Secondary Emissions from Catalytic Active Particle Filter Systems 2003-01-0291
Fine pored hot gas traps have filtration efficiencies exceeding 99% of the solid particles in the diesel exhaust gas. There is a favorable trend to deploy this technology ex-factory and retrofitting on-road and off-road engines.
The trap system however functions as a chemical reactor. The filter has a large effective area and the engine exhaust gas has plenty of reactants, which can promote undesirable chemical reactions that release toxic secondary emissions. These effects may be amplified when traps have catalytic influence, e.g. due to surface coatings or fuel-borne catalysts.
The VERT suitability tests for particle trap systems therefore include a detailed test procedure for verifying the presence of over 200 toxic substances. These include PAH, nitro-PAH, chlorinated dioxins, furans as well as metals.
The paper describes test procedures, test reporting, sample extraction and analysis. Experimental results are obtained for three important topics: dioxins and furans do not form in most trap system. An exception is additives containing copper, which can cause four orders of magnitude jump in these highly toxic emissions. Trap technology curtails the less volatile but tends to increase the more volatile nitro-PAH. Traps coated with precious metals can cause massive increase in NO2 emissions and pronounced sulfating.
The results substantiate the necessity to certify particle trap systems after investigating any possible secondary emissions. This requirement is legislated in Switzerland.