EGR: The good, the bad and the ugly??

[wb292]

Racprops, From the research over the years I’ve done in my quest for better mileage, it does. The better dispersion achieved, the more complete the burn. Although our engines can’t come close to the burn of modern engines.

 

[wb292]

Pinger, when the EGR is open it displacing oxygen in the cylinder. Therefore reducing the combustion temp and power from that particular power stroke. This will require more throttle input to maintain the same road speed. This reduces economy. My experiments gave me a 1 MPG decrease running the EGR. I ran multiple tanks of gas trying to be as accurate as possible. What I learned coincided with what I read. The EGR’s sole purpose is to reduce NOX. It in no way improves efficiency.
The increased vacuum applies In my case since I am running TBI engines/wet intake manifolds. The study I read about vacuum improving mileage was from the 1960’s with carbs. The principal is still the same. The liquid vaporizes at a higher rate in a higher vacuum. Since this produces a better more complete burn, it requires less throttle to maintain the same road speed. Less throttle =better mileage.

 

[Orpedcrow]

It’d probably be easier to add a HHO generator than modifying the EGR for better fuel economy

 

[Schurkey]

It’d probably be easier to add a HHO generator

 

[Pinger]

Pinger, when the EGR is open it displacing oxygen in the cylinder. Therefore reducing the combustion temp and power from that particular power stroke.

It doesn't displace - it is additional.

This will require more throttle input to maintain the same road speed.

However, due to reduced vacuum (as the inlet manifold can draw from EGR source) a larger throttle opening may be required - but only to maintain the same airflow as would be present without EGR - not additional, merely a compensatory measure.

This reduces economy.

Which should theoretically reduce throttling loss and therefore improve efficiency. Note 'theoretically'.

My experiments gave me a 1 MPG decrease running the EGR. I ran multiple tanks of gas trying to be as accurate as possible. What I learned coincided with what I read.

I'm not disputing your findings - merely saying that there should be a reduction in throttling loss which theoretically should improve efficiency.
One problem with exhaust products in the cylinder is that it limits lean operation. Other factors intrude also eg, the temp of the in-cylinder charge prior to compression, etc.

The EGR’s sole purpose is to reduce NOX. It in no way improves efficiency.

It's primary aim is NOx reduction, agreed. If the theoretical increase in efficiency (reduced throttling losses) were realisable I suspect SI engines would employ EGR to a greater extent but in pursuit of lower throttling losses the move has been toward stratified charge via direct (in-cylinder) fuel injection though that aim seems to have fallen by the wayside and the cooling effect is now the benefit sought. Unfortunately, this tends to inhibit proper fuel atomisation hence the requirement of GPFs.

The increased vacuum applies In my case since I am running TBI engines/wet intake manifolds. The study I read about vacuum improving mileage was from the 1960’s with carbs. The principal is still the same. The liquid vaporizes at a higher rate in a higher vacuum.

All of that ceased to a be a concern with port fuel injection aimed at the back of the hot inlet valve. When carbs were prevalent though, it was the driver for Fiat developing a throttle-less engine (long before MultiAir appeared).

Since this produces a better more complete burn, it requires less throttle to maintain the same road speed. Less throttle =better mileage.

The throttle opening at any given time is dependent on the quantity of air the engine requires to produce the power being asked of it (the throttle is a power valve). The vacuum created is incidental. The best efficiency (expressed as bsfc) will always occur at greater outputs ie, larger throttle openings. Which is why 'holding onto' gears leads to poor fuel efficiency and up-shifting (using the same throttle opening) improves efficiency as the engine 'sees' a larger throttle opening at a lower rpm. Throttling losses are the bugbear in SI engines at low load part throttle operation - made worse by high compression ratios.

 

[racprops]

wb292 said:


Pinger, when the EGR is open it displacing oxygen in the cylinder. Therefore reducing the combustion temp and power from that particular power stroke.

It doesn't displace - it is additional.

I have read that it does displace some of the incoming air and fuel.

However, due to reduced vacuum (as the inlet manifold can draw from EGR source) a larger throttle opening may be required - but only to maintain the same airflow as would be present without EGR - not additional, merely a compensatory measure.

This is the theory of more MPG by less pumping loses...

Which should theoretically reduce throttling loss and therefore improve efficiency. Note 'theoretically'.

I'm not disputing your findings - merely saying that there should be a reduction in throttling loss which theoretically should improve efficiency.
One problem with exhaust products in the cylinder is that it limits lean operation.

I would like to read more on this idea, as it seems displacing air and fuel would become lean, and how would it limit more lean operation??

Other factors intrude also eg, the temp of the in-cylinder charge prior to compression, etc.

