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A modular particulate trap system for buses, trucks and other applications consiting of honeycomb traps and an electrical regeneration system has been designed and tested on a test bench and in a city bus. For regeneration, the soot is ignited at the entrance of the trap channel by electric heaters. After ignition, the soot burns self-supporting without further energy supply. Regeneration is possible over the whole engine map. The electrical energy consumption of the heaters for a city bus is in average below 100 W. The filtration efficiency of the system including regeneration is about 80 % during transient city driving. During regeneration, appr. 98 % of the accumulated hydrocarbons adsobed to the soot in the trap are burned off the initiated combustion front. Additionally, the odor of the diesel engine exhaust gas behind the trap is lowered at low engine load even during regeneration.

Particulate traps reduce particle emissions through the physical filtration of solid, predominantly carbonaceous particles and decreasing particle-bound hydrocarbon emissions. Catalyst coated and uncoated traps were examined for their ability to reduce particle-bound hydrocarbons. At low exhaust temperatures some volatile hydrocarbons are particle-bound in the trap and are physically retained. These components become gaseous and are purged from the trap with sharp exhaust temperature rises. Oxidation catalysts considerably improve the ability of traps to decrease particle-bound hydrocarbon emissions, particularly PAH at low exhaust temperatures. Precious metal coated traps generate sulfate particles so that especially at high exhaust temperatures the overall filter efficiency can be reduced.