EPA07 Aftertreatment System
(ATS)
On-road diesel engines built after December 31,
2006, are required to meet EPA07 guidelines for re-
duced exhaust emissions of particulate matter and
nitrogen oxides (NOx). NOx is limited to just over 1
gram per brake horsepower hour (g/bhp-hr), and par-
ticulate matter cannot exceed 0.01 g/bhp-hr.
EPA07-compliant engines require ultralow-sulfur die-
sel (ULSD) fuel, and they should never be run on
fuel with sulfur content higher than 15 ppm. In addi-
tion, they require low-ash engine oil. The following
guidelines must be followed, or the warranty may be
compromised.
•
Use ultralow-sulfur diesel (ULSD) with 15 ppm
sulfur content or less, based on ASTM D2622
test procedure.
•
Do not use fuel blended with used engine lube
oil.
•
Engine lube oil must have a sulfated ash level
less than 1.0 wt %, meeting the API CJ-4 index
specifications.
IMPORTANT: Using non-specification fuels or
oils can lead to shortened diesel particulate filter
(DPF) cleaning or exchange intervals. For ex-
ample, using CI-4+ oil with 1.3% sulfated ash
(30% more ash content) may result in the need
for DPF cleaning or exchange 20 to 30% sooner
than would normally be required.
The "exhaust system" in EPA07-compliant vehicles is
called the aftertreatment system (ATS). The ATS var-
ies according to engine manufacturer and vehicle
configuration, but instead of a muffler, an aftertreat-
ment system has a device that outwardly resembles
a muffler, called the aftertreatment device (ATD).
IMPORTANT: See the manufacturer’s engine
operation manual for complete details and op-
eration of the aftertreatment system.
Inside the ATD on Mercedes-Benz, Detroit Diesel,
and Cummins engines, the exhaust first passes over
the diesel oxidation catalyst (DOC), then it passes
through the DPF, which traps soot particles. If ex-
haust temperature is high enough, the trapped soot
is reduced to ash, in a process called passive regen-
eration (regen). Passive regeneration occurs as the
vehicle is driven normally under load; the driver is
not even aware that it is happening. The harder an
EPA07 engine works, the better it disposes of soot,
as the exhaust heat alone is enough to burn the soot
to ash. Over the course of a workday, however, pas-
sive regeneration cannot always keep the ATD filter
clean, so the filter must undergo active regenera-
tion. In active regeneration, extra fuel is injected into
the exhaust stream to superheat the soot trapped in
the DPF and turn it to ash. Active regeneration hap-
pens only when the vehicle is moving above a cer-
tain speed, determined by the engine manufacturer.
Consult manufacturers’ documentation for details.
Both active and passive regeneration happen auto-
matically, without driver input.
NOTE: Caterpillar engines do not use a DOC;
CAT engines burn diesel fuel at the regeneration
head to superheat the exhaust and burn the
trapped soot to ash. Engine software monitors
and controls this process.
Only when operating conditions do not allow for ATD
filter cleaning by at-speed active or passive regen-
eration, the vehicle may require a parked regenera-
tion. The vehicle must be standing still, and the
driver must initiate the parked regen. Completing a
parked regen takes 20 minutes to an hour, depend-
ing on ambient conditions.
DANGER
During parked regeneration, exhaust tempera-
tures are very high, and could cause a fire, heat
damage to objects or materials, or personal in-
jury to persons near the exhaust outlet.
Before initiating a parked regeneration, make cer-
tain the exhaust outlets are directed away from
structures, trees, vegetation, flammable materi-
als, and anything else that may be damaged or
injured by prolonged exposure to high heat.
The warning lamps in the driver message center alert
the driver of a regen in progress, high exhaust tem-
peratures, the need to perform a parked regen either
soon or immediately, and of an engine fault that af-
fects the emissions.
A slow (10-second) flashing of the high exhaust sys-
tem temperature (HEST) lamp indicates that a
parked regeneration is in progress, and the engine’s
Engines and Clutches
7.1
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