Lean Burn engine
03-30-2011, 10:35 AM
#42
Here's my take:
1. EGR is for emissions control. It is intended to reduce NOx by reducing peak combustion temperatures.
2. EGR has been in use for almost 40 years. Its current implementations are highly refined. Modern ECUs take advantage of EGR to hit highly efficient cruise design points where you can use more open throttle angles (higher VE) and increased spark advance.
3. If you were working a clean sheet engineering design to maximize Otto cycle efficiency where emmissions was not a concern, EGR would not be part of your design.
4. If you are running a stock ECU, keeping EGR (and everything else) intact will maximize your efficiency.
5. If you are running an aftermarket ECU, you're going to need a heck of a lot of test time to optimize use of EGR. Without an engine test cell or a lot of proprietary data, I don't know how you would replicate the efficiency achieved by the OEMs. You're probably better off disabling EGR and just focusing on the basics.
YMMV (pun intended).
1. EGR is for emissions control. It is intended to reduce NOx by reducing peak combustion temperatures.
2. EGR has been in use for almost 40 years. Its current implementations are highly refined. Modern ECUs take advantage of EGR to hit highly efficient cruise design points where you can use more open throttle angles (higher VE) and increased spark advance.
3. If you were working a clean sheet engineering design to maximize Otto cycle efficiency where emmissions was not a concern, EGR would not be part of your design.
4. If you are running a stock ECU, keeping EGR (and everything else) intact will maximize your efficiency.
5. If you are running an aftermarket ECU, you're going to need a heck of a lot of test time to optimize use of EGR. Without an engine test cell or a lot of proprietary data, I don't know how you would replicate the efficiency achieved by the OEMs. You're probably better off disabling EGR and just focusing on the basics.
YMMV (pun intended).
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03-30-2011, 12:54 PM
#44
http://www.eng-tips.com/viewthread.c...=147390&page=1
"Vehicle efficiency gain limit due to EGR affecting piston suction losses is
8.24738372 percent"
"So if you can gently suck in air and recycled exhaust gas instead of struggling to suck clean air against a partial vaccuum there is a real fuel saving to be made. I'm not suggesting you could make an 8% fuel saving. I'm suggesting there is a maximum of about 8% available (for given assumptions) and that if EGR is even 1/4 efficient at helping to make that fuel saving, then you gain a couple of percent in fuel economy when cruising along, and it is a gain worth having - though its worth saying again: you cannot make the same saving twice."
Redact your statement sir, and head to the end of the line.
nuff said.
"Vehicle efficiency gain limit due to EGR affecting piston suction losses is
8.24738372 percent"
"So if you can gently suck in air and recycled exhaust gas instead of struggling to suck clean air against a partial vaccuum there is a real fuel saving to be made. I'm not suggesting you could make an 8% fuel saving. I'm suggesting there is a maximum of about 8% available (for given assumptions) and that if EGR is even 1/4 efficient at helping to make that fuel saving, then you gain a couple of percent in fuel economy when cruising along, and it is a gain worth having - though its worth saying again: you cannot make the same saving twice."
Redact your statement sir, and head to the end of the line.
nuff said.
Holy cow!! Talk about pop culture engineering. What a load.
Exhaust Gas Recirculation is the same thing as eating ****. From a thermodynamic standpoint (not "Thermal Dynamics"), it is just about the worst thing you can do. It was invented in the 70's to lower NOx emmissions to try to comply with the 1970 Clean Air Act. That was about the same time those wonderful big block V-8s went from 10:1 to 8:1 compression -- again, not good from a thermodynamic standpoint. EGR was definitely NOT about trying to accomplish lean burn or increasing engine efficiency.
The other stuff is mostly good information. Note that cylinder head quench regions -- which is a technology that allows you to run higher compression without detonation -- is also pretty old. Widely used in the mid-60s but fell out of favor because, again, high NOx. The change to big-block MOPAR cylinder heads is probably the most obvious example.
