Increasing EGR flow: gasoline engine

[Teemo]

Hello!

I decided to start this new thread to share my experiments with cooled Exhaust Gas Recirculation on spark ignition engine.

To make it clear this thread is about EGR on GASOLINE (also known as "petrol" or just "spark ignition") engine. NO DIESEL please, this is completely different story.

One previous thread about the EGR topic (little out of hand by now, too many replies and no conclusion): Increasing EGR flow for better mileage

The theory:
Gasoline engine running at part throttle is equivalent to running it with very low compression. But compression is main factor in Otto cycle efficiency calculation. So in theory Otto cycle engine runs with maximum efficiency at full throttle only. Adding some inert gasses to intake from exhaust should reduce throttling therefore increase efficiency. Although there are definetly some other factors to consider with this.
Other way to say it is that we need to minimize the intake manifold vacuum to keep the efficiency high at low loads.
Test car:
VW Passat 1990, 2.0l doch, 100kW. Engine code 9A. Original Bosh mechanical fuel injection.

First test:
Last week I added EGR pipe to my car:
Drilled 12mm diameter hole to the exhaust pipe 30cm from the end (at the back of the car. Welded threaded pipe joint to the hole. Connected rubber hose to the joint. Run the hose to the engine room from below the car (actually used some plastic aluminium pipe in the middle).
In the engine room I connected the hose to the idle air intake, so that the full vacuum applies to the pipe.

Experience:
I took the test drive this weekend 2x70 km. Quiet country road, no city driving. I feel that I certanly did not use more fuel than usual. Unfortunatly I do not have exact way to measure the fuel consumption of such a short trips. But based on experience fuel consumption dropped about 0-20%.
I did not have any particularly bad effects. I was afraid of EGR hose overheating, but that was absolutely not the case. The hose felt only slightly warm when touched after driving 70km.
Of course such a simple system is not without drawbacks. Less manifold vacuum upsets the idle stabilization system, and at my case it became
"hunting" when engine warm. Also I noticed slight hesitation at some point. Apart from that the car was completely driveable.
Outside temperature below 0C. No noticeable difference in engine heating up time.

Conclusion:
The increased cooled EGR seems promising for reducing fuel consumption. Despite the idle hunting and that I was scared to use the engine's deceleration fuel shutoff, overall fuel consumption was less than usual, so most of the time it must have been running more efficiently.

To do:
-Add means to adjust EGR amount from inside the cabin.
-Build electronic(or mechanical) regulator to adjust egr automatically, and to disable at idle to make idle stabilisation work as normal.
-Electronic regulator to disable EGR while deceleration fuel shutdown and slightly after that.
-Find the way to measure instant fuel consumption.
-add temperature meter to EGR pipe.

Worries:
-What happens to the catalytic converter?
-Is there possibility for some other engine damage?
-possible condensation inside EGR pipe and freezing in winter.

Thats it for now.
Best Regards.

[razor02097]

Interesting...

As long as the pipe isn't connected directly to the manifold it shouldn't hurt anything. I'm just wondering how much concentration of exhaust gasses you are getting. What I mean is nothing is perfect, there could be oxygen in the air you are pulling from the end of the vehicle's exhaust pipe.

OEM EGR systems typically pull exhaust gas directly from the manifold before the catalytic converter. A test I do to make sure the EGR ports aren't clogged is to actuate the EGR valve with my hand. Doing so makes the engine run really rough because of the lack of good air.

If you want to do something else you could try welding in an O2 sensor bung right up at the manifold then plumb a metal pipe to a brass ball valve then have a cable operate it? Just throwing out ideas.

[Blue Angel]

Very interesting. I don't claim to know much about EGR, but I thought I remembered reading about its cooling effects on the combustion process reducing emissions... let me look that up. Here's the Wikipedia page on EGR:

Exhaust gas recirculation - Wikipedia, the free encyclopedia

I hate to put a downer on your idea, but with the pressure on companies to improve fuel efficiency and the fact that EGR systems are already in use, you would think any potential efficiency gains through EGR would have been thoroughly explored by now, no?

The one thing you may/may not have going for you is the use of post catalytic converter and cooled exhaust gasses. Most EGR systems operate by taking exhaust before the converter where it is still full of pollutants and is very hot. Your tailpipe extraction, plumbing it all the way back to the front of the vehicle, will mean it is "clean" and much cooler than traditional applications.

I don't know what difference that would/wouldn't have on your application, but you will need to do much more accurate testing to prove whether it works or not.

EDIT: Read the sticky on how to improve your testing accuracy:

http://ecomodder.com/forum/showthrea...ery-11445.html

[Teemo]

Originally Posted by razor02097

Interesting...
What I mean is nothing is perfect, there could be oxygen in the air you are pulling from the end of the vehicle's exhaust pipe.

Right now I'm assuming that it does not draw in oxygen through the exhaust pipe, exept when starting. Logic is that EGR must be shut down for starting, because otherwise it leans out the starting mixture.

