Technical  Bulletin

              Diesel Oxidation Catalyst
                  General Information
    National Clean  Diesel Campaign
           www.epa.gov/cleandiesel
Technical Overview

Diesel Oxidation  Catalysts, also  known as DOCs, are
exhaust  aftertreatment devices  that reduce emissions
from diesel  fueled  vehicles  and  equipment.  Engine
manufacturers  have  used DOCs  in  different  in-use
applications for many years, and DOCs are widely used as
a retrofit technology because of their simplicity and limited
maintenance requirements. DOCs generally consist of a
precious metal coated flow-through honeycomb structure
contained  in a stainless steel housing. As hot  diesel
exhaust  flows  through the honeycomb  structure, the
precious metal coating causes a catalytic reaction that
breaks down pollutants into less harmful components.
          Diesel Oxidation Catalyst (DOC)
Emissions Reduction

The  United  States  Environmental Protection Agency
(EPA) and the  California Air Resources Board (GARB)
evaluate the emission reduction performance of  DOCs
and identify engine operating criteria and conditions that
must exist for DOCs to achieve those reductions.
DOCs verified by EPA and GARB are typically effective
at reducing emissions of particulate matter (PM) by 20
to 40 percent. EPA's Verified Technology List also shows
that DOCs may reduce hydrocarbons by 40 to 75 percent
and carbon  monoxide by 10 to 60 percent.  The PM
removed by DOCs is largely the soluble organic fraction
that comes from unburned fuel and oil. DOCs generally
have little impact  on elemental carbon and  oxides of
nitrogen (NOx) emissions. DOCs have also been verified
in  combination with  crankcase  ventilation systems  for
additional emissions reduction.
EPA is aware of concerns that DOCs may increase the
nitrogen dioxide (NO2) fraction of total NOx emissions.
The NO2 produced by a DOC is dependent on the catalyst
formulation. EPA and GARB have established a limit on
increases in  NO2 emissions from diesel retrofit devices
and all DOCs on the lists of verified products comply with
this limit.

Application

Verified DOCs are available for nonroad and highway
heavy-duty  diesel  engines including  those on buses,
school buses,  trucks,  mining  equipment,  construction
equipment,  cargo handling equipment, marine vessels,
auxiliary power units and stationary generators.
Each DOC is verified for use with specific engines and/or
with specific configurations over a range of model years. In
addition to vehicle and engine specifications, the intended
application should be evaluated for exhaust temperature,
fuel sulfur levels and lubrication oil consumption. EPA
and CARB's lists of verified  diesel retrofit technologies
define  the  specific engine operating  criteria  required
to  successfully  apply  a  particular retrofit technology:
www.epa.gov/otaq/retrofit/verif-list.htm.
Fuel

DOCs perform best with Ultra  Low Sulfur Diesel  fuel
(ULSD), and some  DOCs are verified for use with  Low
Sulfur Diesel (LSD). ULSD, which contains up to 15 parts
per million sulfur, is required for highway vehicles and will
begin to be phased in for the nonroad sector beginning in
2010.
EPA is aware of concerns that DOCs may release some
ultrafine particulates. Such concerns are associated with
high sulfur levels in diesel fuel and the potential for sulfur
                                                                                     EPA-420-F-10-031
                                                                                             May 2010

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to accumulate in the DOC and then be released as sulfate
particles. This characteristic may also be associated with
the  precious metal loading and vehicle  operation. When
used with ULSD EPA does  not believe DOCs increase
ultrafine  PM. Although nonroad diesel  fuel will not be
required to meet ULSD sulfur levels until 2010, nonroad
equipment  equipped with  DOCs  should  preferably be
fueled with ULSD.
Cost

DOCs generally cost between $600 to $2,000 or more,
including installation, depending on engine size, installation
requirements or other unique needs. Because a  DOC is
likely to be heavier than a muffler, it is likely that special
mounting is necessary.
Longevity

When properly  installed and  maintained,  DOCs should
remain effective for the life of the vehicle, generally five
to ten years or 10,000 or more hours of operation. Engine
problems with fuel control or oil consumption may quickly
deteriorate  the  performance of a  DOC.  Consequently,
regular  engine  maintenance  is  essential  to   DOC
performance.
Warranty coverage  is typically  part of the commercial
contract negotiated  between the product suppliers and
their customers. Such warranties typically cover defects in
materials or workmanship for a specified period defined in
years, miles and/or operating hours.
As part of their verification program, GARB has established
detailed  warranty   periods  for  CARB-verified   retrofit
technologies as shown in the following table.
California Air Resources Board
        Warranty Period
Vehicle Category
GVWR > 33,000 Ibs.
hp > 250 hp and
miles/year > 100,000
Vehicle miles < 300k
GVWR > 33,000 Ibs.
hp > 250
GVWR 19,500 to
33,000 Ibs.
GVWR < 19,000 Ibs.
Warranty Period
Two years; unlimited
mileage
Five years or 150, 000
miles
Five years or 100, 000
miles
Five years or 60, 000
miles
                                                                     Refuse Truck with
                                                              Diesel Oxidation Catalyst (DOC)

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