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Blazius
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« Reply #60 on: July 30, 2019, 06:56:10 AM »
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That's not how an engine works >.<
What? Explain. If you dont run the required timing for a certain rpm/flame speed etc then you are pushing the peak cylinder pressure envelope way over atdc kw, no ? If you do it too early your cylinder is working against pressure and expansion. You also make less power with less timing because the piston os already on its way when the expansion/combustion is happening but higher egts since it wasnt a proper process and the exhaust valve is opening soon because the crank turned enough already. Also runing timing past over mbt increases peak pressure fast and is a good way to fuck things up. |
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« Last Edit: July 30, 2019, 06:58:45 AM by Blazius »
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nyet
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« Reply #61 on: July 30, 2019, 08:49:08 AM »
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I have done a lot of reading and not all of it concurs, there are quite a few different views as demonstrated by this forum and things like knock control - some documents say to retard the timing others say to advance the timing?
There are no documents that say to increase timing to mitigate knock. |
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prj
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« Reply #62 on: July 31, 2019, 12:42:07 AM »
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What? Explain. If you dont run the required timing for a certain rpm/flame speed etc then you are pushing the peak cylinder pressure envelope way over atdc kw, no ? If you do it too early your cylinder is working against pressure and expansion. You also make less power with less timing because the piston os already on its way when the expansion/combustion is happening but higher egts since it wasnt a proper process and the exhaust valve is opening soon because the crank turned enough already. Also runing timing past over mbt increases peak pressure fast and is a good way to fuck things up.
EGT does not go higher because a valve is open during combustion. EGT increases mostly due to the first law of thermodynamics, that's as much as I have time to explain. |
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GolfSportWagen
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« Reply #63 on: July 31, 2019, 08:32:25 PM »
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IME if the ignition is retarded enough a good portion of the intake charge will still be burning when the exhaust valve opens and thus the EGT and turbine in temps will increase significantly as well as the exhaust pressure which I have actually measured in an engine dyno test lab on numerous turbo engines.
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Blazius
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« Reply #64 on: July 31, 2019, 10:29:15 PM »
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IME if the ignition is retarded enough a good portion of the intake charge will still be burning when the exhaust valve opens and thus the EGT and turbine in temps will increase significantly as well as the exhaust pressure which I have actually measured in an engine dyno test lab on numerous turbo engines.
Yes. |
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prj
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« Reply #65 on: August 01, 2019, 04:04:46 AM »
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IME if the ignition is retarded enough a good portion of the intake charge will still be burning when the exhaust valve opens and thus the EGT and turbine in temps will increase significantly as well as the exhaust pressure which I have actually measured in an engine dyno test lab on numerous turbo engines.
Again, no. Nothing is burning when the exhaust valve opens unless you retard the ignition far ADTC. IDK where this misconception comes from. Seems like just another thing regurgitated on forums and claimed as gospel. Simply, more energy is converted to heat and less of it into kinetic energy, nothing more nothing less. The reason exhaust backpressure increases is because of the ideal gas law - the gas expands as it gets heated. The hotter the exhaust, the bigger the exhaust backpressure. Also, the first thing you are going to melt is the piston, because all of the combustion happens in the cylinder. If you retard the ignition enough so that all the combustion does not happen in the cylinder anymore, then in-cylinder temperature actually goes down. And you are not going to have any cylinder melting issues. But the engine will also make nearly no power anymore with that late of an ignition angle. |
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« Last Edit: August 01, 2019, 04:09:49 AM by prj »
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Blazius
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« Reply #66 on: August 01, 2019, 08:13:15 AM »
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Again, no.
Nothing is burning when the exhaust valve opens unless you retard the ignition far ADTC.
IDK where this misconception comes from. Seems like just another thing regurgitated on forums and claimed as gospel.
Simply, more energy is converted to heat and less of it into kinetic energy, nothing more nothing less.
