Development of a Ceramic Particulate Trap for Urban Buses

Main aspects concerning the development of a burner-assisted ceramic particulate trap for diesel engines equipping urban buses have been examined. First of all the basic phenomena causing particulate accumulation inside the filter and chemical and physical parameters controlling regeneration have been studied. Then systematic measurements were performed in different running conditions on an urban bus equipped with a ceramic filter using a diesel fuel burner to start regeneration in order to verify the theoretical approach. These tests showed that: (1) The amount of particulate collected by the trap is a function of the different flat and/or hilly circuits inside the city; (2) regeneration has to be started with a proper amount of particulate collected (too little does not allow complete regeneration, too much is dangerous for trap life). Therefore an on-line continuous monitoring system of the particulate collected has been developed. When a certain level is exceeded, the filter is bypassed and regeneration starts. The system is based on the direct measurement of the exhaust flow by means of a Venturi and the pressure loss on the trap. The amount of particulate is defined by real time comparison of Venturi differential pressure and filter pressure loss. Urban buses were purposely designed in order to be equipped with a ceramic particulate trap plus the control unit. Tests of the system have been successfully performed on the buses operated on flat and hilly circuits inside the city.