Advanced Engineering Tech - Ping, detonation vs. engine load, GenIII motors

Since this is an advanced performance discussion, I would like to start a thread on the search for fuel economy while maintaining performance.

I would like to understand better why an internal combustion engine operates most efficiently at the verge of detonation.

Not sure I'd agree that an engine is most efficient on the verge of detonation, I'd think it's most efficient at highway speed turning around 2000 rpm (V8)...very little hp being used to sustain a steady speed. Maybe more power output when close to detonation?

In any case the contributing factors that lead to detonation are high combustion chamber temps, low octane fuel, overadvanced timing, carbon deposits/build up, high compression and a lean mixture.

What actually causes the detonation is too high of a pressure in the chamber; in a normal ignition event the flame front travels from the plug evenly across the piston at about 5000 ft per second, when detonation occurs the rate of burn climbs to around 20000 ft per second...way too fast for the piston to get out of the way...the resulting pinging is the pressure waves bouncing off of the piston, cylinder and valves....not good...kinda like lighting off a stick of dynomite in there; the engine wasn't designed to withstand those types of pressures for very long.

So as you can likely surmise; higher pressure = faster piston movement, but get it too high and lose power through detonation.

I'm sure I did not include all causes and scenarios, this is just a brief explanation.

Well Big_Brother, Desert Dog is acutally correct. Engines are most efficient right before they detonate. And the reason for that in short is b.c. they are so lean. And we all know that leaning out a car nets you performance gains. But there is a fine line between performance gains and big problems. If anyone here has blown and engine they will tell you that it was running at it's best RIGHT before it blew.

N/A engines typically have 80-85% Volumetric Efficiency. With a leaned out engine the percentage will rise causing great performance gains but severe damage to the enigine. There are however other ways to increase an engines VE while retaining it's drivibility and reliability while still getting the performance. Forced Induction! Supercharged engines usually have about a 100% VE, where a Turbo can have 110%+.

Hey desert dog, the best way to keep your MPG up as well as HP/TQ is through a great tune. Making use of every bit of air and fuel that enters your combustion chamber.

I understand what you're both getting at, I was trying to say that "efficient" is not wot acceleration, max efficiency and max power are not the same thing in my opinion.

At a steady 2000 rpm (an arbitrary figure, I'm using for an example) the engine will not be consuming much fuel and moving an almost 2 ton weight at around 80 mph (yes, gearing plays role, just an example here), and the combustion cycle will not be on the verge of detonation with a low load situation such as that. To me this scenario more accurately defines the term efficient.

Accelerating hard with each cylinder on the verge of detonation may be the fastest way to attain speed, but I'd hardly call it efficient.

I thought I stated that max piston speed is derived from maximum pressure, without detonation.

I'm not saying your wrong, just saying your measuring LOAD on an engine. He wanted efficiency of an engine which is measured in VE and RPM is not a factor. B/s the scenario you are describing is the best way to get better gas mileage, not measure efficiency.

BTW, detonation can happen at idle. Not just WOT, the severity of it is the variable.

heres some great reading on the subject
j-rods timing thread (http://www.ls1tech.com/forums/showthread.php?t=254868) :)

What measure of 'efficiency' are you talking/concerned about? i.e. How well the engine uses air (BSAC), fuel (BSFC), how well it converts the combustion process into power, etc.? There are different measures of efficiency.

The engine is not necessarily 'more efficient' with a leaner AFR, but it is certainly using less fuel per part of air. This is possible to do when cruising when there is low load on the engine. Fuel injected cars can run much leaner than 14.7:1 with no problems as long as the load remains low. You will have to keep adding timing to allow sufficient time to burn the mixture, but your MPG will definitely increase. If you have a tuning tool, just try to see how lean you can make your car at idle. You will be amazed. Don't worry about melting a piston. It is pretty hard to do with no load. :)

What I mean by efficiency...

I have been reading again... :drive:

I have been learning a lot about the GM electronic control systems, and I picked this blurb up that the PCM will, if conditions are right, adjust to just "see" where and what other sensors are doing when the ping happens, and back off slightly...

This set off all kinds of bells in my head.

N/A engines typically have 80-85% Volumetric Efficiency. With a leaned out engine the percentage will rise causing great performance gains but severe damage to the enigine. There are however other ways to increase an engines VE while retaining it's drivibility and reliability while still getting the performance. Forced Induction! Supercharged engines usually have about a 100% VE, where a Turbo can have 110%+.

You are absolutely 100% wrong and need to learn what the definition of VE actually is. If you put a turbo onto an engine, the VE actually goes down slightly because of the restriction in the exhaust.

As for NA engines, Pro-Stock and F1 cars are 2 examples of engines we see all the time that are over 100%...by a lot.

