Importance

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Abstract

An exhaust gas purification system for an internal combustion engine includes an engine capable of fuel combustion at lean air-fuel ratios, a catalyst constructed of zeolite carrying at least one kind of metal selected from transition metals and noble metals to reduce NOx under oxidizing conditions and in the presence of HC, engine operating condition detecting means for detecting the current engine operating condition, engine operating range determining means for determining whether or not the current engine operating condition is within an insufficient HC amount range, and an HC amount control means for controlling the amount of HC included in the exhaust gas when the engine operating range determining means determines that the engine operating condition is within the insufficient HC amount range. The HC amount control means degrades automization or evaporation of fuel injected from a fuel injection valve to thereby generate unburned fuel and to increase the HC amount in the exhaust gas, so that the NOx purification rate of the catalyst is improved.

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First Claim