Diesel particulates filter clogs if low mileage?

Contessa

Goudy said:

Contessa said:

Goudy said:

A DPF is designed to trap soot in the exhaust, then when it detects the filter is filling with soot it will need to actively regenerate.

This means the engine injects extra fuel on a post combustion cycle so it makes it way into the DPF unburnt which it ignites and burns the larger particles of soot to smaller particle of ash, which it can hold more of.
Even if it all works perfectly it will eventually fill with ash and require attention.

To do this it needs the right conditions, to burn the soot to ash temps have to be really high (some French cars use another fliud, EOLYS to reduce the temps needed) and if you don't quite get them you can start having trouble.

Obviously if the regen cycle doesn't start or complete because you have switched the engine off or it can't meet the right conditions, you fill the filter with soot far quicker than it would fill with ash and the car will detect excess back pressure from the filter and complain via the on board diagnostics.

Another issue if the cycle doesn't complete is the fuel that is injected post combustion.
This can seep down past the pistons and dilute the engine oil.
Not only does this alter the oil properties, but if it happens enough the oil level will rise and if the oil rises enough the engine can "run away" on it (run uncontrollably on it's own engine oil).

If you get the the point of having lots of incomplete regens, it becomes a vicious circle.
The car will try more and more to regen, injecting more and more post combustion fuel which then might not complete, exasperating the problem.

The issue with short tripping a diesel is then tend to make a bit more soot when started cold, the chances of reaching the ideal temp conditions for a regen are greatly reduced and the chances the engine might not be running long enough is also high.

Some cope with this better than others, as already mentioned there are systems that can help the regen process on some cars plus everyone's driving habits are slightly different, but short tripping one isn't ideal.

With your trips being so short, you probably aren't going to see the cost difference in fuel back any time soon either.
Diesel is far more expensive than petrol and to make that back you will need to do a lot more miles.

Some petrol cars have particulate filters but they work very differently.
For one they don't produce as much soot, plus it's a passive system.
Heat from the exhaust gas on the over run (when you take your foot off the pedal) is really really hot and it uses this to burn any soot to ash in the filter.
As there's less soot to start with and the regen is passive and happens many many times when you are driving, these tend to be far more reliable.
In fact, short tripping usually means you're on and off the pedal far more often which helps the process.

Thank you-that's a really clear explanation. One question though-how do you know when regeneration is happening and when it's complete? I drive an old diesel and have never been aware of regeneration taking place.

That's the issue.
If you do enough miles in a modern diesel fitted with a filter you don't really need to know when it happens or when it finishes, it just happens when the conditions are right, mainly when it's DPF is hot and it needs too. It works out the percentage of soot in the filter via sensors that detects back pressure in there.

Some cars have a warning light, others don't but you can tell as described, increased rpm, starts smelling a bit hot with a slight decrease in mpg.

With some diagnostic software you could probably monitor the percentage it's full and anticipate a regen, but it's a lot of bother.

Some cars will monitor the oil as well.
If it increases in volume it's a sign that the post injected fuel in making it's way into the sump diluting the engine oil.
As always, it's a warning something isn't right, it shouldn't replace a periodic manual check of the oil (level, consistency and smell)

As I mentioned it earlier, some French cars like Citroen use a special fluid called EOLYS.
This is fed into a catalyst before the DPF and helps reduce the temperature needed to burn off the soot.
It usually needs 600+c to burn off the soot. EOLYS reduces that to around 450c which is more easily reached.

A full EOLYS system is meant to last around 70,000 miles, but I seem to recall reading the ECU correlates the fuel tank size, miles ran and how often the fuel flat opens.
So if you continually top up rather than fill up when near empty, it will think the system has less in it than there is and set a low level DTC.

My dad had a car fitted with this system and I took it on after, well you know.
Either of us ever noticed it regening, it must have as some point as it was close to 150k when I moved it on.
Then again, it shortest trip I did in it was 300 or so miles.

I currently drive a new petrol Clio with a FAP (French name for particulate filter).
As described, it's a passive system and works every time I take my foot off the gas, as that when the exhaust temps scream mad hot and burns off any soot trapped in there.
Bonus is it's nice shiny tailpipe never gets sooty, though the exhaust does appear to be steamy at times.

I have heard of some petrol systems causing trouble though, like a diesel DPF it all depends on where it's fitted.
If it's close to the mainifold, the chances of it getting hot enough, regularly is higher.
Some manufacturers fit them further along the exhaust system due to packaging problems and they tend to suffer.