More power per displacement isn't always higher VE. VE is essentially the mass of air and fuel in the chamber when the intake stroke has finished and the valve has closed, compared to the mass of air and fuel that would fill a cylinder of the same volume as the total swept volume (don't include the chamber) of that cylinder in the engine at the same pressure that the intake manifold is at during that specific time that you are chosing to measure VE. Thats why a turbo on the same engine isn't higher VE, and is in fact slightly lower. There's more air/fuel mass in the cylinder, but there's higher pressure in the intake manifold, and the cylinder isn't getting as high a % of it out of the chamber as it would without a turbo because of the fact that the turbine poses a restriction and thus on the next cycle of that cylinder, there are old spent exhaust gases still in there taking up room preventing the engine from inhaling as high a % of air/fuel from the intake manifold (based on intake pressure) as it would have without the turbine there.

It can be an extremely difficult concept to grasp and reading my expalanation of it might not explain it to you as it's difficult for me personally to word it.

And I'm not entirely sure if it's the mass of air and fuel, or just air. I would think on a carbureted engine it'd be air and fuel mixed as thats whats in the entire intake manifold, but on an injected engine it'd be just the mass of the air.

DEF- Volumetric Effficiency indicates the total amount of air/fuel mixture each cylinder takes in during the intake stroke. Overall VE can be calculated by applying the formula: VE= 2 x mass airflow rate/ air density x swept volume x rpm. High performance engine builders improve VE by optimizing exhaust scavenging and by taking advantage of inertia.

I'm not saying your wrong, just saying your measuring LOAD on an engine. He wanted efficiency of an engine which is measured in VE and RPM is not a factor. B/s the scenario you are describing is the best way to get better gas mileage, not measure efficiency.

BTW, detonation can happen at idle. Not just WOT, the severity of it is the variable.


Well the title of the thread is Ping, detonation vs engine load, GenIII motors

I also stated that I gave a brief explanation of detonation, I didn't really feel the need to point out that detonation could technically happen at idle as it is a highly unlikely scenario, unless Cooter is tuning the engine.
I don't have the time to write a thesis on the subject.

Mike454SS, well I brushed up on the subject. The actual amount of air the engine ingests compared to the theoretical maximum is called volumetric efficiency (VE). If a turbo/supercharger puts in more air then the displacement of the engine, that alone supports my statement. So with that being said a supercharger or turbo WOULD in fact give a higher VE. Were my percentages excatly correct no, does that really matter? I dont agree that F1 cars would be a good example b.c. of their supperior engines and design.

Big_Brother you are excatly correct about the detonation, i just added my .02c. As for the engine efficiency I beleive we are on two different pages and are not speaking about the same thing.

I would like to understand better why an internal combustion engine operates most efficiently at the verge of detonation.
I didn't beleive that your scenario addressed the question at hand.

Since this is an advanced performance discussion...

Not yet it isn't.

Engines perform best as they near *pre-ignition*, not detonation. There is a huge difference.

Originally Posted by Desert Dog, Since this is an advanced performance discussion...

Not yet it isn't.



:werd:

You are absolutely 100% wrong and need to learn what the definition of VE actually is. If you put a turbo onto an engine, the VE actually goes down slightly because of the restriction in the exhaust.

As for NA engines, Pro-Stock and F1 cars are 2 examples of engines we see all the time that are over 100%...by a lot.

More power per displacement isn't always higher VE.



First off, please learn about what you are saying before you call someone wrong. James O was far closer to the correct answer than you my friend. If a turbo had a lower VE there would be ABSOLUTELY NO REASON TO HAVE IT! The WHOLE POINT to forced induction is the increase in VE!!!!!! Any time you increase the pressure in the intake manifold of an engine you will be increasing VE. Yes, turbos and superchargers get well over 100% ve but how much over depends on a variety of factors.

And the best NA engines only get slightly over 100% (not by alot) due to tuning the intake and exhaust runner lengths to match the pressure pulses which allows the inertia of the air to increase the cylinder filling.

And if all other factors were equal a higher VE with the same AFR would DEFINATELY produce more power. More air + MORE FUEL = more power.

Volumetric efficiency is the measurement of how close the actual volumetric flow rate is to the theoretical volumetric flow rate. If you bolt a turbo onto the engine the theroetical flow rate will increase due to positive manifold pressure, however the engine's actual flow rate will not increase as much as you are now trying to push a larger amount (mass) of air through the same size ports and valves as well as the increased amount of exhaust resriction. Turbocharging may create a more efficient engine but it will not make an engine more volumetrically efficient. BTW, this is the lamest thread in this section... For starters, I want a reliable source that states that an engine runs most efficiently at the verge of detonation (horsepower or fuel consumption rise). That statement is totally false as a blanket statement, AFIK. It sounds similar to the crap about "advance the timing until it pings, then back it off a few degrees for best power". If that uneducated hick tale is what this thread is based on, the thread should get removed from this section.