The reason exhaust backpressure increases is because of the ideal gas law - the gas expands as it gets heated. The hotter the exhaust, the bigger the exhaust backpressure.
Also, the first thing you are going to melt is the piston, because all of the combustion happens in the cylinder.
If you retard the ignition enough so that all the combustion does not happen in the cylinder anymore, then in-cylinder temperature actually goes down. And you are not going to have any cylinder melting issues. But the engine will also make nearly no power anymore with that late of an ignition angle.
"Simply, more energy is converted to heat and less of it into kinetic energy, nothing more nothing less." - yes, because the expansion is not pushing the piston down that much because it is already on its way down, instead it is "wasted" via heat like you said, so that does not result in higher EGT or combustion temperature relative to MBT, or optimal ignition and effeciency scenario ? |
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GolfSportWagen
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« Reply #67 on: August 01, 2019, 04:24:59 PM »
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Again, no.
Nothing is burning when the exhaust valve opens unless you retard the ignition far ADTC.
IDK where this misconception comes from. Seems like just another thing regurgitated on forums and claimed as gospel.
Simply, more energy is converted to heat and less of it into kinetic energy, nothing more nothing less.
The reason exhaust backpressure increases is because of the ideal gas law - the gas expands as it gets heated. The hotter the exhaust, the bigger the exhaust backpressure.
Also, the first thing you are going to melt is the piston, because all of the combustion happens in the cylinder.
If you retard the ignition enough so that all the combustion does not happen in the cylinder anymore, then in-cylinder temperature actually goes down. And you are not going to have any cylinder melting issues. But the engine will also make nearly no power anymore with that late of an ignition angle.
Just to be clear... I have actually measured this on numerous engines on an engine dyno. The timing does not need to be way late, it only has to be retarded enough to allow the combustion to take place mainly after the proper peak cyl. pressure point. Peak cyl. pressure needs to occur in the 12-15 deg. ATDC range. The greatest heat is not in the cyl. with insufficient timing advance which causes late and slow combustion it ends up in the exhaust system and is known as "burn down". The retarded combustion creates a tremendous thermal load on the exhaust valve, guide, exhaust manifold, turbine housing and wheel. This can occur at higher engines speeds from ~3,500 on up with WOT and insufficient timing advance due to octane limitation, excessive IAT or excessive boost pressure. The real time for combustion drops sufficiently with engine speed so that a minimum advance is required to prevent exhaust system burn down and power loss. Some tuners unfortunately don't understand this and they use excessive boost and retard the timing to prevent knock. While you can make good power this way it's destructive to the engine long term. Lean AFRs and detonation are what typically melts pistons and heads. As far as EGT's the temps measured ~2" from the head flange will typically increase 300-500 F putting them in the 1700-1800 F range with insufficient timing and burn down. It's also true that excessive advance can lower power by increasing the cyl. pressure too high before the piston reaches TDC in essence trying to stop the piston. Any ICE college text will show the cyl. pressure graphs to confirm this. |
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prj
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« Reply #68 on: August 02, 2019, 05:14:19 AM »
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Just to be clear...
I have actually measured this on numerous engines on an engine dyno. The timing does not need to be way late, it only has to be retarded enough to allow the combustion to take place mainly after the proper peak cyl. pressure point. Meaning "way late". Peak cyl. pressure needs to occur in the 12-15 deg. ATDC range. On a slow burn head that means running around 5 degrees BTDC advance at the top end. On a fast burn head (such as the EA888) that means running pretty much zero or negative advance on the top end. So hence "way late". You will melt pistons on any VAG engine on a VMAX run before this happens. VAG engines generally have a decent combustion chamber design and massively lose power richer than 0.8. Especially the newer ones. This is also the reason why it is extremely rare to see heat damage to the exhaust manifold or turbo on VAG cars. The engine simply lets go first. Your example is applicable to for example Ford Ecoboost, Subaru, Alfa and a few other engines, which make best power around 0.73-0.74 lambda. As on those it's pretty difficult to melt the pistons and also the super rich mixture reduces flame speed. Which engine did you have on the engine dyno? Probably wasn't a four or five valve VAG (or german) engine, was it? |
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« Last Edit: August 02, 2019, 05:25:44 AM by prj »
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GolfSportWagen
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« Reply #69 on: August 02, 2019, 05:32:53 PM »
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Meaning "way late".
