Here at Car Articles, we’ve long believed that more alternative fuels are the way to go – not only for the environment but also for consumer choice. We also consider it puzzling that no-one has yet developed a synthetic that would replace fossil fuels. In theory, it would be far, far cheaper, better for the environment and plentiful in supply. It appears that Audi has been working on just such a thing in the form of Audi e-diesel.
The only raw materials needed for the artificial fuel 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.
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 stabilise 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 sulphur 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.
Is this how cars will be powered in the future? Only time will tell. As always, comments are welcome in the section below.