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The cordierite filter has been widely studied because of it's inherent, high capacities in the collection efficiency and heat-resistance. During the regeneration process of a cordierite filter, failure of ignition or incomplete burning propagation occurs, and additionally melts or cracks develop sometimes. In this study, the problems stated above are considered from a new standpoint, and a regeneration method that does not strictly depend on accumulated soot quantity is discussed. A filter made of SiC (Silicon carbide) possesses the requisite electric resistance and it's possible to heat it uniformly by using electricity. Accumulated soot can be uniformly incinerated not by burning propagation but by simultaneous ignition and burning of all accumulated soot. Silicon carbide has a higher resistance to heat than cordierite. Therefore, a self-heating filter made of SiC makes it possible to regenerate the filter in a wider range of accumulated soot.

In addition to PM total matter, PM size distribution is recently receiving increased attention because of the dependency of PM size on human health effects. Thus, PM size distributions and the emission behavior under various driving patterns are becoming important in diesel particulate emissions. Electrical Low Pressure Impactor (ELPI)_is a candidate to measure continuously, not only PM mass, but also particulate size distribution. Therefore, we investigated using ELPI to measure diesel particulate mass and size distribution, together with time series behaviors under various driving patterns. This study demonstrated the feasibility of continuous measurement of PM size distribution by means of an ELPI. The typical PM size distribution curve on weight base has a peak of 0.18 micrometer. The typical PM size distribution curve on number base has a peak of 0.11 micrometer. Engine load influences these characteristics.

Direct injection natural gas engines need to produce in the mixing process between the fuel jet and the air in the cylinder a “stratified” fuel-air mixture, with an easily ignitable composition near the spark plug at the time of ignition. Stratified-charge engines have a tendency to produce high NOx emissions due to the high temperature of burning areas at the start of combustion since the fuel-air mixture is not uniform. Therefore, it is necessary to reduce NOx emissions from direct injection natural gas engines. The objective of this study is to investigate measures to reduce emissions, especially NOx emissions, from direct injection natural gas engines. A single cylinder test engine was equipped with a newly developed high-pressure electromagnetic injector and a spark plug.