Exhaust gas purification system for an internal combustion engine
First Claim
1. A system for purifying exhaust gas from an internal combustion engine capable of executing fuel combustion at lean air-fuel ratios comprising:
- a nitrogen oxide reducing catalyst installed in an exhaust conduit of the engine and constructed of zeolite carrying at least one kind of metal selected from transition metals and noble metals, wherein the catalyst produces active species through partial oxidation of the hydrocarbons in an oxidizing gas condition and causes the active species to react with nitrogen oxides included in the exhaust gas to reduce the nitrogen oxides, wherein said catalyst reduces nitrogen oxides more strongly in a catalyst temperature rising condition than in other catalyst temperature conditions; and
means for systematically producing a catalyst temperature rising condition while the engine is running by repeatedly executing a cycle of cooling the catalyst and then stopping the cooling to allow the catalyst to rise in temperature.
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Accused Products
Abstract
An exhaust gas purification system for an internal combustion engine includes a catalyst installed in an exhaust conduit of an engine and constructed of zeolite carrying at least one kind of metal selected from transition metals and noble metals to reduce nitrogen oxides included in the exhaust gas from the engine under an oxidizing gas condition and in the presence of hydrocarbons. The system further includes means for repeating a cycle of cooling the catalyst and then stopping the cooling to allow the catalyst to rise in temperature so that the temperature rising courses of the catalyst are positively and repeatedly produced. Since the catalyst can show a higher nitrogen oxides reducing ability in the temperature rising course than in the temperature lowering course, the NOx purification rate is greatly improved due to the positive production of the temperature rising courses.
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Citations
22 Claims
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1. A system for purifying exhaust gas from an internal combustion engine capable of executing fuel combustion at lean air-fuel ratios comprising:
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a nitrogen oxide reducing catalyst installed in an exhaust conduit of the engine and constructed of zeolite carrying at least one kind of metal selected from transition metals and noble metals, wherein the catalyst produces active species through partial oxidation of the hydrocarbons in an oxidizing gas condition and causes the active species to react with nitrogen oxides included in the exhaust gas to reduce the nitrogen oxides, wherein said catalyst reduces nitrogen oxides more strongly in a catalyst temperature rising condition than in other catalyst temperature conditions; and means for systematically producing a catalyst temperature rising condition while the engine is running by repeatedly executing a cycle of cooling the catalyst and then stopping the cooling to allow the catalyst to rise in temperature. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification