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A diesel particulate filter (DPF) for city buses was developed that combines a SiC filter and a full-flow type burner for regeneration. Filter crack problems were averted by suppressing the peak temperature inside the filter to under 900°C. This was done by setting the maximum tolerable amount of collected particulate mass before regeneration at 50 g and controlling the burner so as to increase the regeneration gas temperature slowly up to a set value. This DPF was retrofitted to a Tokyo metropolitan bus to conduct a field test. The field test has been under way for half a year without any trouble or deterioration of system performance. THE DIESEL PARTICULATE FILTER (DPF) receives much recognition as an effective tool for reducing diesel particulates. However, its practical applications are still quite limited, because to date its durability remains immature.

A recent accomplishment is a selfregenerating soot filter system developed largely for city bus application. The design consists of burner and a subsequent soot filter, which together form a complete system. The burner does not require an extra air supply as it utilizes the remaining oxygen contained in the engine exhaust gas. The burner system is microprozessor controlled and provides for automatic filter regeneration during regular vehicle operation. Since there is full exhaust flow through the filter system the design requires no moving components. A treatment of the filter body by catalyst materials is not required, neither are fuel additives for assistance with the regeneration process. This ensures highest environmental safety. Despite the high power of the burner system, the fuel consumption of approx. 0.5 1 per regeneration cycle (approx. every 6 to 8 hours) is relatively low in consideration with the overall fuel consumption.