Function: particulate filter regeneration Citroen Nemo I

General principal

The aim of the regeneration is to eliminate the soot retained on the walls of the particle emission filter

The regeneration takes place when the temperature of the particle emission filter is above 600°C

This condition cannot be met during the normal operation of the vehicle

The regeneration is initiated by the engine management ECU (regeneration assistance) when the particle emission filter is clogged

The engine management ECU manages the following elements continuously

• The condition of the particle emission filter by a Monitoring of the level of load of the particle emission filter function
• The regeneration assistance by a Regeneration assistance management function
• The condition of the engine oil by a Monitoring of the condition of the engine oil function

Function: monitoring of the particle filter load level

Role

• To determine the driving conditions
• To determine the condition of the particle filter (clogging level)
• To request activation of the regeneration assistance function, when required
• To ensure the effectiveness of the regeneration assistance function

Main information used for monitoring the particle filter

• Calculation of the weight of soot present in the particle filter
• Differential pressure (measure)
• Exhaust gas temperature (downstream of the catalytic converter)
• Inlet air flow
• Information on mixture coming from the oxygen sensor

Driving conditions

The driving conditions have a direct influence on the temperature of the exhaust gases and on the accumulation of soot in the particle emission filter

"A" road or motorway type driving

"B" urban type driving

"a" deposits (particles, soots, unburnt hydrocarbons, oil residues, etc.)

"b" filtered exhaust gases

Example "A"

• The flow volume of the exhaust gases is considerable
• The deposits form at the bottom of the particle filter
• The gases pass through the channels easily, the level of clogging of the particle emission filter is low

Example "B"

• The flow volume of the exhaust gases is low
• The deposits form in a stratified layer on the channels
• The gases pass through the channels with difficulty, the level of clogging of the particle emission filter is high

The engine management ECU determines the driving conditions according to the following parameters

• Vehicle speed
• Engine torque
• Engine speed
• Coolant temperature
• Air temperature at flowmeter
• Quantity of fuel injected
• Temperature (particle filter)

"C" Engine torque

"D" engine speed

Driving conditions

• "E" acceleration
• "F" fast motorway
• "G" downhill
• "H" urban (at low speed)
• "J" urban
• "K" main road
• "L" motorway

Calculation of the weight of soot present in the particle filter

The engine management ECU integrates cartographies that model the mass of particles present in the particle emission filter, according to the type of driving the vehicle experiences

The engine management ECU calculates the emissions of soots from the vehicle during each driving episode

The calculation of the emissions of soots takes the following parameters into account

• Driving conditions
• Information on mixture coming from the oxygen sensor
• Vehicle mileage
• Vehicle speed
• Quantity of fuel injected
• Coolant temperature
• Air temperature at flowmeter
• Particle emission filter temperature
• Volume flow rate of exhaust gases

The volume flow of the exhaust gases is calculated from the following parameters

• Differential pressure
• Inlet air flow
• Atmospheric pressure
• Exhaust gas temperature

The engine management ECU determines the mass of soot present in the particle emission filter and the level of clogging of the filter

Differential pressure

The differential pressure represents the pressure difference between the upstream input and the downstream output from the particle emission filter

The quantity of soots present in the particle emission filter causes the differential pressure to vary, which increases the accumulation of soots in the particle emission filter

The differential pressure is also a security element in terms of a particle emission filter and/or the engine

The mappings of the engine management ECU include 6 load levels

"M" differential pressure

"N" volume flow rate of exhaust gases

"c" filter clogged (critical level)

"d" filter overloaded (alert level)

"e" filter partially blocked

"f" intermediate zone

"g" filter regenerated (nominal operation)

"h" filter punctured

The differential pressure is used by the engine management ECU to carry out the following checks

• To check the coherence of the calculation of the mass of soots
• To ensure the effectiveness of the regeneration assistance function
• To detect a fault in the particle emission filter (filter overloaded, clogged or holed)

The objective of the engine management ECU is to be permanently in the default status "g" (whatever the vehicle mileage)

The engine management ECU requests the activation of the regeneration assistance function in the following circumstances: load level of the filter in zone "e" or "f"

Filter punctured

Possible fault causes

• Incorrect information from the differential pressure sensor
• Sealing fault of the exhaust pipe, upstream/downstream information pipes
• Particle emission filter actually holed
• Particle emission filter removed

The engine management ECU interrupts any request for regeneration assistance and reports a fault accompanied by the illumination of the corresponding indicator light on the instrument panel

Filter overloaded

Possible fault causes

• Regeneration assistance ineffective
• Incorrect information from the differential pressure sensor

The engine management ECU interrupts any request for regeneration assistance and reports a fault accompanied by the illumination of the corresponding indicator light on the instrument panel

The engine management ECU limits the flow of fuel injected at the engine speed to 3000 rpm

Filter clogged

Possible fault causes

• Regeneration assistance ineffective
• Incorrect information from the differential pressure sensor
• The presence of condensation in the particle emission filter (possible during the first kilometres before the first regeneration)

The engine management ECU interrupts any request for regeneration assistance and reports a fault accompanied by the illumination of the corresponding indicator light on the instrument panel

The engine management ECU limits the flow of fuel injected at the engine speed to 1500 rpm

Function: regeneration assistance management

Role

• To manage the requests for regeneration from the monitoring function
• To activate the functions required for regeneration, according to the statuses of the monitoring function
• To check the effects of the regeneration on the engine operation

The regeneration consists of periodically burning the particles that have accumulated on the filter by increasing its temperature beyond the soot combustion threshold (600 °C)

The regeneration assistance function is activated about every 800 to 1000 km, according to the mass of soots present in the particle emission filter

The complete regeneration of the particle emission filter lasts 10 to 12 minutes, according to the mass of soots present in the particle emission filter

