the promising synthetic fuel based on “water and air” compatible with conventional engines

Diesel and water do not get along. Even less inside an engine. But there are solutions to produce energy that have managed to bring these two materials together. Today we are going to talk about e-diesel, a synthetic fuel based on raw materials such as water and CO2 of the atmosphere. That is, diesel produced by components as easy to find in nature as water and “air”. An alternative to the diesel of fossil origin that we find in most cars today.

The e-diesel has its origin in 2014, from an alliance between the German manufacturer Audi and the technology company Sunfire. It is a fuel that does not generate CO2 emissionsbut it is also still a diesel, so works on conventional engines. Here we explain to you what e-diesel is based on, what its advantages are and what many challenges it faces until it can aspire to be a valid alternative to fossil fuels.

What is e-diesel based on?

Audi E Diesel

As we explained, e-diesel is based on water and CO2 to produce a hydrocarbon. The production of this synthetic diesel is possible by obtaining CO2 from the atmosphere, which in combination with hydrogen from water allows create a synthetic gas oil through an electrolysis process.

The ‘e’ of e-diesel should not be confused with the one usually used in biofuels. In this case it is a synthetic fuel.

Therefore, three elements are needed: hydrogen, carbon dioxide and electrical energy. The first element is obtained from water, the second from the air itself captured through filters and the third is produced in the factory by renewable energies such as solar or wind.

The first step is heating water above 800ºC to separate hydrogen from oxygen. It is the process of electrolysis, where hydrogen is separated from oxygen. The former stays in the reactor, while the latter is returned to the atmosphere.

Second, CO2 is incorporated into the reaction. This is obtained directly from the air using direct capture techniques. CO2 is mixed with hydrogen and reacted at elevated temperature and pressure to achieve the desired mixture in liquid form. The combination is known as e-diesel or “raw blue”.

With the liquid created, a final refinement process equivalent to that done with traditional diesel so that it can be used in different cars.

A “neutral” fuel in emissions

E Diesel

The most obvious advantage of e-diesel is its use of “neutral” elements. Contrary to limited fossil components, water and CO2 are abundant resources in nature. But in addition, e-diesel is theoretically also an ecological fuel.

The key to being environmentally friendly is that e-diesel does not increase CO2, the main cause of the greenhouse effect. By its own design, e-diesel helps reduce it as Through filters, CO2 is obtained directly from the air, in a greater proportion than that which is subsequently generated in combustion..

Other advantages of this fuel is that it is a technology adapted to today’s engines, so it does not require vehicles to be offered in specific versions as is the case with gas or electric engines.

Audi has the capacity to produce 400,000 liters per year


At the end of 2014, Audi was allied with the company Sunfire to start producing e-diesel. The pilot project started at a plant in Dresden. The work paid off and in 2018, the German car manufacturer announced plans to expand e-diesel production.

Through an agreement with the electrical producers Ineratec GmbH and Energiedienst Holding AG, a new plant in Laufenburg, in Canton Aargau (Switzerland) for the production of synthetic fuel. This facility has a capacity of around 400,000 liters per year, an amount much higher than that of the initial pilot but far from the figures currently produced from other fuels.

Audi A8 E Diesel
Johanna Wanka, German Minister for Education and Research, filling the tank of an Audi A8 during her demonstration.

In 2015, Audi successfully tested its e-diesel in an Audi A8 3.0 TDI. However, at the same time the company maintains projects in other fuels such as e-gas. In fact, together with the company Global Bioenergies SA, they are also working on e-gasoline. Several “fuels of the future” that promise great advantages but also face multiple challenges.

Mazda Efuel

In 2021, Mazda announced its incorporation into the eFuel Alliance, an association whose objective is to promote neutral fuels, following the Audi e-diesel proposal. In this line there is also Porsche and Siemens Energywith the promise of producing up to 120,000 liters of eFuels in 2022.

The Sunfire company plans a factory in Norway with a capacity of 20 MW, with a capacity of 8,000 tons per year. This is, equivalent to about 13,000 vehicles per year. A high figure, but far from becoming something capable of scratching traditional fuels.

A promising fuel with important limitations

And it is that if the e-diesel is ecological and above all it works in conventional engines; Why has it failed to attract more investment? This is because it also presents several difficulties.

First of all there is the production cost. Audi has not revealed the cost, but it can be anticipated that the cost of e-diesel is considerably higher than that of extracting oil. You only need to see the size of the infrastructure needed to produce a few liters.

Fuel Efficiency
Image: ICCT

On the other hand, there is the question of energy efficiency, a key aspect of any fuel. And here some experts like Robert Rapierof Energy Trends, believe that this e-diesel is not efficient enough to be viable on a large scale and commercially.

El International Council of Clean Transportation (ICCT), explained in mid-2020that synthetic fuels were not the most effective solution to reduce CO2 emissions, the path of betting on electric cars being clearly more effective.

Recently, Audi has announced the stoppage of its future combustion engines due to the impossibility of adapting to the future Euro 7 standard. Audi’s current plans with e-diesel are unknown. A plausible alternative although perhaps not sufficient to change the fate of diesel.

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