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Old 04-27-2008, 05:49 PM   #11 (permalink)
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A couple of factors come into play in an ECM while in EGR mode:

Spark timing vs. EGR rate (Injection timing on a diesel)
Rate of EGR vs. engine load
EGR flow diagnostics.

This has been stated already I think, but to clarify: The EGR by itself does not add fuel economy. What does add fuel economy:
-The ability to run advanced timing while in EGR
-The need to open the throttle slightly with EGR, reducing pumping losses.

I have added 2-4 degrees of extra timing during EGR event in ECM programming, with adverse effects. Unfortunately I have no evidence of whether or not this change improved fuel economy.

Interestingly, the Duramax diesel usually shows a slight improvement in economy with the EGR completely disabled.

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Old 04-27-2008, 09:49 PM   #12 (permalink)
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Since this thread has been pulled back from the dead, I'll pull back information from another dead thread to offer a new response.

Honda uses this technique in their generation 2 L-series engine in place of traditional lean burn. They refer to the technology as "Valve Pause." It supposedly returns slightly better fuel economy then its older d15z1 ancestor.

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Old 04-27-2008, 11:06 PM   #13 (permalink)
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I know BMW was experimenting with a throttleless gasoline engine a few years ago that used EGR to extensively reduce O2 to the cylinders. Not sure what ever happened to it, I am not up on new BMW stuff.

Personally I think EGR is one of the worst technologies we have put on gas or diesel engines and that targeting NOx emissions are counter productive. Traditionally we have countered NOx with the following methods:

Richen A/F mixture up to 14.7:1 for a 3-way Cat (lowers FE, raises CO & HC emissions)
Retard ignition timing (lowers FE, raises CO & HC emissions)
Lower Compression ratio (lowers FE, raises CO & HC emissions)
Add EGR, facilitates pinging so CR & timing are further reduced and while neither leaning or richening the mixture (gas engine), it does dilute the quality of burn. In a diesel it does displace O2 which hurts FE.

The only good thing that EGR does is promote faster engine warmup and reduce pumping losses in a gasoline engine but cylinder deactivation, VVT and using small turbocharged engines are a better ways to do this.

As pointed out in the TDIs it also soots up the engine which increases maintenance requirements and soot in the oil increases wear. I can verify that EGR has not been good for the powerstroke diesels either.

What we need is Urea injection or NOx reduction catalysts to come online so engineers can start building efficient engines again instead of clean ones.
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Old 04-27-2008, 11:14 PM   #14 (permalink)
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After blocking off the EGR pipe at the intake manifold on an 89 volvo fuel economy improved by 2mpg on average over many many tanks. Maybe EGR on newer cars is effective but most older systems are carbage.
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Old 04-28-2008, 03:00 AM   #15 (permalink)
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Hello,
I'm rather intersted in DIY EGR tuning. None of my cars has got OEM EGR, so I collected some OEM EGR parts (Suzuki Swift, Daihatsu Charade). One day I'll weld in such a 'bypass'. The valve is feed by a vaccum switch typically.

A stupid 'controller' would just switch on/off (just for testing) in passengers cabin.
A more practible way would be to provide a PWM depending on load and rpm (and engien temperature).
I picked up also a Swift ECU which should do this. Should be enough for starting. At least I'll see under which circumstances engine runs leaner (less butterfly pressure losses in manifold) - when I dissable EGR from passengers cabin.
I see no disadvantage in bad exhaust - maybe sporty drivebility suffers - but that's not the main goal for eco modders, isnn't it?

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Old 04-28-2008, 09:52 AM   #16 (permalink)
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Quote:
Originally Posted by Duffman View Post
I know BMW was experimenting with a throttleless gasoline engine a few years ago that used EGR to extensively reduce O2 to the cylinders. Not sure what ever happened to it, I am not up on new BMW stuff.

Personally I think EGR is one of the worst technologies we have put on gas or diesel engines and that targeting NOx emissions are counter productive. Traditionally we have countered NOx with the following methods:

Richen A/F mixture up to 14.7:1 for a 3-way Cat (lowers FE, raises CO & HC emissions)
Retard ignition timing (lowers FE, raises CO & HC emissions)
Lower Compression ratio (lowers FE, raises CO & HC emissions)
Add EGR, facilitates pinging so CR & timing are further reduced and while neither leaning or richening the mixture (gas engine), it does dilute the quality of burn. In a diesel it does displace O2 which hurts FE.

The only good thing that EGR does is promote faster engine warmup and reduce pumping losses in a gasoline engine but cylinder deactivation, VVT and using small turbocharged engines are a better ways to do this.

As pointed out in the TDIs it also soots up the engine which increases maintenance requirements and soot in the oil increases wear. I can verify that EGR has not been good for the powerstroke diesels either.

What we need is Urea injection or NOx reduction catalysts to come online so engineers can start building efficient engines again instead of clean ones.
X2!

BTW, NOx reduction catalysts are already in use in most GM products, including the D-max.
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Old 04-29-2008, 06:29 PM   #17 (permalink)
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I don't think standalone NOx reduction catalysts exist in the mainstream yet.

NOx adsorption catalysts have been around for awhile, but they operate on a different, less useful cycle. NOx adsorption catalysts accumulate NOx until the engine runs rich, where the three-way catalyst can operate normally.

Urea & Adblue injection have been around awhile, but I didn't think they made it over to the United States yet. Is this the technology GM's using? In any case, it's kind of a bittersweet solution as Urea is derived from ammonia, which is manufactured from the heavily energy-intensive Haber process.

Standalone NOx catalysts are in the works, though, and I think it will be a huge deal when they are available commercially. Brown skies, (mostly) good bye.

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Old 04-29-2008, 07:25 PM   #18 (permalink)
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Quote:
Originally Posted by LostCause View Post
I don't think standalone NOx reduction catalysts exist in the mainstream yet.

NOx adsorption catalysts have been around for awhile, but they operate on a different, less useful cycle. NOx adsorption catalysts accumulate NOx until the engine runs rich, where the three-way catalyst can operate normally.


- LostCause
Hmmm.... I have from several sources that the TWC that GM uses is in fact a HC+CO catalyst as well as NOx reduction cat, hence the term three-way catalyst. They are very specific that the NOx portion is defined as a NOx reduction. I'll have to go back and look that up to refresh my memory. This TWC will only work efficiently for HC+CO and NOx when it operates around stoich.

At any rate, brown skies do need to go!!!

I may need to doublecheck my statement regarding the cat on the Duramax diesel though...
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Old 04-29-2008, 09:11 PM   #19 (permalink)
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The ones I was thinking about are not available yet but should be ready around 2010 when the regulations step up again.

Your 05 Duramax will only have a 2 way Cat.

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