It's primary aim is NOx reduction, agreed. If the theoretical increase in efficiency (reduced throttling losses) were realisable I suspect SI engines would employ EGR to a greater extent but in pursuit of lower throttling losses the move has been toward stratified charge via direct (in-cylinder) fuel injection though that aim seems to have fallen by the wayside and the cooling effect is now the benefit sought. Unfortunately, this tends to inhibit proper fuel atomisation hence the requirement of GPFs.

And another interesting point, as yes a lower chember temp could lower vaporizing of the gasoline....and farther details on the??

All of that ceased to a be a concern with port fuel injection aimed at the back of the hot inlet valve.

Yes I have read that and that with the early TPI non sequential fuel injection, (batch fired) even promoted more fuel vaporazing as it sat on a hot intake valve for a micro second longer... plus helps keep the intake valve clean and new problem with Direct injection...BUT WHAT "ceased to be a concern"??

When carbs were prevalent though, it was the driver for Fiat developing a throttle-less engine (long before MultiAir appeared).

The throttle opening at any given time is dependent on the quantity of air the engine requires to produce the power being asked of it (the throttle is a power valve). The vacuum created is incidental. The best efficiency (expressed as bsfc) will always occur at greater outputs ie, larger throttle openings.

Which is why 'holding onto' gears leads to poor fuel efficiency and up-shifting (using the same throttle opening) improves efficiency as the engine 'sees' a larger throttle opening at a lower rpm. Throttling losses are the bugbear in SI engines at low load part throttle operation - made worse by high compression ratios.

This last one does not compute, in a lot of road testing for MPG I have seen in every car that running at a low RPM in the highest gear has produced the highest MPG IE: 2000 Mercury GM, 30MPG at 65MPH at 1700RPMs, and 25MPG at 85 MPH and 27MPG at 80...03 Ford Explorer, 27/30 at 50MPH at 1500 RPMs and 15MPG at 75MPH at 2300RPMs....All running is top gear. The only place and time when you point applies is in accelerating at a high rate to a higher speed, if a slow and steady incress in speed is not fast enought then a down shift is the best way.

 

[L31MaxExpress]

I have read that it does displace some of the incoming air and fuel.

This is the theory of more MPG by less pumping loses...

I would like to read more on this idea, as it seems displacing air and fuel would become lean, and how would it limit more lean operation??


And another interesting point, as yes a lower chember temp could lower vaporizing of the gasoline....and farther details on the??

Yes I have read that and that with the early TPI non sequential fuel injection, (batch fired) even promoted more fuel vaporazing as it sat on a hot intake valve for a micro second longer... plus helps keep the intake valve clean and new problem with Direct injection...BUT WHAT "ceased to be a concern"??



This last one does not compute, in a lot of road testing for MPG I have seen in every car that running at a low RPM in the highest gear has produced the highest MPG IE: 2000 Mercury GM, 30MPG at 65MPH at 1700RPMs, and 25MPG at 85 MPH and 27MPG at 80...03 Ford Explorer, 27/30 at 50MPH at 1500 RPMs and 15MPG at 75MPH at 2300RPMs....All running is top gear. The only place and time when you point applies is in accelerating at a high rate to a higher speed, if a slow and steady incress in speed is not fast enought then a down shift is the best way.

NOT a single vehicle I have ever owned has done best on MPG under say 2,000 rpm.. Low rpm and high throttle opening drinks fuel.

 

[racprops]

Well all of mine have V8s...correction one had a V6.

 

[L31MaxExpress]

Well all of mine have V8s...correction one had a V6.

Mine have mostly been V8s too. I have put deeper gears in a couple of them as well and MPG actually increased on them. My Hemi Ram got better mileage with 4.56 gears than it did with 3.55s. My G20 van got better mileage with 4.10s than it did with 3.08s. As I have tried to explain to you atleast a dozen times now, rpm does not dictate fuel mileage. Spin the engine too slowly and you will DRINK gas. My Express van with a 4L85E and 3.73s gets its best mileage at 75-80 mph and near 2,500 rpm. When I still had the 350 and half ton running gear in my 1500 Express I went from a 3.73 to a 5.13 gear in the 9.5 14-bolt. I lost 1 mpg unloaded running 70-75 mph and gained 2+ around town and it towed my 6,000 lbs trailer much easier. Not even exaggerating when I say it got like 3-4 mpg better loaded with the trailer with the 5.13s and felt like it had twice the power from a stop and uphill. Before that when I had the 60E, and 3.42 gears I almost never used overdrive unless I was rolling 75-80 mph on flat land. At 60-70 mph my mileage was WORSE in overdrive.

 

[Caman96]

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