Fleet Maintenance - 28

SPOTLIGHT ON DRIVETRAIN

Keeping up with
EGR systems
It is important for fleets to
understand the challenges
of maintaining exhaust gas
recirculation systems in order to
best prepare their technicians
for diagnostics and repairs.
By Emily Markham

ntroduced in October 2002, the exhaust
gas recirculation (EGR) system was
added to heavy duty engines in order to
meet the U.S. Environmental Protection
Agency's (EPA) emissions standards
at that time. The function of the EGR
system is to reduce NOx emissions.
"EGR systems take a portion of
exhaust gases from the exhaust manifold and recirculate them through the
intake track to reduce oxygen content
in the cylinders," says Kevin Smith, field
analyst for Dorman Products, a supplier of OE dealer replacement parts. "The
main goal of this system is to reduce
NOx emissions made during combustion. By lowering the oxygen content
in the cylinders, the temperature of
combustion is lowered, therefore reducing the NOx emissions that are being
created by the engine. A byproduct of
this system is increased soot production.
This is where the aftertreatment system
steps in to collect and periodically burn
the soot that is collected in the diesel
particulate filter (DPF) into ash."

Technological
advancements

»As EGR technology continues
to progress, the significance
of keeping up with proper
maintenance practices is
more important than ever.
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28 Fleet Maintenance | August 2020

Since the EGR system's introduction, the
main components of this system have
stayed the same - cooler, valve, actuator, etc. However, improvements have
been made.
"Coolant is used to reduce the
temperature of the exhaust gas, and an
important factor in cooling the engine
is pressure through the system," says
Michael Young, Detroit engine marketing manager for Daimler Trucks North
America (DTNA), a manufacturer of
commercial vehicles. "In 2021, the EGR
system in Detroit's DD15 Gen 5 (engine)
will allow for reduced pressure drops
through the system, making the whole
cooling system perform better. With the
DD15 Gen 5, we will also update how
coolant flows and will be able to reduce
the amount of parts in the system."
In addition to the reduced pressure
drops, Young explains that the EGR
valve has been updated. The valve has
been incorporated into the exhaust
manifold center, which will improve

EGR flow management, as well as
control over over-the-road emissions
and performance.
Over the years, as the EPA has lowered
the acceptable levels of emissions, EGR
has been reconfigured to meet those
goals, Smith says. And, with the new,
lower level requirements, other technology has also been introduced. In 2007,
DPFs came onto the scene, and then in
2010 when emissions standards were
lowered again, the selective catalytic
reduction (SCR) system was introduced.
"SCR is a chemical reaction process
where DEF (diesel exhaust fluid) is injected into the SCR unit and when operating properly, the ammonia in DEF reacts
with the NOx emissions and breaks them
down into nitrogen and water molecules," Dorman's Smith explains.
Today, both SCR and EGR systems
are incorporated into heavy duty diesel
engines. Each system plays an important
role in reducing NOx emissions; however,
each system also has its drawbacks.
According to Kristopher Ptasznik,
product manager, heavy duty on-highway for Cummins, a corporation that
designs, manufactures, and distributes
engines, filtration, and power generation products, though EGR systems
shrink NOx emissions, they can cause
an increase in particulate matter (PM).
As for SCR systems, though they also
break down NOx emissions, they create
an increase in DEF consumption.
Regardless of their faults, the SCR and
EGR systems working together are the
best solution to lower emissions levels.
Additionally, when combined with a
DPF, "EGR and SCR [systems have] been
proven to reduce NOx emissions by at
least 80 percent in a well-maintained
truck, and in some systems, even more
than that," Smith says.

Challenges with
EGR systems
It is important to know the challenges
that come along with maintaining an
EGR system.
"There are a few major failures that can
occur," Doorman's Smith explains. "EGR
coolers have two main failure modes:
plugging with soot, which restricts the
flow of the gasses through the system;
and fractures inside the cooler from thermal cycling and constant pressure being
applied to the system."
An internal crack in an EGR cooler
can cause significant damage to any
components or systems downstream,
Smith notes. Additionally, failures with
EGR valves are typically caused by soot
and carbon buildup.
Aside from these major component
failures, many small failures can also

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