Increasing EGR flow for better mileage

[Daox]

I was able to dig through my junk piles and find a PWM controller kit I had gotten a few years ago. Its a simple little circuit kit and it hadn't been made yet. So, I soldered it up last night. Here is a pic of it out of the instruction manual. I don't have actual pics. This little dandy is capable of handling up to 20A, so it should be more than plenty to control the EGR valve. The smaller plastic pot lets me adjust pulse frequency, and the large pot allows me to adjust duty cycle.

[Daox]

Originally Posted by pstrbrc

OK. Some of the control problem you're going to encounter has to do with the contradiction that your intake will draw through whichever has the least restriction. You experience this when a car with an intake gasket leak runs like cr@$ with the throttle closed, but can run just fine at quarter throttle or more. That's becase when the throttle plate is closed, you are developing high intake vacuum, which can suck a lot of air through a little gascket leak, but when you open the throttle, lowering the vacuum, the amount of air drawn through the gasket leak is much less, AND the metered air flowing past the throttle plate is much greater, and the cpu/metering valve puts in fuel to match this air across the throttle. So, under high vacuum, if you use a monster egr valve, it will be next to impossible to adjust it in such a way that is meaningful. You see, the point of egr is % dilution, and at small throttle openings, that means very little exhaust recirculation, or the car don't run.

We're just going to have to see how far down I can dial the larger EGR valve. I might not run into the problem. If nothing else, I could use a smaller valve in addition to the larger one.

But, for those engines that can't alter the exhaust timing, how about an exhaust throttle? You know, they used to call them heat risers? I think GM used them as late as '81 on their V-8s. They used a vacuum dashpot, but you could hook it up to a manual push cable, hook up a pressure gauge to read exhaust pressure, and experiment away.

I can't imagine that placing a restriction in the exhaust is a good way of increasing efficiency.

[Christ]

A tunable (on the fly) exhaust could alter performance curves, though.

Backpressure in an exhaust is never desirable unless it's a design function required by the engine's characteristics. The average engine doesn't need it, but some designs prefer it at certain ranges, and there have been obscure designs (I don't have a link) where exhaust throttling was used in place of intake throttling to control engine speed and power.

I have no idea what the significance of doing so would be, and don't ever intend to test it. I'd prefer to go throttle less altogether.

[mwebb]

Originally Posted by Christ

You realize that the point of EGR is to reroute unburned HC's back into the combustion chamber, right? So they don't get into the cat, being burned off and doing no work as a result of it.

So basically, you're advocating waste.

========================

assuming this is tongue in cheek ?
if not
this is not an accurate description of EGR or what EGR is designed to do

[Christ]

Well, not exactly tongue in cheek, but I did know that it wasn't correct.

EGR recirculates exhaust gas back into the combustion chamber to lower combustion temps so that Nitrogen doesn't combine with other compounds to form NOx, as I understand it.

Of course, if there is unburned fuel in the exhaust, part of it will go back through the EGR system. Not 100% about it, but I believe that to be the reason for sludge/yuck buildup in the EGR passages (unburnt or partially combusted fuel mixture).

I posted it like that because I was waiting for a response, as I frankly don't think he has any idea what it does, either. I was just trying to verify by leading. Lawyers do it all the time!

[mwebb]

Originally Posted by Christ

Well, not exactly tongue in cheek, but I did know that it wasn't correct.

EGR recirculates exhaust gas back into the combustion chamber to lower combustion temps so that Nitrogen doesn't combine with other compounds to form NOx, as I understand it.

Of course, if there is unburned fuel in the exhaust, part of it will go back through the EGR system. Not 100% about it, but I believe that to be the reason for sludge/yuck buildup in the EGR passages (unburnt or partially combusted fuel mixture).

I posted it like that because I was waiting for a response, as I frankly don't think he has any idea what it does, either. I was just trying to verify by leading. Lawyers do it all the time!

========================
your answer was more correct than "his" ...
but
yes over time carbon and doo doo build up in and around EGR passages on some systems --- may be some partialy burned fuel and some
residue from engine oil deposits from
low quality oil use -
................................
EGR does dilute combustion gases with INert gases
so;

combustion temperatures are reduced .
thus reducing NOX

and

EGR can improve fuel economy by reducing suction throttleing loss

because
EGR
effectively
reduces the size / displacement of the engine during the time EGR is active / operating

so
the operator needs to apply more throttle opening for the same amount of power to the wheel s when the EGR is active

[Christ]

Enter key stuck?

Is the opposite of "Inert" just "ert"?

[JackMcCornack]

Originally Posted by Christ

Is the opposite of "Inert" just "ert"?

I derstand exactly what you mean.

Originally Posted by pstrbrc

Ford used variable cam timing on some of the Zetecs (Contour, Cougar, ZX-2) to advance the exhaust timing in such a way that the exhaust stroke wasn't completely scavenged. They were able to use this instead of egr to meet nitrous standards. So how much the intake charge is diluted has much less to do with intake vacuum.

I think keeping exhaust gas in the cylinder via exhaust timing would reduce throttle losses even better than EGR does. Pardon the clumsy sentence (and there's a worse one coming) but wouldn't leaving exhaust gas in there, fully reduce the vacuum (see, I warned you) right from the start of the intake valve opening instead of a gradual reduction as EG dribbles in through the EGR valve?

[Daox]

Originally Posted by JackMcCornack

Pardon the clumsy sentence (and there's a worse one coming) but wouldn't leaving exhaust gas in there, fully reduce the vacuum (see, I warned you) right from the start of the intake valve opening instead of a gradual reduction as EG dribbles in through the EGR valve?

Yeah, I think that does sound more efficient/better/less prone to failure due to clogging etc.


Back to the PWM controller, I tried it out last night and... well there was a fairly violent electrical explosion, the biggest one I've seen from a simple 12V circuit anyway. So, I need to get a replacement mosfet and check what the heck I soldered in wrong. Powering the EGR valve up manually it doens't pull more than 1.3A, so the controller is plenty capable of handling the power requirements. I must have done something wrong at assembly.

[tasdrouille]

Playing with exhaust valves timing to increase the residual gas fraction is called internal EGR. I believe you cannot achieve the same amount of recirculation with internal EGR than the most common short route external EGR setup. Also, external EGR has the advantage of being cooled.