Emission Control Systems: Description and Operation

Emission controls can be separated into four groups of control systems designed to reduce CO, HC, and NOx emissions.

EVAPORATIVE EMISSION CONTROL SYSTEM (EVAP)

Evaporative Emission Control System:

The EVAP system stores fuel vapor in a charcoal canister when the engine is not running. Stored vapor is drawn into the dynamic chamber and burned when the engine is started.

EXHAUST GAS RECIRCULATION (EGR)

Exhaust Gas Recirculation (EGR) System:

The EGR system introduces exhaust gas into the intake manifold to lower peak combustion chamber temperatures and reduce NOx in the exhaust gas. It operates depending on engine load, engine speed, and coolant temperature.

POSITIVE CRANKCASE VENTILATION SYSTEM (PCV)

Positive Crankcase Ventilation (PCV) System:

The PCV valve is operated by intake manifold vacuum. When running at idle, the valve is opened slightly and a small amount of blow-by gas is drawn in. At higher engine speeds, the valve opens further and more blow-by gas is drawn in. The system relieves crankcase pressure without allowing vapors to escape to atmosphere.

THREE WAY CATALYTIC CONVERTER (TWC)

Exhaust System With Catalytic Converter:

Catalytic converters stimulate chemical reactions that change CO, HC, and NOx into carbon dioxide, water vapor, and nitrogen gas. Catalyst elements used are the metals platinum, palladium, and rhodium.