Audi Makes Synthetic Diesel from Co2
and Water
Working
with Joule, Audi has developed a new recipe for renewable diesel fuel: Extract
carbon dioxide from the air; use wind and solar green electricity to split
water into hydrogen and oxygen, and apply high heat and pressure until the
hydrogen combines with the CO2 to form "blue crude."
The
crude is then converted into pure synthetic diesel fuel, which is free from the
sulfur and aromatic contaminants typically found in petroleum diesel. The
synthetic diesel fuel also has a high cetane number for easy ignition, and can
be blended with fossil diesel.
However,
perhaps the most significant fact about Audi's synthetic diesel is that the
fuel is completely carbon neutral. The amount of carbon dioxide released when
the fuel is burned equals the amount consumed when the fuel is made.
Synthetic
e-diesel is just one element of Audi's e-fuels effort, a project to create
renewable and carbon-neutral fuels using environmentally friendly production
processes. Audi's project also involves the exploration of other synthetic
alternative fuels such as e-ethanol, e-gas (methane) and bio-isooctane
(bio-gasoline).
Audi's
tests have shown that e-fuels burn more efficiently and produce fewer emissions
than petroleum-based products. a glass window so engineers could see how the
synthetic fuels performed under actual operating conditions. Part of their
testing creates simulated 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 has a glass window so engineers could see how the
synthetic fuels performed under actual operating conditions. 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.
These processes
are still in a developmental phase and large-scale production is a long way
off. Liquid e-fuels have an advantage of easily being distributed through the
existing vehicle fueling infrastructure.
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, Joule’s Helioculture platform uses engineered microorganisms which
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 as
another component of its e-fuels strategy, as well as a new partnership with
Global Bioenergies on bio-isooctane (bio-gasoline).
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