Diesel Particulate Filter; Filter Regeneration; Passive Regeneration - Volvo EPA2007 D13F Reference Manual

ENGINE COMPONENT AND LOCATION 115

Diesel Particulate Filter

Basically a trap, a diesel particulate filter (DPF) collects the soot and ash to hold
until they can be burned off. A catalyzed DPF also transforms unburned fuel, engine
lubricant and carbon monoxide into carbon dioxide and water.
Depending on vehicle vocation, the operating temperature of the exhaust may or
may not be sufficient to consume the trapped soot and ash. If necessary, a means of
elevating the temperature is included in the system.

Filter Regeneration

Cleaning a filter so it can continue to function is called "regeneration." High heat with
a catalyst breaks down the chemical properties. Depending on the vehicle usage, the
engine will be equipped with a passive or an active regeneration system.
As with any filter, eventually the DOC and the DPF will become clogged. Rising back
pressure caused by plugging the exhaust system decreases fuel economy and reduces
engine efficiency. It is necessary to clean these filters from time to time.
The filters can be regenerated to continue in use. The high temperature needed to
complete the process exists in the exhaust itself. Because some vehicle vocations do
not allow the exhaust temperature to rise to, or continue at, adequate levels, a device
to control the temperature is included.

Passive Regeneration

For vehicles that produce and maintain adequate exhaust temperature, the soot and ash
are consumed at a rate that prevents clogging the filter prematurely. Setting a DOC
ahead of the catalyzed DPF in the exhaust stream reduces the temperature required
to regenerate the filters.
However, the process is not complete. Eventually, the filter must be taken out to
remove the accumulated residue by other means.