DPF active regeneration - 'boot it', or 'steady as she goes?'

[bmbmdmb]

When an active regeneration takes place I have read opposites on what is the best driving manner, lower gear higher revs, ie DSG sport mode or manual select lower gear or select DSG drive and let car select higher gear and lower revs.

Higher revs usually results in more smoke , unburnt fuel but higher exhaust temperatures?

Clarification appreciated. 

[ian_feel_keepin_it_reel]

Just drive it normally. As it's automatic if the active regen required high revs the engineer's would just program it to hold a lower gear during a regen.

[aposhtol]

On 15/09/2018 at 18:14, ian_feel_keepin_it_reel said:

Just drive it normally. As it's automatic if the active regen required high revs the engineer's would just program it to hold a lower gear during a regen.

 

On my 2013 2.0 TDI Estate that's not true. I must switch to manual to obtain higher revs to end regeneration.

 

 

[Sec8200]

no need to rev. It depends on the load of the engine to produce heat..Meaning climbing a hill will help more than additional revs.

+ aircon + other consumers.

Revs will help of course but no a must. And not the biggest influencer...

 

basing my statment on real time data monitoring the regen w/ DPF VAG app.

Edited 7 October, 2018 by TTodorov

[aposhtol]

Makes sense. But if you live in a small town without hills and you make only short trips, revs are inevitable. Especially in cold weather.

[Sec8200]

I do agree.

 

From my humble experience regen takes similar times (~16km and around 20mins) which can be annoying. Specially once it starts just when you are about to park (around 90% of the cases in town )

Edited 7 October, 2018 by TTodorov

[wyx087]

Don't drive a diesel in town, simple  

 

In answer to OP, just drive it normally, the ECU will manage everything. Simply only use your diesel for long trips and avoid any local use.

 

(having an EV helps with latter  )

[Gabbo]

Higher revs makes little difference for me. You are only adding a small bit of extra load (engine friction higher at 2000rpm than 1500rpm for example).

You have the downside that you are letting in more cold air & injecting less fuel per revolution...

 

Just let the ECU do its own thing. The post injection quantity of an active regen is controlled by the ECU to regulate the temperature in the DPF so whichever rpm you are running at you cannot force more fuel.

The only benefit you can give as a driver is adding more load/getting the engine warmer which is driving a little bit faster or driving on a longer run.

[ScoutCJB]

1 hour ago, wyx087 said:

Simply only use your diesel for long trips and avoid any local use.

 

 

Our local shop is a 20 min walk or 6 min drive --- I'm not going to walk that if its a raining!

[PetrolDave]

1 minute ago, ScoutCJB said:

Our local shop is a 20 min walk or 6 min drive --- I'm not going to walk that if its a raining!

So a diesel with a DPF  is not suited to your usage.

[Genoa1893]

...I'm pretty sure the OP didn't choose to have the DPF...

[PetrolDave]

4 hours ago, Genoa1893 said:

...I'm pretty sure the OP didn't choose to have the DPF...

There's no choice if you buy a recent diesel as they come as standard with a DPF, but with his short runs to the local shops he really should have considered either an older diesel without a DPF or a petrol - but of course the 2019 petrols come with a GPF so who knows what the effect of those will be?

[Gabbo]

I'm sure he didnt buy a car just to drive 5minutes to the shops.

Plus, theres no reason why you cant drive short distances in a diesel providing you have occaisonally longer trips.

My wife used my Vrs for 18months for a 7mile commute each day & we had no negative problems except for the expected small decrease in fuel economy (~5mpg).

[bmbmdmb]

5 hours ago, Gabbo said:

Plus, theres no reason why you cant drive short distances in a diesel providing you have occaisonally longer trips.

I knew the car had DPF. The Octavia ticked all the boxes for spec and size. It looks a nice car too. The car gets a good run occasionally as well as commute and for short distances I jog to shop, even if it's raining. I try to do multiple jobs on same day rather than separate days so engine is still at temperature.

2nd hand Petrol was an option. The VRS 230 TSI was overkill that I test drove. I don't think my foot reached the floor board. The car got to 60 mph in no time. The £30 road tax of diesel pays towards higher maintenance costs versus petrol. 

 

If short journeys then I can testify my retired neighbour had a ford focus diesel which suffered blocked injectors as he frequently drove short distances. He sold it after repair for petrol. Dealer said if less than 15 mile journeys then get petrol.

 

I asked the original question as a garage tech seemed to suggest that during a regeneration the car revs should be kept high, this is non Skoda tech at an independent and he was talking about a forced regeneration on some customer's car.

[Genoa1893]

On non DSG this was the recommended practice. I would stick to high rev suggestions, too.

[Gabbo]

higher revs means dont drive below 1000rpm.

With the DSG the ECU controls the gearing & thus engine revs. If regeneration needed higher revs then it would automatically just stay in the higher gear for a little bit longer.

 

Just drive your car like normal & let the ECU do its thing, if there is a problem with regeneration you will get a warning before there are any real problems so you can then take the car for an extended drive somewhere.

