Does an egr help that much?

[user removed]

Originally Posted by mwebb

somehow this subject keeps being reposted
somebody gets it in their mind that removing the EGR system helps the engine run better and somehow magically increases power output and improves fuel economy

all of that is pure blarney -

EGR does not function at idle or WOT - and does not affect maximum power output .
EGR does function at part load or cruise .

the Primary function of EGR is to add INert exhaust gases to combustion to reduce combustion temperature and by so doing
reduce the formation of the pollutant NOX

EGR improves fuel economy by reducing suction throttling loss and reducing engine compression and reducing engine displacement
BY DILUTING THE AIR FUEL MIXTURE IN THE COMBUSTION CHAMBER WITH INERT EXHAUST GASES
while it is active

deleting EGR is going to cause your system to pollute more and it will reduce FE , deleting EGR will have no affect on maximum power available.

and on a 1996 or newer car ;
doing anything to interfere with EGR function is "tampering " with the OBD2 system and a violation of federal law .

bottom line ;
if you do not know EGR theory ....
do not frak with your EGR unless you need to clean out the passages to IMPROVE / INCREASE EGR flow .

Basically correct.

I respectfully disagree with the reduction of suction throttling losses and reduction of compression and displacement statement.

Does it reduce suction throttling losses?

Yes.

Does it reduce compression?

Actually it would increase compression by allowing more mixture into the cylinder to be compressed, but that is offset somewhat by the dilution of that mixture with a basically inert exhaust gas component.

Does it reduce displacement?

Not in the sense of mechanically reducing the physical components of compression, but in the fact that the intake charge would be at a higher temperature than it would be without EGR, and therefore less dense, then the effective compression is reduced slightly. On the other hand the volume of EGR admitted with the combustible air-fuel mixture increases the effective compression.

The reduction in peak combustion temperatures by about 300 degrees, dramatically reduces NOX, and allows significantly greater timing advance than what would be possible without EGR.

Recent experimentation points towards strategically using EGR to even greater extent, with some attempts to combine EGR with direct injection and very lean mixtures, to the point where engine throttling can be accomplished without restricting the incoming air and creating manifold vacuum.

Bottom line is if it makes no difference on your engine if it is working or not, it probably is not working properly. We used to check it by pushing the diaphragm from the bottom manually, and it would immediately make the engine stall at idle. Generally speaking EGR is applied at partial throttle positions, and the control of EGR supply has been evolving for 40 years to improve performance and economy. Some modern engines with the greater computation power accomplish EGR through cam timing, specifically the exhaust cam to leave more exhaust gas in the cylinder after combustion, which eliminates all the rest of the EGR system components altogether.

regards
Mech

[tjts1]

Disabling EGR was worth about 1mpg improvement on my old volvo 240. It also improved throttle response at part load cruise. Definitely worth disabling on some old cars where the EGR was a simple ON/OFF system. The only way to really find out if it helps or hurts your FE is if you try it.

89 volvo 240 without EGR
19/26mpg
89 volvo 240 with EGR
18/25mpg
Model 1 Vehicle Characteristics
Model 1 Vehicle Characteristics

[mwebb]

..."Does it reduce compression?

Actually it would increase compression by allowing more mixture into the cylinder to be compressed, but that is offset somewhat by the dilution of that mixture with a basically inert exhaust gas component.
"...

adding INert gas to the combustion air fuel mixture Reduces displacement and compression because
the INert gases are INert they do not react with anything they act like a big cushion or spring filling up space that normally would be filled by the air fuel mixture
so the effect is , there is less air fuel mixture in the same space .

which
reduces displacement and reduces compression While EGR is active only

these are the facts.
=======================
it appears that this poster feels that the same amount of air fuel mixture is present with the INert gases
in combustion ,
but that is not possible . the INert gas present displaces an equal amount of air fuel mixture

remember ;
EGR works by DILUTING the air fuel mixture in the combustion chamber with INert exhaust gas .

