Does the EPA verify these emission reductions?
Yes, EPA verifies individual DPFs based on information supplied to the
EPA by the DPF manufacturer. Since EPA generally receives results of
testing conducted on a limited number of diesel engine models, a conservative
approach is taken to establish the verified levels of reduction. In
most cases the actual reductions are higher than the verified values. For a
list of DPFs and other technologies that EPA has verified, visit:
www.epa.gov/otaq/retrofit/retroverifiedlist.htm. For more information
about EPA’s verification process, visit:
http://www.epa.gov/otaq/retrofit/verif-process.htm.
How much does a DPF cost?
DPFs for school buses currently cost between $5,000 and $10,000. The
cost depends on the specific bus engine and operating characteristics,
such as exhaust temperatures. Field experience suggest DPFs take about
6-8 hours to install.
What type of fuel does a DPF require?
DPFs must be used with ultra-low sulfur diesel fuel (ULSD – 15 parts per
million sulfur). Use of regular diesel fuel in a DPF equipped bus could
eventually clog the filter. This could lead to exhaust back-pressure increases
and engine damage.
Currently, ULSD costs between 8 and 25 cents per gallon more than
regular diesel. ULSD is available in many parts of the country now and
will be available nationwide beginning in 2006.
Can a DPF be used on any engine?
No. DPFs work best on engines built after 1995. Therefore, knowing the
age and type of each engine in the fleet as well as the exhaust temperature
is an important part of any retrofit project. These factors determine
whether or not vehicles are candidates for filters.
Are there special maintenance requirements for a
DPF?
Manufactures of DPFs recommend that the device be cleaned about
every 100,000 miles. Some of the PM collected does not completely
oxidize and inert ash remains in the filter. After about 100,000 miles this
ash should be removed by blowing or vacuuming it out. Generally this
process takes no more than 3 hours.
H
ow long does a DPF last?
Most DPFs come with 100,000 to 150,000 mile warranty, and can last 7
to 15 years.
Where can I get a DPF?
For more information about manufacturers of DPFs or other retrofit
equipment visit our Web site at: http://www.epa.gov/otaq/retrofit/contacts.htm.
Partial Flow Filters (FTF)
Operating Characteristics and Performance
Flow-through filter technology is a relatively new method for reducing diesel PM
emissions. Flow-through filters employ catalyzed metal wire mesh structures or tortuous flow,
metal foil-based substrates with sintered metal sheets to reduce diesel PM. Technologies
verified to date employ catalysts and/or fuel-borne catalysts to oxidize diesel soot as the exhaust
flows through these more turbulent flow devices. This technology is expected to be more widely
applicable than high efficiency filters because it is much less likely to plug under unfavorable
conditions such as high engine-out PM emissions. Flow-through filters are capable of achieving
PM reduction of about 30 to 75 percent.
Operating ExperienceA flow-through filter based on a tortuous metal foil substrate that contains sintered metal
foil sheets is currently offered in Europe as a retrofit technology for a range of late-model diesel
passenger cars. This metal foil-based filter is offered by one engine manufacturer in Europe on a
family of new heavy-duty diesel engines. A similar flow-through metal filter substrate has
recently been verified as a Level 2 technology by ARB with PM reduction of greater than or
equal to 50 percent. Catalyzed wire mesh flow-through filter retrofit technologies have also
been verified by both ARB and EPA for a range of onroad engine applications. Thus far, there
have been limited commercial use of retrofit flow-though filters but there is an increasing
interest in this technology due to its ability to significantly reduce PM emissions from older,
"dirtier" diesel engines.
Crank-Case Filters (CCFs)
Today, in most turbocharged aftercooled diesel engines, the crankcase breather is vented to the atmosphere often using a downward directed draft tube. While a rudimentary filter is often installed on the crankcase breather, substantial amount of particulate matter is released to the atmosphere. Emissions through the breather may exceed 0.7 g/bhp-hr during idle conditions on recent model year engines. For MY 1994 to 2006 heavy-duty diesel engines, crankcase PM emissions reductions provided by crankcase emission control technologies range from 0.01 g/bhp-hr to 0.04 g/bhp-hr or up to 25 percent of the tailpipe emission standards.
One solution to this emissions problem is the use of a multi-stage filter designed to collect, coalesce, and return the emitted lube oil to the engine's sump. Filtered gases are returned to the intake system, balancing the differential pressures involved. Typical systems consist of a filter housing, a pressure regulator, a pressure relief valve and an oil check valve. These systems greatly reduce crankcase emissions. Crankcase emission controls are available as a retrofit technology for existing diesel engines or as an original equipment component of a new diesel engine.
