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Audi begins initial engine testing of Global Bioenergies, Fraunhofer e-gasoline

Audi remains convinced of the potential of the fuels e-gas, “e-benzin” (e-gasoline) and e-diesel and is continuing to pursue its e-fuels strategy. (Earlier post.) Audi and its development partners Global Bioenergies S.A. (earlier post) and the Fraunhofer Center for Chemical Biotechnological Processes (CBP) now report that they have for the first time produced a sufficient quantity—60 liters (15.9 gallons US), the largest batch yet produced—of synthetic Audi e-gasoline for initial engine tests.

Like all Audi e-fuels, the new fuel has many advantages. It isn’t dependent on crude oil, it is compatible with the existing infrastructure and it offers the prospect of a closed carbon cycle.

—Reiner Mangold, Head of Sustainable Product Development at Audi AG

Audi “e-benzin” (e-gasoline) is essentially a liquid isooctane. It is currently produced from biomass in a two-step process. In the first step, Global Bioenergies produces gaseous isobutene (C4H8) in a demonstration plant. In the second step, the Fraunhofer Center for Chemical Biotechnological Processes (CBP) uses additional hydrogen to transform it into isooctane (C8H18), ETBE and isododecane (C12H26). The fuel is free of sulfur and benzene and is therefore especially low in pollutants when it burns.

Currently, only a small part of Global Bioenergies’ ton scale isobutene production is directed toward e-fuels, using Fraunhofer’s lab scale conversion unit. The e-fuel production capacity will be significantly increased in 2019 with the addition to the Leuna Demo plant of a dedicated fuel production unit, which will allow the production of renewable gasoline batches.

Audi engineers are now examining the combustion and emission behavior of the renewable fuel in a test engine. As a high-purity synthetic fuel with very good anti-knock properties, Audi “e-benzin” (e-gasoline) offers the possibility to further increase engine compression and thus boost efficiency.

Over the medium term, the project partners aim to modify the production process so that it will not require biomass—in this case, CO2 and hydrogen produced from renewable sources should be sufficient source materials. (Earlier post.)

Audi’s alternative fuels already offer great potential for sustainable mobility and are helping reduce CO2 emissions from combustion engines by up to 80% in g-tron models, for example.

For Audi, e-fuels are more than just a subject of research in laboratories. Since 2013, the brand with the four rings has been offering renewable Audi e-gas on the market. It originates in part from the company’s own power-to-gas plant in Werlte (Emsland). (Earlier post.)

Customers fill up their Audi g-tron model at any CNG filling station and pay the regular price for it. By feeding the computed volume of Audi e-gas into the natural gas grid, Audi ensures the green benefits of the program, including the corresponding reduction in CO2 emissions.

Audi e-diesel is also part of the Audi e-fuels portfolio. In Dresden, Audi’s cooperation partner Sunfire operated a pilot plant for this purpose from late 2014 to October 2016. (Earlier post.)

As in Werlte, green electricity supplied the energy, and water and CO2 were also used as raw materials. The end product was called Blue Crude, which was refined into Audi e‑diesel.

Audi is currently planning production capacity in Laufenburg in the Swiss canton of Aargau. Together with partners Ineratec GmbH and Energiedienst Holding AG, a new pilot plant will produce around 400,000 liters of Audi e-diesel per year. (Earlier post.) For the first time, hydroelectric power is the sole energy supply required for this.



Well, let's see about this.  Heat of combustion of octane is -5508.9 kJ/mol.  Producing octane from H2 and CO2 requires 9 moles H2 in the product and another 16 moles H2 in the water byproduct, for a total of 25 moles (50 grams) of H2.

Earlier I recall a figure of 46 kWh/kg H2 for an electrolysis system.  50 grams would require 2.3 kWh or 8.28 MJ of electricity.  This is a conversion efficiency of 66.5% overall, not including the energy required for CO2 capture.  Burned in an engine achieving 30% efficiency, the busbar-to-crankshaft efficiency is about 20%.


  1. The Audi e-fuels have poor commercial potential compared to BEVs.
  2. Audi has to know this, so the effort is most likely a cynical attempt at greenwashing.


They should read your post then stop the whole program. /s


They had to know this going in.  The obvious reason for them to go on with it anyway is because it suits someone's political agenda and they're paying Audi.