because the air fuel mixture has been diluted , the engine has less power
so
the driver steps down farther on the throttle , opening the throttle a bit so the engine produces the same power as without introduction of INert gases
which improves VE volumetric efficiency and REDUCES suction throttling losses
==========================
to sum up
EGR displaces dilutes air fuel mixture with INert exhaust gas
yet the same total volume of gas at the same pressure fills the combustion chamber
which
reduces combustion temperature
reduces NOX
and
reduces the available space in the combustion chamber by partially filling it with INert gas , (reduces displacement)
which also reduces peak combustion pressure and compression

[mwebb]

before someone chimes in and states or asks the question

let me say that the presence of the INert gas does not change the air fuel ratio , the EGR exhaust gas added is INert , the air fuel ratio is UNchanged by the dilution of INert gas .

EGR does not , and can not make the mixture leaner or richer .
there is no usable fuel and no usable 02 in INert exhaust gases present in EGR.

[user removed]

mwebb;

If I introduce more of any type of gas into an engine the compression pressure created by the stroke of the piston will increase.

The type of gas is irrelevant.

The volume, density, and temperature are relevant.

The combustibility of the combined mixture will certainly be affected by the presence of inert components, if you are talking about post combustion pressure and the resulting work created.

If the atmosphere was 100% CO2 and you were testing the compression on an engine, the reading would depend on your ambient atmospheric pressure and any throttle restriction, not on the combustibility of the gas introduced.

Not trying to be argumentative, but my understanding of EGR is that adding an inert component allows increased compression, combined with mixture dilution. This creates a greater leverage component without peak temperatures, which means more power for less fuel consumed with lower emissions.

If that knowledge is flawed (and that is certainly possible) then please enlighten me as to where the flaws exist. Always interested in learning something new, and the last mistake I will make in this life is for the hearse to go to the wrong cemetery.

regards
Mech

[cujet]

EGR is a mixed bag. Certainly, pumping losses are slightly offset by the current crop of EGR systems. Yes, timing can be advanced. Yes, compression can be increased (and still meet emissions targets).

But, when an engineer designs and configures an engine, having more advanced timing and higher compression does not directly correlate to higher efficiency.

Example, many experimental engines with high EGR flow rates require timing advances as high as 50 degrees BTDC, just to function properly. That's not good in any way. Rather than look at timing advance as "good", look at it as necessary under certain circumstances for proper operation. We NEVER want pressure increasing by much prior to TDC. Yet, that's exactly what happens with extremely high EGR flow rates.

Compression ratio's are directly related to efficiency. However, don't confuse the high ratio's used on modern engines with the advent of EGR. Remember, EGR generally does not flow at WOT and/or high power settings. Yet, that high compression functions just fine. EGR simply allows the use of high compression without exceeding oxides of nitrogen emissions.

What's possible with very high compression, very lean burn and moderately advanced timing without EGR is impressive indeed. Experimental air cooled aircraft engines (operated lean of peak EGT, with high compression pistons, 2 plugs per cylinder and timed for optimum efficiency) regularly achieve BSFC numbers well below 0.38 pounds fuel per HP/HR. Some brag about numbers below 0.35, on gasoline! EGR does not help in any way under these conditions.

There is much more, but those are the basics. EGR is generally not helpful or harmful in modern engines with regard to fuel economy.

[Daox]

I'd have to politely disagree with a few statements of yours.

Originally Posted by cujet

... Remember, EGR generally does not flow at WOT and/or high power settings. Yet, that high compression functions just fine. EGR simply allows the use of high compression without exceeding oxides of nitrogen emissions.

This is not completely true. At WOT, engines run in open loop and enrich the air/fuel mixture to function fine. This kills efficiency.

What's possible with very high compression, very lean burn and moderately advanced timing without EGR is impressive indeed. Experimental air cooled aircraft engines (operated lean of peak EGT, with high compression pistons, 2 plugs per cylinder and timed for optimum efficiency) regularly achieve BSFC numbers well below 0.38 pounds fuel per HP/HR. Some brag about numbers below 0.35, on gasoline! EGR does not help in any way under these conditions.

