Exhaust Particulate Filter System Description
Diesel Particulate Filter (DPF)
The diesel exhaust aftertreatment system consists of an under
hood catalyst and an underbody catalyst, which includes the main
diesel oxidation catalyst and coated diesel particulate filter. 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
aftertreatment system reduces exhaust emissions such as
hydrocarbons, carbon monoxide (CO) and particulate matter. The DPF
collects particulate matter from the engine exhaust to minimize
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 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.
DPF Differential Pressure Sensor
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, 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.
Exhaust Gas Temperature Sensor
The exhaust gas temperature sensor is a variable resistor that
measures the temperature of the output of the under hood catalyst
and the underbody catalyst . The engine control module (ECM)
supplies 5 volts to the exhaust gas temperature sensor signal
circuit and supplies a ground to the low reference circuit.
DPF Cleaning
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 oxidized or
burned off to carbon dioxide (CO2).
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