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Old 01-30-2008, 03:13 AM   #1 (permalink)
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EGR dilution for more MPG?

Hello -

While reading this thread :

News: Only 6% of Americans think diesel will succeed as powertrain option
http://ecomodder.com/forum/showthread.php?t=854

I started googling around for research on Diesel NOx solutions, and I found this paper :

Kettering University researchers visualize environmentally friendly combustion engines
http://www.ensight.com/images/storie.../kettering.pdf
Quote:
"EGR is usually used to dilute the inlet charge, which consists of air, by redirecting part of the exhaust into the inlet manifold of the engine," says Bassem Ramadan, associate professor of mechanical engineering at Kettering.

The redirected exhaust gases contain less oxygen because they've already filtered through the engine. The oxygen that does remain is used to burn fuel, with little left over to contribute to contaminants. EGR dilution has also been suggested as a means to improve low part-load efficiency of engines. Part load, also referred to as part throttle, is when the engine doesn't produce maximum power because the throttle is not fully open. The dilution method introduces large amounts of EGR into the cylinder, reducing the need to throttle the intake system at part load and improving efficiency.

If researchers could further optimize the efficiency of the air-fuel ratio in an EGR engine, more than the environment would reap rewards. Consumers would benefit from fuel economy savings similar to that achieved with diesel engines - up to 30 percent over normal car engines.
Now, here's my question. Can we simulate this process in our cars? As Ecomodders, are we already doing this to some degree without knowing it?!?!?!?

These were the articles that led me to the PDF :

Cleaning up diesel emissions - Oct. 28, 2005
http://www.kettering.edu/visitors/st...p?storynum=351

The greening of diesel - Aug. 03, 2007
http://www.kettering.edu/visitors/st...p?storynum=595


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Old 01-30-2008, 03:54 AM   #2 (permalink)
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Hello -

This is beyond our capabilities, but here's a little more from the same professor dude :

Offroad Exhaust
http://www.motorhelmets.com/htm1/bod...le-offroad.htm
Quote:
Researchers at Kettering University are trying a novel approach to increase the efficiency of diesel engines. By recirculating exhaust gas to the cylinder, they will not only cut down on NOx formation, but if they can keep the exhaust gas from mixing with air, they hope also to reduce pumping losses.

They are looking at a two-zone combustion system in which air is held in the center of the cylinder and is surrounded by recirculated exhaust gases, which are all but void of oxygen. An intake system that can control the balance between the air and exhaust controls the amount of oxygen in the cylinder, and can replace a throttle.

During intake, the piston's work to reach the end of its stroke increases with the throttling of the airstream. As intake is restricted, resistance to the stroke increases. The pumping takes some of the engine's power.

If throttling results from the balance of the gases, however, their total volume remains consistent,and the engine avoids pumping losses. Fuel economy could improve significantly, according to Bassem Ramadan,
an associate professor of mechanical engineering who heads the project at the university in Flint, Mich.

The key is in keeping the gases separate.

"Some results look promising, but further work is needed to determine if the two regions will remain unmixed during the engine operating cycle," he said. While complete stratification would be ideal, he expects that maintaining partial stratification of about 80 percent during the compression stroke is acceptable.
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Old 01-30-2008, 08:51 AM   #3 (permalink)
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In TDIs, lots of modding folks disable their EGR for getter performance or prevent intake clogging from the mixing of soot from the EGR and intake oil coming from the crankcase vent and turbo seal.

Disabling the EGR have been shown to reduce FE by as much as 10% on TDIs. So it would make sense that increasing EGR could surely increase FE up to a point, but reducing power. The EGR value in the TDIs ECU can be reprogrammed up to a certain point without throwing a code, but I've never heard of anyone tweaking the value UP for better FE. I might give it a try someday but my vag-com cable (kind of an OBDII cable for VWs) is toast.

With diesels the air charge is more or less always maxed out (there's no throttle plate and on TDIs there's a turbo pushing as much as 15 psi), so they pretty much always run lean, we only play with the amount of fuel injected for the desired power output. It is pretty evident in diesels that more EGR means less fresh air charge hence less injected fuel but also less power. So it's merely a question of FE/power balance.

I don't know much yet about gasoline engines so I can't say what increasing EGR would do.
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Old 01-30-2008, 08:59 AM   #4 (permalink)
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The problem with low load EGR is irregular combustion. An EGR cooler would be a good start IMO, but even if we could avoid pre-ignition stable combustion may still be a problem due to the proportion of exhaust gasses to air/fuel needed to minimize pumping losses at low load with MPFI. If ya g00gl3 GDI you'll likely find some interesting stuff.
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Old 01-30-2008, 09:21 AM   #5 (permalink)
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Its a good idea in theory. But, its very hard to impliment and work properly and reliably. This is especially the case when you consider designing a system that will run 200,000+ miles. EGR is not only hot, but its also dirty after thousands of miles. This tends to clog up valves and other system components.
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Old 01-30-2008, 10:38 AM   #6 (permalink)
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As a TDI driver I have pondered this, but never done anything.

I only know a few things that may be useful
1) TDI's EGR cooler is HUGE, is water cooled, and from the looks of it could flow around %30 of what the intake manifold can flow
2) Just set the EGR to Close at WOT if you are concerned about power.
3) it makes a noticeable difference on gassers as well supra dropped 1~2 mpg when it was off (un-scientific test over about a year)
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Old 01-31-2008, 02:58 AM   #7 (permalink)
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they are working on it. but its not street good let alone epa good.
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Old 01-31-2008, 05:35 PM   #8 (permalink)
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my only would be, if this could easily be done with no adverse effects, and harsh CAFE laws in effect, wouldnt manufacturers be taking better advantage of a system that they designed?!?
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Old 01-31-2008, 08:54 PM   #9 (permalink)
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Is this effectively varing the displacement of the engine? Is the problem that engines are too big for the job most of the time to run efficiently? Why not have two small engines. Or a clutch in the middle of a larger one for trucks. One runs and keeps both warm until needed. For cars a little tiny 3cylinder (5 to 8HP whatever steady state road load is.) diesel running full tilt charging a battery and or running a motor. only need enough battery for a couple mile hill.
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Old 01-31-2008, 09:18 PM   #10 (permalink)
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diesel john, WalMart is actually working on a project like that for their fleet trucks. Hybrid diesels where the diesel doesn't have much excess power, the extra force comes from batteries and electric motor.

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