Turbocharging may create a more efficient engine but it will not make an engine more volumetrically efficient.

Like i told the previous gentlemen, please read up on the subject prior to posting false information. I would like to keep people informed and not have them belive those statements as fact.

"Idealy, a mass of air equal to the density of atmospheric air time the displacement volume of the cylinder should be ingested for each cycle" (Engineering fundamentals of the internal combustion engine, Plukrabek Pg. 69)
VE is based off of displacement volume of the engine and air density evaluated at atmospheric conditions outside the engine

This means the Physical built in piston bore and stroke and atmosphic conditions are the basis for all VE measurements.

I think what he (EdmontonSS) is trying to state is:

Motor 'A' can fill a cylinder to 85% naturally aspirated.

Motor 'B' can fill a cylinder to 105% with boost @ 15 PSI.

As a relative figure, the 15 PSI boost required to make the 20% increase
is not efficient in comparison.

Nonetheless, torque has risen across the board, therefore VE has improved.

"Idealy, a mass of air equal to the density of atmospheric air time the displacement volume of the cylinder should be ingested for each cycle" (Engineering fundamentals of the internal combustion engine, Plukrabek Pg. 69)


So which is it, mass or volume? I don't like that definition because he's saying mass and you're talking about volumetric efficiency. I guess the real question you guys are arguing about is whether ve is the percentage of volume that enters the cylinder at standard atmospheric conditions or at intake manifold actual conditions. (BTW, our VE tables are set up the second way) A turbocharged engine may fill the cylinder less efficiently volume wise, but since the air is more dense it fills it with a greater mass of air.

Also maybe this ve definition stuff should be in a new thread.

Funny, but the original poster didn't ask anything about volumetric efficiency.

He was asking about fuel economy, which, unless we're talking Nextel Cup fuel economy, is usually achieved at part throttle, which absolutely kills volumetric efficiency. So it really doesn't matter how we define VE.

Given the arguments over VE, I think it would be good to have a thread that explains VE properly. But that should be another thread.


I would certainly be interested in this thread actually addressing fuel economy (like the poster asked) and what conditions are favorable for high fuel economy. Ideal lean mix, timing, pre-ignition, detonation, high EGR rates, water injection, etc. What makes for the best fuel economy (besides less vehicle weight / aerodynamic drag / rolling drag / engine displacement)?

'JustDreamin'

When I tune my car for cruise I tend to pump the timing up pretty far. I logged timing recently around 36-38 with IAT's ~50* no KR. This gives the car a punchy feel in higher gears (4th & 5th) which allows you to cruise without bogging. I don't have EGR since my car came with a LS6 intake, but EGR does help fuel economy by cooling down the cumbustion chamber and keeping pre-ignition at bay. I don't run lean cruise.

The original question of operating most efficiently at the verge of pre-ignition is easily answered by understanding that the point of optimal efficiency (where the temperature and timing creates the most complete burn i.e. power) is a degree or two before pre-ignition. If the timing is too far retarded the mixture won't burn as complete resulting in less power and higher combustion temperatures and possibly more pre-ignition. It's a balance between temperature (resulting from compression ratio), timing, fuel mixture, etc. You want the most heat from the power stroke but the least heat during the other three.

You want max pressure at 14 ATDC as per J-Rods thread (not heat), the thread which I think is a good start for some of us.

On the economy side, guys in Oz where the holdens run lean cruise say the stock AFR of 16+ isnt good as you need more throttle to maintain speed. An AFR or around 15.4:1 at part throttle, low load gives best economy. I agree timing will be in the early to mid 30's at this point based on most of the maps I have seen for lean cruise. I guess you could lean up the idle and drop the rpm's as well. Leaner is ok for economy and power, but bad for the engine due to heat and extra risk of ignition issues.

Since pressure is directly proportionate to heat, there is a correlation. Static compression ratios do not change within the engine, but temperature does. Since temperature is a variable, it affects the combustion pressure. That's why your car might not ping at 50*F but does at 90*.

The earlier you start the burn, the more time it will be
contributing energy to the crank. The delivered work
is the integral of pressure(t)*piston_area*
sin(rod:crank_angle(t)) or something like that,
which is a messy thing, but anyway earlier is better,
to a point. So early that you fight the end of the
compression stroke substantially, costs you (and is
the best way to get detonation, spark against a
rising instead of falling cylinder pressure). You don't
want a bunch of extra cylinder pressure left at BDC,
you want to have taken all the heat out as expansion
which means you want it to have started off as
compressed as practical.