Regeneration

The regeneration assistance is a set of provisions managed by the engine management ECU, the aim of which is to increase the temperature of the exhaust gas to the regeneration threshold

When the monitoring function estimates that the mass of soots in the particle is considerable and the capacity of the engine to regenerate the particle emission filter (driving conditions, temperature, etc) is adequate, it requests the activation of the regeneration assistance

When each activation request is issued, the engine management ECU carries out the following operations

• Limitation of the opening of the exhaust gas recycling valve (egr)
• Activation of post-injection
• Manipulation of the air mixer
• Operation of the fan at maximum speed

The post injection consists of several injections of fuel after the top dead centre of the piston, which causes a combustion of the fuel outside the combustion chamber close to the particle emission filter

The throttling of the inlet air together with a slight opening of the EGR valve increases the richness of the mixture

Regeneration assistance activation conditions

• Engine temperature higher than 60°
• Level of load of the particle emission filter above the threshold for triggering the regeneration assistance
• Differential pressure above the trigger threshold of the regeneration assistance

Deactivation conditions of the regeneration assistance

• Engine temperature lower than 60°C
• Level of load of the particle emission filter below the trigger threshold of the regeneration assistance
• Differential pressure below the trigger threshold of the regeneration assistance
• Vehicle stationary for more than 210 seconds
• 6 unsuccessful consecutive regeneration attempts

During the regeneration the engine management ECU updates the level of load of soots of the particle emission filter

Regeneration in after sales

After sales regeneration assistance can be carried out using the diagnostic tool

To facilitate after-sales regeneration it is advised to activate the electrical consumers of the vehicle (heated rear window, lighting, etc.) in order to increase the engine load

During a regeneration in after sales, the engine management ECU updates the particle filter soot load level

Effects of regeneration assistance activation

The regeneration assistance causes an increase in the engine torque, the following additional actions compensate for this effect

• Control of the turbocharger in order to limit the increase in the turbocharging pressure
• Retarding of the main injection

Post-injection

In the presence of unburnt hydrocarbons (HC), the temperature of the exhaust gases increases

The engine management ECU activates up to 3 post injections per engine cycle according to the engine speed and load

The temperature of the exhaust line rises progressively until it is permanently higher than the threshold for regeneration

Once the regeneration limit has been reached, post injection is maintained until all particles have been removed

The flow and post injection time are determined by cartographic maps taking into account engine operating conditions

To retain the same driving pleasure and to prevent engine jerks during the post-injection, the engine management ECU reduces the main injection time

The reduction in the main injection time cancels out the increase in torque due to the post injection

Control of the turbocharger

The increase in the exhaust temperature causes an increase in the engine turbocharging pressure

The engine management ECU controls the turbocharger wastegate solenoid valve to compensate for this increase

Closure of the inlet air mixer unit - valve system

The inlet air mixer unit is controlled to meet the management requirements of the air flow in the particle emission filter regeneration phase

The air mixer unit varies the incoming airflow according to its degree of opening

The partial closure of the inlet air mixer unit allows the following operations

• Limiting the quantity of fresh air inducted by the engine
• Augmenting the combustion richness of the mixture
• Augmenting the engine load
• To aid the rise in temperature of the exhaust gases

Degradation of the engine oil

The post injection takes place after the top dead centre of the piston which causes a dilution of fuel in the engine oil which is in the walls of the cylinder

The engine oil gradually degrades and its level increases in the sump

To prevent any operating condition that is dangerous for the engine, the engine management ECU calculates the level of degradation of the engine oil and determines whether or not the engine oil must be changed

The level of degradation of the engine oil is defined from the following parameters

• Number of regenerations of the particle emission filter since the last oil change
• Distance covered
• Number of the engine starts
• Number of starts with the engine cold
• Average value of the engine temperature
• Duration of the journeys

Driver's information function

Particle filter warning lamp

When starting, the indicator light corresponding to the particle emission filter comes on then goes off after several seconds

The indicator light remains on in the following circumstances: regeneration assistance ineffective

In the event of prolonged idling, regeneration assistance is ineffective (exhaust gas temperature insufficient)

The engine management ECU requests the display of a message on the matrix of the instrument panel (risk of clogging of the particulate emission filter)

The driver must drive at a speed above 50 km/h for at least 3 minutes in order to allow the regeneration of the particle emission filter

Degradation of the engine oil

The engine management ECU controls the flashing illumination of the engine oil indicator light when the level of degradation of the engine oil requires an oil change

It is recommended to carry out the engine oil change in the 1000 km following the flashing illumination of the indicator light

If the oil is not changed when a second degradation limit is reached, the engine oil indicator light remains on continuously and the performance of the engine is limited

Faults - back-up operating modes

The injection system changes to downgrade mode and reduces the flow of injected fuel and the engine speed in the following circumstances

• 6 unsuccessful attempts to regenerate the particle emission filter
• Fault on a component of the particle emission filter
• Particle filter clogged
• Particle filter overloaded
• Engine oil deteriorated

The engine management ECU can apply 2 engine performance limitation strategy is in the event of a fault in a component of the particle emission filter or of excessive degradation of the engine oil

The engine performance limitation strategies authorise an operation of the engine but with limited engine speed and torque, the severity of the limitation depending on the fault

• The first level of severity limits the engine speed to 3000 rpm
• The second level of severity limits the engine speed to 1500 rpm

The engine ECU acts on the fuel flow regulation valve and on the injectors to reduce the flow of fuel injected

The engine management ECU operates on the control solenoid valve of the turbocharger wastegate valve to reduce the turbocharging pressure

The engine management ECU interrupts any request for regeneration assistance and reports a fault accompanied by the illumination of the corresponding indicator light on the instrument panel