E fuels
The liquid fuel is artificially produced using regenerative resources. It can be used in combustion engines just like fossil fuels. E-fuels burn in a climate-neutral manner – only as much CO2 is released as was previously bound in the production process.
Opel Post: Mr. Eitel, Mr. Döhler, Opel is part of “C3-Mobility”, a consortium of research and industry that has investigated the extent to which combustion engines can be powered by e-fuels. But first: what exactly are e-fuels?Dr. Felix Eitel: Classic fuels that you get at the gas station are based on crude oil, a fossil fuel. Synthetic fuels, on the other hand, are artificially produced. BioFuels are based on biomass, for example. In the case of e-fuels, the subject of our investigation, the starting point is green electricity and water. The green electricity is used to first produce hydrogen and then fuel in a multi-stage process – depending on the chemical compound, the properties of petrol, diesel, but also kerosene can be simulated. The special feature: the manufacturing process makes the fuel CO2-neutral.
Opel Post: To what extent? Arndt Döhler: In order to be able to produce e-fuels from hydrogen, you need CO2. If the required CO2 is taken from the air or from industrial exhaust gases, so-called point sources such as lignite-fired power plants, combustion engines can be operated in a climate-neutral manner. Don’t get me wrong: Combustion of e-fuel basically produces a similar amount of exhaust gases as combustion of conventional fuel. But during the production of the e-fuel, the CO₂ is first bound, the greenhouse gas becomes a raw material, so to speak. You can compare this to burning wood – only as much CO2 is released as was previously stored in the wood. The bottom line is that no additional CO2 is released into the atmosphere.
“If you drive an internal combustion engine with e-fuels instead of gasoline, no more CO2 is emitted than was removed from the atmosphere to produce the synthetic fuels.”
–Arndt Doehler –
Can internal combustion engines be used with the synthetic fuel 2-Butanol? The test drives with an Opel Grandland came to a clear result.
From the simulation to the engine test bench to the test vehicle: Group Manager Arndt Döhler (right) and Senior System Engineer Dr. Felix Eitel accompanied the project on behalf of Opel for three years.
Opel Post: Opel has launched an electric offensive: By 2024, all Opel models will also be available in electrified versions; from 2028 onwards, the company will be focusing entirely on battery-electric vehicles in Europe. How does this strategy fit in with your research topic, which is aimed at vehicles with combustion engines?Arndt Döhler: There’s no question that the proportion of electric cars is increasing rapidly. Last year alone, more than 350,000 new electric vehicles were registered in Germany. But the potential use of e-fuels is also about the old stock. And it still consists mainly of cars with combustion engines – around 46.5 million in numbers. Alone in Germany. In other words: There are already 46.5 million potential electric vehicles on German roads. We would only have to operate them with green electricity-based CO2-neutral fuel!
dr Felix Eitel: If you want to effectively reduce emissions in the transport sector, not only new cars but also existing vehicles will have to be reduced in the future
contribute to CO2 reduction. E-fuels can make a significant contribution to this. So it’s not about an “either/or” scenario, but about an additional building block. If only the German passenger car fleet were operated with e-fuels, the annual C
O2 savings potential at around 120 million tons. That would correspond to a reduction of around 15 percent in relation to Germany’s total CO2 emissions. E-fuels can now also be mixed with fossil fuels, which is known as “blinding”. If you were to add just 1 percent e-fuels to the entire German fuel mix, you could use the equivalent of 1 percent of the fleet C
Operate O2-neutral – that corresponds to 465,000 vehicles. This is in the same order of magnitude as the current new registrations of e-vehicles that Arndt just mentioned. It illustrates the great potential that could be tapped here and that should be used in the interests of society!
bezels
E-fuels do not have to be used in their pure form, they can be mixed with fossil fuels, which is called blinding.
”
If you want to reduce emissions in the transport sector quickly and effectively, not only new cars but also the existing fleet must contribute to reducing CO2 emissions.”
– Felix Eitel –
drop-in capability
The synthetic fuel corresponds to the conventional fuel in all essential properties. It can therefore be used directly – without any technical adjustments.
Opel Post: From the production of regenerative fuels to market launch scenarios – the “C3 Mobility” project is pursuing a holistic approach. There are a good 30 partners who have completed 27 work packages in five areas. What exactly is the part that Opel played in this? Arndt Döhler: On the Opel side, colleagues from the design, laboratory, simulation, testing and workshop departments were involved. Together with the RWTH Aachen University and the company Tec4Fuels, we have examined a promising candidate among synthetic fuels: 2-butanol, an alcohol. With an octane number of 105, the fuel is even more knock-resistant than classic premium petrol. And thanks to its high energy density, it is compatible with conventional fuel pumps and injectors. Numerous simulations were carried out before the first hardware test. Among other things, we examined the spray pattern of the injector when using 2-butanol. Only after the virtual “proof of concept” did we run tests with a real engine on the test bench.
