Does an egr help that much?

[George Tyler]

this lead me to think, atkinson cycle lets you win both ways, the mixture in the combustion cycle is one that gives the highest temperature as it has the least mass to heat in relation to the fuel used.
only problem is it pumps air into and out of the cylinders every inlet cycle, so more pumping loss than is ideal. what we need is a system that only has the stroke long enough on the inlet stroke to get the correct amount of chemically correct mixture into the cylinder without throttling, then have the full power stroke.

[old jupiter]

Old guy, new to the site, hoping to find good ideas. This thread is full of ideas . . . such as that diluting your intake charge with inert gas will improve fuel efficiency.

Okay, here's why you have trouble when you disable the EGR. When the system is polluting your fuel/air charge with exhaust gases (something racers have been doing their best to prevent for, oh, eighty years or so) it makes the mixture harder to light and slower to burn (and cooler-burning, which cuts nitrogen oxide emissions). So the ignition advance curve was modified by the manufacturer for more advance to light the fire earlier. If you disable the EGR, you now have an over-advanced ignition, and you'll likely get ping, maybe a lot. You could temporarily stop the ping by disconnecting the vacuum advance (and plugging the line). That's bad for fuel economy, however, so what you really need to do is re-curve the dizzy for less advance in the range where the EGR used to operate.

With some older engines this is easy. If you have a 70's to early-80's smog-motor with EGR, and if the same motor was produced in the 60s, you might be able to get the centrifugal advance springs and weights and the vacuum advancer from one of these pre-emissions engines and put them in your dizzy. Otherwise, get a man with a distributor machine to recurve your dizzy. Simply loosening the hold-down clamp and dialing back the static timing might stop the pinging, but it wouldn't be as good as recurving for best performance including mpg.

There are lots of things you can do to make many engines (especially the older ones that interest me) more fuel efficient, but many of them render the factory advance curve sub-optimal. Changes made either for more power or more fuel efficiency or both have often had disappointing results if the ignition was not re-tuned along with the changes.

BTW, I'm not necessarily advocating deletion of your EGR system here. You can do it right and get better mileage, but you'll put a little more cr@p in the air. One method that was a win-win-win was Pat Goodman's simple and unique full-time water injection system. Allowed more compression to be built into the engine for more torque and fuel efficiency, and cooled the burn slightly at all engine speeds, quelling N-O emissions. I can tell you more, but I've already gone on too long for a newbie here, sorry.

[mwebb]

..."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. "...

EGR does reduce combustion temperature
because
the INert gases take up space in the combustion chamber and act like a cushion
reducing
COMBUSTION PRESSURE which ultimately is what actually reduces
COMBUSTION TEMPERATURE and since NOX does not form below a certain temperature
the formation of NOX is reduced by reduction in combustion temperature which was reduced by reduction in
COMBUSTION PRESSURE which was reduced by the addition of an INert gas to the combustion event
by
Exhaust gas recirculation , EGR .

variable cam timing changes Exhaust ValveOpen and Exhaust Valve Close and Intake Valve Oepn and Intake Valve Close
timing relative to the Crankshaft position
so that the exhaust valve closes before all of the exhaust can escape the combustion chamber from the previous combustion event
thus
trapping some INert exhaust gases in the combustion chamber for the next combustion event
one drawback of this method is that the exhaust gases trapped are much hotter than EGR routed from an EGR valve through external plumbing .

EGR percentage can be very high depending on the application and the engine size measured by displacement
is reduced by the percentage of EGR gases introduced at the time .
a 2 liter engine becomes a 1.5 liter engine with 25% EGR

VW diesels use up to 45% a toyota prius uses up to 30% egr .

smaller displacement engines use less fuel than bigger displacement engines

KISS version s

carry on

[Air-Hybrid]

Originally Posted by mwebb

EGR does reduce combustion temperature
because the INert gases take up space in the combustion chamber and act like a cushion reducing
COMBUSTION PRESSURE which ultimately is what actually reduces
COMBUSTION TEMPERATURE and since NOX does not form below a certain temperature the formation of NOX is reduced by reduction in combustion temperature which was reduced by reduction in
COMBUSTION PRESSURE which was reduced by the addition of an INert gas to the combustion event by Exhaust gas recirculation, EGR.

I find it hard to accept that the change in burn temperature is solely (or even mainly) down to pressure.
A realistic way to check this would be to create synthetic air for the engine to run off (obviously without EGR) - The 'air' would be 80% CO2 and 20% Oxygen. In this experiment the charge drawn in would be at ambient pressure - so negating any sort of increased 'filling' of the cylinder. Rem: CO2 at 1 bar contains less molecules of gas than nitrogen (80% of normal air) at ambient.

I am fairly sure - due to Chemistry NOT Pressure the burn would be considerably cooler under such conditions, but I am not saying 'I'm right'; I just feel that's what my gut tells me :O

[old jupiter]

Sure, KISS; if YOUR engine makes more power with the cylinder back-filled with exhaust gas, why not run it on straight argon and pull third-gear wheelies?!!

