SCRF versus CSF - Are we on the bleeding edge?

Engine, Exhaust, Drivetrain, ECU Faults and Fixes
Rediscovery
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Re: SCRF versus CSF - Are we on the bleeding edge?

Post by Rediscovery » Sun Sep 29, 2019 10:29 pm

Possibly....

Diagram 3 confused me for a while when I first saw it. I think it's easy to explain though: it's simply the DOC-DPF architecture for EU5 markets where SCR was irrelevant, even after 1st September 2015. No NOx to worry about? Then crank up that heat boys!

I think I am on the same page, with reservations. I think we agree that the schematic represents the original design intent, provided that you accept that a functional schematic with oxy-cat (DOC) and catalysed soot filter (DPF) shown as two boxes is not invalidated if, for heat preservation, they combine these functions into a single canister, wherever possible. Better still if the DOC can attach directly onto the turbo. Of the more popular cars this accounts for D7a (XE, XF, F-PACE, and Velar). "close coupled so minimal or no effect" and D7u (RR, RRS and Discovery). medium coupled, may suffer from Oil Dilution.. They're all single canister arrangements and imho they all conform to the schematic in this document.

But I think the functional schematic was rendered useless once the decision had been taken to go with the SCRF system for D8 and at some point they had to abandon the preferred order of the functions. This is because SCRF puts the SCR on the filter which means that the DEF has to come before both. The fact that it says the opposite in the text I think identifies the point at which there had to be a departure. For me the date is still difficult to ignore.

We appear to be left with timing. The argument that SCRF was designed in earlier, rather than later, is somewhat weakened by the fact that this appears to have been very new, untried, technology which clearly needed further improvements in 2016. I think that speaks volumes about its suitability and readiness to be incorporated into a production system in the spring/summer of 2015 ( over a year earlier ). If that was 2015, what on earth was it like in 2014?

The other things that make it difficult to imagine that the crappy SCRF system was fully incorporated into their earliest plans, rather than being forced on them late in the day:
* The hopelessly misleading brochure claims echoing Jaguar XE service performance.
* The comments about "higher than expected" dilution in JLRP00100.
* The disclosures in the letter to dealer sales staff.
* No dealer software, training or worksheets for the known servicing requirements of SCRF.
* Waiting until 2018 to change the dilution to 10% - if they'd known this was coming a lot of grief could have been saved by doing this in 2015.
* AdBlue usage doubled.
* Disappointing fuel economy.

They could have been planning a cheat device to overcome some of these, I know, Anyway, thanks for the chat. I have it on good authority that someone on here does know the answer to the timing issue. Perhaps at some point they'll generously share what they know about the events at Gaydon in 2015... :)


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Re: SCRF versus CSF - Are we on the bleeding edge?

Post by Ian_S » Mon Sep 30, 2019 1:14 pm

I think you're seeing what you want to see and that we're going to have to agree to disagree with the diagrams. :) The only thing we can conclude IMO is they are way too woolly and inexact to be able to take them literally.

It is interesting to look at some regulatory timelines though.

September 2014 - All new type approvals must be EU6 compliant
September 2015 - All new car registrations must be EU6 compliant
September 2017 - EU6 compliance of no more than 2x limit comes into force
September 2019 - RDE comes into effect.

So, the DS is 'launched' in April 2014, when no doubt it gains type approval giving LR some leeway in starting sales with an EU5 engine, while they continue to grapple with EU6 emissions. They start selling cars late 2014.

Ingenium has to be in the car by September 2015 (MY 2016) or they just can't sell them, likewise the Evoque.

DEF usage in MY17 cars and later seems to increase after software updates... 2x compliance factor anyone? MY16 cars now consume DEF at half the rate of MY17 onwards with the same DEF tank size.

MY20 DS arrives for RDE. What changes lurk within?

I think we all realise that a DOC-DPF doesn't fit in the engine bay. It's a little disappointing that it would appear that hasn't changed on the new DS and Evoque.

Is there another fix though? It's clear from all the documents that an SCRF is far less efficient at burning off soot than a more standard DOC-DPF unit. The only hope for improvement there is that the filter technology, i.e. coatings improve to allow more efficient burn off. One option would be to use more fuel to spend more time actively regenerating the SCRF but, that would make the oil dilution even worse. So not really an option....

Or is it... ?

The reason we get oil dilution is because the fuel is injected in the cylinder by the existing injectors. Hence some of it (more than we'd hoped) finds its way down the cylinder wall. We know there is not enough space to replace the DOC assembly with one that contains a DPF, and a change to the chassis to accommodate that would also rule out any kind of retro fit option.

So, why not use that pesky bit of extra pipe work that robs the system of heat to fit a fifth injector purely for active regeneration? That would surely fit. OK, we'd need a new injector rail with a fifth outlet, a replacement DOC assembly that could house the injector (unless you could add a hole to the in-situ one reliably) and also the existing ECU would need to be able to control said injector, *but*, if that could be done, then the ECU could be far more aggressive with it's active regeneration policy as it would no longer have to worry about excessive oil dilution. The main downside would be fuel economy to fund the increased active regeneration, but I think I'd rather have that than a blocked DPF or failed engine. Once you'd got the system working it would be retrofit-able to existing troublesome cars .

