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Pollution is worsening in cities. The exhaust gas from vehicles is the main cause of air pollution in cities. The major drawback of the diesel engine is the Particulate Matter (PM) contained in the exhaust fumes which is also said to lead to cancer. For about 20 years many tests have been conducted in order to reduce PM in diesel exhaust gas. However the exhaust gas in present diesel engines contains a significant amount of PM. This is because there is no practical material for the Diesel Particulate Filter (DPF). Conventional ceramic materials have problems such as cracking and melting during regeneration and conventional metal materials lack adequate corrosion resistance for practical use. The authors present a new type of DPF made of metal porous matter (Celmet) which is designed with a thermal construction and simple control system in order to solve the problem of diesel exhaust gas.

Diesel Particulate Filter (DPF) is one of the promising methods to reduce diesel engine exhaust particulates which cause environmental pollution. Several materials have been studied for DPF for about 15 years. However the ceramic honeycomb type DPF system has problems such as cracking and melting during regeneration and the metal type DPF system is trouble with corrosion and low trapping performance. Currently there are no practical materials for DPF. This paper presents new metal porous matter (Celmet) which have low corrosion in high temperature exhaust gas and high trapping performance, and which is suitable as a DPF. We mainly discuss the relation between the porous metal structure and trapping performance and between the metal component and corrosion in high temperature exhaust gas.