EXHAUST EMISSION CONTROLS

Systems or adjustments designed to limit noxious gases in an engine's exhaust . Such controls can be grouped into two broad categories: those designed to reduce or eliminate the formation of harmful pollutants in the engine itself (e.g., retarded spark setting) and those designed to destroy or otherwise alter the pollutants after they have been formed (e.g., air injection , thermal reactors , and catalytic converters ). Evaporative emission controls prevent gasoline vapors from escaping into the atmosphere from the fuel tank and carburetor , and crankcase controls recycle fumes from the crankcase through the engine.