What Is a Diesel Particulate Filter, and Why is it Needed?

As its name suggests, a diesel particulate filter is a component in the exhaust after-treatment systems on diesel vehicles that filter out diesel soot particles from the gaseous components of diesel exhaust gas.

Contrary to popular belief, the clouds of black smoke that some diesel vehicles still emit are not merely clouds of smoke. These clouds are, in fact, very high concentrations of solid soot particles that are not only finer than the solid particles in cigarette smoke, but also small enough to enter the blood circulation systems of humans via the lungs when they are inhaled.

We need not delve into the medical implications of diesel soot particles in the human bloodstream here, beyond saying that some medical conditions resulting from even short-term inhalation of diesel exhaust and soot particles include eye, nose, and throat irritation, severe coughing fits, bronchitis, asthma attacks, dizziness, and severe nausea.

The above is the good news- the really bad news is that inhaling diesel soot particles for extended periods can cause one or more potentially fatal lung and heart conditions, including sudden heart attacks. Other possible conditions include brain damage, kidney damage, as well as serious immune system problems and several types of cancer.  

However, we need to put the above into some sort of context by saying that the medical conditions listed above are not caused by people intentionally inhaling large amounts of diesel exhaust products over short periods; these conditions are caused by people inhaling low concentrations of diesel exhaust products contained in ambient atmospheric air over extended periods. In fact, the links between diesel exhaust and severe risks to human health are so well established that many cities in Europe have banned diesel vehicles from entering so-called “diesel no-go” zones in rulings that apply even to modern, clean diesel vehicles. Essentially, these rulings mean that "If it [a light vehicle] has a diesel engine, it is not allowed to enter the city”.

It is perhaps worth pointing out that some modern, high-end diesel engines produce fewer gaseous exhaust products than many petrol engines, but the production of solid diesel soot particles is a fundamental and unavoidable function of diesel combustion although modern common rail diesel engines produce vastly less soot than older unit injection engines.

We should perhaps also mention that although modern DPF devices remove about 99 per cent of the soot produced by a modern common rail diesel engine, DPF devices do not contribute to the conversion of harmful gaseous diesel exhaust products into innocuous substances like water vapour and oxygen. On the contrary, DPF devices that use catalysts actually increase the production of NOx (oxides of nitrogen), which is the main component of urban smog but to combat this phenomenon, most diesel vehicles are fitted with highly specialized catalytic converters that split toxic oxides of nitrogen into oxygen and nitrogen.

So, the answer to the question of why diesel particulate filters are needed revolves around the need to remove an extremely harmful pollutant, i.e., solid diesel soot particles from both the air we all breathe and the larger environment. However, although the use of DPF devices on diesel vehicles was mandated in the North American and European automotive markets as long ago as 2008/9 with the introduction of the EURO 5 emissions regulations in those markets, the use of DPF devices in the Australian market only became compulsory in 2016.

It is worth noting that as in all other major automotive markets, it is illegal to remove or tamper with a DPF device on vehicles in Australia that came equipped with DPF devices. Equally important, it is also illegal in the Australian market to delete, modify, or otherwise tamper with DPF-related programming in any control module(s), which means that in practice, it is illegal to run or use performance-oriented engine control modules on diesel vehicles that are programmed to bypass emissions regulations relating to the operation of DPF devices on modified diesel engines.

Ready to get started?
Get an instant estimate, or find an expert mechanic to make a booking.