Fuel/Air Control During DPF Regen

[Lee540]

During a diesel particulate filter regen, what happens to the fuel/air mixture? That would make it different to normal running.

Is it less air and more fuel? What sensors control this function?

No fault codes, no warning lights. Trying to understand an odd running condition only occuring with regen. Lack of power to pull away in 1st or reverse to the point where engine will very easily stall, terrible throttle response, above 2k rpm it takes off like a rocket. Overfueling symptoms? No noticable issues sitting at 60-70mph during regen, only if regen is still occuring at low speed.

Once DPF regen complete, normal running resumes, still achieves 39-40mpg cruising on motorway no problem.

Thanks,

Lee

 

[Dellmassive]

Dpf regen run by engie ECU.

Uses throttle body to control air inlet and turbo and EGR to adjust airflow.

And injection timing to add fuel to outgoing exhaust.

All combined to increae dpf temp.

Various pressure and temp sensors used.

 

[mmi]

What engine - the engine code please?

During a diesel particulate filter regen, what happens to the fuel/air mixture? That would make it different to normal running.

Is it less air and more fuel? What sensors control this function?

Based on what lambda sensor tells - no change in fuel/air ratio. Engine runs always on "lean" mixture - thus enough oxygen to burn all the fuel.

Below a plot of an experiment consisting of four sections:

a) 0...950 seconds - no regen​

b) 950..1500 seconds - DPF regen - "normal" engine revs​

c) 1500...1750 seconds DPF regen - engine revs kept elevated at 2600-3000 RPM​

d) 1750...1930 seconds - DPF regen - "normal" engine revs​

​

My statement would be that there is no difference in fuel/air ratio between normal engine run and DPF regen.



Notes:
Lambda value maxes out at 10 - when the foot is eased off the throttle - thus no fuel injection for combustion at that moment.
Engine RPM and vehicle speed are scaled down - to show on the scale of the plot.
EDIT: lambda in average 2.8 across the journey - well on oxygen rich side.

 

[Lee540]

What engine - the engine code please?

Sorry, I don't know the code. Its a 2018 150bhp 6 speed manual. EU6.

That is a lot of information to read and digest. Thank you for the response. Need to find the cause of this odd running condition, van is undriveable in my opinion when DPF regen is underway and you're attempting low speed, 1st/2nd or reverse driving.

 

[Dellmassive]

do I remember reading somewhere that they can inject fuel on the exhaust stroke to push raw fuel into the exhaust to raise dpf temps?

 

[mmi]

Sorry, I don't know the code. Its a 2018 150bhp 6 speed manual. EU6.

Thanks - most likely CXHA - it's printed on the sticker under dash by steering column.

Need to find the cause of this odd running condition, van is undriveable in my opinion when DPF regen is underway and you're attempting low speed, 1st/2nd or reverse driving.

That's interesting - normally there is no way to know when the DPF regen is going on. I would start monitoring turbo charge pressure (build-up) as it's the main thing these engine run on.

do I remember reading somewhere that they can inject fuel on the exhaust stroke to push raw fuel into the exhaust to raise dpf temps?

Correct.

[T6_measured] DPF regeneration vs. short journeys

Got curious how T6 copes with doing short journeys. And how short would be too short for successful DPF (Diesel Particulate Filter) regeneration. The graphs below are result of doing short journeys - the plotted one is number 3, thus two interrupted DPF regens before this. At this stage the...

www.t6forum.com

Regeneration Cause Fire.

Is there any chance of a regeneration causing a grass fire when parking on long dry grass. Smells extremely hot when fan is cooling on ignition turn off. Have avoided parking on the longer grass at moment just in case but where is the filter is there any risk?

www.t6forum.com

 

[Lee540]

Thanks - most likely CXHA - it's printed on the sticker under dash by steering column.


That's interesting - normally there is no way to know when the DPF regen is going on. I would start monitoring turbo charge pressure (build-up) as it's the main thing these engine run on.


Correct.

[T6_measured] DPF regeneration vs. short journeys

Got curious how T6 copes with doing short journeys. And how short would be too short for successful DPF (Diesel Particulate Filter) regeneration. The graphs below are result of doing short journeys - the plotted one is number 3, thus two interrupted DPF regens before this. At this stage the...

www.t6forum.com

Regeneration Cause Fire.

Is there any chance of a regeneration causing a grass fire when parking on long dry grass. Smells extremely hot when fan is cooling on ignition turn off. Have avoided parking on the longer grass at moment just in case but where is the filter is there any risk?

www.t6forum.com

Thanks. The van is with my specialist for a service and investigate but I want to do my own research alongside with my limited knowledge of these vans.

I know a DPF regen is in progress because I've got the live monitoring through Carista Beta.

Elevated idle to 1000rpm, for the duration of this regen process, car is as described above, undriveable at low speed. I drove 300 miles to Oxford, totally fine, arrive in the P&R carpark, regen decides to start, stalled van twice trying to park in a space.

My van is never driven on short journeys, spends 90% of its life on motorways and the rest on A roads. Generally 250-300 miles at a time, a few times a month. Seemed perfect use case for having a modern diesel.

My specialist said he'll datalog all the systems and anaylse to see if any readings aren't right, his initial thoughts were EGT sensor as van attempts to regen with cold engine.

 

[Lee540]

This bit is interesting.

 

[mmi]

van attempts to regen with cold engine.

That's how it works - when the regen is due it takes less than two minutes to get exhaust temperature above 400 °C.
The green curve below (turbo input)


Some more...

