Increasing EGR flow for better mileage

[Christ]

Oh, jeez, I thought you were doing some work here... lol.

[Daox]

Haha, not more than I have to. The fabbing will be easy. The tuning will be much more difficult I think.

[Christ]

Indeed. You don't see any blame coming from this direction for taking the easy way out, for sure.

[moonmonkey]

doax would a rc car controller work for a egr circuit or would it be to low current handling?

[Daox]

Well, the valve only requires 1.3A @ 12V to stay wide open. If the ESC can supply that (and I'd doubt it can't), then it should work. Good idea.

[Christ]

Ok, I need to question something, because I'm not sure I fully understand what's being done here.

Are you using the EGR flow to enable lean burn under normal circumstances, or are you using the EGR flow as a "filler" to lower effective displacement?

I would guess that with a variable valve, you're doing the latter.

[Daox]

You would be correct, I am using it as filler to lower effective displacement.

That may eventually lead to leaning the mixture (to enable even less fuel injected and lower power output). However, at this time I have no way of trimming fuel or adjusting ignition timing beyond the stock ECU, so we'll see how it deals with it. I know the O2 sensor will correct for the fuel injection. I'm just unsure of how it'll handle the ignition timing. I know leaner mixtures burn slower, so timing advance may be needed. But this really isn't a lean mixture, its still stoichiometric. But, it has filler like you say, so the gas and oxygen molecules will be farther apart. This will probably be the main limitation of the EGR system. If that is the case, I will likely have a bit of leeway to start leaning things before nox even becomes a problem due to the cooler burning nature of an EGR mixture. Using or modifying the head to be a high tumble/swirl head would likely increase the effectiveness of this modification (as it does with lean burn).

I hope that makes sense. That was kind of stream of consciousness there.

[Christ]

What I'm thinking is that if you can get the EGR flow into the cylinder before the clean intake air, you won't have to worry about stratification. The EGR just blocks the bottom of the cylinder, pressing the mixture closer to the top of the cylinder/spark plug.

What I'm worried about is whether or not the EGR flow comes from before the O2 sensor in the exhaust stream. If you're reintroducing pre-measured O2 into the engine from the exhuast, it may cause you to run slightly rich, since the O2 sensor will be reading the same exhaust parts more than once.

[Daox]

Originally Posted by Christ

What I'm thinking is that if you can get the EGR flow into the cylinder before the clean intake air, you won't have to worry about stratification. The EGR just blocks the bottom of the cylinder, pressing the mixture closer to the top of the cylinder/spark plug.

I'm pretty sure theres way too much turbulence inside the combustion chamber to ensure that the EGR will sit at the bottom. If it did, that would be great.

What I'm worried about is whether or not the EGR flow comes from before the O2 sensor in the exhaust stream. If you're reintroducing pre-measured O2 into the engine from the exhuast, it may cause you to run slightly rich, since the O2 sensor will be reading the same exhaust parts more than once.

Interesting idea, but unless I'm missing something, I don't think that this will be a problem either. If the exhaust gas is coming out the engine rich, it will recycle some of that rich exhaust gas, but the rest of the rich exhaust gas will still get to the O2 sensor and it will trim the fuel injectors back until it hits a slightly lean condition, then back again as it normally would with a narrow band sensor setup.

[Christ]

Originally Posted by Daox

Interesting idea, but unless I'm missing something, I don't think that this will be a problem either. If the exhaust gas is coming out the engine rich, it will recycle some of that rich exhaust gas, but the rest of the rich exhaust gas will still get to the O2 sensor and it will trim the fuel injectors back until it hits a slightly lean condition, then back again as it normally would with a narrow band sensor setup.

What I was suggesting, and I don't know for sure if it would work this way:

If the EGR pulls exhaust gasses from after the first O2 sensor (between O2-1 and the cat) it would be pulling in gasses that had already been metered by the O2 sensor, and reintroducing them to the combustion chamber without having been metered by the intake sensors, so now you've got gasses in the combustion chamber (including whatever oxygen was left over in the exhaust gasses) that haven't been compensated for by the intake sensors, that are going to pass the O2 sensor again.

Although it does seem like the O2 sensor should richen the mixture slightly and burn off that O2 that was left over, so it wouldn't pass the sensor again. So maybe it won't be a problem.

Guess I should have worked the path out in my head a little more before posting, eh?

Also, you're correct about turbulence in the combustion chamber - you wouldn't really be able to ensure that it all stayed at the bottom unless it was injected there. Of course, the unburned HC's flowing back into the combustion chamber should help with the stratification of the "normal" intake by providing some "bridging" between the fuel/air molecules of burnable material.

Only experimentation will yield results, though.