Our test shows that as well as electric driving on renewable electricity, there are other concepts that permit long-distance, low-emission driving.

—Reiner Mangold, Head of Sustainable Product Development at Audi

Audi notes that the partnership with Joule is still in a development phase and that large-scale production is still quite a way off.

The Audi engineers were primarily interested in mixture preparation and the synthetic fuels’ combustion characteristics. To investigate these, they simulated the conditions inside an engine in a pressure chamber at up to 15 bar and temperatures of 350 °Celsius. A special camera scans the spray at intervals of 50 microseconds to record how the fuel behaves during the injection process, as only a clean mixture preparation process will assure optimal combustion.

The optical research engine was another test station. This test setup reveals the processes that are otherwise hidden by the metal walls of the cylinders. A small window made of quartz glass enables engineers to observe the fuel’s behavior in the cylinder and how it interacts with the airflow in the combustion chamber.

During each of up to 3,000 revolutions per minute in the research engine, a minute amount of fuel shoots into the glass cylinder, is compressed and ignited, and the exhaust gas then expelled. The engineers mix a tracer that glows when stimulated with a laser into the e-fuels. The laser-induced fluorescence process thus highlights those places in the glass cylinder that are particularly bright as being where most of the fuel is. Using a high-speed camera, the combustion process is captured with time-lapse photography.

The investigators found that unlike fossil fuels, the composition of which varies depending on their place of origin, synthetic Audi e-fuels are pure fuels. Thanks to their chemical properties, fewer emissions are generated when they are burned. They do not contain any olefines or aromatic hydrocarbons. As a result, the synthetic fuels assure a more effective mixture preparation process, cleaner combustion and lower emissions.

Audi is testing different blends of the e-fuels as well as 100% fuel. Fuel specifications are not publicly available yet, nor are emissions results and comparisons.

Audi operates a research facility in Hobbs, New Mexico for the production of e-ethanol and e-diesel in partnership with Joule. At this facility, microorganisms use water (brackish, salt or wastewater), sunlight and carbon dioxide to produce the high-purity fuels.

Audi also has an e-gas project in Werlte, Germany underway (earlier post) as another component of its e-fuels strategy, as well as a new partnership with Global Bioenergies on bio-isooctane (bio-gasoline) (earlier post).

Resources

• Marlon Matthäus, “Tankful Encounter,” Encounter.online, January 2014.

• Reinhard Otten (2013) Alternative Kraftstoffe der 3. Generation: Audi e-fuels (in German)