Audi Makes Diesel Out of Water and CO2

Audi started to produce synthetic Diesel fuel that does not need mineral oil. It is made from water, CO2 and green power. Why are we bothering with electric cars again?

Audi made a surprising announcement recently that slipped through our news filter. The German car maker developed synthetic Diesel fuel that based on the raw materials water and carbon dioxide (CO2). 

“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,” said Reiner Mangold, Head of Sustainable Product Development at Audi.

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.

To proof the synthetic Diesel works, Audi filled up an Audi A8 3.0 TDI clean diesel quattro driven by a Minister of the German Government. The test plant is set to produce over 3,000 liters (792.5 US gal) of Audi e‑diesel over the coming months. This is of course not yet enough to put the oil countries out of business.