Emission Control Systems: Description and Operation

EXHAUST EMISSION CONTROL SYSTEM

Exhaust emissions [carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx)] are controlled by a combination of precise fuel metering (fuel injection), engine modifications, air injection reactor, a catalytic converter and other special control components. Engine design works together with intake and exhaust systems and fuel and ignition systems to produce low emissions while maintaining economy of operation and good driveability. Exhaust gas recirculation is used to reduce emissions of NOx.

CRANKCASE EMISSION CONTROL SYSTEM

A positive crankcase ventilation system is used to prevent blow-by gases escaping to the atmosphere. Fresh air from the throttle body is supplied to the crankcase, mixed with blow-by gases and then into the intake manifold through the PCV valve.
The PCV valve metered orifice limits the flow of crankcase vapors as determined by intake manifold vacuum. Under heavy acceleration or during high speed driving, manifold vacuum may be inadequate for complete scavenging of blow-by gases. When this condition occurs, excess blow-by will back flow into the air cleaner via the crankcase vent tube to be consumed by normal combustion.

EVAPORATIVE EMISSION CONTROL SYSTEM

A closed fuel tank ventilation system is used to prevent evaporative hydrocarbon emissions from escaping the fuel system into the atmosphere. Fuel tank vapors are stored in an activated carbon (charcoal) canister when the vehicle is off and vented to the intake manifold to be consumed when the engine is running.