EGR & DPF

The catalytic converter came into being with the Euro 1 standard. This honeycomb catalyst facilitates a chemical reaction and is made up of two parts: the reduction part and the oxidation part. The reduction part transforms the NOx into N2 (nitrogen) and O2 (oxygen), both of which are harmless. O2 will then react with the other gases, CH and CO, to form CO2 and H2O, which is known as the oxidation part.

However, it is important to calculate the amount of oxygen required for perfect combustion. On a diesel engine, working with excess air, there is no oxidation part. It is therefore very difficult to limit NOx.

Customers regularly ask us to remove the catalytic converter to obtain more power. First of all, removing the catalytic converter is authorised if the vehicle is to be used exclusively on racetracks, as it reduces the exhaust temperature. Depending on the size of the original catalytic converter, removing it may have a greater or lesser impact on power. For the same temperature, this means more pressure or more ignition, but in reality the maximum gain is between 1 and 5%.

In order to comply with the Euro 2 standard, it was necessary to limit NOx. The EGR valve was created with this in mind. The principle is simple: at partial load, part of the exhaust gas is caught, cooled and remixed with the intake air. This reduces emissions in two ways: on the one hand, there will be less oxygen to react with the nitrogen and, on the other, this hotter mixture increases the energy required to reach the same temperature. A lower temperature in the chamber produces less NOx.

Note from the engine manufacturer

Customers regularly ask us to block their EGR valve, without understanding how it works. An EGR valve only works at partial load, i.e. when you are not applying 100% pressure to the accelerator. When the accelerator is fully depressed, the valve closes to let in only fresh air. As mentioned above, as well as limiting NOx, the advantage of the EGR valve is that it also reduces the temperature in the chamber and at the exhaust. Blocking the EGR valve on a recent engine has the effect of increasing the temperature and limiting the life of the particulate filter.

With the arrival of the Euro 3 standard, manufacturers have mainly reworked the use of the EGR valve, thereby limiting NOx as well as other polluting gases such as CO and HC.

The particulate filter (DPF) was introduced as a result of the Euro 4 and Euro 5 standards, and is used to reduce particulate emissions. This filter is made up of small holes that stop larger particles. Once collected, these particles build up additional pressure that could damage the engine, which is why the filter needs to be emptied as soon as it reaches a certain level. This filling level is detected by two differential pressure sensors. A regeneration is then required to clean the filter. In most cases, this regeneration takes place by injecting fuel into the filter, which burns off the particles inside. This regeneration therefore results in higher fuel consumption.

Note from the engine manufacturer

Customers regularly ask us to remove their particulate filters. Although this is strictly forbidden, some vehicles really do suffer from redundant problems. Removal is therefore an understandable idea. However, some people believe that removing the particulate filter (defap) increases performance and want it removed for these reasons. A defap will not increase your injection time, which is often the limiting factor in power, it will simply limit your back pressure and therefore your exhaust temperature. The only gain you could achieve would be a reduction in fuel consumption by eliminating regeneration.

Selective Catalytic Reduction (SCR) is another way of reducing NOx emissions in exhaust gases. This process is available for modern Euro 5 and Euro 6 standards. While the EGR valve combats the formation of NOx, SCR removes the NOx from the exhaust gases. An additional substance is injected into the exhaust gases, called a reducing agent (urea or ammonia, for example). This material and the NOx meet at the catalytic surface, where they react to form harmless compounds (N2, H2O). To use this technology, you need to have an additional tank regularly topped up with Adblue.