predetonation???
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predetonation???
Never heard this term used in automotive nomeclature. Im an expeirenced ASE tech so im not ignorant on what terms are used. (preignition, etc..) i was told it has to do with "compression igniton" as opposed to "spark ignition". This was all relative to a conversation about using 87 octane in a stock engine with 11:0 CR requiring 91 octane.
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Re: predetonation??? (DonF)
you are one of the few whom I'd hope would respond. this is the exact statement made to me:
I think you need to study it a bit closer, yourself.
By "predetonation," I mean compression ignition, as opposed to spark ignition. Compression ratio is the simple way of thinking about it, but what really makes the fuel/air mixture detonate before the spark hits it is purely the pressure that it is under. Octane, a combustion inhibitor, increases the pressure t air/fuel mixture will combust at.
The pressure inside a cylinder before compression is dependent on how much air/fuel is being injected.... it's not constant for all throttle positions. The more you're on the throttle, the more air/fuel is in there.... therefore the higher the pressure will be.
The type of fuel that is specified has just enough octane to resist compression ignition at wide open throttle.
If you're operating the engine at less than that, the cylinders are not reaching those pressures, and the octane does what it is designed to do: inhibit combustion. Generally, that means a lower adiabatic flame temperature and flame front speed. That contributes to lower overall efficiency.
If you never operate your engine at higher pressures, and use a lower octane fuel, you never need the octane and "catostrophic failure" is not likely. If you reach the point of knocking, your ECU sends less fuel/air into the cylinders, thus lowering the pressures.
You're talking to an automotive engineer, and a member of the SAE.
I think you need to study it a bit closer, yourself.
By "predetonation," I mean compression ignition, as opposed to spark ignition. Compression ratio is the simple way of thinking about it, but what really makes the fuel/air mixture detonate before the spark hits it is purely the pressure that it is under. Octane, a combustion inhibitor, increases the pressure t air/fuel mixture will combust at.
The pressure inside a cylinder before compression is dependent on how much air/fuel is being injected.... it's not constant for all throttle positions. The more you're on the throttle, the more air/fuel is in there.... therefore the higher the pressure will be.
The type of fuel that is specified has just enough octane to resist compression ignition at wide open throttle.
If you're operating the engine at less than that, the cylinders are not reaching those pressures, and the octane does what it is designed to do: inhibit combustion. Generally, that means a lower adiabatic flame temperature and flame front speed. That contributes to lower overall efficiency.
If you never operate your engine at higher pressures, and use a lower octane fuel, you never need the octane and "catostrophic failure" is not likely. If you reach the point of knocking, your ECU sends less fuel/air into the cylinders, thus lowering the pressures.
You're talking to an automotive engineer, and a member of the SAE.
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Re: predetonation??? (DCFIVER)
I'm not sure what you want to know?You seemed to ask what predetonation was,although I've never heard the term before myself,and then you put up a perfect example of what it would be if thats what they call it,so what are you asking?
Are you asking if it's right?-sounds possible,diesels do it so if you had high enough comp it could if you used really crappy gas I guess.
Are you asking when will the pressure be high enough to worry about it?-Well since the highest cylinder pressure in a properly running motor is at the torque peak I would think around there.
Are you asking if it's right?-sounds possible,diesels do it so if you had high enough comp it could if you used really crappy gas I guess.
Are you asking when will the pressure be high enough to worry about it?-Well since the highest cylinder pressure in a properly running motor is at the torque peak I would think around there.
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Re: predetonation??? (DCFIVER)
is this the same situation called detonation induced pre-ignition?
well am no automotive engineer so am goin to copy and paste an article i read somewhere
There is a situation called detonation induced pre-ignition.
Imagine an engine under heavy load starting to detonate. Detonation continues for a long period of time. The plug heats up because the pressure spikes break down the protective boundary layer of gas surrounding the electrodes. The plug temperature suddenly starts to elevate unnaturally, to the point when it becomes a glow plug and induces pre-ignition. When the engine fails, I categon'ze that result as "detonation induced pre-ignition." There would not have been any danger of pre-ignition if the detonation had not occurred. Damage attributed to both detonation and pre-ignition would be evident.
Typically, that is what we see in passenger car engines. The engines will typically live for long periods of time under detonation. In fact, we actually run a lot of piston tests where we run the engine at the torque peak, induce moderate levels of detonation deliberately. Based on our resulting production design, the piston should pass those tests without any problem; the pistons should be robust enough to survive. If, however, under circumstances due to overheating or poor fuel, the spark plug tip overheats and induces pre-ignition, it's obviously not going to survive. If we see a failure, it probably is a detonation induced pre-ignition situation.
I would urge any experimenter to be cautious using automotive based engines in other applications. In general, engines producing .5 HP/in3 (typical air-cooled aircraft engines) can be forgiving (as leaning to peak EGT, etc.). But at 1.0 HP/in3 (very typical of many high performance automotive conversions) the window for calibration induced engine damage is much less forgiving. Start out rich, retarded and with cold plugs and watch the EGTs!
well am no automotive engineer so am goin to copy and paste an article i read somewhere
There is a situation called detonation induced pre-ignition.
Imagine an engine under heavy load starting to detonate. Detonation continues for a long period of time. The plug heats up because the pressure spikes break down the protective boundary layer of gas surrounding the electrodes. The plug temperature suddenly starts to elevate unnaturally, to the point when it becomes a glow plug and induces pre-ignition. When the engine fails, I categon'ze that result as "detonation induced pre-ignition." There would not have been any danger of pre-ignition if the detonation had not occurred. Damage attributed to both detonation and pre-ignition would be evident.