Lean for economy and rich for power both are playing
off efficiency against shortage. For some distance from
stoich, you can improve power by enriching because
you gain more from burning more fuel inefficiently, than
from burning airflow-limited fuel more efficiently. Airflow
I think is the deal. Similarly on the economy side you
can use less fuel, burning fuel-starved with some lower
efficiency than burning the "correct" amount. Eventually
on either side efficiency starts to go down faster than
the benefit of more/less goes up. Competing mechanisms
produce a rich and a lean optimum (with some fairly flat
land about it; pic).

"Load" is correlated to the cylinder charge which means
the compressed cylinder pressure which drives the burn
speed of the charge. Low load, low pressure, slow burn
allows / wants more "lead timing" to get the pressure
peak after TDC. Same mixture, higher pressure, same
timing, detonation (burn before TDC).

First off, please learn about what you are saying before you call someone wrong. James O was far closer to the correct answer than you my friend. If a turbo had a lower VE there would be ABSOLUTELY NO REASON TO HAVE IT! The WHOLE POINT to forced induction is the increase in VE!!!!!! Any time you increase the pressure in the intake manifold of an engine you will be increasing VE. Yes, turbos and superchargers get well over 100% ve but how much over depends on a variety of factors.

:werd::werd::werd::werd::werd::werd::werd:



And the best NA engines only get slightly over 100% (not by alot) due to tuning the intake and exhaust runner lengths to match the pressure pulses which allows the inertia of the air to increase the cylinder filling.

I've got to play around some 135VE NA engines. mmmm sexxy. Isn't F1 creeping on 200?







Anyway this thread is a clusterfuck of erronious info (not in regard to dano).
Best (lowest) BSFC in a 2.0 liter 4 cylinder will come at about 1/2 throttle and 2700rpm or so. crazy, huh.


http://me.queensu.ca/courses/MECH435/2.%20Engine%20Performance.ppt

pg 26 or somewhere around there.

The "VE" definition debate has been added to here:
http://www.ls1tech.com/forums/showthread.php?t=419053
I'm not saying the VE calculated relative to atmosphere is "wrong" per-say, just that it's only one definition of VE from thousands, and probably the least useful for the purposes of most technical discussions.

max BSFC in a 2.0 liter 4 cylinder will come at about 1/2 throttle and 2700rpm or so. crazy, huh.


I'm trying to decode what you've written above....

BSFC (Brake Specific Fuel Consumption) is a measure of the fuel required per horsepower. Here a lower number is better. A lower number indicated that for a given amount of fuel you get more shaft horsepower out.

I saw 2 charts in that link.

1st chart said that BSFC goes down as engine displacement goes up, which makes sense. As displacement goes up, there is less surface area relative to the volume enclosed, which means there is less heat (in the burning air fuel charge) lost to the cylinder walls and is therefore available to produce useful work. So, bigger engines (assuming that you're not getting bigger strictly by adding cylinders) have the advantage.

2nd chart said that BSFC is lowest in about the middle of the rpm range and goes up as you get towards idle & redline. This makes sense for most production engines, which have camshafts that are probably the closest to ideal in the 2500 to 3000 rpm range. Above and below that rpm range, the camshaft is less than ideal, and the cost is increased BSFC (more fuel used per delivered hp).

'JustDreamin'

I'm trying to decode what you've written above....

BSFC (Brake Specific Fuel Consumption) is a measure of the fuel required per horsepower. Here a lower number is better. A lower number indicated that for a given amount of fuel you get more shaft horsepower out.

I saw 2 charts in that link.

1st chart said that BSFC goes down as engine displacement goes up, which makes sense. As displacement goes up, there is less surface area relative to the volume enclosed, which means there is less heat (in the burning air fuel charge) lost to the cylinder walls and is therefore available to produce useful work. So, bigger engines (assuming that you're not getting bigger strictly by adding cylinders) have the advantage.

2nd chart said that BSFC is lowest in about the middle of the rpm range and goes up as you get towards idle & redline. This makes sense for most production engines, which have camshafts that are probably the closest to ideal in the 2500 to 3000 rpm range. Above and below that rpm range, the camshaft is less than ideal, and the cost is increased BSFC (more fuel used per delivered hp).

'JustDreamin'

sorry, "Max" I meant "best." that is a bit misleading now that I look at it.

Lower is usually due to increased time for heat in the cylinder to be absorbed into the cylinder walls. Higher is due to friction.

Typically, unless its a radical cam- the cam plays little role as long as it is within an operating range. Its hp vs fuel usage. So it doesn't matter if you make less power, it just matters how efficient the engine is at that rpm.

Bore, stroke, compression, spark timing and rpm are much bigger factors.

