Emission Control Systems: Description and Operation

Emission Control Systems:

To reduce exhaust emissions, these vehicles use an evaporative emission control system, exhaust gas recirculation system, positive crankcase ventilation system, three way catalytic converters, secondary air injection system, and electronic gasoline injection.

EVAPORATIVE EMISSION CONTROL SYSTEM (EVAP)
Evaporative emission control system stores fuel tank vapor in a canister when the engine is not running. Fuel vapor is drawn into the intake system and burned when engine is running. ECU uses a solenoid valve to regulate vapor volume and maintain proper air/fuel ratio.

EXHAUST GAS RECIRCULATION SYSTEM (EGR)
EGR system reduces NOx emissions by lowering combustion chamber temperatures. To accomplish this, the system introduces a small amount of exhaust gas into the intake manifold. It operates depending on engine load, engine speed, and coolant temperature.

POSITIVE CRANKCASE VENTILATION SYSTEM (PCV)
PCV valve is operated by intake manifold vacuum. When engine is running at idle, valve is opened slightly and a small amount of blow-by gas is drawn in. At higher engine speeds, PCV valve opens further and a larger amount of blow-by gas is drawn in.

THREE WAY CATALYTIC CONVERTER (TWC)
Catalytic converters promote reactions that change CO, HC, and NOx into carbon dioxide, water vapor, and nitrogen gas respectively. The metals platinum and rhodium are used as catalysts to stimulate the necessary chemical reactions. Vehicle uses a front converter close to exhaust manifold, and a main converter downstream.

SECONDARY AIR INJECTION SYSTEM (AIS)
This system helps to continue combustion of spent exhaust gases by introducing fresh air into the exhaust port or main converter. Routing of air pump output is ECU determined according to operating conditions and controlled by a number of solenoid valves.