[T6_measured] DPF regeneration vs. short journeys

Got curious how T6 copes with doing short journeys. And how short would be too short for successful DPF (Diesel Particulate Filter) regeneration. The graphs below are result of doing short journeys - the plotted one is number 3, thus two interrupted DPF regens before this. At this stage the...

www.t6forum.com

 

[Lee540]

That's how it works - when the regen is due it takes less than two minutes to get exhaust temperature above 400 °C.
The green curve below (turbo input)
View attachment 249938

Some more...

[T6_measured] DPF regeneration vs. short journeys

Got curious how T6 copes with doing short journeys. And how short would be too short for successful DPF (Diesel Particulate Filter) regeneration. The graphs below are result of doing short journeys - the plotted one is number 3, thus two interrupted DPF regens before this. At this stage the...

www.t6forum.com

Thanks for taking time to reply. It all makes sense.

Its the no fault codes or warning lights which means I can't diagnose it myself. I don't have the time or tools.

 

[Lee540]

@mmi what would be normal charge pressure during active regeneration? If know.. if there anyway to read the values without VCDS?


I could diagnose my running faults as "lack of torque" only during active regeneration.

 

[Dellmassive]

Id imagine it would need a percentage bump ontop of the standard map. The pressure will be variable at each moment depending on what the engine is doing.

 

[Lee540]

Id imagine it would need a percentage bump ontop of the standard map. The pressure will be variable at each moment depending on what the engine is doing.

Would a blocked or blanked and coded out EGR alter the engines ability to control the required charge pressure during active regeneration? Understand passive regeneration doesn't occur with blanked/coded out EGR.

In one ear I have a specialist advising a DPF fault but my DPF monitoring app would suggest a very heathly DPF. I don't want to tamper with it. Considering new OE EGR valve might be only way to resolve this fault of no/insufficient torque during active regeneration, even though there are no fault codes or warning lights.

 

[mmi]

Have to say I have tried to measure that quite a few times. And, I haven't been able to see a significant difference as the pressure varies hugely depending on load and driver's torque request. Below a plot where partially managed to keep steady speed for some time.




My impression based on the above as well as numerous other logs is that charge pressure actually might be even lower during DPF regen - as high exhaust temperatures are partially created by adjusting injection to earlier which already alone creates more torque.

In the above at 1240...1250 seconds I tried to squeeze the maximum out of the engine by accelerating at max on 7th gear.

---

anyway to read the values without VCDS?

Do you have Carista dongle and Android phone? Then we could adapt Torque app below to do it.

[T6_measured] Monitoring DPF regeneration, DPF condition, EGR operation

Here's another approach for T6 DIY enthusiasts - taking advantage of very popular Carista OBDII-reader device - combined with an Android app. Ingredients: T6 EU6 engne: CXEB,CXEC,CXFA,CXGA,CXGB,CXGC,CXHA,CXHB. Carista OBDII device (also other generic OBDII (ELM327) devices will work) Android...

www.t6forum.com

Would a blocked or blanked and coded out EGR

Do you have one?

 

[Dellmassive]

The EGR is an integral part of the system....

If it's been removed, blanked or mapped out..... Then you are in the hands of the mapper Gods. Who knows whats been tweaked or changed.

A map can also effect the sensor readings.... So your dpf App may be giving you affected readings.

 

[mmi]

Would a blocked or blanked and coded out EGR alter the engines ability to control the required charge pressure during active regeneration?

EGR is "OFF" anyways during active DPF regeneration - so shouldn't but as above by @Dellmassive who knows what the mapper has done.

DPF monitoring app would suggest a very heathly DPF

Have you monitored differential pressure across the DPF?

Considering new OE EGR valve might be only way to resolve this fault of no/insufficient torque during active regeneration, even though there are no fault codes or warning lights.

Well, because of the EGR is "OFF" anyways, I don't think replacing it would solve the problem (assuming OEM engine software).
I would check a couple of things - the VCDS might even be the most economical solution at the end by saving unnecessary parts replacements.
Air flow, fuel flow, fuel pressure, specified vs. actual charge pressure, etc.?

even though there are no fault codes or warning lights.

Before even the fault codes appear there are allowed tolerances - e.g. for commanded charge pressure vs. actual charge pressure. E.g a plot in

Fault code P0299 Boost - 2019 Crafter

Hi folks, looking at the soot measures vs calculated amounts, the minus figures is puzzling me? Should I have rest the dpf in any way after completion of the forced regen? Or would this munis fugue suggest : A) a sensor is at fault B) previous ownswer has changed dpf settings to try and hide...

www.t6forum.com

 

[Lee540]

EGR is "OFF" anyways during active DPF regeneration - so shouldn't but as above by @Dellmassive who knows what the mapper has done.


Have you monitored differential pressure across the DPF?


Well, because of the EGR is "OFF" anyways, I don't think replacing it would solve the problem (assuming OEM engine software).
I would check a couple of things - the VCDS might even be the most economical solution at the end by saving unnecessary parts replacements.
Air flow, fuel flow, fuel pressure, specified vs. actual charge pressure, etc.?


Before even the fault codes appear there are allowed tolerances - e.g. for commanded charge pressure vs. actual charge pressure. E.g a plot in

Fault code P0299 Boost - 2019 Crafter

Hi folks, looking at the soot measures vs calculated amounts, the minus figures is puzzling me? Should I have rest the dpf in any way after completion of the forced regen? Or would this munis fugue suggest : A) a sensor is at fault B) previous ownswer has changed dpf settings to try and hide...

www.t6forum.com

I am away today in my other car. Back tomorrow. I will try and log some data.

Thank you again for your support.