If you drive a newer (post around 2010) diesel-powered car or ute, then tucked into the exhaust system under the vehicle will likely be a diesel particulate filter (DPF).
This filter is designed to capture and trap exhaust soot and other nasty particles created by the diesel fuel combustion process and prevent them from being pumped out into the atmosphere during city driving. The aim is to cut, by up to 80 per cent, a diesel’s particle emissions during stop/start driving conditions.
The DPF is an important component and necessary for diesel vehicles to meet emissions regulations. Diesel’s may also have catalytic converters, just like a standard petrol vehicle, and the catalytic converter is placed after the DPF in the exhaust system so that it can further convert the soot-free exhaust gases that have already passed through the DPF into less harmful gases.
Because the DPF works to trap large particles, it does become ‘full’ relatively quickly. However, rather than removing the filter and replacing it – as is the case with other vehicle filters such as the oil or air filter – the DPF is designed to have the particles trapped within it ‘cleaned out’ and burned off through a process called regeneration.
The regeneration process can only happen when the DPF reaches a temperature capable of burning away the soot particles. This happens in one of two ways. The first is called ‘passive regeneration’. When driven at speed for a reasonable period – on a decent highway journey, for example – the temperature becomes high enough for the passive regeneration burn to take place.
For many people, a highway trip is not part of an everyday commute and many diesel-powered vehicles are used for slow-speed, short, urban and town trips. Used this way means the DPF cannot build up the heat, or have enough time, to trigger passive regeneration.
To counter this, diesel vehicles can come with the ability to perform ‘active regeneration’. This happens when the vehicle’s computers (ECUs) detect that a regeneration burn needs to take place and do so by altering and increasing the temperature of the exhaust by adjusting the amount of fuel being burnt in the engine.
The regeneration process is extremely important. If it doesn’t happen and the DPF becomes clogged, then a variety of problems can occur.
WHAT HAPPENS IF THE DPF IS BLOCKED?
The DPF is located within the exhaust system. As it becomes blocked, so does the flow of exhaust gases. This will result in a big drop in performance and fuel efficiency.
A blocked DPF will lead to a build-up of gases and pressure which can cause damage to the exhaust system and even to the engine itself. If the vehicle is being driven and the ECUs detect the DPF is becoming badly clogged, the vehicle may be forced into ‘limp mode’, severely limiting the power of the engine to prevent further damage.
If the passive or active regeneration have not worked and the DPF is just too clogged, then the filter will need to be given either a ‘forced regeneration’ or may need to be replaced.
A forced regeneration requires specialist diagnostic tools and is performed by a mechanic. It allows for the burning off of soot particles that have accumulated to the point that active or passive regenerations don’t work.
It is important that a diesel vehicle is periodically driven at speed, and for long enough that the passive regeneration process kicks in. This will give the DPF the best chance to reach a lifespan that can be as long as 150,000km, while also ensuring that the exhaust system and engine remain healthy.
While heading to the highway on a regular basis to allow the regeneration process to take place may be an irritation, it will save you money. The cost of completing a forced regeneration can be high, as can the DPF cleaning services (which require the DPF to be removed from the exhaust system) offered by some specialists. The scenario that you most definitely want to avoid is that the DPF be so clogged that it needs replacing – the price of a new DPF can run into the thousands of dollars.
16 April 2020