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. No deterioration in the filtering efficiency of particulate matter has been noted after the bus cycle test of 400 hours.
EFFEctive use of public transportation systems can prevent the increase in automotive traffic in cities. It will therefore be beneficial in large cities to reduce particulates emitted from diesel vehicles, thus making public transportation systems, low polluting. Specifically talking, city buses which run closer to pedestrians and residents, should emit exhaust gas which is less polluting.
It is known that diesel particulate filters (DPFs) are effective for reducing particulate matters emitted from diesel engines, and field tests are being conducted actively on city buses equipped with DPF systems in Europe and USA. (1,2)* It was desirable that such field tests would be also conducted in Japan. It is difficult, however, to control driving tests of DPF systems equipped city buses while in service. Therefore we carried out engine bench tests, for the purpose of studying practicality of DPF systems efficiently, simulating actual driving of city buses.
Driving data of route buses operating in Tokyo were collected and analyzed for driving characteristics, and a typical city bus driving pattern was derived for use with tests on DPF systems. The city bus driving pattern was converted to a city bus cycle consisting of engine torques and speeds for engine dynamo test. Four DPF systems of different specifications were attached to a bus engine one after the other, and each system was tested on the city bus driving pattern cycle for an accumulated loading time of 400 hours and evaluated for practicality.