On a slow burn head that means running around 5 degrees BTDC advance at the top end. On a fast burn head (such as the EA888) that means running pretty much zero or negative advance on the top end.
So hence "way late".
You will melt pistons on any VAG engine on a VMAX run before this happens.
VAG engines generally have a decent combustion chamber design and massively lose power richer than 0.8. Especially the newer ones.
This is also the reason why it is extremely rare to see heat damage to the exhaust manifold or turbo on VAG cars. The engine simply lets go first.
Your example is applicable to for example Ford Ecoboost, Subaru, Alfa and a few other engines, which make best power around 0.73-0.74 lambda.
As on those it's pretty difficult to melt the pistons and also the super rich mixture reduces flame speed.
Which engine did you have on the engine dyno? Probably wasn't a four or five valve VAG (or german) engine, was it?
No the timing was not "way late" as you claim. I have run extensive engine dyno testing on numerous 4V turbo engines including German 4V per cyl. engines with boost from 12-22 PSI. Testing typically shows that at WOT these engines require 18-21 degs. ignition advance from 5000-7000 rpm to achieve best power without burn down. Using less timing due to excessive boost, high IAT or octane limitations does cause burn down in the exhaust. Using EGR to reduce knock also reduces power but allows more advance. The fact is if you don't ignite the mixture well before TDC as the RPM increases you have delayed combustion because the real time becomes shorter as the RPM increases and the burn rate simply is not fast enough to compensate. In cases with excessive flame front propagation such as some dual sparkplug engines you can get engine rumble from excessively fast combustion. If you have actual steady state engine dyno data that differs with what I have stated I would suggest that you author a white paper with your specific test set-up and parameters and submit it to the SAE for peer review so that we can review your testing to see why your data is distinctly different from that of auto mfgs. and independent engineering firms who perform calibration work. |
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prj
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« Reply #70 on: August 04, 2019, 05:05:10 AM »
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No the timing was not "way late" as you claim.
I have run extensive engine dyno testing on numerous 4V turbo engines including German 4V per cyl. engines with boost from 12-22 PSI. Testing typically shows that at WOT these engines require 18-21 degs. ignition advance from 5000-7000 rpm to achieve best power without burn down. Using less timing due to excessive boost, high IAT or octane limitations does cause burn down in the exhaust. Using EGR to reduce knock also reduces power but allows more advance. The fact is if you don't ignite the mixture well before TDC as the RPM increases you have delayed combustion because the real time becomes shorter as the RPM increases and the burn rate simply is not fast enough to compensate. In cases with excessive flame front propagation such as some dual sparkplug engines you can get engine rumble from excessively fast combustion.
If you have actual steady state engine dyno data that differs with what I have stated I would suggest that you author a white paper with your specific test set-up and parameters and submit it to the SAE for peer review so that we can review your testing to see why your data is distinctly different from that of auto mfgs. and independent engineering firms who perform calibration work.