But this kind of warning seems rare unless there is really a problem with the car.

DPF technology & the software control behind it has come a long way in the last 15 years....

[aposhtol]

27 minutes ago, Gabbo said:

With the DSG the ECU controls the gearing & thus engine revs. If regeneration needed higher revs then it would automatically just stay in the higher gear for a little bit longer.

 

I don't agree. ECU does nothing to DSG operation during active regeneration. No higher revs, no different regime of shifting gears. Nothing. Driving experience is the same like normal driving. Only clues of active regeneration taking process is disabled start/stop at idle, idling at 1000 rpm and subtle engine shake if you floor it when stationary (rpm goes to 2500 rpm).

Edited 9 October, 2018 by aposhtol

[Gabbo]

2 hours ago, aposhtol said:

 

I don't agree. ECU does nothing to DSG operation during active regeneration. No higher revs, no different regime of shifting gears. Nothing. Driving experience is the same like normal driving. Only clues of active regeneration taking process is disabled start/stop at idle, idling at 1000 rpm and subtle engine shake if you floor it when stationary (rpm goes to 2500 rpm).

 

Then for me its clear that the higher revs are not needed.

If the engine needed higher revs to regenerate it would be fairly easy to implement this in the software (and I'm pretty sure the DSG already holds gear a little longer when regen is active).

If someone wants to keep driving round at 4000rpm until the regen is finished, its not going to do any harm.

All I'm trying to say is its not necessary & I see it personally as a waste of fuel & time.

Just drive the car like normal without worrying about the DPF & let the ECU take care of it.

 

The regen implementation of VW is not great because it is obvious to the driver when it is happening (idle incerase & high cooling fan speed).

In my previous BMW and current volvo there is no external indication when it is happening & this is how it should really be.

[aposhtol]

1 hour ago, Gabbo said:

If the engine needed higher revs to regenerate it would be fairly easy to implement this in the software (and I'm pretty sure the DSG already holds gear a little longer when regen is active).

 

Imagine lots of everyday short trips (5-10 min drive) in town without hills. The system is dumb. Once it starts active regeneration it restarts it every time you start the car again (and get past 50 km/h I think) and in a few days driving like this you get DPF light in instrument cluster. Even if you don't end up with DPF light, it consumes extra injected fuel every time you start the car. So my method is switch DSG to manual -> get at least 2500 rpm -> drive like this 5 - 10 min -> park the car and see if revs are below 1000 rpm and start/stop engaged, if not drive some more like this until it completes.

 

If the higher revs were implemented in the software it would be even more obvious of active regeneration taking place. Maybe it's part of the VW policy to not do so.

Edited 9 October, 2018 by aposhtol

[nidza]

This is our second O3 TDI, first one lasted 5 full years (2013). Majority of trips is flat town, 6km in the morning, 6km in the evening. In total, very little mileage, something like 35.000km after we return it.

 

No issues with DPF, ever. Driver is my wife, absolutely careless about any technical stuff, just sits and drives, if lucky doesn't scratch. 

 

Now she drives until 2020. another O3 TDI, 2015, same story. Issues 0, if we exclude scratching.

 

From what I've learned reading analysis of temperatures on Seat TDI, revs aren't welcome in the same engine load, as they increase the airflow and actually reduce temperature of exhaust gasses. What increases temperature is engine load, not the revs. If you don't have hills, go straight, fast, at lowest feasible revs. 

[Russ77]

2 minutes ago, nidza said:

This is our second O3 TDI, first one lasted 5 full years (2013). Majority of trips is flat town, 6km in the morning, 6km in the evening. In total, very little mileage, something like 35.000km after we return it.

 

No issues with DPF, ever. Driver is my wife, absolutely careless about any technical stuff, just sits and drives, if lucky doesn't scratch. 

 

Now she drives until 2020. another O3 TDI, 2015, same story. Issues 0, if we exclude scratching.

 

From what I've learned reading analysis of temperatures on Seat TDI, revs aren't welcome in the same engine load, as they increase the airflow and actually reduce temperature of exhaust gasses. What increases temperature is engine load, not the revs. If you don't have hills, go straight, fast, at lowest feasible revs. 

 

This makes sense.........  On several occasions my O3 has wanted to do an active regen on the way to work........ first part of the journey (around 4 miles) 30, 50, 40mph speed limits and my first stop at traffic lights I notice the revs are at 1K and S/S is unavailable.

 

For the next couple of miles the limit is 40, usually with lots of traffic so I keep it in a gear or two lower than normal so the revs are around the 2K mark.

 

The limit then changes to 50 and there's a long uphill section, usually towards the top of the gradient S/S becomes available again (about 20 mins/8 miles) so I guess keeping the revs up helps generally helps the engine maintain heat then the extra load of the gradient lets the temperature peak so a regen can happen.

