Exhaust Emission Control (Emission control - Td4)

A vacuum operated EGR valve on the inlet manifold controls the flow of recirculated exhaust gases. The exhaust gases are supplied to the EGR valve through an EGR pipe connected to the LH end of the exhaust manifold. On automatic gearbox models, a cooler, cooled by the engine cooling system, is installed between front and rear sections of the EGR pipe. From the EGR valve, the gases flow into the inlet manifold and the turbocharger inlet.

The EGR valve is controlled by an EGR solenoid, on the front of the cylinder block, which modulates a vacuum supply from the brake servo vacuum pump. The EGR solenoid is controlled by the ECM. The ECM uses the input from the air flow meter to monitor EGR operation, using the principle that an increase in EGR decreases the intake air flow.

Exhaust Emission Control

The engine management system provides accurately metered quantities of fuel to the combustion chambers to ensure the most efficient use of fuel and to minimise the exhaust emissions. In European Union markets, to further reduce the carbon monoxide and hydrocarbons content of the exhaust gases, a catalytic converter is integrated into the intermediate pipe of the exhaust system.

In the catalytic converter the exhaust gases are passed through honeycombed ceramic elements coated with a special surface treatment called 'washcoat'. The washcoat increases the surface area of the ceramic elements by a factor of approximately 7000. On top of the washcoat is a coating containing platinum, which is the active constituent for converting harmful emissions into inert by-products. The platinum adds oxygen to the carbon monoxide and the hydrocarbons in the exhaust gases, to convert them into carbon dioxide and water respectively.