Planning for the future: engine advice

[Clatter]

My main problem with EGR in busses is the temperature of exhaust gas.
Exhaust gas is hot.
Busses already run hot enough pulling in cool ambient air.
On other vehicles, where you are not _doing everything you can_ to keep the motor cool,
It's not so big of a deal.

I'm also not a fan of how the EGR doesn't supply all of the cylinders in the plenum equally, causing imbalance.

Air-cooled motors tend to have more blow-by, from the large temperature differences between components,
Causing oil past rings and guides.
It tends to dirty things up more than water-cooled motors.
EGR isn't applied well in the late bus, even if the theory is sound.
Have fun with your EGR; Don't say you weren't warned.


If you build your motor up even a bit more,
IMHO, it's time to consider an 091 swap, like has been suggested.

[mrbell321]

My problem with the 'warnings' is they are based on factually incorrect information.

Do not think of it as adding hot exhaust to the engine, because that is not what EGR does. The key word is 'recirculation'. That heat in the exhaust already exists in the engine. EGR doesn't _add_ anything to the system so there is no way for heat to be _added_.

Let's say that our engines can convert chemical energy of gasoline to thermal energy in the combustion chamber to kinetic energy of the piston at an overall rate of about 50%(give or take, it makes the math easy). That is, at some point there is up to twice the thermal energy in the combustion chamber than leaves in the form of exhaust(assuming all heat leaves through the exhaust, which it doesn't) because about 50% of the energy is transformed into piston motion. Therefore you can say that exhaust gas is _NOT_ hot compared to the burning gases to which the exhaust is being recirculated.

Another way to look at is as where does heat come from? heat comes from burning of fuel and oxygen or:
fuel: mass of fuel consumed
oxygen: mass of oxygen consumed from the air
heat = fuel + oxygen

Since the EGR gases contain no oxygen and extra fuel is not added:
fuel_{No EGR} = fuel_EGR
oxygen_{No EGR} = oxygen_EGR

heat_{No EGR} = fuel_{No EGR} + oxygen_{NO EGR} = fuel_EGR + oxygen_EGR = heat_EGR
So
heat_{No EGR} = heat_EGR

But it's actually better than that. I think we can all agree that the more completely you fill a cylinder(volumetric efficiency/dynamic compression), the more power you make.

A throttle plate is actually a volumetric efficiency limiter. EGR is an inert gas throttle bypass. Essentially, you get a more volumetrically efficient engine at part throttle because you're filling the cylinder more, but not with combustible so:
fuel_{No EGR} > fuel_EGR
oxygen_{No EGR} > oxygen_EGR

Therefore: heat_{No EGR} > heat_EGR


So all that said, air-cooled motors probably benefit _more_ than water-cooled motors by helping keep temperatures in check, allowing tighter tolerances, less blow-by, less oil consumption, etc

Now, was EGR well applied from the factory on a mid-70's VW? I honestly don't know. There are certainly MANY other weaknesses in the system, but that's precisely why I'm going through the effort of building a custom motor with custom controls. It's interesting that it's perfectly acceptable around here to re-engineer 90% of the system, but when I *offhandedly* mentioned I _might_ add EGR one day, everyone lost their minds and decided automotive technology peaked in 1936.

[wreck]

I'm always interested when someone thinks outside the box but l also strongly believe in the KISS principal . I have first hand experience with using water injection to cool cylinder heads when using full power at lower engine revs where the fan is not up to the job .ie 2.3 litre low rpm torque engine pulling a heavy camper up a long incline in +35C ambient at below 3000 rpm .
I understand that the exhaust gas is inert and won't cause more heat to the combustion but it will still have to increase the heat of the incoming charge which VW also designed as a cooling function of the cylinder heads , this is why they have such a large exhaust to inlet valve ratio compared to water cooled engines , Porsche and Harley also run similar ratios .
It looks like you have all the maths and theory to back your idea so who knows, you may be on to something that others have missed . The only way to know is do it . Make sure you have reliable CHT gauges to monitor if you're right or wrong .It's very easy to destroy heads experimenting like this , I'm talking from experience in that mater . I know run a TC-1 by MGL .

[raygreenwood]

Here is what is not being understood about EGR.

Your intake charge....the mix of air and fuel.....is a 100% equation at any load situation. This means whether at idle, WOT or part throttle cruise.....the ECU has set a mixture of required fuel supported by required air volume. This is your AF ratio.

EGR gasses....aside from carbon and moisture ....which are manifold contaminants......is INERT. It is not flammable or burnable....and contains little if any oxygen to support the required combustion level at any given moment. None.....period.

So you are adding a percentage of unburnable gas into the AF mixture. This MUST.....either displace fuel or oxygen. There are no other choices.....ever.

So you either run rich....or you run lean.....during an EGR event. The only way not to have this happen......is to have a METERING SYSTEM on the EGR inlet.....so the ECU can know what to pull the fuel disage back to.....to keep the AF ratio uniform for the load.

