As the name suggests, the Diesel Particulate Diffuser minimises the amount of PM a truck emits via the exhaust.
(PM is a combination of black smoke and invisible particles emitted from a truck exhaust under load, and is formed during incomplete combustion of fuel. Composed of elemental carbon, heavy hydrocarbons and hydrated sulphuric acid)
The DPD, which is located midway along the truck's exhaust, combines an oxidation catalyst to clean nitrogen oxides and hydrocarbons, and a ceramic filter that traps PM.
Pressure differential sensors within the ceramic filter are used to monitor the accumulation of trapped PM. Once a certain amount of PM is detected, the ceramic filter regenerates; this is done via post-injection which elevates the exhaust gas temperature to burn off the accumulated PM.
The cleaning process is aided by precision control of the exhaust brake and exhaust throttle, which assists in raising the exhaust gas temperature, promoting PM burning.
The truck's engine control unit (ECU) continually monitors the condition of the ceramic filter, and under most operating conditions regenerates the filter automatically without the driver even knowing. However, in some circumstances, the filter will require manual regeneration.
Manual regeneration
Where the truck's operating temperature does not reach the required level for automatic regeneration, generally due to a short distance travelled or the truck's engine being frequently turned on and off, manual regeneration may be required.
The DPD warning lamp in the instrument cluster will begin to flash slowly alerting that manual regeneration will be required within the next 60 to 100 kilometres, depending on the model.
Within this distance, the driver will need to engage the manual regeneration cycle - stop the truck, keep the engine idling and press the DPD button. Regeneration takes between 15-20 minutes, during which time the truck must remain stationary.
