Emission Control System - Porsche 928 1979 Owner's Manual

How Emission Control Works
When an automobile engine is running, it
uses energy generated through the c o m -
bustion of a mixture of air and fuel. Depend-
ing on whether a car is driven fast or slow
or whether the engine is cold or hot, some
of the fuel (hydrocarbons) may not be burn-
ed completely but be discharged into the
engine crankcase or exhaust system. A d d i -
tional hydrocarbons may enter the
sphere through evaporation of fuel from the
fuel tank. These hydrocarbons released into
the air contribute to undesirable pollution.
In addition, carbon monoxide
oxides of nitrogen (NO ) contribute to harm-
x
ful engine emissions. They, too, are formed
during the combustion and discharged into
the exhaust system. To reduce these pol-
lutants all Porsche vehicles are equipped
with a special emission control system.
Your Porsche is equipped with the follow-
ing major components:
Controlled Combustion System
The amount of pollutants emitted from an
engine greatly depends on the combustion of
the air/fuel mixture. Complete burning of the
air/fuel mixture is therefore very important.
An improved combustion process
Porsche makes it possible to keep harmful
emissions from the engine at the required
low level.
Your Porsche engine
precisely calibrated
that assures a finely balanced air/fuel mix-
ture under all operating conditions. D e p e n d -
ing on engine demand the ignition distributor
is monitored via vacuum lines to assure ig-
nition at exactly the right moment for c o m -
atmo-
plete combustion.
Secondary Air Pump
(CO) and
A special air pump delivers fresh air to the
engine exhaust ports. The additional air is
used to " a f t e r b u r n "
as they leave
Through this method cleaner exhaust reaches
the outside air.
Exhaust Gas Recirculation (EGR)
Your Porsche is equipped with an exhaust
gas recirculation system. Some of the ex-
haust gas is recirculated to the engine be-
fore it reaches the muffler. The exhaust gas
recirculated into the combustion chamber of
the engine helps
oxides of nitrogen (NO
bustion process.
in your
is equipped with a
fuel injection system
the harmful emissions
the combustion chambers.
lower the formation of
) during the c o m -
x
Catalytic Converter
The catalytic converter is an efficient "clean-
u p " device built into the exhaust system of
the car to further help reduce engine pol-
lutants.
Harmful carbon monoxide and hydrocarbons
in the exhaust gas are chemically changed
into harmless carbon dioxide
vapors before they pass
through the muffler.
The use of unleaded fuel, however, is c r i -
tically important to the life of the converter.
Deposits from leaded gasolines will ruin the
catalyst and make it ineffective as an emis-
sion clean-up devise. Therefore, only un-
leaded gasoline should be used.
Crankcase Ventilation
Through Crankcase Ventilation harmful emis-
sions 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.
and water
to the outside
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