These engines are specifically designed to run lean. Engines designed to run EGR could do the same thing. Perhaps not to the extent of lean burn, but it can be used in a similar fashion and without the NOx problems that lean burn causes. I'm not saying all engines do do this (especially older ones), but some definitely do.

There is much more, but those are the basics. EGR is generally not helpful or harmful in modern engines with regard to fuel economy.

Sorry, a bunch of published SAE papers would disagree.

[tjts1]

Wow, a lot of gibberish being thrown around here but nobody has any clue what they're talking about. If your car has EGR, disable it temporarily and see how it affects your FE. If you have an OBD2 car and some OBD1 cars, chances are it will trigger a CEL light. Consider yourself warned. To avoid this, the best way to defeat the system is to block off flow at the intake manifold after the temperature sensor. My bet is your FE will improve. The vast majority of cars from the 80s and 90s that had EGR used a simple ON/OFF system. It didn't have a variable flow control. These systems existed to reduce NOx emissions. Thats it. At best, they have a very small negative effect on FE. At worse, they increase fuel consumption by 3-5%. Most newer cars no longer need an EGR system to reduce NOx because they usually have multiple modern catalytic converters and VVT which can be used for internal EGR inside the combustion chamber. No cars use EGR at WOT.

[cujet]

Originally Posted by Daox

I'd have to politely disagree with a few statements of yours.

1) This is not completely true. At WOT, engines run in open loop and enrich the air/fuel mixture to function fine. This kills efficiency.

2) These engines are specifically designed to run lean. Engines designed to run EGR could do the same thing. Perhaps not to the extent of lean burn, but it can be used in a similar fashion and without the NOx problems that lean burn causes. I'm not saying all engines do do this (especially older ones), but some definitely do.

Sorry, a bunch of published SAE papers would disagree.

1) So, for point one, you are saying that since modern high compression engines are run with a fatter mix, they don't detonate? That's inaccurate. While the risk of detonation is high at peak BMEP, high power mixes, it's lowest at very lean of peak mixes. In fact, detonation is near impossible with very lean mixtures. I know we've all been led to believe otherwise. But, it's only a disgustingly overly rich mix that can quell deto and that, of course relates to this forum in a very negative way, economy.

2) No they are not. In fact, the manufacturers prohibit, discourage or simply don't mention lean of peak operation. Yet, it works. Come fly with me sometime and I'll demonstrate what can be done with a Lycoming IO-360A1B6, with 25 degrees timing (a fuel injected, high compression, big piston, low RPM, 2 sparkplug eng). You'll be impressed. It's the simple fact that these engines were equipped with adjustable props, mixture and throttle (not a single power lever) AND modern instrumentation that makes the difference. Maybe I'll put up a YouTube video to demonstrate. My point is that these engines are world class efficient when operated like this. Testing with EGR under similar conditions does not help economy. And, that testing has been going on since the 40's. FWIW, piston engine aircraft can teach us quite a bit about high power levels and BSFC. CAFE Foundation

3) I've not read all the papers SAE has published. I'd love to read some of these where high power, lean burn and peak BSFC numbers all come together, and do some personal testing. If you have some info, please share!

[ShadeTreeMech]

How does the EGR affect engine performance/economy? I don't know.

But if it works correctly it reduces NOx, otherwise known as smog, which is a bad thing to pump into the atmosphere for everyone to breathe.

I was born in LA county, California and in the late 70s smog was BAD (add as much emphasis as possible!!!) It resulted in me getting asthma as a baby. Mysteriously, being moved to Arkansas (very little smog due to lack of congestion) has put the asthma down as a footnote of my life, not something i have to deal with. And with cali's strict regulations, smog is nearly nonexistant now.

the design of the EGR is to reduce smog. So if I want to get an extra 1 mpg, i'll lighten up on the throttle or use some better oil but the only thing I'll ever do to an EGR system is repair it back to OEM specs.

Is 1 mpg really more important than taking the chance of poisoning our air with NOx? Wouldn't that be considered selfish if it was?