With the use of diesel particulate filters the remaining diesel particulate matter can be reduced by more than 99%. The storage capacity of the diesel particulate filter is limited. This means that the diesel particulates accumulated in the diesel particulate filter have to be removed periodically. This is achieved by burning off the diesel particulates at set intervals.
A burn-off of diesel particulates takes place chemically at a temperature of approximately 600 °C. As the exhaust gas temperature during the approved European driving cycle rarely exceeds 270 °C due to the low engine load, measures have to be initiated to enable burn-off of the diesel particulates.
These measures are:
• Sustained increase in exhaust gas temperature,
• Lowering the oxidation temperature by using a fuel additive.
The increased exhaust gas temperature is achieved by:
• Closing of the intake manifold flap,
• Opening the intercooler bypass (increasing the intake air temperature by bypassing the intercooler),
• Two post-injections,
• Closing of the EGR valve,
• Actuation of the guide vanes of the turbocharger to deliver minimum boost pressure.
A fuel additive (cerium) is used to lower the oxidation temperature. With the help of the fuel additive, the oxidation temperature is lowered to 450 °C.
1 Supervisor software
2 Manager software
3 Regeneration
4 Regeneration is to take place
5 Monitoring of the regeneration
For regeneration of the diesel particulate filter, the PCM features a separate data record.
The decision on whether, and if so when, regeneration has to take place must be made by two different software applications:
• Supervisor software and
• Manager software.
The Supervisor software decides on the basis of the following parameters whether regeneration should be carried out:
• Soot load of the diesel particulate filter (value of the diesel particulate filter differential pressure sensor),
• Distance traveled,
• Operating conditions driven,
• Favorable conditions for regeneration,
• Probability of improved conditions in the near future.
By taking these parameters into account, it is possible to achieve minimum fuel consumption levels, minimum oil dilution and optimum performance whilst the vehicle is in operation.
If the Supervisor software makes the decision that regeneration should be carried out, the Manager software is informed.
The Manager software monitors the regeneration process and constantly interrogates the following inputs:
• Coolant temperature,
• Intake air temperature,
• Fuel temperature,
• Exhaust gas temperature,
• Manifold absolute pressure.
Regeneration Process
After the Supervisor software has enabled regeneration, the following actuations occur in two stages:
Stage 1:
• Deactivation of the EGR system,
• Actuation of the guide vanes of the turbocharger to deliver minimum boost pressure,
• Driver does not accelerate.
Stage 2:
• Opening of the intercooler bypass,
• Closing of the intake manifold flap,
• Advanced post-injection,
• Retarded post-injection.
If regeneration has commenced, it will be completed, regardless of the operating condition of the engine. Regeneration is only stopped then by shutting off the engine. Regeneration is started again once acceptable operating conditions are detected by the system.
Regeneration takes a maximum of 10 minutes.
Regeneration cycle
The post-injections result in high oil dilution and must therefore be kept within limits. To avoid excessively high oil dilution, a minimum driving distance has to be maintained between two regeneration cycles (approx. 350 km).
Depending on operating conditions, the diesel particulate filter is regenerated every 350 to 1000 km. Regeneration cycles are increased depending on ash content, which increases with every regeneration of the diesel particulate filter.
As the ash content increases, the pores of the diesel particulate filter become increasingly blocked. This means that regeneration cycles also become increasingly shorter.
For this reason, the diesel particulate filter has to be replaced at a defined service interval (every 60,000 km at the time of going to print).
Note: Increased oil consumption and reduced fuel quality (high sulphur content), as well as high fuel consumption accelerate the build-up of ash in the diesel particulate filter, shortening regeneration intervals more quickly.
If the minimum distance between regeneration cycles, currently 350 km, cannot be adhered to, this is detected by the diesel particulate filter differential pressure sensor, and the engine system fault warning lamp is switched on. The diesel particulate filter must be serviced early.