It could be a barking mad idea... but you never know...

I only suggest it as it seems the underlying tech chosen in these cars will never perform that brilliantly and options to regen the DPF even more are limited by oil dilution. Remove the dilution and are there then more options in ECU software to help the DPF?
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Re: SCRF versus CSF - Are we on the bleeding edge?

Post by Barnsh » Mon Sep 30, 2019 1:57 pm

Iain
I looked into this many moons ago , you need to look more closely at the categories, it’s not quite as simplistic as

It is interesting to look at some regulatory timelines though.

September 2014 - All new type approvals must be EU6 compliant
September 2015 - All new car registrations must be EU6 compliant
September 2017 - EU6 compliance of no more than 2x limit comes into force
September 2019 - RDE comes into effect. “

Eu 6 a/b/c/d all have specific conditions attached
Timelines for full compliance are conditions attached to the suffix.

This was when EU6b to 6c doubled adblue useage...around 2017.
Eg they get issued as 6x compliance with the aim of being fully compliant with in y months.
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Passive Regeneration - Why it can't work in Normal Driving

Post by Rediscovery » Wed Oct 02, 2019 12:09 am

Regarding the potential for passive regeneration on the DS...

In the attached 2015 paper JM scientists explain that passive regeneration at 200°C to 400°C would be "significantly retarded" whenever SCR NOx treatment was also "active" due to the competition for NOx (this was still an issue in 2016). Their "experimental results" were presumably obtained on a compact architecture where 400°C might actually have been achievable ("compact" in this context not the same as "close-coupled" referring to DEF-DPF architectures).

There are two main problems frustrating passive regeneration on the D8 architecture:
* The "normal driving" temperatures are in the lower half of the 200°C to 400°C range (due to 70 cm of additional pipework).
* Soot oxidation is in any case "significantly retarded" during SCR activity due to competition for NO2.

When JLR stated in 2017 that "normal" driving didn't create enough heat for passive regeneration to occur they would have already processed this information. They would also have been aware that in 2016 JM still hadn't overcome several major obstacles:

* CSF has higher passive soot oxidation > 270°C compared to an SCRF® catalyst";
* The soot burn efficiency in a CSF is significantly higher than an SCRF® catalyst under active regen conditions (550°C to 600°C);
* The higher soot burn efficiency observed for the CSF compared to the SCRF® catalyst under active regeneration conditions can be attributed to the NO2 produced in the CSF (no competition);
* 600°C / 30 minute regen for the SCRF® catalyst matches the same regen efficiency as that of a 600°C 10 min regen for the CSF;
* 600°C for 20 minutes will only get you to about 75% soot burn on engine;
* The SCRF® catalyst can be fully regenerated (>95%) in approximately 30 minutes at 600°C;

… and asking / proposing:

* We need to adapt a suitable active regeneration strategy;
* How do we overcome the thermodynamic equilibrium limitation of producing sufficient NO2 under active regeneration conditions for reaction with soot?
* Increasing filter inlet temps to >600°C will be beneficial to reduce length of regeneration event;

This product was clearly still not finished more than one year after DS EU6 production started.
One point of interest with SCRF® is the interaction between the NOx reduction (SCR) and soot oxidation functionalities; NOx removal results in a reduction in the availability of NO2 for soot oxidation, while soot oxidation by NO2 lowers the NO2/NOx ratio, which is unfavourable for SCR if it moves away from the optimum value of 0.5. Therefore the SCRF® model has been applied to investigate this. The presence of soot on the SCRF® is predicted to have no significant impact on NOx conversion.

Conversely, SCR activity (NOx reduction) is predicted to significantly retard the rate of soot removal at lower temperatures (200°C–400°C), where soot oxidation is predominantly by reaction with NO2, but to have little effect at higher temperatures (450°C–550°C), where soot is predominantly oxidised by O2. Both predictions are in agreement with experimental results.
Computer Simulation of Automotive Emission Control Systems
Key developments in modelling of diesel emissions control components and catalysts are highlighted
152-165-pmr-apr15 (1).pdf
(1.73 MiB) Downloaded 15 times


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Re: SCRF versus CSF - Are we on the bleeding edge?

Post by Ian_S » Wed Oct 02, 2019 11:39 am

As a picture tells a 1000 words... (ANR = 0 means no SCR activity, ANR = 1 means SCR is actively converting NOx)

passive_regen.jpg

So below 250C passive soot burn-off is negligible even after 60 mins. Looks like you regularly need to exceed 300C to stand any chance of making a dent in the soot build up and reach the maximum of 250 miles before the next scheduled active cycle will begin anyway.

I wonder if later SCRF units have improved filter chemicals that perform better at lower temperatures.