Wonderful head engineering these days to introduce swirl while still preserving flow. Charge stratification is the enemy (unless you do it on purpose to preserve a combustible mixture in a specific area near the spark source -- which is what a lot of the discussion above is about).
EGR . . . 100% bad. Rule of thumb . . . don't eat ****.
Exhaust Gas Recirculation is the same thing as eating ****. From a thermodynamic standpoint (not "Thermal Dynamics"), it is just about the worst thing you can do. It was invented in the 70's to lower NOx emmissions to try to comply with the 1970 Clean Air Act. That was about the same time those wonderful big block V-8s went from 10:1 to 8:1 compression -- again, not good from a thermodynamic standpoint. EGR was definitely NOT about trying to accomplish lean burn or increasing engine efficiency.
The other stuff is mostly good information. Note that cylinder head quench regions -- which is a technology that allows you to run higher compression without detonation -- is also pretty old. Widely used in the mid-60s but fell out of favor because, again, high NOx. The change to big-block MOPAR cylinder heads is probably the most obvious example.
Wonderful head engineering these days to introduce swirl while still preserving flow. Charge stratification is the enemy (unless you do it on purpose to preserve a combustible mixture in a specific area near the spark source -- which is what a lot of the discussion above is about).
EGR . . . 100% bad. Rule of thumb . . . don't eat ****.
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03-30-2011, 01:50 PM
#45
http://www.eng-tips.com/viewthread.c...=147390&page=1
"Vehicle efficiency gain limit due to EGR affecting piston suction losses is
8.24738372 percent"
"So if you can gently suck in air and recycled exhaust gas instead of struggling to suck clean air against a partial vaccuum there is a real fuel saving to be made. I'm not suggesting you could make an 8% fuel saving. I'm suggesting there is a maximum of about 8% available (for given assumptions) and that if EGR is even 1/4 efficient at helping to make that fuel saving, then you gain a couple of percent in fuel economy when cruising along, and it is a gain worth having - though its worth saying again: you cannot make the same saving twice."
Redact your statement sir, and head to the end of the line.
nuff said.
"Vehicle efficiency gain limit due to EGR affecting piston suction losses is
8.24738372 percent"
"So if you can gently suck in air and recycled exhaust gas instead of struggling to suck clean air against a partial vaccuum there is a real fuel saving to be made. I'm not suggesting you could make an 8% fuel saving. I'm suggesting there is a maximum of about 8% available (for given assumptions) and that if EGR is even 1/4 efficient at helping to make that fuel saving, then you gain a couple of percent in fuel economy when cruising along, and it is a gain worth having - though its worth saying again: you cannot make the same saving twice."
Redact your statement sir, and head to the end of the line.
nuff said.
Now, off to the end of the line.
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04-05-2011, 11:58 AM
#46
Elite Member
Join Date: Jul 2005
Posts: 6,420
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I looked at Millerizing my turbo setup with VVT. The idea being:
raise compression ratio than I would otherwise run (i.e. choosing 9.4:1 pistons instead of 8.6), then reducing VE / reducing dynamic compression with "non optimal" cam timing, and raising the boost pressure.
The theory is that doing "some of the work of compression" in the turbo (i.e. higher boost), is better because the charge gets intercooled, then doing the rest of the compression in the cylinders on the compression stroke, would result in more powah due to having a high expansion ratio with a reduced effective compression ratio (resulting in lower peak compression temperature thus reduced tendency to knock).
The problem I saw is that, if you look at a family of torque curves at different intake cam settings, low and high RPM torque went up and down (reduced VE), but the midrange RPM torque sort of mostly overlapped. That is, the change in VE in the midrange RPMs where you would need the knock resistance the most, was the RPM range least affected by the cam timing changes. So I said I'll just go with 8.6:1 pistons, if this idea doesn't work I'll be stuck with a knocky engine.
