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In order to meet the reinforcement of worldwide environmental regulations, latest diesel engines for industrial machinery are required to reduce the emission of harmful gases such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx), and particulate matter (PM). For this reason, some of the diesel engines are equipped with exhaust gas treatment devices such as diesel particulate filter (DPF), diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) catalyst. However, applications of such industrial diesel engines bring about excessive back pressure increase and deterioration in the performance of the catalysts when continuous operation is performed at low load conditions: soot accumulates on the inlet faces of DOC and DPF, causing face plugging issues. To resolve this issue, it is necessary for the system to be equipped with certain additional devices to raise an exhaust gas temperature to a high level enough to burn out the soot [1].

Diesel Particulate Filter (DPF) has become a standard after treatment device to remove particulate matter (PM) exhausted from diesel engines. Cordierite and Silicon Carbide are commonly used materials for construction of DPF. Customers, however, require further improvement concerning the performance of DPF. Cordierite has low limitation of PM loading capacity due to its lower thermal shock resistance, while silicon carbide has higher back-pressure due to its larger grain size. Generally, silicon nitride which is one of the typical thermal resistant ceramics has high mechanical strength and thermal shock resistance. Kubota's development of porous silicon nitride is structured with controlled small grain crystals of elongated hexagonal systems. This enables high PM filtration efficiency with low back pressure increase and higher filtering efficiencies for smaller PM.