Development of PM Trap System for Urban Buses

Abstract

In response to stringent particulate matter (PM) emission regulations worldwide, developments of diesel particulate filter (DPF) continue apace in addition to engine modification for PM reduction. Particularly with buses used in urban areas, reduction methods in black smoke emissions are being researched in addition to the efforts to satisfy the aforementioned PM regulations. The system described in this paper was developed for use mainly with buses in large urban concentrations. The system consists of both wall-flow monolith filters for filtration of PM emissions and electric heaters for regeneration. A key feature of this system is that exhaust gas is used for effective combustion of PM during regeneration. Optimization of the exhaust gas flow rate drawn into the filter under regeneration has resulted in regeneration efficiency comparable with those achieved using air pumps. The difficulty of putting DPF systems to practical use has been due to cracking and melting of filters caused by excessive PM accumulation and subsequent increases in temperature in excess of tolerable levels. To prevent these problems, some means of controlling the accumulated PM mass was required. Since bus routes in large urban concentrations follow common patterns, the mass of PM accumulated over a given time period ismore » more or less constant. Thus, the amount of PM accumulated over a given time period can be estimated easily and filter damage can be prevented.« less