Water, CO2 and green power - Audi's e-diesel recipe

Audi's water-based green diesel provides alternative to electromobility

German car maker Audi has developed a new zero-emission fuel made from water and CO2, offering a possible alternative to electromobility.

Produced at Audi’s new plant in Dresden, Germany, the fuel, dubbed the e-diesel, doesn’t require any mineral oil and is of such high quality it can be safely tanked into the car-maker’s premium engines.

To further improve the fuel’s carbon footprint, Audi is using energy from renewable resources to power the processes in the plant and utilises CO2 from biogas manufacturing.

“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,” said Reiner Mangold, Head of Sustainable Product Development at Audi, pointing to the range anxiety issues related to the use of electric vehicles. “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.”

To prove that the e-diesel is perfectly safe for Audi’s vehicles, the car maker invited Germany’s Federal Minister of Education and Research Professor Johann Wanka to test the fuel with her official car, an Audi A8.

“This synthetic diesel, made using CO2, is a huge success for our sustainability research,” Wanka said. “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.”

The Dresden plant is operated by Audi’s partner Sunfire and uses technology developed by Swiss firm Climeworks, which allows collecting additional CO2 directly from the ambient air.

In the first stages of the e-diesel production, water is heated up to vaporise. The steam is then broken down into hydrogen and oxygen through electrolysis at temperatures of more than 800 degrees Celsius. The firms involved in the project say the high temperature process is more efficient than conventional techniques thanks to better heat recovery. Moreover, the process can be used dynamically in response to renewable energy generation to stabilise the grid in peak production periods.

The resulting hydrogen further reacts with the CO2 in special reactors, producing a liquid consisting of long-chain hydrocarbon compounds. This liquid, called the blue crude, can be further refined similarly to conventional fossil crude oil.

The final product, the synthetic diesel, doesn’t contain any sulphur or aromatic hydrocarbons. Its high cetane number makes it readily ignitable and suitable either for mixing with conventional fuel, or possibly for powering vehicles on its own.

The whole production process is said to be up to 70 per cent energy efficient.

Audi aims to produce more than 3,000 litres of the fuel in the upcoming months and said it had already started developing a synthetic gasoline, dubbed the e-petrol, for vehicles with petrol engines.

Construction of the Dresden plant commenced in July 2013.

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