Having said all that, my cam timing in cruise is full retard even though the cam timing which produces max torque at those RPMs is some advance. That means VE is reduced requiring a bit more throttle opening. Because my max advance anywhere in my map is nowhere near what the VVT is capable of, I considered moving my intake cam 1 tooth so I could have even more retard than stock, in order to retard even further.
You can reduce VE by either over-advancing or over-retarding the intake cam. The advantage of over retard is you don't have possible issues with the intake charge fuel blowing out the exhaust. Thoughts?
raise compression ratio than I would otherwise run (i.e. choosing 9.4:1 pistons instead of 8.6), then reducing VE / reducing dynamic compression with "non optimal" cam timing, and raising the boost pressure.
The theory is that doing "some of the work of compression" in the turbo (i.e. higher boost), is better because the charge gets intercooled, then doing the rest of the compression in the cylinders on the compression stroke, would result in more powah due to having a high expansion ratio with a reduced effective compression ratio (resulting in lower peak compression temperature thus reduced tendency to knock).
The problem I saw is that, if you look at a family of torque curves at different intake cam settings, low and high RPM torque went up and down (reduced VE), but the midrange RPM torque sort of mostly overlapped. That is, the change in VE in the midrange RPMs where you would need the knock resistance the most, was the RPM range least affected by the cam timing changes. So I said I'll just go with 8.6:1 pistons, if this idea doesn't work I'll be stuck with a knocky engine.
Having said all that, my cam timing in cruise is full retard even though the cam timing which produces max torque at those RPMs is some advance. That means VE is reduced requiring a bit more throttle opening. Because my max advance anywhere in my map is nowhere near what the VVT is capable of, I considered moving my intake cam 1 tooth so I could have even more retard than stock, in order to retard even further.
You can reduce VE by either over-advancing or over-retarding the intake cam. The advantage of over retard is you don't have possible issues with the intake charge fuel blowing out the exhaust. Thoughts?
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04-05-2011, 12:42 PM
#47
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I like your ideas including jumping a tooth on the intake cam sprocket. I also think another point of the miller is to retard the intake valve to the point it's closing somewhat far into the compression stroke (against the typical supercharger), resulting in a longer power stroke compared to the compression stroke. Kinda sorta.
EDIT to be a little clearerer: For arguments sake say you close the intake valve halfway up the compression stroke. You are now compressing half the engine capacity; It is like you have a .9l engine fueling but with the power stroke applied twice as long. The miller's I know of (millenia S) I believe use a supercharger that's always under positive pressure so the intake charge doesn't...I dunno...go backwards too far to where it's not supposed to go? Plus the intake duration is much longer...it's not just a standard duration lobe that's retarded. It opens when it typically should, just closes later. I'm sure you could get some of the miller effect however just retarding your standard cam.
EDIT to be a little clearerer: For arguments sake say you close the intake valve halfway up the compression stroke. You are now compressing half the engine capacity; It is like you have a .9l engine fueling but with the power stroke applied twice as long. The miller's I know of (millenia S) I believe use a supercharger that's always under positive pressure so the intake charge doesn't...I dunno...go backwards too far to where it's not supposed to go? Plus the intake duration is much longer...it's not just a standard duration lobe that's retarded. It opens when it typically should, just closes later. I'm sure you could get some of the miller effect however just retarding your standard cam.
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08-09-2017, 06:02 PM
#50
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As I opened this thread, I thought "which jackass bumped this thread?? It better not have been RTC..."
Then I see Yank in here.
One of the few on here who would actually do it. Report back mang.
Then I see Yank in here.
One of the few on here who would actually do it. Report back mang.
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08-09-2017, 07:53 PM
#52
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Join Date: Apr 2016
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I think thats a lofty goal.
Check out this guy:
https://forum.miata.net/vb/showthread.php?t=441727
Put a 1.3L festiva engine in his Miata and did a bunch of cool stuff and ended up with ~45MPG.
Check out this guy:
https://forum.miata.net/vb/showthread.php?t=441727
Put a 1.3L festiva engine in his Miata and did a bunch of cool stuff and ended up with ~45MPG.
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