Originally Posted by Blue Angel

I hate to put a downer on your idea, but with the pressure on companies to improve fuel efficiency and the fact that EGR systems are already in use, you would think any potential efficiency gains through EGR would have been thoroughly explored by now, no?

Definetly there are some dawbacks for this approach, I'm hoping i can live with those, and benefits are larger, compared to. I am sure this is the field that is thoroughly explored, but unfortunately by the people who are unwilling to share their test results. So to all others this remains unknown.
There may be some kind of compromise:efficiency vs. short maintenance interval.

Originally Posted by Blue Angel

The one thing you may/may not have going for you is the use of post catalytic converter and cooled exhaust gasses. Most EGR systems operate by taking exhaust before the converter where it is still full of pollutants and is very hot. Your tailpipe extraction, plumbing it all the way back to the front of the vehicle, will mean it is "clean" and much cooler than traditional applications.

This is exaxtly what I am talking about: I like that EGR gasses are cleaner and cooler,

[t vago]

Typically, EGR systems are shut off when the engine is under very light loading (such as when the engine is at idle). They're also shut off at wide open throttle, in order to maximize power output of the engine at that point.

I would have to share razor02097's concern about your cooled EGR pipe actually sucking in oxygen from the end of the tailpipe. And is your idle air intake always "seeing" intake manifold vacuum, or does it only "see" intake manifold vacuum when you're not using the accelerator?

[Teemo]

Originally Posted by t vago

I would have to share razor02097's concern about your cooled EGR pipe actually sucking in oxygen from the end of the tailpipe. And is your idle air intake always "seeing" intake manifold vacuum, or does it only "see" intake manifold vacuum when you're not using the accelerator?

In practice it probably does suck some oxygen in because of small leaks in my exhaust pipe.
Intake definetly is seeing the vacuum. I could have connected the egr pipe to some other point in the intake manifold, but since this is a fuel injected engine and intake manifold is designed according to that, some resonant pipes, I need to consider the even distribution to all cylinders. Idle air intake have small holes leading to all cylinders intake, so it should mix the air and exhaust gas more evenly across the cylinders. When there is uneven distribution of EGR between cylinders, the air/fuel ratio is also uneven.

I try to post some pictures of mu setup tomorrow.

[razor02097]

Originally Posted by Blue Angel

I hate to put a downer on your idea, but with the pressure on companies to improve fuel efficiency and the fact that EGR systems are already in use, you would think any potential efficiency gains through EGR would have been thoroughly explored by now, no?

Yes I believe you are correct. One of the reasons we with older cars seek to improve our ancient EGR systems.... or in the case of the OP... to ADD an EGR system

EGR systems when they were put on cars initially was to pass emissions more than improve fuel economy... In today's vehicles the computers are much smarter about using the EGR system and much of the time it will improve FE as a secondary benefit.

[Blue Angel]

Originally Posted by razor02097

Yes I believe you are correct. One of the reasons we with older cars seek to improve our ancient EGR systems.... or in the case of the OP... to ADD an EGR system .

I see... I was under the assumption that a 1990 gas VW would already have an EGR circuit!

Originally Posted by razor02097

In today's vehicles the computers are much smarter about using the EGR system and much of the time it will improve FE as a secondary benefit.

Yes... also, many of today's cars are not using a dedicated EGR circuit: they are able to use variable cam timing overlap to keep a certain amount of exhaust gas in the chamber. This cuts the cost/complexity of the EGR system completely.

I wonder how the OP's idea would apply on a modern car with a mass air sensor and variable cam timing? I would think the exhaust gasses would need to be introduced post-MAF so the computer was unaware, but then the manifold vacuum/airflow ratio might not make sense to the ECU?

Lots of questions I have... looking forward to this thread!

[razor02097]

Originally Posted by Blue Angel

I see... I was under the assumption that a 1990 gas VW would already have an EGR circuit!



Yes... also, many of today's cars are not using a dedicated EGR circuit: they are able to use variable cam timing overlap to keep a certain amount of exhaust gas in the chamber. This cuts the cost/complexity of the EGR system completely.

I wonder how the OP's idea would apply on a modern car with a mass air sensor and variable cam timing? I would think the exhaust gasses would need to be introduced post-MAF so the computer was unaware, but then the manifold vacuum/airflow ratio might not make sense to the ECU?

Lots of questions I have... looking forward to this thread!

In a newer vehicle the computer should be able to see changes with the O2 sensors. In theory the ECU should be able to achieve stoich with less fuel...

Not really sure how the 90 VW would do... I have zero experience with mechanical fuel injection systems

[Teemo]

Originally Posted by Blue Angel

I see... I was under the assumption that a 1990 gas VW would already have an EGR circuit!

I've read that Calofornia models did have EGR from the factory, but I've never seen that. Of cource it was hot EGR from the factory, just enough to pass emissions test.