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Brief description

Brief description

To meet the exhaust emission requirements applicable in certain markets, the cars are equipped with one of the following exhaust emission control systems:


Crankcase ventilation

• The combustion gases flowing past the pistons and piston rings must be allowed to pass out of the engine. If the gases in the crankcase are not evacuated, the pressure in the crankcase will continue to rise until something breaks. The crankcase gases must not be allowed to pass out into the engine bay as they contain a large proportion of unburnt hydrocarbons. A system which recovers the hydrocarbons and prevents the pressure in the crankcase from rising excessively is used to evacuate the gases. See .



Three way catalytic converter

• To reduce the amount of harmful exhaust gases the car is equipped with a three-way catalytic converter. The engine's exhaust gases pass through the catalytic converter where the catalytic material starts a chemical process. Provided that the closed loop fuel injection system maintains the fuel-air mixture at an optimum level, the catalytic converter reduces nitrous oxides (NO x ) and oxidizes carbon monoxide (CO) and hydrocarbons (HC). The end products are carbon dioxide (CO 2 ), water (H 2 O) and nitrogen (N 2 ).

The ability of the catalytic converter to reduce emissions is conditional on the use of unleaded petrol. Lead destroys the active components of the three-way catalytic converter. See .



Closed-loop fuel injection system

• The three-way catalytic converter has a high degree of conversion within extremely narrow limits. If the fuel-air mixture is not maintained within these limits, one or more gases will exceed permissible values. A closed-loop fuel injection system ensures that the fuel-air mixture is absolutely correct at all times. The oxygen content of the gases in the exhaust pipe before the three-way catalytic converter is used as a basis for controlling the fuel injection pulses so that the correct fuel-air mixture is maintained. The oxygen content is measured by an oxygen sensor and the value transmitted to the Trionic or Motronic engine control module which controls the fuel injection pulses to keep the fuel-air mixture at the proper level. See .



Evaporative emission system

• Hydrocarbons which evaporate in the fuel tank pass through a pipe to a canister filled with active charcoal (the evaporative emission canister) where they are stored when the engine is not running. The fuel vapours are subsequently sucked into the engine and burnt there together with the regular fuel-air mixture when the car is driven. See . For a description of ORVR, see “Evaporative emission system, ORVR“.



Deceleration device

• The purpose of the deceleration device is to prevent the emission of unburnt hydrocarbons during engine braking. It is incorporated in the IAC valve. See .