According to the National Oceanic and Atmospheric Association, carbon dioxide levels are at an 800,000-year high, but what if we could pluck CO2 particles out of thin air to use as a raw material for a carbon-neutral fuel? It’s not a pipe dream, because it’s exactly what Audi is doing at a research facility in Dresden, Germany. Called e-diesel, the fuel is currently being produced (following an incredibly rapid commissioning phase of just four months) and already powering an A8 3.0 TDI.

Researched and produced in partnership with Dresden-based energy company Sunfire, the only raw materials needed to make e-diesel are CO2 and water. The method works using the power-to-liquid principle and primarily uses CO2 supplied by a biogas company. The secondary source of CO2 is even more impressive: Another Audi partner, Climeworks in Zurich, has developed a way to capture CO2 particles from ambient air. That means CO2 emitted from e-diesel cars (and anything else that emits CO2, including humans) can potentially be recaptured and reused as fuel, making it a carbon neutral energy source.

Continue reading to learn more about the Audi e-diesel.

Why it matters

Reducing carbon emissions is absolutely essential, but this is something different. If e-diesel technology is taken to its logical conclusion, it means 100 percent of the CO2 emitted from our tailpipes can be reused as fuel — an incredibly obvious solution. Unlike hydrogen and electricity, it also has the added benefits of being compatible with the world’s existing fuel infrastructure and eliminating the need for toxic batteries required by EVs, fuel-cell vehicles and hybrids. But these are early days.

The plant at Dresden aims to produce around 800 gallons over the next few months, but with current backing from the German government, the program will likely expand. It’s also possible to mix e-diesel with fossil based diesel, similar to how ethanol and gasoline are mixed to make E85.

Production of e-diesel requires heating water to 800 degrees Celsius to trigger a high-temperature electrolysis that breaks down the steam to hydrogen and oxygen. The hydrogen then reacts with CO2 in synthesis reactor, which results in a hydrocarbon compound, called blue crude. This blue crude is then refined to make e-diesel. It’s an energy-intensive process that Audi says is powered using green energy sources.

To its credit, Audi has been incredibly active when it comes to alternative fuels. The company already has a plant in Werlte, Germany producing a synthetic methane called e-gas, which fuels the A3 Sportback g-tron. Audi’s other e-fuel ventures include a joint project with Global Bioenergies in France to research e-gasoline, and a microorganism-based diesel and ethanol with U.S. company, Joule.

Audi Produces Its First Batch Of e-diesel
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Press Release

Audi has taken another big step in the development of new, CO2 neutral fuels: A pilot plant in Dresden has started production of the synthetic fuel Audi e diesel.

Audi Produces Its First Batch Of e-diesel
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After a commissioning phase of just four months, the research facility in Dresden started producing its first batches of high‑quality diesel fuel a few days ago. To demonstrate its suitability for everyday use, Federal Minister of Education and Research Prof. Dr. Johanna Wanka put the first five liters into her official car, an Audi A8 3.0 TDI clean diesel quattro*, this Tuesday. “This synthetic diesel, made using CO2, is a huge success for our sustainability research. If we can make widespread use of CO2 as a raw material, we will make a crucial contribution to climate protection and the efficient use of resources, and put the fundamentals of the “green economy” in place,” declared Wanka.

The Dresden energy technology corporation sunfire is Audi’s project partner and the plant operator. It operates according to the power‑to‑liquid (PtL) principle and uses green power to produce a liquid fuel. The only raw materials needed are water and carbon dioxide. The CO2 used is currently supplied by a biogas facility. In addition, initially a portion of the CO2 needed is extracted from the ambient air by means of direct air capturing, a technology of Audi’s Zurich‑based partner Climeworks.

Audi Produces Its First Batch Of e-diesel
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Reiner Mangold, Head of Sustainable Product Development at Audi, sees Audi e‑diesel and Audi e‑fuels in general as an important component that complements electric mobility: “In developing Audi e-diesel we are promoting another fuel based on CO2 that will allow long‑distance mobility with virtually no impact on the climate. Using CO2 as a raw material represents an opportunity not just for the automotive industry in Germany, but also to transfer the principle to other sectors and countries.”

Production of Audi e‑diesel involves various steps: First, water heated up to form steam is broken down into hydrogen and oxygen by means of high-temperature electrolysis. This process, involving a temperature in excess of 800 degrees Celsius, is more efficient than conventional techniques because of heat recovery, for example. Another special feature of high-temperature electrolysis is that it can be used dynamically, to stabilize the grid when production of green power peaks.

In two further steps, the hydrogen reacts with the CO2 in synthesis reactors, again under pressure and at high temperature. The reaction product is a liquid made from long‑chain hydrocarbon compounds, known as blue crude. The efficiency of the overall process – from renewable power to liquid hydrocarbon – is very high at around 70 percent. Similarly to a fossil crude oil, blue crude can be refined to yield the end product Audi e‑diesel. This synthetic fuel is free from sulfur and aromatic hydrocarbons, and its high cetane number means it is readily ignitable. As lab tests conducted at Audi have shown, it is suitable for admixing with fossil diesel or, prospectively, for use as a fuel in its own right.

Audi Produces Its First Batch Of e-diesel
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The Federal Ministry of Education and Research is supporting the sunfire project, which started in May 2012. Construction work on the facility in Dresden‑Reick kicked off in July 2013 and the plant was commissioned on November 14, 2014. The plant is set to produce over 3,000 liters (792.5 US gal) of Audi e‑diesel over the coming months. Audi is sunfire’s exclusive partner in the automotive sector.

Over and above the partnership with sunfire, Audi has been active in the development of CO2‑neutral fuels – Audi e‑fuels – since 2009. The Audi e‑gas plant in Werlte, Lower Saxony, already produces Audi e‑gas (synthetic methane) in a comparable manner; drivers of the Audi A3 Sportback g‑tron* can fill up on it using a special fuel card. Audi is also conducting joint research into the synthetic manufacture of Audi e‑gasoline with Global Bioenergies, of France. In a further project, Audi has joined forces with the U.S. company Joule, which uses microorganisms to produce the synthetic fuels Audi e‑diesel and Audi e‑ethanol.

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