How does the DPF regen system work?

[Welly]

In basic terms what does the Pug/Citroen system actually do?

I know it squirts some eolys fluid into the fuel tank but then what? I mean is there always some eolys mixed with your diesel?

I know the DPF has a pressure sensor to tell the ECU it's dirty but how does the car initiate the 'burn off' process?

Reason for asking is horror stories about aborted regens filling your oil sump with diesel, I don't think we* inject diesel like other systems do which got me wondering how is actually works (having never really needed to know).

[jonsowman]

The 406 (and all PSA passenger systems, as far as I know) system works by dosing the fuel with Eolys fluid, which has the effect of changing the chemical composition of the soot that is generated in the combustion process. Diesel soot usually needs temperatures of around 600C to combust. The addition of Eolys reduces this to around 450C. The result of this is that it is possible to regen such a DPF by simply increasing engine load. That is to say, injection and burning of more fuel in the normal combustion process. Hence the need for enabling so-called "large consumers" - the rear window heater and mirror heaters, to increase the brake torque demand from the engine which in turn increases fuelling. Coupled with the oxi-cat (the pre-DPF catalyst), this enabled exhaust temperatures at DPF-inlet to reach the necessary temperature to burn off the soot.

Dosing systems were found to be undesirable - there's an extra tank, some more fluid to fill up at each service, etc. So, some manufacturers have found a different way around the problem. Without Eolys, the DPF-inlet gas temperature needs to reach about 550-600C. This is done by so-called post-injection, in which diesel is injected into the combustion chamber after the main injection and power stroke, when the exhaust valve is opening. The cylinder is hot enough to ignite the fuel, which leaves the cylinder and heads down the exhaust pipe. This still-burning fuel increases the temperature of the exhaust gases to the necessary level.

The reason this can cause oil dilution is if the quantity of post-injection fuel is calculated wrongly for the combustion chamber wall temperature. If not all of this fuel vaporises, it drains down past the piston into the crankcase and then the sump. Over time, this causes the oil dilution you speak of. It is very difficult to get this quantity correct, hence some cars suffering quite badly with this.

[steve_earwig]

It's magic, eolys is actually liquefied pixie dust.

[highlander]

The active ingredient in EOLYS fluid is apparently Cerium Oxide, chemical formula Ce2O3. This stuff is also found in catalytic converters.

Note that AdBlue is completely different stuff. It's around 66% distilled water and 33% urea, which is derived from pig urine.

[Welly]

Cheers for the clear explanation jon, eolys sounds quite a simple and clever system to be fair but I guess once the sensors etc start messing up then it gets expensive.

So really then you only need to load the engine for it to complete a regen (once called for that is) I have been known to take our C4 out and give it mega blast so I guess that would delay regen's on its own, almost cleaning the filter through extra heat.

I don't like the systems that drizzle fuel on the exhaust stroke, I've already heard about broken engines because of thinned oil so I guess as DPF systems go the Pug one is fairly straight forward, or presents the least danger to your engine.

[Bailes1992]

You don't need to hammer the car to complete a regen. Infact full throttle loads would probably interrupt the regen process.
I assumed the Citroen would use post injection sequences as well as the Eyolys?
I know my Focus does and it's recommended to keep the engine under as little load as possible but keep the revs up (I. E. 60mph in 5th) as this makes sure there is an abundance of oxygen still left after the combustion strole to facilitate with burning the diesel during post injection sequences.

[jonsowman]

I assumed the Citroen would use post injection sequences as well as the Eyolys?

Quite possible.

Correct with respect to maximising O2 in the exhaust - in fact most ECUs will disable EGR during a regen to aid this also.

[Doggy]

most ECUs will disable EGR during a regen to aid this also.

This bit seems to be missing from my VW manual.

[OllieNZ]

I assumed the Citroen would use post injection sequences as well as the Eyolys?

Quite possible.

Correct with respect to maximising O2 in the exhaust - in fact most ECUs will disable EGR during a regen to aid this also.

The dv6 definitely uses post injection.

[OllieNZ]

From the dv6 manual I have.... please excuse the dodgy polish to english translation.
"5.1. The principle of the particle filter regeneration
Regeneration consists of periodic burning particles accumulated in the filter
Particle . Composed essentially of hydrocarbons and carbon particles are embedded in the
particulate filter burn in the presence of oxygen at a temperature of 550 ° C (threshold of regeneration).
Particulate filter regeneration is controlled injection system.
Additional injection system initiates fuel injection, in order to increase the initial temperature
Exhaust from about 150 ° C (Urban cycle) to 450 ° C at the entrance of the catalyst.
This rise in temperature occurs in 2stages:
Additional injection (after TDC) causes combustion in the cylinder and pushes
temperature from 200 to 250 ° C
Additional post-combustion, controlled oxidation catalyst placed before
particle filter, burn unburned hydrocarbons (HC) from the injection
additional. The temperature rises about 100 ° C. Allowing a break
incineration 550 ° C"

[rwb]

There is a tank of additive.
Every time you remove the fuel cap the fuel tank is dosed with a fixed amount of additive.
The computer calculates the amount of additive remaining (there is no level sensor) and when it's run out you get a warning message.

The additive builds up in the particle filter where it acts as a catalyst to reduce the temperature at which the soot can be burned to 'only' 400 degrees.

The computer calculates the amount of sood accumulated in the particle filter, and when it reaches a certain threshold triggers a regen.

During a regen the exhaust temperature must be raised to over 400 degrees. This does not happen during normal operation; it is not true that the soot naturally burns off during motorway driving.

To increase the exhaust temperature the car chanages the injection timing and places additional load on the engine by activating the glow plugs and the heated rear screen.

When the heated rear screen is on so are the heated mirrors. If you put an LED across the mirror heating terminals then you effectively create a warning lamp for when a regen is in progress.

During a regen you will notice the engine note change to become more raspy, the car will feel down on power, and the fuel efficiency will plummet.

The regen does not burn off the additive that is in the filter, therefore over time the filter becomes blocked with additive. This is also calculated by the computer.

The differential pressure sensor across the particle filter is there to detect puncture rather than blockage, and acts only as an emergency override to the computer's calculations.

You can measure in PP2k the amount of additive remaining and the amount of additive in the particle filter. Becuase I run the tank empty then fill it full I am using the least possible amount of additive, and I have enough left for 200 fills which should cover about 120k miles. I have 94g in my filter and I've seen a 607 at 136g without problem, but I do not know what the limit is (plus, different cars have different size filters which presumably have different thresholds).

[rwb]

My 400 degrees came from the DW12B docs.
550 for the DV6?

[Doggy]

Pretty sure the 406 DW12 info states 450 degrees, (reduced from 550 by the action of the catalyst).
FWIW, it uses post injection, all the heavy electrical loads it can muster and uses the intercooler bypass heat exchanger to raise the inlet air temperature.
Additive is injected into the tank every time the fuel cap is removed, but it does try to calculate how much eolys to add based on the increase in fuel tank level before & after filler cap removal. (I never trusted it and filled it from virtually empty every time).
Please also be aware that regens are triggered based on both differential pressure AND distance since last regen. On the 406 at least, there has to be a reduction in differential pressure for a regen to be judged "successful".

I read the manual many, many times before it finally became useful, (for lighting the woodburner).
8.5k miles in limp mode gives you a true and lasting appreciation of the benefits of dpf's

[Welly]

Interesting stuff this, thanks.


*goes off to look for DV6 DPF removal and remapping companies

[OllieNZ]

Interesting stuff this, thanks.


*goes off to look for DV6 DPF removal and remapping companies

OMG tuning did my remap. I took care of the filter myself.