Using EGT as a timing adjustment aid?

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anarchyx34
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Using EGT as a timing adjustment aid?

Post by anarchyx34 »

I was wondering, since EGT temp is somewhat proportional to ignition timing, would it be possible to use it as an aid when making a spark table? Tuning a fuel table is relatively easy because you have feedback via a WBO2, but where's your feedback when adjusting ignition? As of now I'm running what I think may be a fairly conservative ignition map, but I'm not sure how far I can go. I'm afraid that I wont hear detonation at high-load/rpms due to the exhaust/engine noise, and I havent properly adjusted my KnocksenseMS module.
'94 Miata. MSPNP with MS2 extra.
'96 BMW 328i.
fiat132
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Post by fiat132 »

i asked a question close to yours a while back but i got no answer.... :(
Jim
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Post by Jim »

The ideal Timing for any engine , if it was practical , is what is called
"Incipient Knock" , this means being right on the edge of Detonation .
This will produce the best efficiancy in both power and economy .
However , it is a very dangerous thin line , and once you find this line
you need to back off of it by at least 3 degrees , 5 would be safer ,
detonation will destroy your engine .

You can use EGT to verify other measurements and make sure that you
don't melt your engine , but it doesn't always change in exact proportion
to timing and can go higher if the Timing is too advanced , it will also go
higher if your Timing is too retarded .

Without absurdly expensive test equipment ,
probably the best way to find your ideal timing is by using "regular" gas
and installing a Knock Sensor that is attached to a small amplifier that
powers a set of headphones that you wear while driving .
(be carefull this is illeagal in most States)
The headphones should be the type that seal around your ears ,
these are harder to find now but they are still availible , if you have
plenty of cash the "Bose" Noise Cancelling Headphones are the way to go.

When you get this setup working you should be able to hear almost
everything going on inside your engine , including Detonation or "Knock"
VERY obviously . It's much easier for your ears to tune out all the other
engine noises than it is to design an electronic filter that singles out the
sounds of detonation and then triggers another curcuit .

Keep advancing your entire Advance table by doing a Table Transform
and "shifting" your whole table up about 3 degrees at a time until you
get your engine to knock at Wide Open Throttle WFO ,
start at low rpm and work your way up ,
this is dangerous business for your engine ,
when you hear Detonation back off imeadiately and let your engine
recover for at least 15 or 20 seconds .
Take note of the rpm and kPa , (kPa should be close to 100)
back off the timing 2 degrees in that bin and try again until the engine
will not knock at that particular rpm and kPa bin ,
once you get all of your 100 kPa bins done you need to reduce every
100kPa bin by 3 to 5 degrees ,
now you can move down to the 90 and 80 kPa rows ,
below 80kPa you may not be able to get your engine to Knock ,
in that case you need to progressively add a total of appox. 60% of
the new timing figure at 100kPa , in that particular rpm column ,
to the 20kPa bin .

Example:
3000rpm , 100kPa ,
ideal timing = 30 degrees ,
30 x .6 = 18 degrees ,
30 degrees plus 18 degrees = 48 degrees at 20kPa and 3000rpm ,
the bins between 20 and 80kPa should have progressively less
advance added , 2 or 3 degrees less per bin as pressure goes up .
The 3000rpm column would then look like this :
30 100kPa
32 90kPa
35 80kPa
38 70kPa
40 60kPa
42 50kPa
44 40kPa
46 30kPa
48 20kPa

Keep going until every column is done .

On a different note ....
There is a technology that , when it works , is the perfect set up ,
I've forgotten what it's called but it works this way :

Your ignition system or spark plugs have to be modified so that a
special curcuit can be added that will sense the resistance across the
spark plug gap , this resistance figure is put into a computer at very high speed ,
the computer uses the resistance measurement to calculate
how many degrees after Top Dead Center the PRESSURE in the cylinder
reaches it's peak and then starts to fall off again .

With most engines the Peak Cylinder Pressure needs to occur at approx.
14 degrees After Top Dead Center .

Much earlier than this and the engine will Knock and self destruct ,
much later than this and your power and economy goes
right out the tailpipe , BOTH conditions raise EGTs .

From researching this I've come up with a rule of thumb that can get
you close when running Boost , decrease your timing from the
ideal 100kPa figures by....
1 degree for every 8% increase in VE over 100 kPa .
Example :
110kPa subtract 1.25 degrees
120kPa subtract 2.5 degrees
130kPa subtract 3.75 degrees
140kPa subtract 5.0 degrees

Of course if you use other methods to cool the combustion temps this
"could be" too much timing reduction ,
with acurate Alcohol Injection no timing retard is usually nessesary .
fiat132
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Post by fiat132 »

i once read that during detonation...the egt actually drops....i dont know why but the article stated that alot of people destroyed their engines because they thought their engines were fine with the lower egts while in fact it was detonating
zguy36
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Post by zguy36 »

EGT is proportional to timing because it dictates when the cylinder fires and also on the efficiency of the firing. A more retarded timing will postpone the burn resulting in still burning gasses exiting the exhaust. This also raises coolant temps because more cylinder wall is exposed to flame.
Jim
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Post by Jim »

To zguy36 :
I think you've been misinformed .

