Catalisis

Washington State University Extension Energy Program

Diesel Oxidation Catalyst A diesel oxidation catalyst (DOC) is a flow through device that consists of a canister containing a honeycomb-like structure or substrate. The substrate has a large surface area that is coated with an active catalyst layer. This layer contains a small, well dispersed amount of precious metals such as platinum orpalladium. As the exhaust gases traverse the catalyst, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles (unburned fuel and oil) are oxidized, thereby reducing harmful emissions. About 30 percent of the total particulate matter (PM) mass of diesel exhaust is attributed to liquid hydrocarbons, or soluble organic fraction (SOF). (See Ref. 1.) Under certain operating conditions,DOCs have achieved SOF removal efficiencies of 80 to 90 percent. (Refs. 1, 2) As a result, the reduction in overall PM emissions from DOC use is often cited at 20 to 50 percent. Actual emission reductions vary however, as a result of engine type, size, age, duty cycle, condition, maintenance procedures, baseline emissions, test procedure, product manufacturer and the fuel sulfur level. Emissions Intheir 1999 review of heavy-duty diesel retrofits, the U.S. Environmental Protection Agency summarized emissions data for 60 heavy-duty diesel two and four stroke engines utilizing DOC technology (Ref. 3). The following table presents these results, which ranged from 19 to 50 percent reduction in total PM, with an average PM reduction of 33 percent. Table 1 Diesel Oxidation Catalyst Use in HeavyDuty Diesel Study/report PM Reductions Urban Bus and Engelhard Data 38% avg.-two stroke; 27% avg.-four stroke SAE 960134 32.8% avg. (2-two stroke; 5-four stroke) SAE 970186 24% avg. (5-twostroke; 5-four stroke) SAE 932982 44-60% (four stroke) SAE 950155 32-41% (two stroke) London Bus Report –MBK 961165 45% (6-four stoke) Engelhard Report-980342 49% (avg for three catalysts) APTA Report 19-44% (twostroke) Source: Heavy-Duty Diesel Emission Reduction Project Retrofit/Rebuild Component, US EPA, EPA420R-99-014, June 1999. In developing the California Diesel Risk Reduction Program, the California Air Resources Board (CARB) also reviewed a number of products and technologies that were reported to reduce diesel particulate emissions.(Ref. 2) While much of this information was based on manufacturerprovided data, it provides a reasonable summary of DOC technology at that time. The PM reductions identified are similar to those reported by EPA’s 1999 study of diesel retrofit technologies. CARB reported achievable emission reductions resulting from DOC use ranging from 16 to 30 percent depending on product and test cycle. A summary of the CARB analysis is presented in Table 2. Table 2 DieselOxidation Catalyst PM Emission Test Results Test ISO 8178-D2 ISO 8178-D2 8-mode Engine type Ford-150 hp Ford-150 hp 1979 Deutz F6LPM Control Efficiency 8% 21% 16%

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steady- state Transient cyclebulldozer FTP FTP 912W Cummins TD-25G 450 Hp 1992 Cummins L-10 280 Hp 1998 DDC Series 60 400Hp

24% 30%

5 separate DOCs- 23%, 25%, 5%, 29%,27%. Source: Diesel PM Control Technologies-Appendix IX, California Air Resources Board, October, 2000. A number of other studies also document the effectiveness of DOCs in reducing PM emissions, with PM emission reductions of 23 percent or more. (Refs. 4,5) However, emission results will vary and retrofit device performance should be verified. To date, the EPA has verified PM reductions of 25percent for three manufacturers of DOCs. Verification data is available at http://www.epa.gov/otaq/retrofit/retroverifiedlist.htm. California also provides a list of verified DOCs at http://www.arb.ca.gov/diesel/verifieddevices/verdev.htm. Cost The initial cost of DOCs will vary with engine size, application, and sales volume. CARB reported costs ranging from $2,100 for a 275 horsepower engine, to as...