SAE Update - April 2024 - 21

renewable diesel offers drop-in
solution for decarbonization
TECH FOCUS:
MATEriAlS
What are the main differences between biodiesel
and rD in terms of production and chemistry?
We use the same feedstocks as biodiesel, but RD and
biodiesel are not the same product. Chemically,
biodiesel is not a hydrocarbon because it still contains
oxygen. That changes the performance characteristics
of the fuel as well as how much control the producers
have over the final product. Once we perform our first
step in the process (hydrotreating) where we break
apart that molecule, we get a straight chain of
paraffinic hydrocarbons. The only issue with that is
the paraffins we make are a solid, so we do one more
step called isomerization where we take that straight
chain molecule and branch it. Meaning that we move a
few molecules to different places. This keeps the same
number of hydrogen molecules but reshapes it to
make a liquid. The more we isomerize it, the lower we
can get the cloud point of the fuel. By isomerizing, we
can also guarantee winter performance characteristics
that biodiesel cannot.
What are the combustion characteristics of rD
compared to biodiesel?
RD has a very high cetane number. Fossil diesel has a
cetane of 41 or higher. Biodiesel cetane will usually
come in around the mid-40s to lower 50s. RD
typically has a minimum of 70 and sometimes closer
to 80. So that's really going to promote quicker and
cleaner combustion. Both are aromatic free which is
good. However, biodiesel still has oxygen which
means in combustion, that oxygen will create more
NOx. Obviously, we want to reduce NOx, so if you're
looking at pure engine emissions (excluding
aftertreatment systems) biodiesel will have an
increase in NOx, whereas RD will have a decrease in
NOx.
UPDATE
What is an example of a longterm
benefit of running
exclusively rD?
The fuel is incredibly clean. It
looks and smells like water and is
free of contaminants, which
means it will not start producing
injector deposits that decrease
the performance of the engine
over time. Detroit Diesel did
some testing on a DD15 where
they artificially aged the fuel and
ran it through an engine on a test
bed. They were testing to see
what would happen first: would
the fuel break down and go off
spec as time goes on, or would
the parts physically fail because
of deposits and corrosion? The
B5 bio-blend lasted 13 days in
the test before the injector
seized. B0 pure fossil made it
roughly 43 days. The fuel broke
down enough that it had a lot of
acids and the injector had
deposits. After two months of
testing with our fuel, they found
that it didn't break down when
they pulled the injectors apart
there were zero deposits.
What are some other net
benefits of rD for engine OEMs
and fleet owners?
Our fuel can help reduce NOx for
2006 and older off-road (pre-Tier
April 2024
21
SAE Update - April 2024

Table of Contents for the Digital Edition of SAE Update - April 2024