And.....if you CAN manage that.....it still....still reduces the overall volume of fuel and air being put in because you input a portion of intake air that has "0" combustion value for either the fuel or air part of the equation. This means that your engine is automatically lowered in efficiecy. Not enough fuel and air.

By the way...you ant easy starts? I have worked on literally more than a thousand 1.7L engines from 411/412/914....which are all the same exact engine snd not the detuned version in the bus......and with ancient D-jet injection, proper high compression, careful tuning of injection timing, fuel mixture and ignition timing and advance....to include a better than stock coil......I can,routinely get them to start clean....stone cold....in cold weather one the first revolution of the starter. No kidding!

This is a little more easy to do with D-jet because you do not need t9 crank until the metering flap moves like L-jet and digifant...to get initial injection enrichment. D-jet triggers,injection in at least one injector pair within any single revolution of the crank. This is also true of course with CIS systems.

But the point is that instant starts do not need a bunch of arcane systems and new engineering....and EGR has nothing to do with changing pumping losses.
Ray

[mrbell321]

Here is what is not being understood about EGR.

Your intake charge....the mix of air and fuel.....is a 100% equation at any load situation. This means whether at idle, WOT or part throttle cruise.....the ECU has set a mixture of required fuel supported by required air volume. This is your AF ratio.

EGR gasses....aside from carbon and moisture ....which are manifold contaminants......is INERT. It is not flammable or burnable....and contains little if any oxygen to support the required combustion level at any given moment. None.....period.

So you are adding a percentage of unburnable gas into the AF mixture. This MUST.....either displace fuel or oxygen. There are no other choices.....ever.

So you either run rich....or you run lean.....during an EGR event. The only way not to have this happen......is to have a METERING SYSTEM on the EGR inlet.....so the ECU can know what to pull the fuel disage back to.....to keep the AF ratio uniform for the load.

And.....if you CAN manage that.....it still....still reduces the overall volume of fuel and air being put in because you input a portion of intake air that has "0" combustion value for either the fuel or air part of the equation. This means that your engine is automatically lowered in efficiecy. Not enough fuel and air.

Actually, no, it does NOT displace fuel or oxygen. Without EGR, at part throttle, before the intake valve closes, the cylinder is not filled w/ air/fuel with 100% volumetric efficiency. That is the purpose of the throttle and the reason is called 'throttle'. Because of the vacuum, your dynamic compression is lower than it could be and you will not extract as much power from the fuel as is actually possible for the amount of fuel used.
Adding EGR, which enters the intake airstream AFTER throttle, allows the engine to get closer to 100% VE(altho, not all the way), bringing dynamic compression up without changing the ratio of fuel to oxygen.

By the way...you ant easy starts? I have worked on literally more than a thousand 1.7L engines from 411/412/914....which are all the same exact engine snd not the detuned version in the bus......and with ancient D-jet injection, proper high compression, careful tuning of injection timing, fuel mixture and ignition timing and advance....to include a better than stock coil......I can,routinely get them to start clean....stone cold....in cold weather one the first revolution of the starter. No kidding!

This is a little more easy to do with D-jet because you do not need t9 crank until the metering flap moves like L-jet and digifant...to get initial injection enrichment. D-jet triggers,injection in at least one injector pair within any single revolution of the crank. This is also true of course with CIS systems.

But the point is that instant starts do not need a bunch of arcane systems and new engineering....and EGR has nothing to do with changing pumping losses.
Ray

My reason for considering EGR wasn't to do w/ cold starts...Instant cold starts are one of the reasons to go EFI and computerized ignition. I was considering EGR for economy, emissions and because it would be fun.
And at this point, it's just become a personal goal to clear up all of the misunderstandings of EGR.

[mrbell321]

It occurs to me that it doesn't matter if it replaces some air and you have the open the throttle a bit more to compensate... in fact, that is kind of the point. As an example, say it takes 50% throttle to maintain a constant 65mph without EGR.
EGR opens, and it now takes 55% throttle to go 65mph. So what? At worst, you're still burning the same ratio of fuel to oxygen, you just get to do it more efficiently and cleanly.

[mrbell321]

It occurs to me that it doesn't matter if it replaces some air and you have the open the throttle a bit more to compensate... in fact, that is kind of the point. As an example, say it takes 50% throttle to maintain a constant 65mph without EGR.
EGR opens, and it now takes 55% throttle to go 65mph. So what? At worst, you're still burning the same ratio of fuel to oxygen, you just get to do it more efficiently and cleanly.

[raygreenwood]

The problem with your plan here....is that with proper fuel mixture and ignition control.....EGR is not needed or even useful for "emissions". Its sole function was to reduce NOX. Yes.....it worked for that with engines that had no other means of controlling NOX. And its contribution to that function was trivial percentage wise.....and did not balance out its bad points.

It also has virtually 0 function for economy. This is another common myth...that displacing a portion of intake charge with inert gas....gains mileage. It loses power and the foot compensates. Ray