Goudy said:

Contessa said:

Goudy said:

A DPF is designed to trap soot in the exhaust, then when it detects the filter is filling with soot it will need to actively regenerate.

This means the engine injects extra fuel on a post combustion cycle so it makes it way into the DPF unburnt which it ignites and burns the larger particles of soot to smaller particle of ash, which it can hold more of.
Even if it all works perfectly it will eventually fill with ash and require attention.

To do this it needs the right conditions, to burn the soot to ash temps have to be really high (some French cars use another fliud, EOLYS to reduce the temps needed) and if you don't quite get them you can start having trouble.

Obviously if the regen cycle doesn't start or complete because you have switched the engine off or it can't meet the right conditions, you fill the filter with soot far quicker than it would fill with ash and the car will detect excess back pressure from the filter and complain via the on board diagnostics.

Another issue if the cycle doesn't complete is the fuel that is injected post combustion.
This can seep down past the pistons and dilute the engine oil.
Not only does this alter the oil properties, but if it happens enough the oil level will rise and if the oil rises enough the engine can "run away" on it (run uncontrollably on it's own engine oil).

If you get the the point of having lots of incomplete regens, it becomes a vicious circle.
The car will try more and more to regen, injecting more and more post combustion fuel which then might not complete, exasperating the problem.

The issue with short tripping a diesel is then tend to make a bit more soot when started cold, the chances of reaching the ideal temp conditions for a regen are greatly reduced and the chances the engine might not be running long enough is also high.

Some cope with this better than others, as already mentioned there are systems that can help the regen process on some cars plus everyone's driving habits are slightly different, but short tripping one isn't ideal.

With your trips being so short, you probably aren't going to see the cost difference in fuel back any time soon either.
Diesel is far more expensive than petrol and to make that back you will need to do a lot more miles.

Some petrol cars have particulate filters but they work very differently.
For one they don't produce as much soot, plus it's a passive system.
Heat from the exhaust gas on the over run (when you take your foot off the pedal) is really really hot and it uses this to burn any soot to ash in the filter.
As there's less soot to start with and the regen is passive and happens many many times when you are driving, these tend to be far more reliable.
In fact, short tripping usually means you're on and off the pedal far more often which helps the process.

Thank you-that's a really clear explanation. One question though-how do you know when regeneration is happening and when it's complete? I drive an old diesel and have never been aware of regeneration taking place.

That's the issue.
If you do enough miles in a modern diesel fitted with a filter you don't really need to know when it happens or when it finishes, it just happens when the conditions are right, mainly when it's DPF is hot and it needs too. It works out the percentage of soot in the filter via sensors that detects back pressure in there.

Some cars have a warning light, others don't but you can tell as described, increased rpm, starts smelling a bit hot with a slight decrease in mpg.

With some diagnostic software you could probably monitor the percentage it's full and anticipate a regen, but it's a lot of bother.

Some cars will monitor the oil as well.
If it increases in volume it's a sign that the post injected fuel in making it's way into the sump diluting the engine oil.
As always, it's a warning something isn't right, it shouldn't replace a periodic manual check of the oil (level, consistency and smell)

As I mentioned it earlier, some French cars like Citroen use a special fluid called EOLYS.
This is fed into a catalyst before the DPF and helps reduce the temperature needed to burn off the soot.
It usually needs 600+c to burn off the soot. EOLYS reduces that to around 450c which is more easily reached.

A full EOLYS system is meant to last around 70,000 miles, but I seem to recall reading the ECU correlates the fuel tank size, miles ran and how often the fuel flat opens.
So if you continually top up rather than fill up when near empty, it will think the system has less in it than there is and set a low level DTC.

My dad had a car fitted with this system and I took it on after, well you know.
Either of us ever noticed it regening, it must have as some point as it was close to 150k when I moved it on.
Then again, it shortest trip I did in it was 300 or so miles.

I currently drive a new petrol Clio with a FAP (French name for particulate filter).
As described, it's a passive system and works every time I take my foot off the gas, as that when the exhaust temps scream mad hot and burns off any soot trapped in there.
Bonus is it's nice shiny tailpipe never gets sooty, though the exhaust does appear to be steamy at times.

I have heard of some petrol systems causing trouble though, like a diesel DPF it all depends on where it's fitted.
If it's close to the mainifold, the chances of it getting hot enough, regularly is higher.
Some manufacturers fit them further along the exhaust system due to packaging problems and they tend to suffer.

Thanks again. My car is great for motorway cruising but I rarely do that now. As it's mainly short journeys I'm intending to sell it soon-it will be much kinder to my car if it's used more appropriately by someone else.