Opel Post: Which engine was used on the test bench? dr Felix Eitel: It was a 1.2-litre three-cylinder petrol engine. A series engine, so to speak off the shelf without any modifications. We tested pure 2-butanol, but also mixtures with fossil and synthetic petrol. The tests have shown that the engine can be operated in all variants. What is exciting is that if you mix conventional, i.e. fossil, petrol with 2-butanol or synthetic petrol, the e-fuel acts as a kind of booster – the higher the synthetic proportion in the mixture, the less fossil CO2 the combustion releases.
Arndt Döhler: I would like to point out here that an important part of the project was to test the so-called backward compatibility of the fuels in accordance with EN228 in the existing fleet.
Opel Post: Backwards compatibility according to EN228 – what is behind it?
dr Felix Eitel: The EN228 standard describes the current, commercially available petrol that you can already fill up at the pump today. In addition to 2-butanol, we tested how our engines react to synthetic gasoline according to this current standard. Specifically: A synthetic fuel according to EN228 is a so-called drop-in fuel. And these drop-in fuels can already be used today in all engines on the market without any restrictions. And it is precisely this drop-in capability that enables the large lever in CO2 reduction described.
Climate-neutral fuels
C3-Mobility is a joint project funded by the Federal Ministry for Economic Affairs and Energy. The goal: to develop CO2-neutral ways for future mobility. The project focuses on synthetic fuels based on methanol. The entire value chain is considered, from production to market launch. The consortium includes 30 partners from energy supply, process engineering, engine and vehicle construction as well as research and development. Within the consortium, Opel examined the vehicle suitability of synthetic fuels in small-volume gasoline engines under real driving conditions.
Successful practical test: Great importance was attached to a smooth start “under the key” during the calibration. And that already during the simulation and the subsequent optimizations on the engine test bench.
A Grandland full of measurement technology: The value of Lambda=1.00 indicates the stoichiometric combustion of the fuel-air mixture. It is the same value as in a standard fuel Grandland production vehicle. Additional components for optimal exhaust aftertreatment are therefore not required.
Opel Post: In order to test the practical suitability of the e-fuel under real conditions, you chose an Opel Grandland with the 1.2-liter petrol engine as the test vehicle in a further step. You have optimized the unit for use with 2-butanol. What surprises were there on the street?
Arndt Döhler: None – despite the massive modifications to this engine. In order to exploit the full potential of 2-butanol, the compression ratio has been increased to 13:1. During the approximately 3,000 kilometers that we have traveled on the road and on the test bench so far, we have tested the engine calibration developed on the test bench – and confirmed its quality. Whether engine cold start at 10 degrees or exhaust roll test: The practical test under real conditions has confirmed the compatibility in all respects – also with regard to the applicable Euro 6d emissions standard. The emissions could be complied with.
Opel Post: Not many people have ever driven a car powered by e-fuels – what remarkable experience have you had?
dr Felix Eitel: (laughs) Unfortunately I have to disappoint you. Our vehicle is equipped with measuring technology to record temperature, pressure and lambda while driving and it is also wrapped in the “C3 Mobility” design, but everything else is largely unspectacular. You can fill up with liquid 2-butanol like normal fuel. You don’t notice any difference while driving. But that is exactly the big advantage of synthetic fuels: basically nothing changes for the driver.
“We have confirmed its suitability for practical use: the internal combustion engine can be used with synthetic fuel.”
– Arndt Doehler –
Opel Post: The work packages have now been completed, and the final event with all project participants will take place soon. What is your conclusion?Dr. Felix Eitel: Our research results are promising and show the high potential of e-fuels: 2-Butanol can already be used in existing engines without major modifications. The synthetic fuel used could also be used in engine tests and special material tests without loss of performance or problems and did not lead to any failures. These results are also supported by the investigations of the other project partners in C³-Mobility and let us look to the future with optimism for the future use of e-fuels.
Arndt Döhler: We have confirmed the suitability for practical use: combustion engines can be used with the synthetic fuel 2-butanol and synthetic gasoline. A central advantage of this solution is that the existing logistics, distribution and tank infrastructure is already in place. A disadvantage of 2-butanol and synthetic fuel in general is currently the high price. Politics is also important here. For example, the price of fossil fuels and synthetic fuels could be equalized by adjusting the mineral oil tax.
The potential of e-fuels demonstrated: On the Opel side, colleagues from the design, laboratory, simulation, testing and workshop departments were involved in the project. Shown here are (from left) Felix Eitel, Niklas Neumann, Johannes Neuhäuser, Martin Schumann, Timo Beck, Arjun Chandrashekar, Jan Fritzsche, Arndt Döhler and Gregor Ochmann.
June 2022
Interview: Tina Henze, photos: Andreas Liebschner/Opel; Adobe Stock