The Diesel Particulate Filter and the diesel engine
Ever since talk of the harmful gas emission by diesel car engines became worldwide news, automobile manufacturers started to introduce components in the engine of diesel cars to try and eliminate or at least contain the problem caused by what is known as Particulate Matter. Fact is that “Particulate Matter” is a health issue and therefore a serious environmental problem.
Major particulates emitted by exhaust gas are NOx emissions such as nitrogen, carbon and waste matter mainly due to unburned fuel. This problem called for stern measures to control the buildup of soot (a dust-like component) that is the major component of nitrogen dioxide, in NOx emissions.
This led to the development of the Diesel Particulate Filter (DPF) to compensate for emission increases by exhaust gas recirculation.
Although the DPF cleans the exhaust of soot, remains of the latter causes a reduction in fuel efficiency mainly due to the effect of the soot on the EGR – which is an exhaust gas recirculation valve.
If the buildup of soot is not regularly regenerated the valve will either stick wide open or closed and that will affect the performance of the diesel engine. If you are lucky the engine may go into “limp me home mode” and the vehicle will not go faster than 40 km/h to limit possible damage.
There are ways of preventing the DPF and EGR of degenerating. Some are simple some are rather complex.
If you drive short distances with your diesel vehicle or you let it often idle for extended periods you will promote the accumulation of soot in the DPF and especially in the Exhaust Gas Recirculation valve (EGR).
It is advisable, after about 300 kilometers of town or short distance driving, to take your vehicle on the open road, accelerate and decelerate at full power and run the engine at a higher speed than town driving to give the exhaust the opportunity of heating up to about 400C.
This will assist the DPF to burn off the soot that has built up and clean the exhaust for better performance and increased fuel efficiency.
Telltale signs of problems with the EGR valve are inter alia, poor accelerations, excessive fuel consumption, black smoke especially when the engine is idling, misfire – which can actually become so bad it may cause a knocking sound and overheating. The latter can have many consequences, one of which is causing the turbo bearings to seize, that will cause turbo failure and or total engine failure due to, for instance, melted pistons.
Some of these problems with sticky filter valves can be resolved by simply cleaning it.
Although it is not a cheap option at the time, the long term and financially clever thing to do is to take your vehicle to an authorized auto workshop, such as Steves Auto Clinic, and have them replace the DPF, EGR and reset the ECU.
In South Africa it is not yet illegal to have the DPF system removed and drive without it, but it is most definitely not the eco-friendly option and when legislation comes through it will be quite an expensive exercise to have the system reinstalled and reprogrammed.
In EU countries such as the United Kingdom it is not illegal to remove the DPF, but you are not allowed to drive the car on public roads as the car will be deemed not to be roadworthy.
The Volkswagen Group in the United States of America learned an expensive lesson with “Dieselgate” when they tried to circumvent the prescribed emission control measures.
We trust that this article pointed to the need for regular upkeep and servicing of your diesel vehicle. We see too many customers who still cling to the false belief that diesel engines can keep on running for endless kilometers. That is simply not true – look after them and they will look after you for longer than anything else.