US Patent 7096664 Internal combustion engine

An internal combustion engine is provided in which the temperature of an exhaust gas gradually decreases from its upstream side to its downstream side, and the temperature of a working medium of a heat exchanger, which flows in the opposite direction to the exhaust gas, gradually increases from its upstream side to its downstream side. The temperature difference between the exhaust gas temperature and the working medium temperature is the smallest at the interface between a liquid phase region and a two-phase region of the working medium, and since a catalyst device is incorporated at the upstream side, relative to the flow of exhaust gas, of the vicinity of the position where the temperature difference is the smallest, it is therefore possible for the heat exchanger to utilize the heat generated by the catalyst device effectively. Since the catalyst device is disposed in the two-phase region of the working medium, in which the temperature is constant, and this constant temperature is a temperature at which the catalyst is active, the catalyst can exhibit a stable exhaust gas purification performance.