How Emission Control Works - Porsche Cayenne 2009 Owner's Manual

Parking
Danger!
Danger of fire resulting in serious personal
injury or death.
f Do not park or operate the vehicle in areas
where the hot exhaust system may come in
contact with dry grass, brush, fuel spill or
other flammable material.
f If your car catches on fire for any reason, call
the fire department. Do not endanger your life
by attempting to put out the fire.
Undercoating
Danger!
Danger of fire resulting in serious personal
injury or death.
f Do not apply additional undercoating or rust-
proofing on or near the exhaust manifold,
exhaust pipes, catalytic converters or heat
shields. During driving the substance used for
undercoating could overheat and ignite.
266
Maintenance and Car Care

How Emission Control Works

When an automobile engine is running, it uses
energy generated through the combustion of a
mixture of air and fuel. Depending on whether a
car is driven fast or slowly or whether the engine
is cold or hot, some of the fuel (hydrocarbons)
may not be burned completely, but may be
discharged into the engine crankcase or exhaust
system. Additonal hydrocarbons may enter the
atmosphere through evaporation of fuel from the
fuel tank. These hydrocarbons (HC), when
released into the air, contribute to undesirable
pollution.
In addition, carbon monoxide (CO) and oxides of
nitrogen (NOx) contribute to engine emissions.
They, too, are formed during the combustion
process and discharged into the exhaust system.
To reduce these pollutants, your Porsche is
equipped with a precisely calibrated fuel injection
system to assure a finely balanced air/fuel mixture
under all operating conditions.
Oxygen sensor
The oxygen sensor, installed in the exhaust pipe
continuously senses the oxygen content of the ex-
haust and signals the information to an electronic
control unit. The control unit corrects the air/fuel
ratio, so the engine always receives an accurately
metered air/fuel mixture.
Crankcase ventilation
Through crankcase ventilation, undesirable
emissions from the engine crankcase are not per-
mitted to reach the outside atmosphere. These
emissions are recirculated from the crankcase to
the air intake system. From here the emissions
mix with the intake air and are later burned in the
engine.
Catalytic converters
The catalytic converters are efficient "clean-up"
devices built into the exhaust system of the
vehicle. The catalytic converters burn the
undesirable pollutants in the exhaust gas before it
is released into the atmosphere.
The exclusive use of unleaded fuel is critical-
ly important for the life of the catalytic con-
verters. Therefore, only unleaded fuel must
be used.