The "VE" definition debate has been added to here:
http://www.ls1tech.com/forums/showthread.php?t=419053
I'm not saying the VE calculated relative to atmosphere is "wrong" per-say, just that it's only one definition of VE from thousands, and probably the least useful for the purposes of most technical discussions.


No, there is ONE definition of VE. It is not negotiable.

jesus...


by the way, there is no such thing as detonation in a motor only "Knock" Detonation is something that is completely impossible to happen in an internal combustion motor. They also discussed and confirmed this at the SAE convention prior to the PRI show...

I think Jesus might want to read this:

http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

Detonation, or knock, or whatever you want to call it...is the name given
to uncontrolled combustion which causes sudden spikes in pressure within
the chamber.

The 'knock' is the pinging that is picked up by a frequency sensitive sensor
which reports back to the computer.

I think Jesus might want to read this:

http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

Detonation, or knock, or whatever you want to call it...is the name given
to uncontrolled combustion which causes sudden spikes in pressure within
the chamber.

The 'knock' is the pinging that is picked up by a frequency sensitive sensor
which reports back to the computer.

What we all hear when our engines ping or knock is combustion taking place too soon but after the spark plug has fired. Not necessarily a second burn of end gases. If the mixture is fired off too soon and propagates before the piston reaches TDC it pings. That's why the PCM retards the timing. According to that article, we would call that detonation since the plug has fired but it isn't a second combustion of end gases so it doesn't quite fit their definition. I was taught that scenario fell under pre-ignition since combustion occurred too early even though the spark plug fired. A hot spot caused by a formation of carbon can do the same thing. Either way it's that scenarion that causes all the damage.

What we all hear when our engines ping or knock is combustion taking place too soon but after the spark plug has fired.

OK.

Not necessarily a second burn of end gases. If the mixture is fired off too soon and propagates before the piston reaches TDC it pings. That's why the PCM retards the timing. According to that article, we would call that detonation since the plug has fired but it isn't a second combustion of end gases so it doesn't quite fit their definition.


Are we reading the same article? What page did you find otherwise?


I was taught that scenario fell under pre-ignition since combustion occurred too early even though the spark plug fired.

I have a few books and charts that show detonation spikes which occur
after the plug fires and after TDC. I don't recall that link being any different.
The author specifically says deontation occurs after the spark and while the
piston is going downward.

Here are three other sources to confirm detonation occuring after TDC:


http://www.tfxengine.com/images/nitrouslatedetonation.gif

http://zhome.com/ZCMnL/PICS/detonation/crank.gif

http://www.avweb.com/newspics/pp43_detonation_medium.jpg

Are we reading the same article? What page did you find otherwise?



I was referring to this section...

Detonation
Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.

Pre-ignition
Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. The two are completely different and abnormal phenomenon.


Those statements do not include TDC as a qualifier. I agree with those statements and yours that detonation occurs after TDC, but the scenario that I describes happens after the plug fires but before TDC. What I am on the fence about is the terminology.

The article describes pre-ignition...

There is no very rapid pressure spike like with detonation. Instead, it is a tremendous amount of pressure which is present for a very long dwell time, i.e., the entire compression stroke.

...which would be true for the scenario we most commonly deal with (the one I described). The same reason a diesel pings.

So which is it, mass or volume?

It's mass, volume is limited to the displacement of the cylinder. Mass changes with density.

From what I've learned (some from EFI 101 basic & advanced, other from experience) there is a "sweet spot" where maximum controlled cylinder pressure is desired. This "sweet spot" is around 15 degrees past TDC which allows for the energy released in the power stroke to do the most work (think leverage). Much like pedaling a bicycle, less energy is wasted in trying to expand a volume that isn't ready to expand yet (like when firing at 12 and 6), but well-timed maximum cylinder pressure just after TDC is optimum. The "sweet spot" is the point where maximum (controllable, I'll address this later) cylinder pressure is desired in the cylinder, assuming that it does take time for the pressure to build (known average is about 100 ft/sec), attaining this means finding the correct moment to fire the spark (usually before TDC, and even sooner as RPM increases). This is why more efficient heads and engines generally require less timing than their less-efficient counterparts, a CC that allows a fast flame front doesn't need to begin that process so early in order to arrive get max pressure at the same point after TDC. Larger bores, lower compression, higher octane, etc. also generally require more timing.

As described earlier, detonation before the desired point in the crank revolution, whether caused by deposits, IAT, fuel, too much timing, etc. is undesirable because of the intense pressure spike created by the detonation itself, along with the fact that the mixture is trying to force a power stroke while still the engine is still on an intake stroke-- too much of this will take it's toll on everything that serves to seal a cylinder and soon enough, you'll find the weakest point. EFI 101 has some great intra-cylinder photography showing flame fronts at different crank angles and head designs, great to help conceptualize the mixture burning process.

