Technical Bulletin
Diesel Particulate Filter
Operation and Maintenance
National Clean Diesel Campaign
www.epa.gov/cleandiesel
Diesel Particulate Filter (DPF) manufacturers and product
suppliers should provide vehicle service technicians
with training on proper retrofit product maintenance
procedures.
Backpressure Monitoring
DPFs work by physically trapping and removing PM from
the engine's exhaust. As the DPF collects PM, the passage
of exhaust gas through the pores of the filter element may
be progressively blocked causing an increase in exhaust
backpressure. Backpressure increases are caused by the
short term build up of PM, which is remedied in the short
term by regeneration. The long term build up of ash is
remedied by periodic cleaning.
Engine manufacturers place limits on the exhaust
backpressures for their engines; therefore, an exhaust
backpressure monitoring and operator notification system
must be installed with every DPF. If exhaust backpressure
exceeds certain thresholds, the operator is notified that
maintenance is needed. It is important that all vehicle/
equipment operators and fleet service technicians
are properly trained to recognize and respond to high
backpressure alert signals. Backpressure monitoring
systems should be periodically inspected for proper
operation.
Inlet
Catalyst
Filter
Outlet
Diesel Particulate Filter (DPF)
Filter Regeneration
Regeneration occurs when the filter element reaches
the temperature required for combustion of the carbon
in the PM, converting it to gaseous carbon dioxide (CO2)
and carbon monoxide (CO). The minimum frequency of
regeneration is determined by the rate of PM build-up and
is generally once per day or shift.
"Passive" regeneration occurs when the exhaust
temperatures during the normal duty cycle are hot
enough to sufficiently raise the temperature of the filter
element. Metal based catalysts applied to the filter
alter the combustion chemistry and reduce the exhaust
temperature needed for passive regeneration. Passive
regeneration requires no action or maintenance by the
operator.
"Active" regeneration must be used when the engine
exhaust temperature during the normal duty cycle is not
hot enough to initiate combustion of the collected PM, and
an additional heat source is required to sufficiently raise
the temperature of the filter element. Active regeneration
can be accomplished through either "on-board" or "off-
board" strategies. For on-board regeneration, an electric
heater is built into the upstream section of the DPF and
regeneration takes place while vehicle is off duty. For off-
board regeneration, the DPF is removed fromthe equipment
and placed into a filter regenerating system. Regeneration
times can range from two to eight hours depending on
DPF size, filter media, and type of regeneration system.
The regeneration time dictates the time required every
shift or every day that the vehicle must be out of service.
Filter Cleaning
In addition to PM, the filter also traps noncombustible
materials (ash) resulting primarily from lubrication oil and
fuel additives. The removal of the ash from the DPF is
called "cleaning" and is done much less frequently than
regeneration. Intervals for DPF cleaning generally vary
from biannually to annually, or longer, depending on
engine-out PM emissions. Monitoring engine exhaust
backpressure is the best way to determine if and when
DPF cleaning is necessary. The need for very frequent
filter cleanings may indicate incomplete filter regeneration
orthe need forengine maintenance. Periodic filtercleaning
for ash removal is necessary for both active and passive
DPF systems.
In general, cleaning requires heating the filter and using
compressed air combined with a vacuum system to blow
the ash from the filter and capture it in a sealed container.
EPA-420-F-09-009
February 2009
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Professional filter cleaning services are available. Highly
automated cleaning stations are also becoming available,
allowing fleet service technicians to perform cleaning on-
site. Costs for cleaning stations or professional cleaning
services should be considered when purchasing DPFs.
Cleaning requires manually removing the DPF from
the vehicle. If equipment down time during cleaning is a
concern, fleets may consider buying extra filters so that
each vehicle will always be equipped with a filter. The filter
must be reinstalled on the original vehicle and in the correct
flow direction to maintain proper operation. Track the serial
numbers for each retrofit device and which vehicle on
which it is originally installed. Removal of the DPF for filter
cleaning and reinstallation is typically performed by fleet
service technicians.
It is important that all vehicle/equipment operators and fleet
service technicians are properly trained on filter cleaning
procedures.
Engine Maintenance
It is important to properly maintain vehicles and monitor
fuel and lubrication oil consumption. A bad fuel injector or
increased in oil consumption may be masked by a DPF. A
DPF may be damaged by a poorly maintained engine.
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