[Joenavy85]

Originally Posted by Air-Hybrid

I am fairly sure - due to Chemistry NOT Pressure the burn would be considerably cooler under such conditions, but I am not saying 'I'm right'; I just feel that's what my gut tells me :O

Correct (as far as i can tell). INERT gasses don't support combustion, that tells me that there is less combustion (relatively speaking) and therefore less total heat generated. here's another way to look at it. same amount of fuel x less oxygen = richer mixture = less heat. if it came down to being about pressure than having EGR on an engine with a MAP sensor wouldn't work. just my 2 cents

[mwebb]

no
the AF mixture is not "rich" or "lean" when EGR is operating .
because these systems are feedback systems , the ECM responds to inputs from the AFR or 02 sensor to keep the mixture at stoich , 14.7 to 1

systems with AFR sensors can operate rich or lean of stoich BUT the ECM still will maintain Air Fuel ration where the ECM wants it to be using information from the AFR sensor , in these systems the ECM can maintain the Air Fuel ratio where it is programmed to with out changing due to
EGR operation .

so
Combustion pressure is reduced by the presence of the INert gases which do take up space but do not support combustion
the INert gases behave like a cushion , to reduce compression ratio and therefore combustion pressure
while EGR is operational

combustion temperature IS reduced because Combustion pressure IS reduced,
not the other way around

NOX forms at high temperatures Reducing combustion pressure also reduces Combustion temperature which
reduces NOX formation
EGR is Good .

EGR does NOT increase Power output
EGR does not reduce maximum power output because EGR does not operate at WOT or close to WOT
WOT = Wide Open Throttle
EGR on a gasoline engine does NOT operate at idle

EGR is good

KISS
thank me very much

[old jupiter]

[QUOTE=mwebb;231261]

EGR does NOT increase Power output
EGR does not reduce maximum power output because EGR does not operate at WOT or close to WOT
WOT = Wide Open Throttle
EGR on a gasoline engine does NOT operate at idle

(end quote)

Agreed. If EGR did operate at wide open throttle, it would reduce power. Since it does operate through the part-throttle range, it reduces the fuel economy that can be obtained by removing it AND re-tuning the engine for the changed configuration. The engine will then do the same work with slightly reduced throttle settings, i.e., it will be slightly more fuel-efficient. And it will release more of the pollutant that contributes to photochemical smog.

My wisecrack should properly have suggested you try improving your part-throttle fuel economy with argon . . .

So, EGR is both good and bad. I'm an old guy and remember when the first two generations of emission controls cluttered up our previously wide-open engine bays with bundles of vacuum lines and semi-mysterious valves and air pumps. Worse, to eliminate a small amount of HCs, the factories had to ditch Harry Ricardo's wonderful high-compression, closed-chamber, squish-type combustion chambers and go to low-compression (for the lousy gasoline) open-chamber "smog heads," all of which killed performance AND fuel efficiency. There was a lot of ranting among hot rodders about "the smog crap," and the magazines offered articles on how best to get rid of it.

But some of us didn't particularly feel good about putting unnecessary glop into the air, and were willing to learn how all those new systems worked. And to our surprise, we sometimes ended up admiring the relative simplicity and cleverness of some of these systems (especially the first one, the EGR valve, which reduced the total emissions of the engine by nearly 30% all by itself, with no drawbacks other than very occasional maintenance!). A few of us fine citizens (Moi) even ADD some of these systems to pre-emissions vehicles .

EGR isn't a system I'd add to an old car, and the manufacturers of cars, big diesel trucks, or anything between wouldn't put it on their machinery either if not forced to it by emissions regulations. But until a better method is found, EGR is a net positive. I alluded to a better method, available (still is, I think) to the DIYer. Bottom line, CarbonAltima: getting rid of the EGR won't do your fuel economy or your engine any good unless you re-calibrate and re-tune, especially the ignition, and even then the improvement will likely be disappointing.

[roflwaffle]

Originally Posted by Joenavy85

Correct (as far as i can tell). INERT gasses don't support combustion, that tells me that there is less combustion (relatively speaking) and therefore less total heat generated. here's another way to look at it. same amount of fuel x less oxygen = richer mixture = less heat. if it came down to being about pressure than having EGR on an engine with a MAP sensor wouldn't work. just my 2 cents

Kinda.... Provided there isn't excessive EGR and the mixture is homogeneous, just as much fuel should be combusted as w/o EGR. According to wikipedia, what the exhaust gases do is lower the specific heat of the mixture. The amount of heat is the same, but the temperature of the reaction drops.

[Joenavy85]

just to throw out the old saying "Silence is agreeance" i googled a bunch of stuff to educate myself, and mwebb is correct, he was just saying it in a way that i wasn't understanding. i stand corrected as to what i had said. i was refraining from commenting to avoid possibly putting my foot in my mouth again