All of this my take on the current topic-- thats it, feel free to comment.

Technical,

Pre-ignition occurs before the spark plug fires. The mixture ignites from hot
spots in the cylinder. The hot spots could be a glowing sliver of metal on the
edge of the cylinder head, or a very hot spark plug (wrong heat range), among others.

The mixture begins to burn/combust while the piston is moving upward (much
before the spark plug was to fire). The mixture expands in the volume created
by the piston rising toward TDC and the cylinder head chamber.

If the rate of expansion is faster than the piston is able to reach , or pass TDC,
the pressure created by the mixture will try to press the piston back down
(as the piston tries to move up).

This of course creates a huge loss of power due to counter active forces, and
it will present major damage to the mechanicals.

Detonation on the other hand may/could (?) occur before TDC, but since it happens
after the plug fires, the piston is able to get around TDC and begin moving down before
the mixture presents damaging opposing pressure on the piston crown.

Just think that the mixture takes time to react and begin to combust; also
keep in mind that the piston is moving at great speeds. The time intervals are
measured in milliseconds.

So by definition, what YOU are talking about cannot be pre-ignition because
it is happening after the spark plug fires.

The same reason a diesel pings.

I've studied diesel technology in short bursts. I can tell you that diesel ignition
has nothing to do with ping. It uses extremely high compression and high
pressure injection systems to present an air/fuel mixture into the chamber at the point when compression can cause ignition through heat.

Do you guys always argue like this? You’re worse than my project engineers…..

You are all saying basically the same thing, but including variables that apply to both sides of this argument. It would appear to an outsider that you are simply thinking too hard. In other words, you’re acting like engineers.

I’ve always understood it like this, in very simple terminology.

Detonation: An Erratic form of auto-ignition caused by excessive heat and cylinder pressure. Instead of a single point of ignition (plug), there are several ignitions sources created multiple flame fronts typical to spontaneous combustion. These multiple flame fronts collide creating an explosive peak in cylinder pressure (shock waves). These peaks are what you hear as a metallic pinging. Detonation can occur prior to, or after the plug has fired depending on cylinder pressure and heat. Diesel engines use detonation as a means of continued cylinder firing after the initial firing via glow plugs, which is then controlled by injector timing relative to piston position. Retarding the cam and using higher octain fuel have always eliminated this for me. Or, more overlap.

Pre-ignition: Another form of auto-ignition, but occurs when cylinder pressure and heat create a ‘hot spot’ that acts like an ignition source and ignites the air/fuel mixture prior to the ignition spark. – Hence the “pre” part of pre-ignition. Pre-ignition generally occurs prior to the piston reaching TDC which is why it is much more damaging than detonation. Causes of pre-ignition can include; A bur on a valve or valve relief, too hot of a plug, carbon deposits. I was taught to reduce the chances of pre-ignition during assembly by polishing everything in the combustion chamber and rounding off all sharp edges that could become sources of ignition.

Maybe I’ve been wrong all these years??? Damn, hope not…..

Technical said: "What we all hear when our engines ping or knock is combustion taking place too soon but after the spark plug has fired. Not necessarily a second burn of end gases. If the mixture is fired off too soon and propagates before the piston reaches TDC it pings."
Not so. combustion is always pretty much silent (by comparison anyway) 'Preignition' could theoretically occur (by somewhat changing the definition to "Before the spark-triggered flame front arrives at the location) due to a hot spot, etc. lighting off a normal burn in the as-yet unburned mixture. This too would be relatively silent. If you hear it, it's detonation by its various names. The only difference between ping, knock and broken parts is how large a mass of end mixture explodes

mdrew,

Sorry if we (I) came across as arguing. I'm very passionate about cars, but
this is hardly arguing for me.

There's one part of your response that goes against my schooling:

These peaks are what you hear as a metallic pinging.

I have been taught that the 'ping' we hear is the shock wave contacting
the cylinder, or chamber...not two flame front colliding.

Splitting hairs? Does it matter? That's where I differ from most.

Nobody in this thread should take my reply as argument. Maybe a little sarcasm
in reference to the 'Jesus' reply.

Wow, no offense guys but there is a lot of arrogance going on here...

Cool, so my worry with part-throttle cruise will be pre-ignition.

I have also seen engines that had badly carboned up CC's that would develop "hot spots" around the deposits and pre-ignite the fuel...

Very informative.

Mike

Technical,

Pre-ignition occurs before the spark plug fires. The mixture ignites from hot
spots in the cylinder. The hot spots could be a glowing sliver of metal on the
edge of the cylinder head, or a very hot spark plug (wrong heat range), among others.

