Exhaust recirculation

In a spark ignited internal combustion engine having a carburetor type fuel/air induction system and an exhaust system, said engine having an exhaust recycle passage through which a portion of the exhaust gas is recycled from said exhaust system to said fuel/air induction system thereby lowering the nitrogen oxides content of the exhaust gas emitted by said engine, the improvement comprising a liquid-cooled heat exchanger in said exhaust recycle passage whereby exhaust gas flowing through said recycle passage passes through said heat exchanger and comes into heat exchange contact with the cooled surfaces within said liquid-cooled heat exchanger and is cooled below about 250.degree. F, said exhaust recycle passage including a condensate trap, said trap comprising a housing having a recycle exhaust gas inlet and outlet, said trap being operatively connected in said exhaust recycle passage between said heat exchanger and said induction system, said housing having a drain opening at a low point, said drain opening being connected by a drain conduit to said exhaust system at a location downstream from where said exhaust recycle passage connects to said exhaust system, said recycle passage being connected to deliver cooled recycle exhaust to said fuel/air induction system downstream from the throttle plate of said carburetor whereby the nitrogen oxide content of said exhaust gas is lowered to an extent substantially greater than that obtained without said cooling.