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Exhaust Particulate Filter System Description

The diesel exhaust after-treatment system consists of an under bonnet pre-catalytic converter (1) and an underbody catalytic converter (2), which includes the main diesel oxidation catalyst and coated diesel particulate filter (3). The diesel particulate filter (DPF) consists of a solid honeycomb-like body made from silicon carbide, which is full of microscopic channels, and is coated with noble metal. The diesel exhaust after-treatment system reduces exhaust emissions such as hydrocarbons (HC), carbon monoxide (CO) and particulate matter. The DPF collects particulate matter from the engine exhaust to minimise discharge of soot to the atmosphere. The exhaust flows through the channels and soot particles are deposited on the channel walls.

The soot particles accumulate in the channels (3) of the DPF and are burned off at regular intervals, through a process called regeneration or cleaning. The DPF cleaning process prevents the DPF from clogging. Excess soot in filter can cause a drop in engine performance and crack the filter during regeneration.

A DPF differential pressure sensor is connected across the DPF and provides feedback on soot level or exhaust back pressure to the engine control module (ECM). The pressure pipes (1, 5), which are connected to the differential pressure sensor, measure the pressure differential between the entrance and exit of the diesel particulate filter. The pressure differential or back pressure indicates the amount of soot collected in the DPF. To protect the engine, the ECM enables a regeneration when critical soot level is detected in the filter.

The exhaust gas temperature sensor is a variable resistor that measures the temperature of the output of the pre-catalytic converter and the underbody catalytic converter. The engine control module (ECM) supplies 5 volts to the EGT signal circuit and supplies a ground to the low reference circuit.

During the cleaning process, additional fuel is injected via multiple post injections to increase the exhaust gas temperature. During this period, the DPF temperature is raised to approximately 600°C (1,112°F) and the deposited soot is oxidised or burned off to carbon dioxide (CO2).