Abstract: An exhaust gas purification system for internal combustion engines comprising two exhaust gas passages which are substantially equal in length and each of which has a substantially constant cross-section. A thermal reactor communicates with the exhaust gas passages, and a collector is provided on the open ends of the exhaust gas passages. Since the ignition timing of every cylinder is different from each other, the mass of exhaust gases and the mass of secondary air are ejected from the exhaust passages in different phases. The collector is formed to collect and mix the mass of exhaust gases and the mass of secondary air which are ejected from both of the exhaust gas passages at a different time, and has an outlet for discharging the exhaust gases and the secondary air into the chamber of the thermal reactor with mixing thereof.

Abstract: An internal combustion gasoline engine comprises a determined region which is so formed in an exhaust passage from an exhaust valve to a thermal reactor as to pass exhaust gases therethrough in their discharging order, a secondary air passage with a check valve means communicating with the exhaust port near the exhaust valve, and means for maintaining the temperature of exhaust gases over the trigger temperature of the thermal reactor. The exhaust passage has a volume equal to or more than the displacement of the engine and less than four times the displacement volume and has a cross-sectional area less than three times the opening area of the exhaust valve.