Nitrogen oxides adversely affect human lungs, the climate, smog and ozone formation. Additionally, engine efficiency might be diminished. That is the 3-dimensional trade-off we usually deal with: efficiency, soot, nitrogen oxides. If one of those factors improves, the others often worsen. With certain variations of OME, though, both soot and nitrogen oxides can be reduced substantially. There is the additional advantage that OME can be used with current engines and fuelling infrastructures. However, it is expensive.
Were the companies that produce these fuels involved in the project?
Yes, Neste Oil has provided us with HVO. ASG Analytics provided OME and the stabiliser at a reduced rate. In addition, we partnered with ETH spin-offs combustion and flow solutions GmbH and Vir2sense GmbH. In similar projects using OME as a test substance, FPT and Liebherr are involved.
The project is financed by the Swiss Federal Office of Energy. Besides the ETH Institute of Energy Technology, EMPA is a research partner.
What other companies could take advantage of the platform ReVerDi?
First and foremost, engine manufacturers. But also any company using diesel engines. Take data centres, for example, which use diesel engines as backups to secure power supply.
The results of ReVerDi could help to reduce CO2-emissions of existing vehicle fleets. That is the main advantage over technologies such as electro mobility.
Contact / Links:
Institute for Energy Technology
Publication:
Parravicini M., Barro C., Boulouchos K., “Compensation for the differences in LHV of diesel-OME blends by using injector nozzles with different number of holes: Emissions and combustion”, Fuel Volume 259, 1 January 2020, 116166. external pagehttps://doi.org/10.1016/j.fuel.2019.116166
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