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The DPF System and how it works

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C6Dave   
Sun Oct 06 2019, 12:44pm

Joined: Oct 01 2009
Member No: #1
Location: Northumberland
There have been a few queries about how the system works in a C6 Diesel so I have copied this from an original Citroen document which basically explains how the ECU decides when the DPF requires a 'regeneration' cycle':
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Particle filter Presentation :

 The aim of the filtration system is to reduce particle emissions released into the atmosphere (black smoke emitted at full load or during transitory operation)

 A particle filter is fitted on the exhaust pipe, and traps passing particles in the exhaust gases

 The accumulation of particles whilst the engine is operating leads to the progressive clogging up of the particle filter

 To prevent the particle filter from becoming blocked, it must be "regenerated"

Principal evolutions optimising the aid to regeneration of the particle filter:

 Calculation of the weight of soots present in the particle filter, depending on the type of driving of the vehicle

 Differential pressure used only as SAFETY for the particle filter and/or engine

Calculation of the weight of soot present in the particle filter




Vehicle driving conditions Reference Designation

"a" Traffic conditions difficult
"b" Traffic conditions fluid
"c" Traffic conditions very fluid
"d" Main road
"e" Motorway
"f" Soot (=carbon) present in the particle filter

A engine torque (daNm)
B Vehicle speed ( kph)
C Calculation of the weight of soot present in the particle filter

The injection ECU incorporates mapping representing the weight of soots present in the particle filter, depending on the type of driving encountered by the vehicle.

One distinguishes five different types of driving:

 " a" - Traffic conditions difficult
 "b" - Traffic conditions fluid
 "c" - Traffic conditions very fluid
 "d" - Main road
 "e" - Motorway

A type of driving is defined as a function of the following parameters:

 engine torque
 Vehicle speed

For each hour of driving, the injection ECU determines the type of driving encountered by the vehicle.

For each type of driving, the injection ECU calculates a weight of soots present in the particle filter in g/mn.

This value is added to the preceding values to constitute a value representing the total weight of soots accumulated, since the last regeneration.

The addition of these quantities of soots determines the theoretical moment of regeneration.

History of vehicle usage:

 The injection ECU registers the driving conditions of the last 6 hours
 The register of driving conditions is updated every hour
 The injection ECU defines the driving profile of the vehicle and predicts the most favourable moment for activating the regeneration of the particle filter, as a function of this record of use of the vehicle

Operating safety features : Differential pressure

CAUTION: The differential pressure is used only as SAFETY vis-à-vis the particle filter and/or the engine: In the event of the filter becoming overloaded or clogged (very unfavourable driving conditions).

The amount of particles present in the filter causes its load loss to vary (input / output differential pressure).

This permanently measured value represents the load level of the particle filter.

The cartographic maps of the injection ECU incorporate 4 operating levels determined by curves, from the

calculation of the volume flow rate of the exhaust gases.

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

 Differential pressure
 Inlet air flow
 Atmospheric pressure
 Exhaust gas temperature (downstream of the catalytic converter)

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So in Plain English, lots of short runs are not what you want in a C6 HDi
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5 User said Thank You to C6Dave for this Post :
 FraserG (06 October 2019) , Tjensen (06 October 2019) , Paulius (07 October 2019) , cruiserphil (07 October 2019) , Hattershaun (13 October 2019)
rwb   
Sun Oct 13 2019, 05:30pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford
I have FAP app installed on an old phone in the car. It starts up and shuts down on the ignition. I'm a bit obsessive about collecting statistics.

The following is what I've found for a 2.2 HDi in a 407.

The soot counter increases at a rate of about 26 percentage points per 100 miles on local journeys and about 15 percentage points per 100 miles on the motorway.

When the soot counter reaches 65.5% (it was 70% on our 2.0 HDi 140 508) a regen is triggered. A regen lasts about 8 minutes if you're lucky, or up to about 12 minutes during which the exhaust temperature reaches about 500 degrees.

I've found that the shorter regens happen at 70mph in 6th on the motorway; it needs steady load on the engine.

After a regen the soot counter resets to zero.

After a regen some ash is left in the DPF and it's this that eventually blocks the DPF which must then be replaced. My 407 is currently on 149g as and this is the hightest I've seen the soot counter on any car. I do not know what the threshold is for the risk of blocking error -- of course it will vary between models because of the differently sized particle filters.

I have found that the fuel is dosed with about 10ml to 15ml of additive per 100 litres of fuel.
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3 User said Thank You to rwb for this Post :
 cruiserphil (13 October 2019) , Hattershaun (13 October 2019) , C6Dave (14 October 2019)
C6Dave   
Mon Oct 14 2019, 07:30am

Joined: Oct 01 2009
Member No: #1
Location: Northumberland
rwb wrote ...


After a regen some ash is left in the DPF and it's this that eventually blocks the DPF which must then be replaced. My 407 is currently on 149g as and this is the hightest I've seen the soot counter on any car. I do not know what the threshold is for the risk of blocking error -- of course it will vary between models because of the differently sized particle filters.

That's a good question and searching all the tech docs I haven't seen anything that indicates the actual 'weight' of soot, everything seems to be based on differential pressure of gas flow through the DPF.

This article, specifically from page 21 onward is about PSA's method of calculation: - Click Here -

Very technical reading but worth going through.
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2 User said Thank You to C6Dave for this Post :
 cruiserphil (14 October 2019) , rwb (25 October 2019)
rwb   
Fri Oct 25 2019, 08:36pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford
Good find on that PDF

My understanding was that the differential pressure sensor is used only to detect puncture.

For reference: my 2.7 C6 is on 163g at 110k miles and my 2.2 406 is on 143g at 209k miles.

I notice that in parameter measurements in Diagbox the Siemens 2.7 also describes the cinder count at 73% whereas the Bosch 2.2 only gives the weight.

Strangely, the 2.2 gives the additive fluid level but the 2.7 does not.

I've now found that the 2.7 triggers a regen at 80% soot, and the regen is much less noticeable than on the 2.2. The 2.2 sounds raspy and feels down on power during a regen, and the instantaneous MPG readout plummets. (The 2.0 140 (Delphi) I drove in a 508 had similar symptoms but much less noticeable.) However, I didn't realise the C6 was doing a regen until there were clouds of smoke from LDS spilled on the exhaust burning off! (That was a brown trouser moment!)
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2 User said Thank You to rwb for this Post :
 C6Dave (26 October 2019) , cruiserphil (29 October 2019)
 

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