Exhaust Gas Temperature does not "dictate" anything .

It is simply an indicator of what is PROBABLY happening inside the engine .

Many other factors have to be considered when trying to make a
determination as to exactly what caused a change in EGTs .

There are NO professional engine builders or racers that set thier
ignition timing by observing the EGTs .

If this was practical at all ,
car manufacturers would have had them installed on every car made ,
instead of Knock Sensors .

Thermocouples are relatively cheap when compared to Knock Sensors ,
and they are much easier to interface to a computer .

If it was that simple , some big Performance Parts manufacturer would
have a DIY kit out , and would be bragging on all the advantages .

If EGTs were that important , O2 manufacturers would be
selling Oxygen Sensors that also had an extra output for EGT .

Combustion efficiency is determined BEFORE a particular EGT is generated .
EGT can be an indicator of combustion efficiency ,
but it is not the only indicator , and it is not the only determining factor .

To fiat132 :
What you read was correct , EGTs go down when the engine
Detonates , all of the energy goes into the block , heads and
piston crowns , almost instantly ,
there is not much energy left over to push the piston down and the
pistons start to melt almost immediately .

There is no "Magic EGT" number that indicates that everything is perfect .
fiat132
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Post by fiat132 »

i guess it makes sense.....
when the engine detonates....the thin layer of gases closest to the cylinders breaks up...these are the coolest gases...so now there is a cool cylinder wall exposed to the hot gases....ready to absorb some heat up...i guess thats what causes the egts to drop
Jim
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Post by Jim »

Most of what causes the EGTs to drop during detonation is the fact that
the entire mixture is converted to a different form of energy in an extremely
short period of time , in the range of 20 degrees of crank rotation ,
right when the crank is at TDC
making it impossible to move the piston down to relieve the pressure build up.

With normal combustion the mixture is still burning for over 360 degrees of
crank rotation (at high rpm) , if you were to remove your exhaust pipes
from your exhaust manifolds and look at the manifolds while running
full throttle at 3000rpm you would see flames shooting out of the manifolds ,
this is because the mixture is still burning even after the full power stroke and the full exhaust stroke .
Monotalonawd
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Post by Monotalonawd »

Really interesting stuff here! :D I'm taking notes!
88 BMW 535i, Holset turbo project
90 Eagle Talon TSi Turbo Awd
92 Eagle Talon Tsi Turbo Awd (sold)
Ken
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Using EGT as a timing adjustment aid?

Post by Ken »

Yes me too.
In fact I have been doing a lot of EGT recording lately and am seeing
examples of some of what Jim has talked about. With the probes that I
have the EGT is quite sluggish and takes at least 20 seconds to
stabilize after something is changed. And it is not very sensitive to
small timing changes.
Ken

Monotalonawd wrote:

> Really interesting stuff here! Very Happy I'm taking notes!
>


Posted by email.
fiat132
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Post by fiat132 »

i dont understand...if the mixture burns....heats up...expands.... then why would it be impossible for the piston to move down...thats how engines operate...the burning moves the piston down. designers always try to make the peak pressure occur at 12-15 degrees crankshaft
the mixture cant be burning over 360 degrees of rotation because then it wont turn over easily and it would increase whats called the pumping losses...that would also cause extreme thermal stresses on the pistons...the flames you see shooting out the ports are the unburned hydrocarbons....just like the flames that come out of the exhaust pipes of cars that had their mixtures enriched...if the mixture was still buring during the exhaust stroke then that would induce huge torsional stresses on the mechanical parts...
detonation is a phenomenon that occurs to the end gases only....not the entire mixture...
jakobsladderz
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Post by jakobsladderz »

The whole of this discussion is based on some interellated physical phenomena that go on simultaneously inside the engine..
The main one is that the pressure, temperature and volume of the air are related, such that for the same molar quantity of gas (same number of molecules), if say the temp goes down, either the pressure has been decreased or the volume has decreased.
At the top of the stroke when the spark plug fires, the mixture is quite compressed. if all of the combustion takes place soon, much of the energy is used pushing the piston down in the cylinder. if it takes place later (less advance) less of the heat is used to push on the piston and more is released as exhaust heat. The burning in the exhaust stroke thing is a nonissue because the exhaust valve is open, sure pumping loses may increase but they are small in comparison to the main explosion..
Detonation is where part or all of the fuel-air load get to a pressure where they ignite spontaneously. The flame front moves at the speed of sound through the rest of the mixture and all of the energy is released, often before the cylinder even reaches TDC.. Because the fuel is completely burned very early, there is much more time for the heat to transfer to the pistons, cylinder wall and whatever else. In normal combustion the coldness of the cumbustion chamber wall is enough to quench the fuel burn and hence ensure a layer of cooler air over the same. Because of the violence of the explosion, the turbulence is able to clear the colder layer of air from the surface and really get the heat in well..
The upshot is that when the engine pings/knocks, there is lots of heat in the combustion zone exactly when there is a large heat difference between the burning mixture and the cyl walls, causing much greater heat transfer. It is this that melts holes in pistons (and the shock that breaks rings).