It could be a conspiracy & greenwashing or it could be rational economics.....
If you take your numbers and given there are about 700 grams of isooctane per litre,2,4-Trimethylpentane

then (700/50) x 2.3 = 32.2 kwhrs / litre and wind and solar 2c/kwhr or under in places = around 65c/ litre.

Current German fuel price around $1.20 to $1.50 / litre.


You have the molecular weight of iso-octane wrong; it's 114, not 50.

Maybe some favored customers can buy power for 2¢/kWh in Germany, but that's a long way from the all-in price (especially given the transmission lines financed by surcharges on customer bills).

Remember that you also have to amortize and maintain your equipment.  Germany will go broke trying to run on "free" energy.  It is already giving up its CO2 emissions targets.  How many ways is "Energiewende" already synonymous with "failure"?


Iso octane is of course 114, you are right.
C8 H18
As you correctly point out 9 moles H2 in product and 16 moles to get rid of O2.
so 25 moles hence 50 grams H2 / mole but a mole of iso-octane weighs 114 grams so
690/114 = 6 moles / litre iso-octane
x 50g/l = 300 grams H2 / liter.
At 46 kwhr / kg then there is 13.6 kwhrs or 27cents of H2 per liter

Looking better. Thanks for this.
Again you are right that there are amortisation and maintenance costs but typically energy costs are 70 to 80 % of operating costs.
Do you have any objection to the renewable fuel plants being located in sunny or windy places and the fuel being exported to poor old Germany? Tanker transport pretty cheap.


I have no objections to anything that works.  All I want is for it to be PROVEN that it works before anyone demands we rely on it.



Interesting discussion; haven't used 'moles' since college chem.

I think Audi/VW is stalling going to BEVs as long as they can still sell ICEVs to the uninformed. It's interesting their VW CEO is starting to beat the drum again for diesel even after the Monkey Diesel Gas Testing flap. I was hoping for a culture change at VW after DieselGate. Don't think it will happen soon.


Like Poet Engineer I am inclined to the pragmatic. BEVS seem most important for city cars and in particular light / medium urban transport in places smog and Nox bad.
Get rid of lots of smelly dirty diesel trucks delivering all the stuff a city wants.
But you need synthetic fuels for long distance heavy haulage, mining machines and aeroplanes where the energy density critical

Co2 to fuel can work, obviously needs more effort to get economical.
(Finland not where I would put a solar power plant for example.)
Demo plant produces renewable fuel from carbon dioxide captured from the air


The idea is to not burn any fossil fuel in the atmosphere.

The Chevron CEO recently said he's not worried by EVs as they only represent 25% of worldwide oil sales; the other 75% is petrochemicals, aircraft and marine sales. So how do we transition away from the damaging effects of burning carbon chemicals? I think in time all cars and trucks will be battery powered and trains will ether run on overhead lines or batteries. Also, with the gathering storm against ocean shipping, in time these dirty bunker oil burners will transition to natural gas as an interim fuel and then to fuel cell hybrids...airliners will be the last to transition...they could be fuel cell hybrids or also fully battery fueled, when battery tech advances.

Look on fossil fuels as an obsolete solution that been allowed to linger way too long because of greed.

typically energy costs are 70 to 80 % of operating costs.
Amortization costs per unit increase as the inverse of the capacity factor.  If you're operating at 0.2 capacity factor because of intermittent surpluses of wind/PV, amortization will be 5x as much as if you ran all-out.

There's only one way around this problem, and that's for your intermittent stuff to have really low capital cost.  That is a tall order.

Ocean shipping is an interesting case.  With robotized plants, the labor arbitrage which drives a lot of the trans-oceanic transfer of manufacturing disappears.  This is so extreme, even Foxconn is looking to move iPhone production to the USA.  There are a lot of costs associated with the language barriers and shipping delays which also disappear when production is re-shored.  I suspect that it's going to become a much smaller problem over the next 10 years.

I'm imagining container ships the size of the Emma Maersk becoming obsolete because it takes too long to assemble cargoes big enough to make them economic to run.


Audi answers to their shareholders,
I don't think they read Green Car.


If Audi is being paid to put on this performance, the shareholders won't see any impact to their stock price or dividends.  However, that doesn't make the program less greenwashing propaganda.

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