1 Oxidation catalytic converter
2 Catalytic converter exhaust gas temperature sensor
3 Flexible pipe
4 Diesel particulate filter exhaust gas temperature sensor
5 Diesel particulate filter heat shield
6 Diesel particulate filter
7 Rear pipe – diesel particulate filter differential pressure sensor
8 Front pipe – diesel particulate filter differential pressure sensor
NOTE: After replacing the diesel particulate filter, using WDS it is necessary to perform a supervisor parameter reset as well as a reset of the parameters of the diesel particulate filter differential pressure sensor in PCM. In this regard, always refer to the instructions in the current Service Literature.
A coated diesel particulate filter is used in certain versions of the Mondeo 2001 (02/2006-). The diesel particulate filter is shaped like a honeycomb and is made from silicon carbide, similar to the diesel particulate filter in the system with fuel additive.
A passive regeneration of the diesel particulate filter is possible at temperatures above 300 °C with the aid of the coating (platinum ceroxide).
In this temperature range, the trapped diesel particulates are converted catalytically.
The exhaust gas temperature required for passive regeneration is often not attained. In this case, the trapped diesel particulates must be burnt off from time to time with the aid of an active regeneration process.
Passive regeneration
The exhaust gases flow through the walls of the silicon element. In doing so, the diesel particulates remain adhered to the ceramic wall that has been coated with a platinum ceroxide layer.
Oxidation of carbon monoxide (CO) and hydrocarbon (HC):
• As with the oxidation catalytic converter, CO and HC are oxidized. With high levels of CO and HC exhaust emissions, the energy release is considerable. The resultant jump in temperature acts directly at the point at which high temperatures are required for oxidizing the diesel particulates.
Oxidation of nitrogen monoxide (NO) into nitrogen dioxide (NO2):
• NO is oxidized into NO2 at the catalytic coating.
• NO2 is a more active oxidation agent than O2 and therefore oxidizes the diesel particulates even at low temperatures (for example at 300 … 450 °C). The effect is known as the CRT (Continuously Regenerating Trap) effect or as passive regeneration.
Oxidation of carbon monoxide (CO) into carbon dioxide (CO2):
• Another operative mechanism is the oxidation of the CO, which is produced at low regeneration temperatures during the oxidation of diesel particulates, into CO2. The combustion of diesel particulates is improved by the localized generation of heat.
At temperatures between 300 °C and 450 °C (attained largely outside of cities) a passive regeneration of the diesel particulate filter therefore takes place continuously. It is not necessary for the engine management to intervene.
Active regeneration
For situations when the vehicle is frequently operated on short journeys, an active regeneration must be initiated at certain intervals.
The PCM detects the engine’s operating data and initiates the active regeneration after evaluating the data from the diesel particulate filter differential pressure sensor.
An attempt is then made by the engine management system to attain the necessary temperature of approximately 600 °C for combusting the trapped diesel particulates. The following measures are taken to achieve this:
• a post-injection close to the main injection,
• increasing the injected fuel quantity,
• retarded main injection,
• restricting the intake air via an intake manifold flap,
• a second post-injection at a distance from the main injection (if necessary).
Note: The measures listed above are not all active always. The timing map decides, depending on the operating conditions, which measures have to be taken to increase the temperature.
During active regeneration, the EGR system is deactivated.
The active regeneration process can last up to 20 minutes.