Contents: Passive regeneration ⇩ Active regeneration ⇩
The DPF is located in the exhaust system, behind the catalytic converter. The main characteristic of the DPF is its ability to regenerate. Regeneration is the combustion of solid particles captured by the filter, which prevents the filter from clogging and ensures the free passage of exhaust gases. The regeneration process occurs at calculated intervals and is not noticeable to the driver of the car.
Regeneration is very important because overfilling the filter can cause engine damage due to excessive exhaust back pressure, and the filter itself can also break or be destroyed. The products trapped by the filter are mainly carbon particles with absorbed hydrocarbons.
| Pos. | Spare part number | Name |
| A | - | Front side with alternating closed cells |
| B | - | Side view showing exhaust gas flow through the filter and particulate matter collecting in the filter |
| C | - | Back side with alternating closed cells |
The DPF uses catalytic coated filter technology. The DPF is made of silicon carbide enclosed in a steel container, which has excellent thermal shock resistance and thermal conductivity characteristics. The DPF is designed to meet operational needs to maintain optimum back pressure.
The porous surface of the filter consists of thousands of small parallel channels arranged longitudinally to the exhaust system. Adjacent channels in the filter are alternately closed at the ends. This design forces the exhaust gases to pass through the porous walls of the filter, which act as a filter medium. Solid products too large to pass through the porous surface are collected and stored in the channels.
If the solids collected on the filter are not removed, the exhaust gas flow may be obstructed. The process of regeneration, in which the solids are burned, serves to remove the solids.
The regeneration process uses NO2 to remove particulate matter from the DPF. NO2 is generated by the catalytic converter before the DPF. The catalytic converter generates temperatures in excess of 250°C (482°F), the level at which the regeneration process begins.
DPF regeneration is controlled by the exhaust gas and DPF temperature. The DPF has a filter surface with a "wash coat" treatment, which includes platinum and other active components and is similar to the treatment of a catalytic converter. At a certain exhaust gas and DPF temperature, the "wash coat" activates the combustion of particulate matter in addition to the oxidation of carbon monoxide and hydrocarbons.
The exhaust gas and DPF temperatures are controlled by the DPF software in the ECM. The DPF software monitors the DPF load based on driving style, distance travelled and signals from differential pressure and temperature sensors. When a predetermined particulate matter level is reached, active regeneration of the DPF occurs. This is carried out in cooperation with the ECM by regulating various engine management functions such as:
- fuel injection
- regulation of intake air flow using a throttle
- exhaust gas recirculation
- boost pressure control
The regeneration process is possible due to the elasticity of the engine with the common-rail injection system, which ensures precise regulation of fuel supply, fuel pressure and injection. These parameters are fundamental for ensuring an effective regeneration process.
To regenerate the DPF, two filters are used - active and passive.
Passive regeneration
Passive regeneration does not require any special intervention from the engine management system and occurs during normal engine operation. Passive regeneration slowly converts solid particles deposited in the DPF into carbon dioxide. This process is active when the DPF temperature reaches 250°C (482°F). At high speeds and high engine loads, this process becomes continuous.
During passive regeneration, only a portion of the particulate matter is converted to carbon dioxide. This is because the chemical reaction process is only effective within the normal operating temperature range of 250°C to 500°C (482°F to 932°F).
Above this temperature range, the efficiency of converting particulate matter into carbon dioxide increases with increasing DPF temperature. Such temperatures can only be achieved through an active regeneration process.
Active regeneration
Active regeneration begins when the amount of particulate matter in the DPF reaches a threshold level, which is monitored or determined by the DPF control software. The threshold calculation takes into account the vehicle's driving style, the distance traveled and the backpressure signals from the differential pressure sensor.
Active regeneration typically occurs every 725 km, but the frequency of regeneration depends on the vehicle's driving conditions. For example, when driving a vehicle with a light load in city traffic, active regeneration will occur more frequently. This is due to the faster accumulation of solid particles in the DPF compared to when the vehicle is driving at high speed and passive regeneration occurs.
The DPF software contains a mileage counter that initiates regeneration and serves as a backup for active regeneration. Regeneration is requested based on the distance traveled, unless it has been initiated by a backpressure signal from the differential pressure sensor.
Active DPF regeneration begins when the DPF temperature rises to the combustion temperature of the particulate matter. The DPF temperature is increased by increasing the exhaust gas temperature. This is achieved by introducing an additional injection after the pilot and main injection.
The DPF software monitors signals from two DPF temperature sensors to determine the DPF temperature. Depending on the DPF temperature, the DPF software requests the ECM to perform one or two post-injection cycles:
- The first additional fuel injection slows down combustion inside the cylinder, which increases the exhaust gas temperature.
- A second additional injection of fuel occurs later in the power stroke cycle. The fuel is partially burned in the cylinder; some of the unburned fuel enters the exhaust system where it initiates an exothermic reaction in the catalytic converter, further increasing the DPF temperature.
The active regeneration process takes approximately 20 minutes. The first phase increases the temperature of the DPF to 500°C (932°F). The second phase further increases the temperature of the DPF to 600°C (1112°F), which is the optimum temperature for combustion of particulate matter. This temperature is maintained for 15-20 minutes to completely burn the particulate matter in the DPF. The combustion process converts the carbon particles into carbon dioxide and water.
The DPF active regeneration temperature is closely monitored by the DPF software to maintain the required temperature of 600°C (1112°F) at the DPF inlet. The temperature management system ensures that the operating temperature limits of the turbocharger and catalytic converter are not exceeded. The turbocharger inlet temperature must not exceed 830°C (1526°F), the catalytic converter temperature must not exceed 800°C (1472°F) and the outlet temperature must remain below 750°C (1382°F).
During active regeneration, the following processes occur, controlled by the ECM:
- The turbocharger is kept in a fully open position. This minimises heat transfer from the exhaust gas to the turbocharger and reduces the exhaust gas flow rate, allowing optimum heating of the DPF. If the driver wishes to increase torque, the turbocharger blades can be closed if necessary.
- The throttle valve closes as this helps to increase the exhaust gas temperature and reduces the exhaust gas flow rate, which reduces the time it takes for the DPF to warm up to optimum temperature.
- The exhaust gas recirculation (EGR) valve closes. Using EGR reduces the exhaust gas temperature and therefore does not allow the DPF to reach its optimum temperature.
If, due to vehicle use and/or driving style, the active regeneration process cannot be carried out or the DPF cannot be regenerated, a dealer may perform a forced regeneration of the DPF. This can be done by either driving the vehicle until the engine has reached normal operating temperature and then driving at a minimum of 30 mph (48 km/h) for 20 minutes, or by connecting a Land Rover approved diagnostic system to the vehicle to assist the specialist in performing the regeneration procedure to clear the DPF.
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