Exhaust gas purification system for an internal combustion engine

An exhaust gas purification system for an internal combustion engine comprising:

• an internal combustion engine capable of fuel combustion at lean air-fuel ratios, the engine having a combustion chamber, an intake conduit, an exhaust conduit, and a fuel injection valve for injecting fuel into the intake conduit or the combustion chamber;
• a catalyst installed in the exhaust conduit of the 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 exhaust gas from the engine under oxidizing conditions and in the presence of hydrocarbons;
• engine operating condition detecting means for detecting a current operating condition of the engine;
• engine operating range determining means for determining whether or not the current engine operating condition detected by the engine operating condition detecting means is within an insufficient HC amount range where an amount of hydrocarbons included in the exhaust gas from the engine and supplied to the catalyst is insufficient for the catalyst to reduce the nitrogen oxides included in the exhaust gas;
• and
• HC amount control means for momentarily degrading atomization of fuel injected from the fuel injection valve to thereby increase the amount of hydrocarbons included in the exhaust gas from the engine when the engine operating range determining means determines that the current engine operating condition is within the insufficient HC amount range.