The mixture begins to burn/combust while the piston is moving upward (much
before the spark plug was to fire). The mixture expands in the volume created
by the piston rising toward TDC and the cylinder head chamber.

If the rate of expansion is faster than the piston is able to reach , or pass TDC,
the pressure created by the mixture will try to press the piston back down
(as the piston tries to move up).

This of course creates a huge loss of power due to counter active forces, and
it will present major damage to the mechanicals.

Detonation on the other hand may/could (?) occur before TDC, but since it happens
after the plug fires, the piston is able to get around TDC and begin moving down before
the mixture presents damaging opposing pressure on the piston crown.

Just think that the mixture takes time to react and begin to combust; also
keep in mind that the piston is moving at great speeds. The time intervals are
measured in milliseconds.

So by definition, what YOU are talking about cannot be pre-ignition because
it is happening after the spark plug fires.



I've studied diesel technology in short bursts. I can tell you that diesel ignition
has nothing to do with ping. It uses extremely high compression and high
pressure injection systems to present an air/fuel mixture into the chamber at the point when compression can cause ignition through heat.

Like I stated previously, I'm not arguing the scenarios themselves...only the terminology.

If the rate of expansion is faster than the piston is able to reach , or pass TDC,
the pressure created by the mixture will try to press the piston back down
(as the piston tries to move up).


This is the "other" scenario I described. If you advance the timing far enough, you can create this situation. The other scenarios are products of something in need of fixing vs. a tuning issue. And since we have all bumped our timing far enough to hear this, then we know it is indeed audible. The question is what to we call this? The plug fires, but it's the normal combustion taking place...just too soon.

Listen carefully: The only sound you will ever hear, no matter when the mixture is lit, by whatever means and at whatever throttle opening is DETONATION.
Preignition makes no more sound than normal ignition, it just silently destroys your engine.
And Adrenaline is right. "Colliding flame fronts" is total bunk. Any dual plug engine (of which there are plenty) has colliding flame fronts every cycle...

So then an engine that someone tunes to say 32* advance "pings" not because the flame propagates too soon (before TDC) but because a second instantaneous combustion of end gases ignites (detonates)?

I was taught that the ping is the flame front trying to expand while the piston is still attempting to compress it. It seems unrealistic that there would be enough heat since advancing the timing that far drops cylinder temperatures. i.e. If temperatures weren't high enough to spontaneously *detonate* at 26* then they wouldn't at 32*. Does it have to do with the incomplete burn from the normal combustion (that far advanced, too little heat) leaving behind more unburned end gases?

I would estimate your scenario is detonating from heat.

As the mixture expands, the compression of the upward moving piston
against the pressure of combustion increases the temperature within the
cylinder.

This may cause the end gases to detonate, and this is the ping you are
hearing after the spark, but before TDC(?).

So then an engine that someone tunes to say 32* advance "pings" not because the flame propagates too soon (before TDC) but because a second instantaneous combustion of end gases ignites (detonates)?
EXACTLY
I was taught that the ping is the flame front trying to expand while the piston is still attempting to compress it. It seems unrealistic that there would be enough heat since advancing the timing that far drops cylinder temperatures. i.e. If temperatures weren't high enough to spontaneously *detonate* at 26* then they wouldn't at 32*. Does it have to do with the incomplete burn from the normal combustion (that far advanced, too little heat) leaving behind more unburned end gases?

Sorry, but you were taught wrong. Any textbook I have read supports my previous statements. Also, the earlier the spark occurs, the higher the cylinder temperature and pressure, because the pressure rise from the burn is added to that from the piston's on-going compression of the mixture. This causes the end mixture to reach critical temperature sooner and detonate a larger mass.

Sorry, but you were taught wrong.

Either that, or I switched it in my head over the years. As for temperature I was confusing engine temp vs. cylinder temp which is why it didn't make sense to me.

So when we say that timing has been advanced too far, the gases detonate before the combustion is entirely consumed (flame front propagation) vs. a second ignition of gases? The definition of detonation always led me to believe that a second ignition from heat occurred in a sparse mixture of unburned fuel which "detonates" or flashes which causes ping. That's why I couldn't figure out what to call "ping caused by too much timing."

The ‘ping’, or whatever someone wants to call the noise, is a product of detonation. Whether it’s colliding flame fronts, or comeing from bouncing off hard parts, who really cares? Does it really matter??? This is all speculation and theorecical babble anyway. Text books are written by men and women and every friggin one of them has their own opinion and twist on what’s going on. And of course, each one is correct, or wrong, depending on what a person wants to believe.

