Diesel Exhaust
Fluid systems are becoming very common, and many haulers understand that it’s
supposed to be good for the environment, but more drivers would like a better
understanding of the system before they buy into it. In this month’s edition we’ll take you inside
to see what the system is comprised of, what the system actually does, how it works
and whether it will save you money over the long haul.
The diesel
exhaust fluid system is fairly straight forward. It has a DEF storage tank, lines
to the DEF dosing valve, decomposition reactor, selective catalytic reduction
chamber and slip catalytic chamber. This is just a series of long descriptive
names that hide a simple concept. Change one noxious gas {Nitrous Oxide (NOx)}
coming from your engine into two harmless gasses {H2O and Nitrogen} coming from
the exhaust.
As opposed to a
fuel additive, DEF is actually an exhaust additive. This is the reason for the
separate tank. The tank is usually made of plastic, as the diesel exhaust fluid
is composed of 67.5 % water. The plastic tank allows for freezing (DEF starts
to freeze at 12 degrees F), and corrosion protection. A metal tank would
rupture in the cold because of the water, and corrode because of the second
ingredient used in DEF -- 32.5% urea! It should be said that this is an
industrial grade urea that is colorless, and can have an ammonia odor to it,
but is non-toxic, and safe to work around. Interestingly, the proportion of
each allows them to thaw together in proportion so there are no higher
concentrations of either ingredient when thawing.
The system works
by introducing the fluid after the exhaust has been through the particulate
filter. Once the exhaust passes through the particulate filter, the diesel
exhaust fluid is sprayed in a fine mist through the DEF dosing valve. With a 2%
consumption rate, you will use about 1 gallon of DEF for every 50 gallons of
fuel burned. From there the exhaust moves to the decomposition reactor, where
the urea and water react to become ammonia. Further down the line the exhaust
and ammonia meet a catalyst chamber where the heat and the catalytic reaction
create a combination of water and nitrogen gas for exhausting. Some systems
will have an additional catalyst chamber to mop up any remaining ammonia called
a slip catalyst. Fairly simple, but it works.
 |
Diesel Exhaust Fluid System Operation |
So, does this
system save you money? The short answer is - yes. Why? With the DEF system, it allows
for tuning the engine to the point where you get between 5 to 7 % better fuel
efficiency. Additionally, you get more torque. Unlike some other systems used
to control NOx, the DEF system allows the diesel engine to run at its optimum
range in terms of fuel mixture – some other NOx reduction systems require the
engine to run richer, which can be harmful to diesel engines. Some even older
technologies used diesel fuel for the system, cutting your mileage even
further. Additionally, with DEF, you’ll have
to have fewer oil changes. How would you like to have to only change the oil
after 1000 hours of operation, as opposed to every 10,000 miles? There’s a
truck manufacturer that recommends just that. That’s money in your pocket.
On the down
side, you will have to keep the DEF tank full, because if it goes empty, your
truck will slow to a crawl until you re-fill that tank. My advice would be to
carry a spare container, even if there are now over 3500 DEF retailers with
everything from 1 gallon containers to pump type applications.
Finally, while the
Environmental Protection Agency (EPA) is requiring all service, public
transport and fleet vehicles to switch over to Diesel Exhaust Fluid (DEF)
technology, this is one of their few programs that actually can save you money.
Sean Dewey
E-Commerce Manager
East Coast Truck and Trailer Sales
1-800-849-2178
