AGR and After-treatment DPF

Hello everyone,

not from a problem, but rather out of pure curiosity: Has anyone already thought about or investigated how the AGR and DPF work together in the event of a retrofit solution?

(Well... there's definitely some personal interest, my car is getting its Seat subsidy next week)

My thought process on this:

The AGR is designed such that, with normal exhaust backpressure and a specific actuation of the AGR valve, a certain proportion of exhaust gases enters the intake manifold. If the air mass decreases too much, the control will be reduced; if it increases too much, it will be increased.

Now, if we add a DPF, the exhaust backpressure will increase slightly, thereby, in my opinion, changing the system's tuning. With the same control input, more exhaust gases enter the intake, as the excess portion, besides the position of the valve, is determined by the pressure differences on both paths (exhaust and intake). The interesting question is now whether the control system, despite the now changed exhaust backpressure, is still able to counteract the presumed decrease in air mass so that the returned exhaust gas amount is again identical to the case without the DPF. In my opinion, it is sufficient if it does not achieve this 100%, but only returns a slightly higher amount of exhaust gas. This creates more rust, which also settles more in open filters, especially under partial load, and further accelerates the entire process.

What do you think of these considerations? Complete nonsense? Or could it be that the AGR (Exhaust Gas Recirculation) actually contributes to properly "loading" open filters in part-load operation, until they are blown out on the AB (Exhaust Gas Analyzer) or become hot enough to dispose of the exhaust gas loading themselves? Or are the fluctuations due to tolerances of the components, the aging of the valves, the fouling of the intake, etc., greater than this possible effect?

Please note: I am only talking about replacement filters for cars that were not originally equipped with a filter, and in which the MSG (Motor Control System) essentially has no knowledge that there is now a blockage. That a system, which was designed from the outset to handle this specific situation, should not have any problems, should be clear.

Best regards,

Jan

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The interesting question now is whether, despite the now changed exhaust gas resistance, the regulation is still able to counteract the presumed decrease in air mass, so that the recovered exhaust gas volume is once again identical to the case without a DPF.

That already fulfills the requirement.

Could you try a bit of MWB 3 without the cork, and then log it with the cork? Maybe you'll notice a slightly smaller tendency towards shorter key presses. Or, one might not see anything... that would be quite interesting.

Hi,

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Could you try a bit of MWB 3 without the cork, and then log it with the cork? Maybe you'll notice a slightly smaller tendency towards shorter key presses. Or, one might also see nothing... that would be quite interesting.

I'll see if I can get this sorted out before Tuesday (I'm currently very busy), but it probably won't make much of a difference because my LMM isn't really doing well anymore.

My concern is also that the key ratios will hardly change, but nevertheless, more emissions than "planned" will be released. Exactly, but you can't measure that.

Best regards,

Jan

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My concern is also that the key ratios will hardly change, but nevertheless, more emissions than "planned" will be released. Exactly, but you can't measure that.

How should this work?? This would require a change in the quantity of exhaust gas relative to the displaced air mass . For example, a higher temperature is good, but the DPF is not an AGR cooler.

When the pressure conditions change, for example, when the AGR valve position remains the same, more exhaust gas flows in, then the control system will adjust accordingly.
If the printing ratio has not changed significantly, then the printing pressure ratio has also hardly changed.

With my 1.4 HDI with a retrofitted open filter, the EGR rate was actually reduced. I can notice the increasing load on the filter in city traffic when it doesn't run properly there. Then it demands a long drive on the highway. At least, none of the colorful lights are turning on for me!

mhh, I can't really contribute anything further, except that with the aftermarket DPF, I don't have the AGR in operation.

But the Seat filter is also the replacement for the original OxiCat (maybe the new part can even reduce the back pressure, at least temporarily, because it's clean), unlike mine, where there's now a huge TwinTec part behind the MiniOxiCat. I think the exhaust back pressure won't change much, as the AGr is located before the turbo... mmm, I don't think anything will change. I can only imagine that, even with a fully functioning AGR, the filter's loading will likely increase in frequent urban environments.

Regarding the Twin Tec part, after approximately 10,000 km, I can say that I haven't noticed any significant changes in my consumption figures. The consumption remains within the normal range, as it was before. I haven't experienced any issues during long trips either. However, I haven't specifically made any "before and after" comparisons. That's your ultimate chance.

The effects will be marginal and not measurable.
Should the situation escalate, then it will resolve itself. Exhaust backfire increases - more fuel is being injected for the same performance - AGR will continue to be restricted.


Furthermore, an open AGR (Exhaust Gas Recirculation) may help to "regenerate" the DPF in the LL (Lean Lean) by, on the one hand, increasing the exhaust temperature (Note: do not confuse with local peak temperatures during combustion), and on the other hand, increasing the emissions of HC and the amount of HC attached to soot, which "feeds" the oxygen cat, and this keeps the DPF at operating temperature due to increasing temperatures during oxidation.

I wouldn't worry too much about it, and if in doubt, I would slightly reduce the AGR rate using VCDS.

Hi,

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mhh, I can't really contribute anything further, except that with the aftermarket DPF, I don't have the AGR in operation.

I can easily imagine that this is precisely the reason why consumption hasn't increased...

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But I also never made explicit "before/after" comparisons. That's your ultimate chance.

I'm keeping track of all my car expenses... so it will definitely add up, especially since I have a pretty high proportion of city driving.

River cruises... see above - I will probably unfortunately not be able to come anymore. This is quite complicated in a big city, as you need comparable conditions, which always means having to drive a good distance. My commute is too dependent on traffic to be a reliable indicator... as you can see, I've been able to drive it with a minimum of 4.8 l/100km and a maximum of 6.7 l/100km – both under the same driving conditions, but influenced by the surrounding traffic.

