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Diesel Particulate Filters (DPF) as well as the Environment
Diesel Particulate dpf cleaners Filters (DPF) as well as the Environment

Reducing diesel soot emissions by 80%:

Changes to new auto emissions legislation scheduled for 2009; the 'Euro 5' standards, will make particulate filters as trivial in diesel auto exhausts as catalytic converters are on petrol cars.

The target is an 80% decrease in diesel particulate (soot) emissions, but the technology's not without problems; roadside assistance patrols are already being called to cars with the particulate filter warning light illuminated, which usually indicates a partial blockage of the DPF filter.

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Clearly, changes to driving styles might be required for maximum advantage from these emission-reducing systems.

How do the filters work?:

Diesel Particulate filters (DPF) or 'traps' do just that, they catch bits of soot in the exhaust.

As with any filter (think of the bag in your vacuum cleaner) they must be emptied frequently to keep functionality. For a DPF this process is called 'regeneration'; the collected soot is burnt off at high temperature to make only a miniature ash deposit. Regeneration could be either active or passive.

Passive regeneration

Passive regeneration occurs automatically on motorway-kind runs when the exhaust temperature is high. Many cars do not get this kind of use though manufacturers have to design-in 'active' regeneration where the engine management computer (ECU) takes control of the procedure.

Lively regeneration

When the soot loading in the filter reaches a set limit (about 45%) the ECU can make little adjustments to the fuel injection time begin regeneration and to increase the exhaust temperature. In case the journey's a bit stop/start the regeneration may not finish along with the warning light will illuminate to show the DPF is partly blocked.

It must be possible to start a regeneration that is complete and clear the warning light simply by driving for 10 minutes or so at speeds greater than 40mph.

If you keep driving in a relatively slow and ignore the light, stop/start pattern soot loading will continue to build up until around 75% when you are able to expect to see other dash warning lights illuminate too. At this stage driving at speed won't be sufficient as well as the auto might have to attend a dealer for regeneration.

Expensive repairs:

If warnings continue to be dismissed and soot loading continues to raise then the most likely outcome will be a new DPF.

Mostly town driving that is established:

If lease car use or your own car use is mostly town-based, stop/start driving it'd be a good idea to decide on petrol as opposed to risk the hassle of DPF regeneration that is incomplete.

DPF additives:

The most usual type of DPF features an integrated oxidising catalytic converter and is located quite near the engine where exhaust gases will still be relatively hot so that passive regeneration is potential.

There's not consistently space close to the engine though some manufacturers use an alternate form of DPF which relies on a fuel additive to reduce the ignition temperature of the soot particles in order that the DPF could be found further from the engine.

The additive is stored in a separate tank and is automatically mixed with the fuel whenever you fill up. Tiny amounts are needed though so a litre of additive should treat around 2800 litres of fuel, enough to cover 25,000 miles at 40mpg.

With this particular sort of DPF regeneration will be initiated by the ECU every 300 miles or so depending on vehicle use and will take 5 to 10 minutes to complete. You should not see anything other than perhaps a puff of white smoke from the exhaust when the procedure is finished.

AA encounter:

The AA has seen evidence of DPF systems neglecting to regenerate - even on autos - which are used predominantly on motorways. Their decision is the fact that on cars with a very high sixth gear engine revs are excessively low to produce sufficient exhaust temperature, but occasional tougher driving in lower gears ought to be enough to bum off the soot in such instances.

Assess the handbook:

Should you buy or lease an automobile with a DPF fitted it is vital that you read the related section of the automobile handbook so you understand precisely what actions to take if the warning light illuminates and how, if at all, your driving style might need to be corrected to ensure maximum DPF efficiency and life.

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