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Four different diesel particulate filter (DPF) systems for city buses have been studied on an engine bench, and based on the results, their practicalities are discussed. On road data of buses operating in Tokyo were collected, and a city bus driving pattern for engine bench test was prepared. Evaluation tests were carried out on an engine bench using an 11-liters engine, used on city buses. The test engine equipped with a DPF system was operated on cyclic test of the city bus driving pattern for the accumulated loading time of 400 hours. Each of the DPF systems has a wall flow monolith filter. A diesel fuel burner or an electric heater with or without catalyst-coated filter is used for regeneration. It is possible to remove about 90% of particulates from the exhaust gas by the use of DPF systems for diesel engines. Soluble organic fraction (SOF) is reduced by about 30%. It is difficult to sufficiently remove SOF.

Five diesel particulate filter systems have been studied for their practicality in the case of their application to garbage trucks operating in urban areas. Driving data of garbage trucks operating in Tokyo were collected, and a driving pattern was prepared to evaluate filter systems. Test engines fitted with a wall-flow-monolith filter were in the range of 2.8 to 3.6 liters in displacement. Each test engine was operated for an accumulated loading time of 400 hours using an engine dynamometer. Regeneration used was electric heater, diesel fuel burner and intake-exhaust gas throttling. Regeneration temperature of the throttling system was lower and more stable than other systems at every regeneration. In the electric heater regeneration, on the other hand, the temperature distribution in the filter was different at every cycle, and its temperature gradient was steep.