[Gabbo]

1 hour ago, aposhtol said:

 

Imagine lots of everyday short trips (5-10 min drive) in town without hills. The system is dumb. Once it starts active regeneration it restarts it every time you start the car again (and get past 50 km/h I think) and in a few days driving like this you get DPF light in instrument cluster. Even if you don't end up with DPF light, it consumes extra injected fuel every time you start the car. So my method is switch DSG to manual -> get at least 2500 rpm -> drive like this 5 - 10 min -> park the car and see if revs are below 1000 rpm and start/stop engaged, if not drive some more like this until it completes.

 

If the higher revs were implemented in the software it would be even more obvious of active regeneration taking place. Maybe it's part of the VW policy to not do so.

 

As Nizda above, I have already driven this kind of profile for 18months without any issues and only around 5mpg reduction in fuel consumption (even if all of this is because of regen its still not so bad).

Regeneration only starts once the engine is warm & Im not sure how the ECU should know when you are going to drive enough for it to complete a regen in one try?

If a regen is needed, it will try each time the conditons for regeneration are available & stop when it is interrupted. This is what the system is designed to do.

It doesnt have to complete a full regen in one go, its quite normal to perform more frequent partial regens rather than a full regeneration. The system is designed for this too, it is a normal use case.

 

How much extra fuel does driving round unecessarily for 20minutes use compared with the fuel for warming up the DPF for 2 or 3 partial regens?

Probably its about the same, so my philosophy is why not let it regen when you are driving the car somewhere you need to go rather than waste your time driving with no destination?

 

Again, theres nothing wrong with what you are doing but from my point of view, its not necessary, the same for driving with higher revs.

[aposhtol]

46 minutes ago, nidza said:

From what I've learned reading analysis of temperatures on Seat TDI, revs aren't welcome in the same engine load, as they increase the airflow and actually reduce temperature of exhaust gasses. What increases temperature is engine load, not the revs. If you don't have hills, go straight, fast, at lowest feasible revs. 

 

This may be true for normal driving, but when regeneration is active fuel is injected in 4th stroke so that DPF heats up more quickly. So, I think, more revs, more heat to DPF.

 

32 minutes ago, Gabbo said:

Probably its about the same, so my philosophy is why not let it regen when you are driving the car somewhere you need to go rather than waste your time driving with no destination?

 

I tried this, and in winter I end up with DPF warning. Again, I cannot discern between DSG behavior in normal driving and during regeneration so I think is cheaper to switch it to manual and end it with higher revs.

[DavidY]

The manual for mine says this about when the DPF warning light comes on:

Quote

 

To clean the diesel particle filter, and where traffic conditions permit, drive for at least 15 minutes or until the warning icon goes out as follows.

• 4. or gear 5 engaged (automatic gearbox: Position D/S).
• Vehicle speed at least 60 km/h.
• Engine speed between 1800-2500 rpm.

 

 

I always assumed that the D/S meant keep out of Eco mode, although it's not totally clear.

Edited 9 October, 2018 by DavidY

[CRASH67]

Wow I can see a lot of thought goes in to DPF regens lol.

 

well the general rule of thumb seems to be a longish drive keeping constant speed/revs so ideally a trip down the motorway etc... 

most vehicles will sit in the required optimum range in flowing motorway traffic.

 

most DPF we see now the public seems more clued up relates to mileage and becoming filled up

we are seeing less and less relating to short trips as 1, drivers/owners are more aware. 2, warning lights being added when vehicles need to advice drivers a regen is needed. Which early vans in didn’t... this was a update for early vans using DPFs as a lot of couriers hit the issue with a lot of stop start driving.

 

for my personal exprience. I’m only 2months in to owning/long term driving of one vehicle fitted with a DPF. (With work drive many different diesels just not in long enough spells to comment on DPF regen).

 

and I’m sure I’ve park it’s up a once of twice potentially mid regen as the smell and the more noticeable fans running after a drive.

now I brought the Octavia to replace a Fabia TSI, preferably wanted a TSI, but this partially TDI was a nice spec at the right time a price I was happy with.

 

i use my TDI no differently to my TSI. I’ve not changed any of driving habits or not used it for a short journey.and that is purely because I know my commute gives the car ample opportunity to regen. 5 or 6 days a week it does a 26mile each way commute on. At least half is a stint on the motorway after back roads in the morning the route home half motorway half dual carriage way.

 

i guess what I’m trying to say is, we must all appreciate, cars have to be simple to use. Cos many won’t know or don’t care  how they work. And if you tried to sit someone down and explain a lot of the above... you would bore them or you’d put them off diesel even if it was the right choice for them.

hence why when you break it down really, a simple drive down a motorway can Be the ideal situation, the DPF light acting as a way to advise drivers to action to avoid costly premature bills. Remembering this is a filter and at some point will fill up and need changing regardless of actions, though there do appear to many cleaning filters. 

Most trucks now use DPFs and they have a surcharge where they will go back to the manufacture and be remanufactuer or reconditioned.

 

the key thing, and that is now being pushed is buy the right fuel type for your use! 

If you commute and doing many thousands a year. You buy a diesel and chances are You won’t have a  DPF unless you have a used car on a high milage...

 

sometime to me... too much knowledge can lead to overthinking, of somethings that to be honest, has to be simple or wouldn’t work in the real world.