A positive crankcase ventilation system flushes vapors from the crankcase into the intake manifold, to join with the inlet air-fuel mixture. Once there, the vapors are drawn into the engine for burning.
Maintaining the stoichiometric ratio is necessary for a catalytic converter to operate efficiently. It receives all the engine's exhaust gases, and chemically converts remaining pollutants to less harmful substances.
A closed loop is part of a feedback system that collects information on how a system is operating & feeds that information back to affect how the system is working.
Air pollutants are classified as either primary or secondary contaminants. Typically the regulated emissions are carbon monoxide, hydrocarbon, nitrogen oxides and particulate matter.
A PCV valve, controlled by manifold pressure, regulates gas flow between the crankcase and the inlet manifold. With the engine off, the valve is closed. Air cannot enter the inlet manifold. This allows the engine to start.
The EGR valve lets some exhaust gases pass into the intake system. During combustion, these exhaust gases absorb heat. This lowers peak combustion temperatures, and reduces formation of oxides of nitrogen.
Electronic fuel injection and engine management systems deal with emissions more effectively than carbureted engines by more closely controlling the air-fuel ratio entering each cylinder, and by ensuring the ignition timing matches operating conditions.
A charcoal canister can store large quantities of fuel vapor. It has connections for the fuel tank vent line, the atmosphere, and the purge line, which carries the vapors to the intake manifold.
