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PARTICLE TRAP EFFECTS ON HEAVY-DUTY DIESEL ENGINE EMISSIONS
Impact/Purpose:
Diesel exhaust is a complex mixture of gases and particles. Thousands of chemicals, including some that are potent carcinogens in laboratory animals, are present as gases or re bound to the surface of the carbon particles. Because of the potential risk to public health when these particles are inhaled, the Clean Air Act Amendments specifically mandate reductions in particle emissions from vehicles with diesel engines. While substantial reductions have been achieved by engine refinements, new devices are being developed to reach the increasingly demanding standards required for 1994 and beyond. Among these new devices is a trap that filters the particles from the exhaust. Periodically, the trap is cleaned (regenerated) by electric heating, thereby burning the particles before they can clog the trap. Although the use of ceramic traps substantially reduced the weight of particles in diesel emissions, there is concern that potentially harmful chemicals associated with the particles may be emitted from the trap during normal use and regeneration.
Description:
The ceramic trap used in this study was highly effective in reducing particle emissions in the diesel exhaust; the weight of emitted particles and their associated chemicals in the filtered exhaust was reduced by over 90% under the two different work loads. As a consequence, the ability of the particle extract to cause mutations in bacteria was also reduced by over 90%. There was no consistent indication that increased amounts of chemicals were emitted during normal use of the trap. However, when the trap was used, a greater number of particles that were much smaller than the average diesel particles were emitted. The nature of these smaller particles is unknown and needs to be investigated. The trap had little effect on the amount and kinds of chemicals present in the gas phase, including nitrogen oxides (NOx) and hydrocarbons. Periodic combustion of the particles in the loaded trap during regeneration contributed only small amounts of additional particles and mutagenic chemicals.
This study is important because it demonstrates that using a particle trap to filter diesel exhaust reduces the amount of particles as well as the chemicals bound to them. Also important is the finding that trap use does not increase the amounts of mutagenic chemicals released as gas. The investigators made a major contribution to our understanding of the nature of emissions from modern diesel engines with new control devices by providing extensive data on chemical composition and mutagenicity of both particles and gases from the same engine. Future reports will provide information on the effects of a low-sulfur fuel on emissions from diesel engines equipped with an oxidation catalytic converter.