Temp measurement is good for getting mixture right, aim for ~950C at WOT on an NA engine for ~max power (so long as timing is adjusted correctly). As has been mentioned, the temp will reduce as advance is increased as more heat is turned to mechanical energy, but drops of more when knocking begins, so sounds risky/questionable as a timing aid.
Exeter: (noun) the nut or bolt always left over after putting something back together (Douglas Adams, The meaning of Liff)
fiat132
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Post by fiat132 »

detonation is the ignition of the END GASES....not the entire mixture
the burning of entire mixtures happens when PREIGNITION occurs....
thats the defdifniton of detonation in combustion books...
the spoontaneous burning of end gases due to heat radiated by the flame and from the heat caused by the heat of compression
the whole idea of turbocharging....cams...porting and all of that is to reduce pumping losses..it is work done by the engine...ie..a loss to the user...designers try to decrease it as much as possible....having any extra losses due to burning in exhausts in a definite no no
what you mentioned about a mixture burning before the piston reaches tdc is called pre ignition...because as the definiton of detonation states
its the sponatneous detoantion of the END GASES....end as the ones at the end of the flame front
when the mixture burns during the comppression stroke....pre ignition...the heat is tremendous....the heat of compression + heat of combustion...thats what causes holes in pistons...detonationh is much milder that pre ignition...engines can tolerate some detonation but not as much pre ignition...
egts drop on detonation because the boundary layer covering the cylinder walls gets displaced by the violent turbulence caused by the shock waves from the wave fronts colliding which exposes relatively cooler walls...and as its known the greater the temperature differnce the greater the heat transfer....hence more heat is lost by the gases to the walls and the exhaust is cooler
where did my diagrams go ????? :( :? :( :?
fiat132
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Post by fiat132 »

if you boost an engine and the inlet temperature rises then the temperatures of the whole cycle increases...so every time you raise the inlet temps expect a rise in egts
fiat132
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Post by fiat132 »

a note to the guy with the talon...monotalonawd...if that turbo from a diesel engine then it wont last long...since diesel engines run cooler egts, the turbines made for them are made from different materials that wont last as much....
i have been through 2 turbos in the past 18 months....the materials are differnt...just thought i should mention it
rb26dett
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ion sensing

Post by rb26dett »

Jim,

the technology that you couldnt remember the name of is called ion sensing. still havent got to the bottom of exactly how it works, but thats what its called.

anarchy : hi from fredio54

fred.
Jim
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Post by Jim »

To : fiat132

I see you've been doing some reading , good for you !

I also see that some terms need further explaination so , here goes .

"END GASES"
means any fuel/air mixture not in the immediate vicinity of the spark plug ,
(or a hot spot in the combustion chamber in the case of Pre-Ignition) .
"End Gases" are also defined as the gases that will be ignited last in the combustion cycle .
They are also defined as the gases that are trapped in crevasses where they can't be ignited ,
like between the piston and cylinder wall and the top piston ring .

Detonation

Here is the sequence of events when detonation occurs :

The spark plug has STARTED the mixture burning in a relatively slow and controlled manner ,
and is forming a "flame front" or a "ball" or a "kernel" that is progressively growing
larger and larger , away from the spark plug , in all directions .
This "flame front" is still small at this point , it has probably only ignited 1/8th of the mixture .
This is happening as the piston is still approaching TDC .
The pressure , and the heat , and the speed of the "flame front" are all
increasing more and more as the piston gets closer to TDC .
This process may increase to the point where
ALL of the remaining fuel and air , (the "END GASES") ,
spontainiously EXPLODE like a stick of dynamite .
This usually occurs anywhere between 5 and zero degrees before TDC ,
meaning that the piston is still moving up in the cylinder , making things worse .

Detonation can be a very mild , almost undetectable , tinkleling sound called "Trace Ping" ,
or it can go all the way to smashing pistons and bending rods and
breaking crankshafts and cracking cylinders .

"Pre-Ignition"
Just like the name says , it is ignition of the fuel , BEFORE THE SPARK PLUG FIRES .
It is exactly the same thing the spark plug does ,
only instead of a spark , the mixture is started burning with heat from a
sharp metal corner or from a wrong heat range sparkplug or
from carbon deposits that have gotten hot enough to get glowing red hot .

