WHAT IS DIESEL PARTICULATE FILTER?
Diesel particulate filter, commonly named as DPF, is used in diesel engines for cleaning the harmful particles in the exhaust gas.
The harmful particles inside the burnt fuel – air mixture coming out from the engine are piled up inside the particulate filter so they are not released to the nature. These particles are burnt by the raise of the exhaust temperature (regeneration) so this way air pollution is prevented. Exhaust gas temperature is detected by ECU during the regeneration. Temperature data is sent to the ECU by the help of the heat sensors placed on the DPF so it is possible to calculate the exact fuel amount needed for increasing the exhaust temperature.
How It Works?
The particles piled up inside the filter should be removed by burning to avoid to be clogged. Regeneration has various strategies:
Particles are burned continuously without the interference of the ECU. This is provided in 3000 rpm/min in standard highway speed.
Exhaust temperature usually doesn’t reach the level needed for completing the passive regeneration in city usage. The soot cannot be cleaned and it is piled up inside the filter. When it reaches the blockage threshold (18 grams) ECU triggers the active regeneration. The level of collected carbon inside the diesel particulate filter is calculated using the 2 models programmed inside the ECU:
- A model based on the driver profile that is calculating the saturation according to a specific signal model coming from the exhaust gas temperature sensors and oxygen sensors,
- A model calculating the saturation according to the signals received from differential pressure sensor, temperature sensors and air flowmeter.
The pressure difference sensors placed between the input and output of the DPF on the exhaust, are measuring the pressure differences that is reaching to the saturation level in the filter. When the blockage of the filter is detected with the help of the sensors, the voltage coming to the ECU is increased. So the ECU raises the exhaust gas temperature to 550 C – 650 C level. To provide this increase;
- It adjusts the air flow
- The EGR valve is deactivated
In short distance usage, ıt is impossible to reach the needed temperature for regeneration. The DPF warning light is on when the saturation level reaches to 24 grams. This signal tells the driver to complete the regeneration route. In other words, vehicle should be used in enough speeds for a certain distance and needed temperature should be reached for regeneration of the DPF.
In case of unsuccessful forced regeneration and if the saturation exceeded the threshold value until 40 grams, glow plug indicator and engine warning lights are on. In this case, active regeneration is blocked by ECU to avoid filter breakdown. At this point, diesel particulate filter should be cleaned by experienced mechanics.
If the saturation exceeds 45 grams threshold, no regeneration is possible. Because it cannot be cleaned, the DPF should be replaced.
This regeneration method depends on the travel distance. It avoids the DPF to exceed the unhealthy saturation level. Regardless of the charging level, ECU triggers the active regeneration if no regeneration is activated during the last 750 – 1000 kilometres.