Technologies
-> Diesel Particulate
Filters -> Active Systems
Active DPF regeneration
Any application in which it cannot be
guaranteed that the exhaust gas conditions will be
suitable for a passively regenerating system will
require some active regeneration. Even in these cases,
it is desirable to maximise the amount of passive
regeneration that can be achieved since passive regeneration
is “free”, requiring no additional energy.
Almost all active filter regeneration techniques
operate by raising the temperature of the filter to
around 600°C. As described in the DPF
regeneration section, this is the temperature
at which the particulate (PM) collected in the filter
will combust rapidly in oxygen.
Combustion of HC over a catalyst
The CRT®
and CCRT®
systems can form part of actively regenerated DPF
systems in which the HC content of the exhaust stream
is periodically enriched, either by in-cylinder post
injection or by direct injection of fuel into the
exhaust stream. The HC is burnt over the catalyst,
raising the temperature of the DPF to combust the
collected PM.
In the chart below, we show this process and its
effects. In the chart, the red lines are temperatures
measured in a CRT® system before the
catalyst, between the catalyst and the filter, and
after the filter. The temperature is shown on the
left-hand y-axis. The blue line shows the pressure
drop over the filter, which is an indication of the
amount of particulate it contains. The pressure drop
is shown on the right-hand y-axis.
| 0 – 200 secs |
The temperature throughout the system is around
260°C and the back pressure is 80mbar. |
| 200 – 400 secs |
When diesel fuel is injected upstream of the
catalyst, the temperature before the catalyst
remains constant but the temperature after the
catalyst and after the filter rises steeply towards
600°C. The back pressure also increases as
a result of the increased gas flow caused by the
fuel combustion over the catalyst. |
| 400 – 1000 secs |
As the temperature in the filter reaches 600°C,
the pressure falls sharply as the soot in the
filter is burn away. As can be seen from the blue
line, this process is largely completed in the
first 200 seconds. |
| After 1000 secs |
After the injection of fuel is stopped, the
temperature throughout the system quickly returns
to below 300°C and the back pressure effect
caused by the combustion of the fuel stops. |
Johnson Matthey has developed a range of catalysts
specifically for this type of system.
These systems require careful control of the HC enrichment
of the exhaust stream and are therefore much more
suitable for OE applications than for retrofit systems.
Typical applications:
Truck and
Bus
Non-road
Mobile Machinery
Cars, Vans and Light
Trucks
Related products:
CRT®
systems – a DPF system giving excellent
passive performance. Its configuration also makes
it very suitable for active regeneration by HC-combustion.
CCRT®
systems – a CRT® system with
catalysed filter, which further improves passive and
active regeneration performance
Regeneration by electrical heater
In some markets, Johnson Matthey also offers a DPF
system incorporating an electrical heater. This system
is used in retrofit applications in which exhaust
temperature are too low to ensure adequate passive
regeneration from CRT® systems. With
the engine off, an air stream provided by a compressor
is heated to 600°C and passed through the filter,
burning away the collected particulate.
Typical applications:
Non-road
Mobile Machinery
|