The aspect of this convsation that rally matters, is that detonation and pre-ignition are both harmful to engine components and reduce engine longevity. Both are also completely avoidable by the engine builder. It’s the builder’s responcibilty to get it right while putting the build to paper prior to placing the order for components, not to just ‘wing it’. Pre-ignition, in my opinion is caused by incompetence. Whether it’s the builder’s fault or the owner’s fault, there’s no reason for it to ever occur. Detonation should also not occur if the builder has even a slight grasp of the differences between static and dynamic compression ratio and how they play into cylinder pressure.

This is all speculation and theorecical babble anyway. Text books are written by men and women and every friggin one of them has their own opinion and twist on what’s going on.

I hear you. It's sometimes difficult to believe what you read even in texts
these days.

I tend to leaf through every thing, and stick to information that is written by
those with "Ph.d.", "Dr.", or some professional designation wrapped around
their name.

I'm basing my information on what I'd like to believe are credible and accurate
sources.

Whether we're coming across as arrogant to some is probably perception. Those
who have the resources to discuss topics in greater depth tend to come across
as argumentative.

I see it as correcting in the form of passing on education.

There are certain members here that I can learn a great deal from such as
Madbill. I feel privileged to learn something at a higher level and not brush it
off as theoretical babble, or speculation.

Thank you again to the select few that can moderate these topics. I certainly
appreciate learning about even if I'll never need to use it.

...who really cares? Does it really matter??? This is all speculation and theorecical babble anyway.

That's why the title of this forum it "*Advanced* Performance Tech". I personally find the discussion enlightening. :cheers:

I didn't know incorrect timing was detonation vs. pre-ignition even though I understood the two when caused by something wrong within the engine and not the ignition system being calibrated incorrectly. I feel more "learn-ed" now. :)

99% of the people on this forum do no research, and don't know what they are talking about. They just spout off at the mouth based on bad info from other forums!!! :bang:

The only way you learn is to "listen", not much of that going on here.
I think posters to this forum should be limited to people who have learned this art, JimmyBlue for instance. He "listens" and only comments if he has something relevant that is based on experience or technical experts.
I would delete this whole thread as it has too much crap in it (including my post).

I hope you guys aren't referring to me????

I don't know it all and sometimes make mistakes, but I learned what I do know in tech school and subsequent years working as a dealer tech.

I hope you guys aren't referring to me????

I don't know it all and sometimes make mistakes, but I learned what I do know in tech school and subsequent years working as a dealer tech.



I think some people just have a tendency to forget that they weren't born knowing everything.

forums and such provide a good place for people to get answers because they can ask for clarification and details when they don't understand something.

Everyone starts somewhere and for a basic beginner some information is sufficient though untrue due to being incomplete.
for example : a bigger cam makes more power but revs higher.

You grow to find out that the camshaft thing is much more complex.

In the year 726, the sun rising and setting was sufficient, but incorrect. In 2005, the complexity of solar system comes into play. A 726 farmer could be told of the all the complexity of outerspace- but it really doesn't do him any good.

I've seen some serious BS posted here that has gone unchallenged. I don't bother because its not worth it.
I learned a lot of stuff here and learned a lot of if was bs once I read a few books, took a few classes, and did a bit of work in the field. No need to pull a holier than thou attitude (although I get a bit aggravated myself when I hear something like "You need more backpressure so your turbo will spool up faster" type crap.

I had boss deeply involved in the corvette ZR1 program and he would tell me about what pieces of crap they were on the track, their serious deficiencies etc- and when I told this to my friends they wouldn't believe it because corvetteforum.com said they got stronger the more they were driven.

the important thing is to keep an open mind and remember that just because it was said doesn't mean its correct.

The majority of the internet apparently believes that the LS7 is one of the most reliable engines ever built.

one other thing-
A lot of statements are made because of assumptions, and not neccisarily unreasonable assumptions. However, many times the corrilation people are looking for is nonexistant or underminded by an overlooked factor.

Well, seeing how we’re listing pet peeves, mine is when someone quote’s me, but only part of the quote. Then, others chime in without reading the entire statement, but only a part of it.

To clarify, what I was calling theoretical babble, was the noise one hears. Not the subject content of this discussion.

If anyone doubts my skills or experience, I posted it all above for the world to see. There are some incredibly knowledgably individuals that have done the same. I feel humbled to be in the same company with some, and to share thoughts and experiences with them.

And Technical, keep reading, it makes you even more curious. And that’s when you learn. Then apply what you learn to see how it all plays out. That’s the real joy associated with this craft. – to see a dyno curve come out the way you intended it to when putting the build on paper…..

And Technical, keep reading, it makes you even more curious. And that’s when you learn. Then apply what you learn to see how it all plays out. That’s the real joy associated with this craft. – to see a dyno curve come out the way you intended it to when putting the build on paper…..

Thanks for the advice. I've been doing that for over 10 years...never gets old.

:cheers: