How Emission Control Works - Porsche 911 GT3 Owner's Manual

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
exhaust 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
permitted 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 undesi-
rable pollutants in the exhaust gas before it is
released into the atmosphere.
The exclusive use of unleaded fuel is criti-
cally important for the life of the catalytic
converters. Therefore, only unleaded fuel
must be used.
The catalytic converters will be damaged by:
– push or tow starting the vehicle
– misfiring of the engine
– turning off the ignition while the vehicle is
moving or
– driving until the fuel tank is completely empty
– by other unusual operating conditions.
f Do not continue to operate your vehicle under
these conditions, since raw fuel might reach
the catalytic converters. This could result in
overheating of the converters. Federal law
prohibits use of leaded fuel in this car.
Maintenance, Car Care
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