Best regards,

Jan

I also can't provide a comparison between "before" and "after." I bought my 206 like that. I can only subjectively feel the loading state of the DPF. However, I clearly noticed that during my 12-week stay in Münster at the end of last year, the daily trips I usually took for work decreased. Instead, there were no short trips, and the trips I did were almost exclusively on the highway. Despite my usual cautious driving style, I noticed after 1000 - 2000 km how smoothly the engine suddenly ran, how well it responded to acceleration, and that the finally warmed-up exhaust system even produced a rather fun idle rumble. Since I've resumed my normal trips to work (50/50 countryside(bus and city transport) this humming noise in idle mode disappeared within a few days.

Subjectively, the little HDI is running a bit rougher again, but I can't exactly prove it with logs. Regardless, the fuel consumption is in the lower third of the manufacturer's specifications (for the 1.4 HDI without a filter), and I can only compensate by making the engine work harder for faster highway trips. At speeds up to 140 km/h, the engine power (50 kW) is sufficient for relatively low fuel consumption thanks to aerodynamic optimizations. Above that speed, it's too fast for the engine's power, and the engine has to work harder. Those who are interested can view my fuel monitoring data.

However, one cannot fault the open DPF system for its ineffectiveness. When I look at the chrome exhaust pipe of my 206, I notice less rust buildup compared to the 1.4-liter petrol engine (55 kW), which is comparable in terms of performance.

@hutfahrer:

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Since I've resumed my regular commutes (50/50 highway and city traffic), this humming noise when the engine is idling has disappeared within a few days.

Can you confirm that you observed a plume of smoke while accelerating on the highway? In an open system and under higher load, I imagine that it would initially suck up a large portion of the loose, adhered soot (which is not firmly embedded in the metal mesh).

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That's too much for the engine's performance, and the engine has to work harder. Those who are interested can view my fuel monitoring data.

Check out the intake air temperature and air mass (available via OBDII). You will notice that the air mass decreases drastically with increasing air temperature, and the engine runs smoothly in wide ranges .
And that could explain why you experience the loading effect more strongly, compared to, for example, TDI drivers with corks, whose STG (engine control unit) regulates the amount according to the torque limitation. It will be like this with you: more exhaust back pressure -> poorer washing -> less fresh air mass -> smaller injection volume.

On a 1.4 HDi engine, we measured a temperature of 174°C in the intake manifold last summer. At 35°C outside and 1 bar LD (Series).

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Und genau das könnte erklären, warum du den Beladungseffekt stärker spürst, als etwa TDI-Fahrer mit Korken, deren STG die Menge gemäß... Torque Limiting Control

In TDI, the injection mass is also limited after the haze (air mass).

Only in certain engine speeds. In a healthy TDI, the lowest value represents the torque limit.

->

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-> Initially, the intake air volume limits (MWB 8 and 9): Here, the torque limit should specify the lowest value. If the air mass/soot limit is significantly lower, this suggests a problem with the turbocharger system or the air mass meter (LMM). Exception: In the case of tuned engines, the particulate matter limit may always be active at full load in order to "not waste air".

/viewtopic.php?t=3322

vwSchrauber wrote:

Only in certain speed ranges. In a healthy TDI, the lowest value represents the torque limit. -> Quote: -> Initially, the intake air volume limits (MWB 8 and 9): Here, the torque limit should specify the lowest value. If the air mass/soot limit is significantly lower, this suggests a problem with the turbocharger system or the air mass meter (LMM). Exception: In the case of tuned engines, the particulate matter limit may always be active at full load in order to "not waste air". /viewtopic.php?t=3322

Yes, I understand.

I understand the statement

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. And this could explain why you experience the loading effect more strongly than, for example, TDI drivers with cork stoppers, whose STG (specific torque) limits the amount according to... Torque Limiting Control

aber trotzdem nicht. Does this then mean that there is no torque limitation in PSA, and that it is exclusively limited by opacity? I can hardly imagine that, since they mainly use Bosch EDC, as far as I know.

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Only in certain speed ranges

If the TDI doesn't get air, the opacity is also limited, regardless of the speed... I still don't understand what the difference should be if the PSA doesn't get air.

Regarding my car, which also has an aftermarket DPF since the summer, I monitor the exhaust pressure between the turbocharger and the catalytic converter/DPF. The pressure is not necessarily higher than before with the partially clogged catalytic converter. Now, in winter, it increases slightly more after a longer short trip. At partial load, the pressure is always relatively low because the flow rate is low. The change that I can't read on my small gauge is definitely being caused by the MSG and needs to be calibrated.

Hi,
I can report that a 2003 V70 with an aftermarket open DPF (add-on) did not experience a significant increase in fuel consumption.
haithamina

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but still not. Does this then imply that there is no torque limitation in the PSA, and that it is exclusively limited by opacity? I can hardly imagine that, since they mainly use the Bosch EDC as well, at least according to my knowledge.

There is already a torque limitation, but it is usually the smoke/opacity limitation that is active, as the hot intake air allows less air mass to enter the cylinders. It (provenly) produces more torque if you cool the intake air, because this increases the air mass.
Of course, only with HDi without LLK.

Regarding the DPF, this means that the effect –reduced air mass– is amplified because the engine no longer releases as much exhaust gas from the cylinder, and the air mass sucked in decreases accordingly. At the same time, the cylinder temperatures increase during the exhaust stroke, which in turn hinders gas relaxation, and takes up space that would otherwise be used for fresh air.

Since the TDI is not directly related to the opacity (should be related to the opacity), you don't/can hardly notice it, because the opacity table should always release/release a few mg more than what is specified in the torque limitation curve.