Emission Control Systems: Description and Operation

GENERAL INFORMATION
The emission control system consists of the following subsystems:

^ Positive crankcase ventilation ([1][2]PCV) system
^ Evaporative emission control (EVAP) system
^ Exhaust gas recirculation (EGR) system
^ Three-way catalytic converter


POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM
PCV system prevents blowby (emissions produced by the engine combustion chambers which escape into the crankcase) from entering atmosphere. Blowby gases are routed into intake system, where they are burned with air fuel mixture.

EVAPORATIVE EMISSION CONTROL (EVAP) SYSTEM
The EVAP system prevents evaporated fuel from escaping into atmosphere. As the fuel and vapors in the fuel system expand, they are routed to the charcoal (EVAP) canister.

The fuel and vapors are stored in the canister until certain conditions are met. When these conditions are met the purge solenoid is de-energized, allowing the engine to draw air through the charcoal canister. As the air passes through the canister it picks up fuel stored in the canister and carries it into the engine, where it is burned in the combustion process.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM
Injects a metered amount of exhaust gas into the intake manifold, lowering peak combustion temperatures. Lowering peak combustion temperatures inhibits the production of Oxides of Nitrogen (NOx) . (Production of NOx is greatest at combustion temperatures over 2300° F.)

THREE-WAY CATALYTIC CONVERTER
Changes (converts) Carbon Monoxide (CO) and Hydrocarbons (HC), into carbon dioxide (CO2) and water (H2O), in an oxidation reaction.

Changes (converts), Oxides of Nitrogen (NOx), into oxygen and nitrogen, in a reduction reaction.