Talk:Exhaust gas recirculation

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Is it really 'polution' or is this a mis-spelt 'pollution'? -- SGBailey 23:36 Dec 16, 2002 (UTC)

Do modern engines actually have EGR? I was under the impression that fuel injection rendered it obsolete due to improved mixing, and that was the primary reason that fuel injection seemed to have better gas milage. Maury 16:11, 18 February 2006 (UTC)

At the Iron Ore processing plant im working at they have a massive EGR there it stands for Electric Gas Recirculation is this basically the same thing as the purpose is to clean the emissed gasses and to reuse material from that process, anyone have any idea if this requires a separate article?

Contents

[edit] Yes, modern engines have EGR.

EGR is a critical part of modern automotive engine emissions reduction strategies. It's virtually impossible to meet existing emissions regs (in developed countries) without utilizing EGR.

Port fuel injection allows precise metering of fuel as well as good mixing, which has a lot to do with good fuel economy, low emissions, and good driveability. But EGR still has a vital role in NOx reduction. Given that it also improves part-load fuel efficiency, manufacturers would be motivated to include it even if it didn't affect emissions.


EGR is usually more effective with SI engines than with diesels ... why these trends are different.... please explain me the points related to this as soon as possible

Ratish "( rat.in.uk@gmail.com )

[edit] EGR: SI vs. CI effects

In an SI engine, the inert EGR is *added* to an existing mixture. The addition of inert exhaust gas, with its high specific heat, results in a rather large reduction in peak temperature (and corresponding reduction in NOx production).

In a CI engine, the inert EGR *substitutes* for a portion of the atmospheric air entering the cylinder. The *substitution* (rather than addition) of exhaust gas, with its high specific heat, results in a smaller reduction in peak temperature (and therefore a smaller reduction in NOx) than is observed in SI engines.

short version of EGR effects:

SI - same energy, larger total in-cylinder mass, larger specific heat ---> much lower temperature/NOx

CI - same energy, SAME total in-cylinder mass, larger specific heat ---> modest reduction in temperature/NOx

Joe Frickin Friday 15:47, 21 March 2006 (UTC)

[edit] EGR: other benefical effects

It's my understanding that the addition of exhaust gas also increases the mass of gas in the cylinder at part throttle during the compression/power strokes. This increases the compression ratio at part throttle. This increased pressure improves the thermodynamic efficiency. (Warning, I'm not a physicist, just a motorsickle sumbitch). I think this effect in not trivial.

Also, the heat rejection bit could be elaborated. Because the peak temperature of the combustion gasses is lower, the entire engine runs cooler. Usually, the manufacturer/designer uses an engine thermostat that's a little higher temperature to ensure the engine stays warm enough to keep the fuel vaporized, keep water vaporized, and further improves heat rejection by reducing the temperature differential between the exhaust gas and the cylinder head.

Finally, it might be helpful to dispel the idea that EGR is an attempt to 'reburn' unburnt exhaust gasses. This is the most common misperception about EGR and the main reason that uninformed guys with tools remove EGR systems.

Pcmenten 22:08, 29 December 2006 (UTC) Paul Menten


EGR can definitely hurt efficiency. I performed very careful measurements with a 1995 Toyota Corolla (1.8L non-Calif. model) on a weekly commute, mostly highway, air conditioner off. After EGR was disconnected, highway mileage went from 34-35 mpg to a consistent 38-40mpg. This makes sense, since EGR reduces combustion temperatures and thus Carnot efficiency. It is interesting to note that the 1.6L version of this car is not equipped with EGR, except in California. This leads me to think that its effect is largely detrimental, and it's there mainly as an emissions band-aid. This is a vacuum-modulated EGR valve with an ECU-controlled VSV acting as an on/off switch.

Also, the Heywood book is largely regarded as outmoded as far as its empirical data in it is concerned. The section on EGR seems to be based exclusively on simulations, which may not be terribly accurate. Unilaterally stating that EGR helps efficiency is obviously incorrect. 64.251.148.91 07:35, 31 July 2007 (UTC)

So, if EGR hurts fuel economy in order to reduce harmful emissions, how is that helpful? Surely you then have to buy fuel more frequently to offset the reduction in fuel economy, thus producing more emissions. Just curious, because I'm thinking of blocking the EGR valve off on my '91 Shogun[/Pajero/Montero]. ahpla 17:17, 13 September 2007 (UTC)

in a diesel engine using an egr system, is the aim to obtain an overall air / fuel ratio of 14.7:1 (the stochimetric ratio) by using the exhaust to subsitute the excess air? 84.66.42.255 22:48, 31 March 2007 (UTC)

[edit] EGR: should be removed from engines

It greatly reduces engine life. Exhaust gasses are abrasive and contain particles that will combine with oil in PCV and form sludge in the intake. Modern Diesels are recirculating as much as 30% of their exhaust gasses back through the engine.

Is this really a big effect on engine wear? Any abrasive particles in the exhaust will have already gone through the cylinders, anyway. Intake sludging is a problem, especially on older diesels that also have significant blowby, but I don't see it as affecting engine life -- just performance.
69.91.158.177 21:00, 19 September 2007 (UTC) Orv
Perhaps engines with EGR just shouldn't use PVC as intake piping. As far as the abrasiveness of exhaust gases, I don't really see that. What kind of abrasive particles would you say are in exhaust gases?
- Victor van Poppelen (talk • contribs)

[edit] Team Barnstar!

The Technology Barnstar
I can't see a single editor who wrote most of this article so I'm awarding the entire EGR editing team a barnstar. The information on this page got my wife's Mazda running this morning and won me major skillz points! I owe you one! SteveBaker (talk) 15:22, 12 December 2007 (UTC)


She had a check engine light - the computer said "EGR problem" and had gone into "limp home mode". 2 minutes of reading here told me that EGR valves are frequently switched by vacuum - which immediately lead me to find a pinhole in a vacuum hose leading to the valve. One strip of electrical tape later and the check engine light went out and the car runs fine! Yeaaaaahhhh! Many thanks! SteveBaker (talk) 15:22, 12 December 2007 (UTC)