Importance

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Abstract

An exhaust gas purification system includes a lean burn engine having an exhaust conduit, a lean NOx catalyst installed in the exhaust conduit, an HC amount increasing device capable of increasing an amount of HC included in exhaust gas flowing to the lean NOx catalyst, a catalyst temperature determining device for determining a catalyst temperature and determining whether the catalyst temperature is below a predetermined value, and an HC amount increasing device operating device capable of intermittently operating the HC amount increasing device when the catalyst temperature is below the predetermined value. The HC increased at low catalyst temperatures is partially oxidized to generate a large amount of radicals which are held within small cells of the lean NOx catalyst. When the catalyst temperature rises, the radicals held in the cells are effectively used to reduce NOx until the radicals are compensated.

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First Claim