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Old 10-08-2014, 01:41 AM   #31 (permalink)
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Originally Posted by mechman600 View Post
Not quite.
When I monitor NOx sensor values on a 2010+ 15L diesel, engine out NOx is around 300-400 PPM at max load (EGR engine). After SCR NOx (out of the exhaust stack) stays around 5-20 PPM at cruise and goes up to maybe 80 PPM at max load.
Well, keyword SCR. With SCR, gas engines would be doing a lot better than they are right now.

Most diesel powered vehicles on the road still stink up the air, based on experience.

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Old 10-08-2014, 02:03 AM   #32 (permalink)
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Well, keyword SCR. With SCR, gas engines would be doing a lot better than they are right now.
Will you please give me the full name so I may look it up? Thank you very much!
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Old 10-08-2014, 02:07 AM   #33 (permalink)
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Well, keyword SCR.
Yup. Whatever it takes to keep trucks from "producing far more NOx than a passenger car ever could".
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With SCR, gas engines would be doing a lot better than they are right now.
Nope. Gasoline engines use a 3-way catalyst to very effectively scrub NOx. Diesel engines cannot use a 3-way catalyst because they run far too lean, so they require SCR to scrub NOx.

GM was working on prototype lean burn gasoline engines that required a form of SCR to keep NOx levels acceptable. There are links to that project in this forum somewhere....
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Old 10-08-2014, 02:07 AM   #34 (permalink)
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Will you please give me the full name so I may look it up? Thank you very much!
Selective Catalytic Reduction.
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Old 10-08-2014, 08:28 AM   #35 (permalink)
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Nope. Gasoline engines use a 3-way catalyst to very effectively scrub NOx. Diesel engines cannot use a 3-way catalyst because they run far too lean, so they require SCR to scrub NOx.
That's what I mean though. Instead of using the 3-way catalyst system, use lean burn and SCR to get rid of the NOx. Not needing to worry about NOx opens so many doors.
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Old 10-08-2014, 10:50 AM   #36 (permalink)
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Here is GM's project along those lines: http://www1.eere.energy.gov/vehicles...ith_2011_o.pdf
Instead of using urea to create NH3 for NOx scrubbing, it seems that they can run brief rich periods to create HC + CO (engine out) for the TWC to convert to NH3 to "regen" the NOx trap. Funny...this is similar to what the VW 2.0L TDI does, using a NOx trap instead of a NOx catalyst.
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Old 10-08-2014, 04:04 PM   #37 (permalink)
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Originally Posted by mechman600 View Post
Here is GM's project along those lines: http://www1.eere.energy.gov/vehicles...ith_2011_o.pdf
Instead of using urea to create NH3 for NOx scrubbing, it seems that they can run brief rich periods to create HC + CO (engine out) for the TWC to convert to NH3 to "regen" the NOx trap. Funny...this is similar to what the VW 2.0L TDI does, using a NOx trap instead of a NOx catalyst.
Since it's been 4 years since that presentation, it sorta implies that GM was not able to 'make things work' as *rosaly* as they'd proposed.

Last edited by gone-ot; 11-04-2014 at 08:03 PM..
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Old 10-08-2014, 09:24 PM   #38 (permalink)
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leanburn was not the purpose of this thread but in any case I rather run leaner and produce more nox than go richer and produce more CO2, HC and CO, one leads to global warming and the other is highly toxic. nox is just a visible gas which is why epa has gone so mental about it. otherwise its no where near as toxic as other emissions. PLUS lean conditions such as 17+AFR create less nox than at stoich.



also after checking my wideband / data-logs, it seems i'm running more in the 17.5:1 range due to maf and o2 sensor scaling being off on the lean side. I could go leaner but I will need more timing to prevent surging and unfortunately I cannot get any more than 50* BTDC.
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Old 10-08-2014, 09:58 PM   #39 (permalink)
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PLUS lean conditions such as 17+AFR create less nox than at stoich.

Except your cat doesn't work at >stoichiometric and so your NOx out the tailpipe is way higher. Stoichiometric is cleanest overall precisely because the cat can react the remaining CO and NOx together.

Lean burn reduces HC and CO up till a certain point but at the cost of a lot more NOx. I am not sure if the EPA is right to freak out over NOx so badly but it is what it is with 3-way cats.

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