Exhaust gas purifying system and exhaust gas purifying method using the same

An exhaust gas purifying system, comprising:

• an internal combustion engine which generates exhaust gas;
• an exhaust gas flow path connected to the internal combustion engine;
• a NOx purifying catalyst disposed in the exhaust flow path to purify nitrogen oxide in the exhaust gas;
• an HC generator, disposed upstream of the NOx purifying catalyst in the exhaust gas flow path, to generate at least one of acetylene, a hydrocarbon with a carbon number of 2 to 5 other than acetylene, and an aromatic hydrocarbon from a hydrocarbon contained in an exhaust gas;
• and
• an engine control unit, connected with the internal combustion engine, configured to control the internal combustion engine to adjust an oxygen concentration in the exhaust gas supplied to the HC generator to 0.8 to 1.5 vol % to generate hydrogen in the HC generator when an air-fuel ratio of the exhaust gas is stoichiometric or rich.