Does an egr help that much?

[tjts1]

Originally Posted by 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?

Its a trade off. 1mpg can be many tons of CO2 over the life of the car. Our government for many years chose to look at NOx and HC instead of so the negative effect on FE and CO2/mile of emissions control devices was considered irrelevant. Now they're finally starting to look at the whole picture.

[mwebb]

Originally Posted by Old Mechanic

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.....
regards
Mech

this is your error

the volume of gas in the combustion chamber does not increase with introduction of EGR
the total volume of gas remains the same only now
some of it is INert EGR gases that can not support combustion
the rest is the same mix of air fuel that was present without EGR

so
peak combustion temperature is reduced
peak combustion pressure is reduced
NOX formation is reduced

these are the facts.
i intend to take one INcorrect concept at a time
(regarding EGR) and refute it .
focus , on this fact , provide evidence to prove me wrong
if you can.

when you can not , we will proceed to the next concept
========================
understand
there is no bad side to EGR , only good .
when the system is functioning as designed , FE is enhanced and pollution is reduced . another fact .

i can explain the HOW and WHY EGR may cause problems on some systems but first i need to be clear on theory

[user removed]

the volume of gas in the combustion chamber does not increase with introduction of EGR
the total volume of gas remains the same only now
some of it is INert EGR gases that can not support combustion
the rest is the same mix of air fuel that was present without EGR

Wrong.

Test this with a vacuum gauge when you manually introduce EGR.

Vacuum drops, which means more mixture in cylinder at BDC on intake stroke, which means more compression at TDC on compression stroke. More in=less vacuum=more compressed=more compression.

Basic physics

The same applies for a vacuum leak introduced by disconnecting any hose from the manifold, except that allows more air into the cylinder instead of more exhaust.

regards
Mech

[Christ]

Where are you testing vacuum? This is very important. If you're testing vacuum at the manifold, vacuum will drop when EGR is introduced, because EGR is flowed by vacuum.

EGR does not add volume to the intake. If it did, that technically would increase the volumetric efficiency of the engine. Ok, not really, because for that to happen, EGR would have to be combustible. However, in theory, it would increase VE because, assuming the engine was already running at peak VE, filling the cylinder 100% on every intake stroke, then introduction of EGR would have to be under pressure (which it is not, at least not significantly) and would then cause more than 100% of the available capacity of the cylinder to be filled. This, however, is not the case.

EGR is designed to characteristically limit the mixture available to a cylinder by introducing a percentage of the cylinder's volume as inert gas, which then only allows (given a specific VE for that stroke) the cylinder to be filled less with overt fuel/air mixture.

Because of this, throttled control of a gasoline engine can be kept with only EGR flow. No throttle plate is actually necessary.

When you say that a vacuum leak in the manifold allows more air into the cylinder, I presume you're respondent to the fact that a vacuum leak will cause a lean condition. It does not, however, improve the VE of the cylinder being tested. The cylinder can still only draw in X amount of mixture per intake stroke, and because you now have a vacuum leak, more air will be drawn than fuel (per ratio), so the resultant exhaust gasses will show a lean condition for that cylinder.

A test you can do to confirm that vacuum drops with introduction of any gas is to measure the vacuum force at the end of the hose on a shop vac which has the variable vacuum control sleeve installed. While measuring the vacuum drawn at the end, begin to slowly open the sleeve, and observe the vacuum at the "throttle" area drop. Measure output at the exhaust port of the shop vac, and it remains the same, even though measured vacuum at the intake port has decreased.

[abogart]

I have a '96 GM 3.1L (3100) and keep getting the PO401 error code: Insufficient EGR flow. However, in the documentation I have read that this can also mean EGR system malfunction. I had fabricated a metal plate to cover the openings on the EGR mount a while ago (admittedly, in the stupid notion that this improved engine operation). After realizing that the EGR probably helped improve FE, I removed the plate and reinstalled the EGR properly, but I still get the PO401 code. I'm wondering if having the ports covered for so long has gummed them up. I can't help but think that this is hurting my FE, and it's going to bug me until I fix it. I'll take the EGR back off next time I get a chance and clean out the intake port and see if that fixes the problem. It's possible that the tube coming from the exhaust manifold could be blocked too, though I think a good run with the other end open should solve that. I doubt that the EGR valve itself has gone bad, though there is really no easy way to test it with the equipment that I have.

