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
retrofit technologies that  reduce  emissions from diesel
fueled vehicles and equipment. DOCs generally consist of
a flow-through honeycomb structure which is coated with
a precious metal  and  housed in a metal casing. As hot
diesel exhaust flows through the honeycomb structure, the
precious metal coating catalyzes a chemical 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. DOCs verified by EPA also 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
PM and nitrogen  oxide (NOx) emissions. DOCs can be
combined 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  NO  produced  by  a DOC  is  dependent on the
catalyst  formulation. EPA has  established  a limit  on
incremental NO2 from diesel retrofit devices and all DOCs
on the EPA list 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 wide 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 in order to successfully apply a particular
retrofit technology: www.epa.qov/otaq/retrofit/verif-list.htm
Fuel
Generally,  DOCs are verified for  use with Low Sulfur
Diesel fuel, which contains up to  500 parts per million
(ppm) sulfur. Ultra Low Sulfur Diesel fuel (ULSD), which
contains up to15  ppm 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 produce some
ultrafine particulates. Such  concerns are  associated
with  high sulfur levels in diesel fuel and the potential for
sulfur to accumulate in the DOC and then be released
as sulfate  particles.  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 and their installation generally range from $600
to  $2,000 or more,  depending on  engine  size  and
whether installation is a muffler replacement or custom
configuration.
                                                                                     EPA-420-F-09-012
                                                                                         February 2009

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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.
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 requirements for CARB-verified retrofit
technologies as shown in the following table.
           California Air Resources Board
               Warranty Requirement
       Refuse Truck with
Diesel Oxidation Catalyst (DOC)
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 Requirement
Two years; unlimited mileage
Five years or 150,000 miles
Five years or 100,000 miles
Five years or 60,000 miles

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