A recent episode of the BBCs popular Watchdog series included a feature on the problems that many owners of diesel cars purchased as ‘city run-arounds’ are having with Diesel Particulate Filters (DPFs). When the cars are only used for short journeys, the DPF may not be able to regenerate and becomes blocked; Watchdog argued that dealers and manufacturers have a responsibility to highlight this potential problem to customers at the point of purchase to help them avoid damage to the DPF.
Klarius, can confirm the claims made in the programme as its new product development cycle is partly driven by direct market demand. Unsurprisingly the company has developed and introduced several replacement DPFs for smaller cars recently, including a new type-approved replacement DPF for the Fiat 500, launched just this week.
Klarius also supports the point made during the BBC consumer show that there is a clear knowledge gap with regards DPFs and that extends into the automotive trade, not just the general public.
The importance of DPFs
Even the most refined and modern diesel car produces exhaust gasses with high levels of soot particles. On average a diesel engine will produce several billion particles per kilometre; soot particles are between 1/100 to 1/600 times the width of a human hair and are severe irritants, known to be a cause of lung cancer. Our natural defences cannot filter such fine particles, which enables them to penetrate our respiratory system. It is, therefore, essential that we reduce soot particle emissions as much as possible.
Diesel Particulate Filters are designed to remove the particles from exhaust gases before they are expelled into the atmosphere. The process works by forcing gasses through a honeycomb structure with porous walls. Unlike a catalytic converter, the DPF is not a flow-through device, the gasses move across the honeycomb cell walls while the particulate matter is trapped. A well designed DPF can reduce soot particulate emissions by as much as 85% and also drastically reduces Hydrocarbon and Carbon Monoxide emissions.
Blocked filters and regeneration
The particulate that is removed from the gasses is deposited onto the cell walls of the DPF. Over a period of time the soot builds-up within the DPF, however, to prevent frequent replacement, DPFs are designed to operate a regeneration process when they reach 45-50% capacity to keep them clear and operational. Regeneration occurs every 300 – 500 miles depending on engine and driving style. During regeneration the soot particulate is burnt off using the heat from the exhaust. The process can be coupled with a short expulsion of dark looking ‘smoke’ from the exhaust; this is perfectly normal and not indicative of any failings.
Regeneration can be triggered in two separate ways, depending on the model of car that is being driven. Active regeneration waits for the ECU to recognise that the DPF’s recommended capacity has been reached and then self-triggers. Passive regeneration requires exhaust temperatures of 550°C – 650°C to occur, at which point the soot is burnt off naturally. In some designs an additive such as AdBlue is used to initiate the burn-off process when exhaust gas temperatures are not sufficient often enough.
When on a long journey with steady high-speeds – such as travelling on a motorway – it is common for exhaust temperatures to reach the required level for passive regeneration to occur. A car that is taken on the motorway as part of its regular routine will regenerate when required and the driver may well never know that the DPF exists; however, if a car is used only for short journeys or stop / start city driving then it is likely that temperatures will never reach far beyond 200 degrees C.
Smaller cars, such as the Fiat 500 and Nissan Qashqai (as featured in Watchdog) are often bought with the sole intention of short school and shopping runs that will be economical and easy to park. These cars are ideal for this purpose as they are economical to run, so long as consumers are aware of the necessity to facilitate regeneration every 500 miles or so. A well-managed DPF can last many regenerations before needing to be replaced.
If the vehicle does not have an active system to initiate burn-off at lower temperatures, and isn’t taken on periodic long journeys, then problems tend to occur; the cell walls can become blocked which affects the engine backpressure and impacts on the overall performance and efficiency of the engine. Once this occurs and a regeneration cycle cannot be started then it is necessary to replace the DPF, as with all automotive components it is important to ensure that replacement parts have been type approved and manufactured by a reputable brand.
Replacing a DPF
Given an appropriate driving style a DPF will survive many regeneration cycles, however, as with all automotive components, it will eventually need to be replaced. It is important that the replacement DPF is of a high quality in order to ensure reliability and suitable performance. Opting for a DPF that has been type approved is the best way of ensuring that a car’s particulate emissions will remain low and that regeneration will occur regularly.
The Klarius Group is Europe’s largest manufacturer and distributer of OE and aftermarket automotive parts; it has a dedicated, UK development and manufacturing centre that specialises in exhaust and emissions control components. Its philosophy of continual product development ensures that its customers benefit from the widest range of aftermarket DPFs in Europe – and often means that Klarius is first to market for new model types.
The expertise within the development centre means that new products can be designed, tested and put into production on a very short lead time. Since the Watchdog feature highlighted the Fiat 500 as a potentially problematic model, Klarius has finished testing on a replacement DPF for the vehicle that meets OE standards and has put the product into production.
Klarius type approves DPF’s in accordance with European Legislation. Testing is carried out in partnership with TÜV, a testing institute in Germany that is renowned across Europe. When a product is type approved it must be tested against OE products and relevant legislative standards which guarantee its performance to the same level or higher than the original part.
The popularity of Diesel cars is still on the rise as their performance continues to improve and they offer ever better mpg figures – without the seeming cost and weight penalty of some hybrid systems. The DPF is a vital component in this trend and it is important that it is understood by the average consumer.
For more information: www.qh.com