Audi tested the new synthetic fuel in an engine modified with a glass window so that the combustion process could be observed.

Audi e-diesel, a synthetic diesel fuel made from water and carbon dioxide using only green power as the manufacturing energy source is now in limited production in a pilot plant in Dresden, Germany.

Working with a company specializing in high-temperature fuel cells and reversible electrolysers called Sunfire, the pilot plant operates on the power-to-liquid principle but uses only green energy to produce the liquid fuel.

The only raw materials needed are carbon dioxide (CO2) and water. The CO2 is currently supplied by a biogas facility, but a portion is also extracted from ambient air.

“This synthetic diesel, made using CO2, is a huge success for our sustainability research,” says Dr. Johanna Wanka, Germany’s federal minister of education and research.

“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,” adds Reiner Mangold, head of sustainable product development at Audi.

The clear fuel is made from just water and carbon dioxide, which can be pulled from the air.

Producing Audi e-diesel involves three basic steps. Water is heated into steam, then broken down to hydrogen and oxygen using electrolysis. The hydrogen then reacts with the CO2 in synthesis reactors under high pressure and temperature. The reaction product is a liquid made from long-chain hydrocarbon known as blue crude. Just like fossil crude oil, blue crude can be refined to produce other fuels such as Audi e-diesel. As a synthetic fuel, it’s free of sulfur and aromatic hydrocarbons. Also, its high cetane number means it’s readily ignitable. Lab tests also show it’s suitable for mixing with fossil diesel or as a stand-alone diesel fuel.

With positive results from the pilot plant, future considerations for commercial production are more likely.