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Discussion Starter · #1 ·
Every long journey starts with a short one; so every nice long journey starts with a cold engine/exhaust and lots of crud/particulates filling up your DPF. The normal Engine Management System induced regeneration (the one that injects diesel to bring the exhaust temperature up and raises the idle speed from 800 to 950) will obviously reduce the particulates in the DPF to ash but is there something else going on?

If you do a lot of short cold journeys the this type of regeneration appears to occur quite frequently; but what if you do a lot of long hot journeys? Even on these you have started with a cold journey until the engine warms up so the DPF will still have filled up with crud. So do you get the same number (frequency) of regenerations, say 1 regeneration per 10 long journeys as you would with 10 short cold journeys? We are told that diesels with a DPF are not suitable for short journeys so what extra do the long hot journeys give you?

Does the long hot journey on its own burn to ash particulates stuck in the DPF? Or does one of these regenerations that we see so frequently on the short cold journeys happen during the "hot" part of the long journey as well but the regeneration is a lot more effective? If it is the latter, then the injection of diesel into a late part of the firing cycle is not doing its job properly and raising the temperature of the DPF on the short cold journeys - so why do it?. If it is the former then why do we sometimes find that a regeneration is occuring when taking the exit slip after a long hot motorway journey? Is 70mph in 6th gear for an hour or more not deemed "hot enough" to burn soot particulates to ash?

Why do many people suggest one nice long journey per week to clear the DPF - why should this clean the DPF any more than letting the normal regenerations complete when you do lots of short cold journeys?
 
G

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I don't have a DPF on my X-Type but I do on my VW Passat. Whilst it keeps the exhaust nice and clean with no smoke I just wish I could choose when to do a regeneration as it will indeed suddenly decide to start it when I've just got back home after a long motorway drive. I then have to spend the next twenty minutes going back onto the motorway or dual carriageway to let the regeneration complete itself as you must not switch off the engine as the excess fuel gets dumped into the sump.

The frequency of regenerations varies from 500 miles to 800 or so depending on the type of driving: frequent cold starts with short journeys will not allow a regeneration to start as the engine won't be hot enough so you may eventually get a warning light. I can usually tell when my Passat wants a regen or starts to do it but there will be times during a long motorway drive when there is a passive regeneration so the more fast runs you do the more miles between regenerations.
 

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Discussion Starter · #4 ·
This article on Land Rover DPF protocol may be of interest: https://www.honestjohn.co.uk/news/h...ohns-motoring-agony-column-04-11-2017-part-1/. Scroll down to "The regeneration game".
An interesting article that, presumably written with some authority, summarises what most people believe. It does not go into detail - in particular the when and why - and leaves me scratching my head to know the exactly what is going on.

those that continually do long journeys seem to fair rather better on the oil dilution front.
That does seem to be the experience of most X-type owners. My question is "why?".

It used to be short journeys weren't good for diesels, which is well known. In the case of the DiscoSport this appears to be moderate journeys too. The DS seems to regenerate around every 200 to 250 miles
Now is this 200 to 250 miles between regenerations on short journeys. What is it on long journeys? So on one long 837 mile journey (Lands End to John O'Groats say) will it regenerate 3 to 4 times or perhaps twice - once after 250 miles and then, say, again after the next 600?

if you park up just short of the next required generation, the next few short journeys are not enough to permit regeneration, so then dump fuel into the sump
Not sure I understand this bit. By "not enough to permit regeneration" does he mean not long enough to complete a regeneration once started?. Now the regeneration will not start until the engine is warm and if the regeneration does not start then no fuel will be dumped into the sump (and if you do enough of these not warm journeys then regenerations will not happen, the DPF will fill up, and you will end up with a DPF warning light). But what if you do allow a started regeneration to complete (as a lot if us do). In this case why will you get lots and lots of fuel dumped into the sump - you will only get one regenerations worth which you would get if you then carried on driving and turnred your short journet into a long journey.

The old EU5 used to regenerate approx every 500 miles and thus was more forgiving and a few short trips didn't interfere too much, as long as a long trip occurred to permit the burn.
This is the crux. Exactly what does the "long trip" do that extends the time (in number of journeys that start with a cold engine) between regenerations?
 

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This is the crux. Exactly what does the "long trip" do that extends the time (in number of journeys that start with a cold engine) between regenerations?
In short, on long trips the DPF heats up to a temperature (around 600 deg C) that burns off the crud. The input/output pressure sensors read good (little back pressure) so no regen.

It's all about temperature of the DPF and in the case of our beloved Jags, the DPF is simply in the wrong place (too far from the manifold) due to the engine design.

Tony
 

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Regeneration will not occur until the engine temperature reaches 400 degrees. With multiple short journeys the DPF fills because the engine has not reached the required temperature to start the regeneration process. The diesel in oil problem is also partly due to this, because the engine temperature rises and lowers above the required temperature, starts to regenerate and stops. This puts too much diesel into the cylinders and fuel bore washes and oil is dragged down into the oil. The engine temperature is reached more easily during a longer journey and allows for a complete regeneration to take place. Vehicles typically regenerate 3 times a week on average.
 

