Skip to content

What is a DPF (Diesel Particulate Filter)?

  • Lexicon
  • 4 min read
DPF in C9.3 engine Caterpillar D7E Crawler Tractor

What is a DPF filter?

Diesel Particulate Filter (DPF) is a component of the exhaust system in diesel engines, meeting Euro4 or newer Euro5, Euro6 standards in EU and Tier 4 and Tier 4 Final emission standards in the USA. It is much less commonly installed in petrol engines (GPF). 

The main task to be performed by the DPF is to filter the particulate matter occurring in the fuel during combustion process. The exhaust gas is filtered, and the particulates are caught by the filter. The DPF thus prevents the pollutants from entering the atmosphere. 

What is a Particulate matter?

Particulate matter (PM) is made of solid particles and liquid droplets in the air. In general, all kindsof burning or activities that are dust-generating are sources of this occurrence.One of the examples is of course Emission that is caused by all the vehicles and things such as industrial chimneysThere are different types and sizes of Particulate matter.

Our solution pays attention only to smaller ones that comes for example fromburning of fossil fuels diesel in trucks PM is also divided into primary or secondary categories. Primary PMs are pollutants emitted directly from a muffleror smokestack. Secondary PM is formed mainly as a result of chemical reactions

How does DPF works?

There are alsotwo types of the DPF to be distinguished. Those that are meant for single use and to be replaced after they’re used up, and those that are reusable. The reusable DPF filters burn the accumulation of soot from their surface, either with the help of some sort of catalyst or simply by using the fuel to burn in very high temperature the accumulated particulate matter from the particulate filter’s surface.

This process is called filter regeneration, regen orfilter burnout. The exhaust gas temperature sensor is responsible for controlling the exhaust gas regeneration processes that take place in the DPF. The system also includes an engine controller (ECU), which in turn is responsible for analyzing the information sent by the temperature sensors. It also guards the filter regeneration process. It does this by adjusting the amount of fuel injected.

Temperature sensors

The construction of the sensor is not complex, and at the center of the housing there is only a thermistor (most commonly NTC or PTC). Negative Temperature Coefficient is a semiconductor element whose resistance decreases with increasing temperature. In Positive Temperature Coefficient the opposite phenomenon occurs.

Filter regeneration requires high temperatures for a long period of time. This means that filter regeneration takes place when high revs or high RPM’s are kept for a long period of time. For instance, when the vehicle is driving on a freeway. In case of heavy-duty equipment these conditions are impossible to meet, that’s why the machines with heavy-duty engines require what’s called a parked regen. During a parked regen, the machine’s revs or RPM’s rise dramatically for a period of time necessary to burn all the soot away from the filter. 

Naturally, this solution is not ideal, it requires the machine to go into downtime or so called ‘limp mode’, what’s more the process burns away the soot from the filter, but it leaves the ash in the process anyway. The solution to this problem can be an installation of the DPF emulator.


Particulate filters are meant to absorb pollutants on the largest possible surface area. After a certain period of use, the efficiency of the DPF is reduced. If the efficiency of the particulate filter falls below certain standards, the ECU performs filter regeneration. This involves significantly increasing the temperature in the exhaust system to burn off accumulated contaminants.

One of the most important aspects is to take care of what kind of fuel you pour into your machine. The most important thing is that it must be of high quality. It is also important to keep the engine in proper condition. Drivers don’t worry about improper compression or increased oil consumption, and this clogs the DPF filter. What does this mean? High repair costs, which are a consequence of negligence, especially if the issue of removing the defect is addressed.