Technical Bulletin
Diesel Particulate Filter
Operation and Maintenance
National Clean Diesel Campaign
www.epa.gov/cleandiesel
This bulletin is intended to provide general guidance.
Diesel Particulate Filter (DPF) manufacturers and product
suppliers should provide more detailed device-specific
information and training to vehicle service technicians
on proper retrofit product maintenance procedures for a
specific product. DPFs are currently installed on all new
on-highway engines in the United States, and DPFs may
also be installed on most vehicles as a retrofit device.
DPF Operation
DPFs work by physically trapping and removing
particulate matter (PM) from the engine's exhaust. The
DPF can accumulate and combust PM within the filter
element to achieve greater than 85 percent reductions in
PM emissions. The combustion of PM in a filter occurs
during regeneration. During normal operation a DPF will
cause fluctuations in exhaust backpressure as PM is
accumulated. Consequently, a DPF is used in conjunction
with an exhaust backpressure monitoring system.
Inlet
Catalyst
Fitter-
Outlet
Diesel Particulate Filter (DPF)
Backpressure Monitoring
As a 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.
Collected PM is combusted and reduced to ash during
filter regeneration, effectively unblocking the pores of
the filer element and decreasing exhaust backpressure.
Normal filter operation will include fluctuations in exhaust
backpressure; however, overtime the accumulation of ash
will gradually continue to increase backpressure. Long
term buildup of ash is remedied by periodic filter 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.
Filter Regeneration
Regeneration occurs when the filter element reaches
the temperature required for the combustion of the
accumulated PM, converting it primarily to ash, gaseous
carbon dioxide (CO2) and water (H2O).
"Passive" regeneration occurs when the exhaust gas
temperatures are high enough to initiate combustion of
the accumulated PM in the DPF, without added fuel, heat
or driver action. "Active" regeneration may require driver
action and/or other sources of fuel or heat to raise the
DPF temperature sufficiently to combust accumulated
PM. Active regeneration can be accomplished either
during normal vehicle operation or during a controlled
event while the vehicle is stationary. During operation,
active regeneration may use extra fuel to raise the DPF
temperature to combust accumulated PM. An active
system that requires the vehicle to remain stationary
dictates the time required every shift or every day that
the vehicle must be out of service. The frequency of
regeneration is determined by the engine's duty cycle, PM
emission rate, filter technology, and other factors. When
using an active filter, it is particularly important to follow
the manufacturer's instructions for regeneration.
EPA-420-F-10-027
May 2010
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DPF Maintenance
In addition to PM, the filter also traps noncombustible
materials resulting primarily from lubrication oil and fuel
additives (ash). Cleaning of ash from retrofit DPFs is
typically required every 6 to 12 months. An engine emitting
excessive PM or experiencing inadequate regeneration will
cause a DPF to require more frequent cleaning. Diagnostics
should be performed to identify the cause for more frequent
cleaning intervals. It is important to avoid excessive PM
and ash accumulation in a DPF, so proper maintenance
and cleaning instructions should be followed closely. A
backpressure monitoring system should always be used
with a DPF and periodic inspection of the monitoring
system should be performed to confirm proper operation.
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.
Cleaning requires manually removing the DPF from the
vehicle and placing it in a cleaning station designed for this
purpose. Highly automated cleaning stations are becoming
available, allowing fleet service technicians to perform
cleaning on-site. Professional filter cleaning services are
also available. Costs for cleaning stations or professional
cleaning services should be considered when purchasing
DPFs.
If equipment down time during cleaning is a concern, fleets
may consider buying extra filters to have in stock at the time
of cleaning. The filter must be reinstalled in the correct flow
direction to maintain proper operation. 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.
Documentation should remain with the vehicle and/or in fleet
records which lists installation and vehicle information such
as mileage, opacity readings, date, device model number,
DPF serial number, installer, etc. Records should also be
maintained to document when service is performed and
when the DPF is cleaned. If a fleet moves a DPF between
different vehicles, records should be carefully monitored to
identify if a particular vehicle or device appears to require
different service intervals than another.
Engine Maintenance
It is important to properly maintain vehicles and monitor
fuel and lubrication oil consumption. A bad fuel injector or
increase in oil consumption may be masked by a DPF. The
DPF may be damaged by a poorly maintained engine. When
a DPF is removed for cleaning, it may be useful to check
the opacity of the vehicle to determine if a potential engine
problem exists. Maintaining service records is advisable to
track potential concerns or changes in operation.
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