Any suggestions/experience with EGR problems?

ALSO... Has anybody been able to successfully program an XGauge for SG that shows EGR operation?

[notanarborist]

Originally Posted by Old Mechanic

the volume of gas in the combustion chamber
Wrong.

Test this with a vacuum gauge when you manually introduce EGR.

Vacuum drops, which means more mixture in cylinder at BDC on intake stroke, which means more compression at TDC on compression stroke. More in=less vacuum=more compressed=more compression.

Mech

I disagree. The vacuum is dropping because you are displacing the oxygen available for combustion with the inert gas as was described. The requires the the throttle to open further to maintain torque. It is the increased throttle angle or increased IAC air volume that results in the drop in manifold vacuum.
This is want we want for fuel efficiency, that increase in throttle angle for the same load is what puts an engine with throttled intake closer to it's best bsfc.
What happens when EGR valve without a positino sensor gets stuck open? You get an engine that runs rich, or runs lean?

[mwebb]

...."Wrong.

Test this with a vacuum gauge when you manually introduce EGR.

Vacuum drops, which means more mixture in cylinder at BDC on intake stroke, which means more compression at TDC on compression stroke. More in=less vacuum=more compressed=more compression.

Basic physics

The same applies for a vacuum leak introduced by disconnecting any hose from the manifold, except that allows more air into the cylinder instead of more exhaust.

regards
Mech"....

ooops
you forget that the pressure that we are working with is Baro pressure , not intake vacuum , Baro pressure is constant
Baro pressure is what forces air into the combustion chamber when the intake valve opens ,
and the EGR originates in the exhaust , where pressure is slightly above Baro

there fore , the amount / volume of gases in the combustion chamber is NOT changed by the addition of INERT EGR gases
, the INERT EGR gases displace some of the airfuel mixture , the combustion chamber AF ratio is not lean or rich .
it is diluted
with
INERT EGR gases

basic s
now that that is corrected
thank me

next

[ShadeTreeMech]

wow, it suprises me this discussion is still alive.

EGR is for reducing the combustion temperature (less O2=less NoX produced) and it has the side advantage of reducing power losses from the engine having to work to make a vacuum in the intake. All of this has been trumped by variable valve timing, which adjusts the effective compression ratio per the currents needs of the engine by adjusting the timing and duration of the valves opening and closing. This technology allows a vehicle such as a late model Corvette get over 30 mpg at cruise while still being able to smoke the tires when asked to. It also mean cars with VVT don't need EGR.

I've been trying to figure out if I could have a reverse throttle on a modern engine and it work. If you have a throttle that is wide open to EGR gases at throttle, with a second opening to atmosphere, by modulating the amount of EGR gasses instead of the atmosphere you could theoretically get a gas engine without pumping losses due to intake constriction.

[George Tyler]

I think you guys disagree because you are not specifying the initail conditions, and then what you change in response to the ERG.
Lets say you have the car doing a steady 60 MPH. then, with everything the same, you turn on EGR.
1) How much exhaust gas is sucked it?
2) What happens?
3) what do you do to maintain speed?
4) what does the fuel injection change?

[George Tyler]

First of all, air flow by mass is maybe 10% of the total capacity of the engine, at 60 MPH, before ERG. then, EGR is turned on. (maybe 10% of inducted air?) engine speed cannot change immediatly, either up or down, but the trottle is where it was before EGR and now it has an additional source of (exhaust) gas, engine is doing the same RPM, so Vacuum drops, less air flows through the air flow meter, so ECU cuts back on Fuel.
But now, less heat is supplied because there is less fuel, so torque drops, we still need the same torque, so throttle is opened and ECU increases Fuel again. Now there is even less vacuum because throttle is opened and it also reduced whe EGR was enabled. Less Vacuum means less torque is taken sucking against the throttle plate, so consumption is improved.
BUT, in the combustion chamber you have more gas and less oxygen and fuel, so temperature is reduced, (causing less NOX) but efficiency is proportional to Tmax/Tmin (amoungst other things), so efficiency is reduced, consumption is increased!
the one fights the other, not sure which wins! Well, we know that with excess air consumption is reduced, so it will probably be the same, consumption will improve