Unlike regular diesel, which is derived from crude oil drilled from the ground, e-diesel is derived from CO2 and water. The plant producing e-diesel operates according to the power-to-liquid principle, and uses power sourced from renewable sources to produce liquid fuel.
To demonstrate its suitability in everyday use, Prof Dr Johanna Wanka, the German Federal Minister of Education and Research, put five litres of the synthetic fuel into her official car, a Audi A8 3.0TDI clean diesel quattro. Not a lot, but with a rated fuel consumption of 5.9L/100km, that is enough to give the diesel-powered A8 nearly 85km worth of range.
To produce the synthetic e-diesel fuel, the plant heats up water to form steam that is broken down to its core elements of hydrogen and oxygen by means of high-temperature electrolysis at temperatures of excess of 800oC. From there the hydrogen gases will react with CO2 gases in synthesis reactors, again under high pressure and temperatures. This produces a liquid with long-chain hydrocarbon compounds known as blue crude. As it is form merely from pure elements of carbon and hydrogen, blue crude is free from chemical impurities such as sulphur and aromatic hydrocarbons, while its high cetane number means that it is readily ignitable.
According to Audi, the efficiency of the overall process of producing blue crude from renewable power is rated at around 70 per cent.
The e-diesel is just part of Audi’s involvement in the development of CO2 neutral fuels since 2009. Audi’s e-gas plant in Werlte already produces synthetic methane known as e-gas, while they are concurrently conducting research into the manufacture of e-gasoline with Global Bioenergies of France, and joined forces with American company Joule which uses microorganisms to produce synthetic fuels, e-diesel and e-ethanol.
While there is no news if Audi's e-diesel will see widespread commercial implementation, if ever in any form or volume, this represents an interesting step in the progress of synthetic fuels. Interesting times for Audi and human mobility in general lie ahead.