december2021 - 30

SPOTLIGHT ON TECHNOLOGY TRENDS
» Future regulations are expected
to limit the amount of NOx
emissions by more than 90%.
48646070 | Trekandshoot | Dreamstime and
1127543295 | Stadtratte | Getty Images
ment of its BlueTec emissions technology,
said Len Copeland, product
marketing manager
for Detroit
Diesel Corp., a Daimler subsidiary
and the OEM's engine manufacturer.
Copeland touted the existing SCR
in Detroit Diesel power plants, its
DD13 and DD15 Gen 5 engines, as
already-efficient reducers of NOx
with their advanced communication
among various components.
The two engines use asymmetric
fuel injection, which " biases "
fuel towards different cylinders
based on engine load or through
a thermal control valve, modulating
exhaust flow at low load, high
idle, or extended PTO operation to
increase exhaust temperatures.
" While dual SCR is newer to
Preparing for
dual SCR
The differences between SCR and
dual SCR technology, and what new
maintenance will need to be considered.
By Scott Achelpohl
W
hen it comes to reducing the nitrogen
oxide (NOx) emissions of
diesel-burning commercial vehicles,
selective catalytic reduction (SCR) is
firmly in place as today's technology.
And these systems are not without
their challenges when maintaining
them. Soon fleets will also have
a new technology with which to
contend: dual SCR. Coming in the
next five years-and according to
two OEMs, might very well be the
future-dual SCRs will come with
their own unique challenges.
How dual SCR
differs from today's
catalytic reduction
First let's talk SCR. Current SCR is
itself a quite advanced active emission
control technology system that
30 Fleet Maintenance | December 2021
injects a liquid-reductant agent-
automotive-grade urea in the form of
diesel exhaust fluid (DEF)-into the
exhaust stream of a diesel-burning
engine. SCR technology is designed
to permit NOx reduction to take
place in an oxidizing atmosphere. It's
called " selective " because it reduces
NOx levels using ammonia (the
urea after it is exposed to heat) as a
reductant within a catalyst system.
When operating optimally, this
aftertreatment technology cuts NOx
by up to 90% and meets current U.S.
Environmental Protection Agency
(EPA) and California Air Resources
Board (CARB) standards.
Dual SCR promises perhaps more
than 90% reduction, where government
rules are almost certain to
land in a few years. The question for
fleets is how to keep current systems
working well enough to perform up
to today's NOx rules? But it's also
critical for them to anticipate what
might arrive in their shops to fix in
the next five to 10 years.
Think of dual SCR as SCR with an
extra urea injector, with designs in
R&D that place one injector closer to
the engine and one farther away from
it. The difference between the two is
NOx emissions get processed by the
DEF at two locations rather than one.
No heavy-duty truck in production
today uses dual SCR. OEMs
such as Volvo Trucks and Daimler
Trucks North America, and aftermarket
manufacturers such as
Bosch and Eaton, are all in R&D with
dual systems or their likely components.
And they all anticipate a tightening
of government standards in
the U.S. by the EPA and CARB, which
is usually even stricter.
Volvo's director of product marketing,
Johan Agebrand, said regulators
might also restrict the warmup periods
for on-highway diesel engines,
which is quite long with SCR, called
the " emissions slippage " time. " They
won't be allowed to have a warmup
period anymore, no more emissions
slippage, " Agebrand said.
Volvo, which is pioneering electric
trucks coming into the heavy-duty
market, also is a leader in sustainability
solutions for trucks that still
burn diesel-and dual SCR is no
exception, Agebrand said.
Daimler also helped lead the way
with SCR in 2007 with the developthe
industry, it functions on the
same principle and with the same
efficiency as existing systems, "
Copeland added.
Dual SCR " increases NOx conversion
due to the two catalysts can also
be achieved by increasing the size
of a single Diesel Oxidation Catalyst
(DOC), where packaging permits.
Newer
aftertreatment
systems,
such as the new ATS paired with the
heavy-duty Detroit Gen 5 engines, are
smaller and lighter (60-plus lb. in this
case) than previous generations without
increased complexity or cost. "
Any R&D that produces a system
that cuts NOx above 90% might be
a prescient investment, whichever
OEM pioneers it first.
In August, the EPA announced
plans to lower greenhouse gas (GHG)
emissions and other air pollutants
from heavy-duty trucking via several
rules over the next three years. All
part of the Cleaner Trucks Initiative,
the first will be finalized next year
and will apply starting with 2027
model year heavy-duty trucks.
The EPA said " from 2007 to 2017,
NOx emissions in the U.S. dropped
by more than 40%. But there is more
work to be done. Heavy-duty vehicles
are the largest contributor to
mobile-source NOx emissions and
will be one of the largest contributors
to ozone in 2025. The EPA last
revised NOx standards for on-highway
trucks and engines in 2001. "
The EPA is also developing ways to
stregnthen and streamline existing
technologies to further reduce emissions.
SCR and dual SCR would fall
under this category.
december2021

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