Emission Control Systems: Description and Operation

The emission control systems are used to reduce harmful gases (CO, HC, and NOx) in accordance with federal and state regulations.

Four basic systems are used.

1. CRANKCASE EMISSION CONTROL SYSTEM.
The crankcase emission control system prevents blow-by gases from escaping into the atmosphere. The blow-by gases in the crankcase are routed, through various components, back into the intake manifold for combustion.

2. COMPUTERIZED ENGINE CONTROL SYSTEM.
The computerized engine control system is made up of an electronic control unit (ECM), various sensors and output devices. This system controls engine operation (i.e. A/F mixture, idle speed and ignition timing) to reduce pollutants while maintaining optimum driveability conditions and reducing fuel consumption.

3. EVAPORATIVE EMISSION CONTROL SYSTEM.
The evaporative control system prevents fuel vapors from escaping the fuel tank into the atmosphere. It consists of a charcoal canister, gravity/roll-over valve, solenoid valve(s), and vapor hoses. The system collects fuel vapors from the fuel tank and directs them to a charcoal canister to be condensed and stored. When the engine is running, fuel and vapors stored in the canister are drawn into the engine to be burned.

4. EXHAUST EMISSION CONTROL SYSTEM.
The exhaust emission control system can (depending on model and engine) consist of three-way catalytic converters and an exhaust gas recirculation valve to reduce exhaust emission levels.