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Also, regeneration occurs when the DPF is 40% full. It does not have a mileage set to it. Air pressure is pumped into the DPF and the ECU analyses the pressure out. It uses this pressure calculation to work out how full the DPF is. When the DPF is 70% full it throws a warning light up. When it is 95 (does vary) % full it will go into limp mode.
 

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Regeneration will not occur until the engine temperature reaches 400 degrees.
Isn't that wrong ? the engine should never get that hot the H/G would go
 

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Isn't that wrong ? the engine should never get that hot the H/G would go
I took it that Bluechem was referring to the DPF temperature which is why having confused the issue he should explain passive and active regeneration as there is a huge difference.:-D:-D

Tony
 

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Discussion Starter · #11 · (Edited)
In short, on long trips the DPF heats up to a temperature (around 600 deg C) that burns off the crud. The input/output pressure sensors read good (little back pressure) so no regen. It's all about temperature of the DPF and in the case of our beloved Jags, the DPF is simply in the wrong place (too far from the manifold) due to the engine design.
Tony, are you saying that on a long trip the DPF heats up to a sufficient temperature to burn the soot to ash without the injection of (extra) diesel into the cylinders. If this is the case why can you come off a motorway and find that it is doing precisely this (main sympton being increased idle speed)?
 

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Discussion Starter · #12 · (Edited)
...because the engine temperature rises and lowers above the required temperature, starts to regenerate and stops...The engine temperature is reached more easily during a longer journey and allows for a complete regeneration to take place. Vehicles typically regenerate 3 times a week on average.
Ah, this is interesting. You think that the regeneration (high idle, injection of diesel) may run for approx 15 minutes and stop on its own accord because the engine temperature dropped (or it decided enough was enough and stopped to try again later) and not because the regeneration had finished?
 

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Discussion Starter · #13 · (Edited)
...The input/output pressure sensors read good (little back pressure) so no regen...
Also, regeneration occurs when the DPF is 40% full. It does not have a mileage set to it. Air pressure is pumped into the DPF and the ECU analyses the pressure out. It uses this pressure calculation to work out how full the DPF is. When the DPF is 70% full it throws a warning light up. When it is 95 (does vary) % full it will go into limp mode.
There is an interesting app called "VAG DPF" by Daaren Fonloil which measure various EMS and DPF characteristics to see when regenerations are happenning, when they last happened, whether a regen is due, and soot mass. Unfortunately it uses CANBUS commands and not OBD2 commands so is restricted to certain VAG group diesels. Something like this for the X-Type would be of immense help.
 

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Now you will have to explain the difference between passive and active regeneration...:-D

Tony
I don't know if someone has explained this later in the thread, but passive regeneration is when the vehicle runs normally and the contaminants are cleared from the DPF. If you use a good additive in the tank, it will passively regenerate, by bringing down the required burn temp. to normal exhaust gas temp. 400 degrees. Active regeneration is when the vehicle goes into regeneration on the road. Forced regeneration, is when a diagnostic tool is used to force the DPF into regeneration mode.
 

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Ah, this is interesting. You think that the regeneration (high idle, injection of diesel) may run for approx 15 minutes and stop on its own accord because the engine temperature dropped (or it decided enough was enough and stopped to try again later) and not because the regeneration had finished?
Just about right, but active regeneration usually actually takes only a few minutes. Your 20 minute drive is getting the exhaust gases to the correct temp. before it starts to regenerate. If it pops just above and below the required temp it is that time that lots of injections of diesel can take place and bore washing occurs.
 

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When the fuel is injected, it is dragged down the exhaust. At the front of the DPF is a catalyst that burns the fuel and the DPF temperature is raised to the required 600 degrees.
 

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Discussion Starter · #19 · (Edited)
Just about right, but active regeneration usually actually takes only a few minutes. Your 20 minute drive is getting the exhaust gases to the correct temp. before it starts to regenerate. If it pops just above and below the required temp it is that time that lots of injections of diesel can take place and bore washing occurs.
When I notice the idle speed has gone up to 950rpm (from the usual 800) I go off to my local bit of mile long dual carriageway where I can bomb up and down it at 40mph for about 10 times, turning round the roundabout at each end, until the idle speed falls back to 800rpm at one of the roundabouts and then I go home. To be clear in my mind, are you saying that for the most of that time the increased idle speed is just to get the DPF up to temperature and there is no injection of extra diesel?
 

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Tony, are you saying that on a long trip the DPF heats up to a sufficient temperature to burn the soot to ash without the injection of (extra) diesel into the cylinders. If this is the case why can you come off a motorway and find that it is doing precisely this (main sympton being increased idel speed)?
Active regeneration will take place when the sensors think the DPF is around 40% full. This can happen even on a long run as the temperature in the DPF will vary according to conditions, the amount of crud being burnt off slows down and the DPF will slowly fill up. As DPFs get older, they are harder to clean by passive or active regeneration.

When I take mine on short trips towing my trailer, sods law always finds an active regen taking place as I get home (burning rubber smell and lumpy running) so I have to leave the car running, drop the trailer and take it round the block until the damned thing stops.

Did I tell you I hate DPFs?

Tony
 
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