So tell me mr. expert, how much timing does a STOCK EA888 run up top in a Golf R? or how about an Audi S1? Your numbers do not match up in the slightest. Because if they did, we'd have all STOCK EA888 cars tuned by VAG with massive turbine damage and cracked heads. This is not the case. Also you do realize that head design significantly affects burn speed, and your numbers for some cases are past MBT, right? Perhaps you should write to Audi that they don't know anything about designing and tuning an engine - no need to argue with me. Other than that, you're stating the obvious. As for EGR - it slows combustion, of course you can add more advance, but there is no point on WOT, and there is not a single VAG turbocharged performance engine with EGR (apart from TDI). As for my personal testing, I have had plenty a car with 2-3 EGT locations, yes I personally own a steady state dyno. EGT has always without fail been lower the further you get from the port for me. I don't try things like running 5 degrees on top with 2000mbar boost on a slow burn head design though. As I said before - on any VAG engine (from the old 2.2T on through the EA888 last gen designs), insufficient advance specifically will melt the pistons long before anything else happens to the engine, the manifold or the turbocharger. If you get the advance really low, the exhaust valve seats will fail and then the valve will melt through, and the cylinder will lose compression. It will do that within 1 VMAX run. But you will never ever crack the manifold or damage the turbocharger with heat before this happens, unless running ATDC ignition angle for antilag, and even then the manifold and turbo will hold up for 1-2 rallies, if not more. Just real world experience, sorry, not a lab rat. |
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« Last Edit: August 04, 2019, 06:08:14 AM by prj »
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nyet
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« Reply #71 on: August 04, 2019, 10:13:37 AM »
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insufficient advance specifically will melt the pistons long before anything else happens to the engine, the manifold or the turbocharger.
Are you saying excessive retard from KR can melt pistons? Sorry, not sure I follow  |
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prj
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« Reply #72 on: August 04, 2019, 10:25:13 AM »
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Are you saying excessive retard from KR can melt pistons? Sorry, not sure I follow It doesn't matter if it's from KR or from the base map not running enough timing. If you get ignition timing low enough and the boost high enough for a prolonged period of time you will either melt the piston or an exhaust valve/seat. |
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« Last Edit: August 04, 2019, 10:26:47 AM by prj »
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GolfSportWagen
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« Reply #73 on: August 06, 2019, 01:56:47 PM »
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So tell me mr. expert, how much timing does a STOCK EA888 run up top in a Golf R? or how about an Audi S1?
Your numbers do not match up in the slightest. Because if they did, we'd have all STOCK EA888 cars tuned by VAG with massive turbine damage and cracked heads. This is not the case.
Also you do realize that head design significantly affects burn speed, and your numbers for some cases are past MBT, right?
Perhaps you should write to Audi that they don't know anything about designing and tuning an engine - no need to argue with me.
Other than that, you're stating the obvious. As for EGR - it slows combustion, of course you can add more advance, but there is no point on WOT, and there is not a single VAG turbocharged performance engine with EGR (apart from TDI).
As for my personal testing, I have had plenty a car with 2-3 EGT locations, yes I personally own a steady state dyno. EGT has always without fail been lower the further you get from the port for me.
I don't try things like running 5 degrees on top with 2000mbar boost on a slow burn head design though.
As I said before - on any VAG engine (from the old 2.2T on through the EA888 last gen designs), insufficient advance specifically will melt the pistons long before anything else happens to the engine, the manifold or the turbocharger.
If you get the advance really low, the exhaust valve seats will fail and then the valve will melt through, and the cylinder will lose compression. It will do that within 1 VMAX run.
But you will never ever crack the manifold or damage the turbocharger with heat before this happens, unless running ATDC ignition angle for antilag, and even then the manifold and turbo will hold up for 1-2 rallies, if not more. Just real world experience, sorry, not a lab rat.
As I suggested since your data does not agree with my experience or that of the car companies who I have worked for as a contractor, instead of getting personal professionals submit white papers to the SAE for peer review. I'd like to see why your results differ from everyone elses'. |
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prj
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« Reply #74 on: August 07, 2019, 12:56:40 PM »
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As I suggested since your data does not agree with my experience or that of the car companies who I have worked for as a contractor, instead of getting personal professionals submit white papers to the SAE for peer review. I'd like to see why your results differ from everyone elses'.
You are not "everyone else", you are just another no one on a forum. It is also clear you have never worked on an EA888 engine before. As I said - go argue with Audi if you like. I didn't tune those engines at the factory with ignition angles that according to you are supposed to blow them up  |
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