I also wonder what performance would have been like in 'cheat mode' where we know the engine would produce more NOx and also remove less in the after-treatment. It looks like in that scenario, you might actually get some passive regen, especially if they also ran it hotter to produce less soot and also increase exhaust temps? Looks like a win-win to me. Higher engine burn temp = less soot = more NOx = higher exhaust temp = better passive regen and turn down the SCR wick and less competition for NOx to prevent passive regen.

However, the evidence all seems to suggest that for diesels, by far the most effective solution is a combined DOC-DPF and separate SCR system. One thing done at a time with the chance to optimise each process and not have to cheat to make it all work effectively.

It's looking more and more disappointing that the new platform hasn't tried to properly address this in the new models. The best we can hope for is that the active regeneration has improved enough to be able to work in challenging situations, especially as the new Evoque is being heavily advertised for use in the Urban Jungle... I guess the first indicator of better active regeneration will be fewer blocked DPFs in urban driving.

I suspect it goes without saying that the new models will be using the 10% oil dilution threshold from the start in the hope it gets most people past the 12 months point, which is probably the line where 'early' oil changes become more acceptable.

I wonder who else uses an SCRF?
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Re: SCRF versus CSF - Are we on the bleeding edge?

Post by Rediscovery » Thu Oct 03, 2019 11:03 pm

I don't know of another auto manufacturer using SCRF apart from JLR. And JLR only used it because it had no choice, remember.

I think you are right about the defeat devices. One raises the temperature in the SCRF to shift along the curves to the right. The other turns SCR OFF to keep PR on the blue curve.

And DEF usage would then be more appropriate for the size of tank.

Push SCRF temperature towards 650 deg C and it would make a significant improvement in AR to boot.


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Re: SCRF versus CSF - Are we on the bleeding edge?

Post by Mamil » Fri Oct 04, 2019 9:56 am

Ian_S wrote:
Mon Sep 30, 2019 1:14 pm

So, why not use that pesky bit of extra pipe work that robs the system of heat to fit a fifth injector purely for active regeneration? That would surely fit. OK, we'd need a new injector rail with a fifth outlet, a replacement DOC assembly that could house the injector (unless you could add a hole to the in-situ one reliably) and also the existing ECU would need to be able to control said injector, *but*, if that could be done, then the ECU could be far more aggressive with it's active regeneration policy as it would no longer have to worry about excessive oil dilution. The main downside would be fuel economy to fund the increased active regeneration, but I think I'd rather have that than a blocked DPF or failed engine. Once you'd got the system working it would be retrofit-able to existing troublesome cars .

It could be a barking mad idea... but you never know...
That's the way most commercial diesel's regenerate their DPFs. The reason normally given for not using it in cars is the extra expense and limitations in space. But, Toyota have tried it on SUVs and pickups equipped with their 2.8L diesel and the results haven't been good. Apparently they've had problems with the fifth injector getting stuck closed or open. The former results in no regeneration, a blocked DPF, and limp-home mode. The latter isn't much better and results in excess fuel consumption and a fried DPF as it's regenerating all the time! It's currently the basis of a class action lawsuit against Toyota in Australia involving 250,000 cars. Just goes to show there's no easy answer to making a DPF that simply works!
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Re: Newbies Should Read This

Post by Rediscovery » Tue Oct 08, 2019 9:36 pm

Rediscovery wrote:
Sat Sep 28, 2019 10:41 pm
The first DS with Ingenium and SCRF® shipped in September 2015. Here's a taste of the evidence that SCRF® was still undergoing significant development in 2016. Our 16MY and 17MY diesels were, in effect, JLR's test platforms.

https://www.discosportforums.co.uk/download/file.php?id=9669
The full scientific paper to go with the presentation.

SCRF vs CSF Active Regeneration 2016.pdf
(3.24 MiB) Downloaded 16 times
2016CLEERS_Cumaranatunge.pdf
(786.13 KiB) Downloaded 9 times


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DfT - VW Emissions fix explained

Post by Rediscovery » Sun Oct 13, 2019 10:45 am

Regarding the suggestion made above and elsewhere that late/forced removal of a NOx cheat device upped the HC/PM output, thereby triggering problems with oil dilution, DPF clogging/premature failure, EGR faults, etc.

A letter from Dept for Transport explains what happens to VAG cars after the removal of their EDC17 cheat devices.

vw-deiselgate-letter-EGR-VW-page-1.png

vw-deiselgate-letter-EGR-VW-page-2.jpg

vw-deiselgate-letter-EGR-VW-page-3.jpg

So far I can only find this rather poor copy which came from https://www.hypermiler.co.uk/dieselgate/dieselgate-department-for-transport-confirms-vw-fix-causes-twice-the-level-of-carcinogenic-diesel-particulate-matter

The data corelates precisely: three times as much soot, double the amount of active regeneration, soot up the EGR channel. I've read the Guardian account but that contained only anecdotal evidence. This is official data from the DfT and it seems to match the owner-provided data on here.

Put a cheat device on the L538/L550 2.0) diesels and everything would have worked fine. Just like it said in the brochure.


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