The effects of Pre-Ignition are EXACTLY THE SAME as too much ignition timing advance .

Pre-Ignition , may or may not cause DETONATION .

"Pre-Ignition" does NO damage alone ,
when Pre-Ignition CAUSES DETONATION the detonation can cause engine damage .

Model Airplane Engines run in "Pre-Ignition mode" at all times , they don't have a "spark plug" .

Your engine could occasionally be running in "Pre-Igniton" mode with NO noticeable problems .

There are even "some" circumstances where Pre-Ignition can actually make
your engine run BETTER (but probably not , because it is not controlled) .


Some explanations of Pre-Ignition explain it like this :
A "Hot Spot" in the combustion chamber starts a "Flame Front" ,
somewhere around the same time the spark plug starts a "Flame Front" ,
then these two "Fame Fronts" collide into each other causing DETONATION .

This is obviously an incorrect explanation , here's why :
Ford and Nissan and maybe others have a 4cyl. engine with two spark plugs in each cylinder .
Mazda Rotary engines have two spark plugs for each rotor .
None one of these engines have any problem with "Flame Fronts Colliding" with each other .
They all run just fine .

Pumping Loses :
Pumping loses are equal to the amount of power it takes to make the engine pump "X" amount of air at "X" rpm .

Turbos and Superchargers both INCREASE pumping loses , but they also increase the total output power .

Turbos and Superchargers both decrease the efficiency of an engine .

the whole idea of turbocharging....cams...porting and all of that is to reduce pumping losses..
Incorrect , the reason for those things is to get more Oxygen into the cylinders .
having any extra losses due to burning in exhausts in a definite no no
Just about every gasoline engine ever made will shoot flames out of
the exhaust port if you remove the exhaust manifold , even your lawn mower .
(try it at night with your lawn mower , you can see the flames much better in the dark)
This flame has been burning for 180degrees of crank rotation AFTER the power stroke was completed .
This is not something you can engineer-out of the engine , it's just a fact of life .
'95 GM 4.3 Vortec V-6
Single Plane Intake w/ported GM Throttle Body
Ported Heads , stock roller cam retarded 8 degrees
MS-II 2.6 , V-3 board , MT 3.0
EDIS ignition , Innovate WB 02
250hp , 28mpg @60mph in a 2 ton wagon
Jim
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Post by Jim »

To : jakobsladderz

I stopped looking into EGTs early in my learning curve , (mid '70s) ,
and my interest has been peaked again in these MS Forums .

Could you possibly provide a link to more info ?
Like where you found the 950C number ?

Thanks in advance .
Jim
'95 GM 4.3 Vortec V-6
Single Plane Intake w/ported GM Throttle Body
Ported Heads , stock roller cam retarded 8 degrees
MS-II 2.6 , V-3 board , MT 3.0
EDIS ignition , Innovate WB 02
250hp , 28mpg @60mph in a 2 ton wagon
fiat132
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Post by fiat132 »

to jim
i am really impressed...i think youve put what i wanted to say in much better words than i could have.. :D
i dont agree with all the stuff but thats ok
if you were to take out a combustion book and search for P-V DIAGRAM then you would find an area called a pumping loop.this area is considered as work done by the engine on the mixture....the boundaries of this area are the exhaust pressure and the intake pressure....
asyou would already know,that the area between the pressure lines are the work done by the engine...turbocharging works on getting these 2 lines as close to each other as possible...therefore minimizing the pumping loop...it gets really better when the area is actually considered POSITIVE work, thats when the intake pressure is higher than the exhaust pressure...thats how F1 turbo engines of the 80s got outrageous outputs
i have to say that i am impressed at the level of knowledge that you have....good for an engineering degree... :D :D
pumping losses are a function of gas velocities and areas...
losses=FL(V^2)/D2G..... as the diameter of the ports increase, the speed of the gases decrease...the lossed decrease...thats what porting...cams and so on do..in a way or another
as for effieciency...which one are you talking about?
thanks for the reply...it was beautifully written...better than i could have explained...for ages :D :D
i totally agree with you that turbo increase the pumping losses...at a certain rpm range though...thats why the enginess are so dead off boost, after all a turbine is an exhaust restriction and raises exhaust pressure
but i cant see supercharger adding to the pumping losses..could you explain that one please...
what i meant by buring in theexhaust was burning on the exhaust stroke which would tremendously increase the exhaust pressure....increasing the pumping losses in turn...dont you agree???
if you reduce pumping losss then you are able to get more oxygen in the cylinders...they are related
thanks for the reply
fiat132
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Post by fiat132 »

i just took a look at the quench link you gave a while back...nice stuff :D :D
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