Typically, that is what we see in passenger car engines. The engines will typically live for long periods of time under detonation. In fact, we actually run a lot of piston tests where we run the engine at the torque peak, induce moderate levels of detonation deliberately. Based on our resulting production design, the piston should pass those tests without any problem; the pistons should be robust enough to survive. If, however, under circumstances due to overheating or poor fuel, the spark plug tip overheats and induces pre-ignition, it's obviously not going to survive. If we see a failure, it probably is a detonation induced pre-ignition situation.
I would urge any experimenter to be cautious using automotive based engines in other applications. In general, engines producing .5 HP/in3 (typical air-cooled aircraft engines) can be forgiving (as leaning to peak EGT, etc.). But at 1.0 HP/in3 (very typical of many high performance automotive conversions) the window for calibration induced engine damage is much less forgiving. Start out rich, retarded and with cold plugs and watch the EGTs!
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Re: predetonation??? (Fkned)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Fkned »</TD></TR><TR><TD CLASS="quote">I'm not sure what you want to know?You seemed to ask what predetonation was,although I've never heard the term before myself,and then you put up a perfect example of what it would be if thats what they call it,so what are you asking?
Are you asking if it's right?-sounds possible,diesels do it so if you had high enough comp it could if you used really crappy gas I guess.
Are you asking when will the pressure be high enough to worry about it?-Well since the highest cylinder pressure in a properly running motor is at the torque peak I would think around there.</TD></TR></TABLE>
I want to know if anyone is familiar with the term and if the explanation given in bold is valid. I dont need your guesses and assumnptions. If you are unfamiliar with the term then kindly bow out...
Are you asking if it's right?-sounds possible,diesels do it so if you had high enough comp it could if you used really crappy gas I guess.
Are you asking when will the pressure be high enough to worry about it?-Well since the highest cylinder pressure in a properly running motor is at the torque peak I would think around there.</TD></TR></TABLE>
I want to know if anyone is familiar with the term and if the explanation given in bold is valid. I dont need your guesses and assumnptions. If you are unfamiliar with the term then kindly bow out...
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From: Looking for SloMofo....
Re: predetonation??? (Fkned)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ef92b »</TD></TR><TR><TD CLASS="quote">is this the same situation called detonation induced pre-ignition?
well am no automotive engineer so am goin to copy and paste an article i read somewhere
There is a situation called detonation induced pre-ignition.
Imagine an engine under heavy load starting to detonate. Detonation continues for a long period of time. The plug heats up because the pressure spikes break down the protective boundary layer of gas surrounding the electrodes. The plug temperature suddenly starts to elevate unnaturally, to the point when it becomes a glow plug and induces pre-ignition. When the engine fails, I categon'ze that result as "detonation induced pre-ignition." There would not have been any danger of pre-ignition if the detonation had not occurred. Damage attributed to both detonation and pre-ignition would be evident.
Typically, that is what we see in passenger car engines. The engines will typically live for long periods of time under detonation. In fact, we actually run a lot of piston tests where we run the engine at the torque peak, induce moderate levels of detonation deliberately. Based on our resulting production design, the piston should pass those tests without any problem; the pistons should be robust enough to survive. If, however, under circumstances due to overheating or poor fuel, the spark plug tip overheats and induces pre-ignition, it's obviously not going to survive. If we see a failure, it probably is a detonation induced pre-ignition situation.
I would urge any experimenter to be cautious using automotive based engines in other applications. In general, engines producing .5 HP/in3 (typical air-cooled aircraft engines) can be forgiving (as leaning to peak EGT, etc.). But at 1.0 HP/in3 (very typical of many high performance automotive conversions) the window for calibration induced engine damage is much less forgiving. Start out rich, retarded and with cold plugs and watch the EGTs!
</TD></TR></TABLE>
This is simple preignition. not the same. but thanx..
well am no automotive engineer so am goin to copy and paste an article i read somewhere
There is a situation called detonation induced pre-ignition.
Imagine an engine under heavy load starting to detonate. Detonation continues for a long period of time. The plug heats up because the pressure spikes break down the protective boundary layer of gas surrounding the electrodes. The plug temperature suddenly starts to elevate unnaturally, to the point when it becomes a glow plug and induces pre-ignition. When the engine fails, I categon'ze that result as "detonation induced pre-ignition." There would not have been any danger of pre-ignition if the detonation had not occurred. Damage attributed to both detonation and pre-ignition would be evident.
Typically, that is what we see in passenger car engines. The engines will typically live for long periods of time under detonation. In fact, we actually run a lot of piston tests where we run the engine at the torque peak, induce moderate levels of detonation deliberately. Based on our resulting production design, the piston should pass those tests without any problem; the pistons should be robust enough to survive. If, however, under circumstances due to overheating or poor fuel, the spark plug tip overheats and induces pre-ignition, it's obviously not going to survive. If we see a failure, it probably is a detonation induced pre-ignition situation.
I would urge any experimenter to be cautious using automotive based engines in other applications. In general, engines producing .5 HP/in3 (typical air-cooled aircraft engines) can be forgiving (as leaning to peak EGT, etc.). But at 1.0 HP/in3 (very typical of many high performance automotive conversions) the window for calibration induced engine damage is much less forgiving. Start out rich, retarded and with cold plugs and watch the EGTs!
</TD></TR></TABLE>
This is simple preignition. not the same. but thanx..
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Re: predetonation??? (DCFIVER)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DCFIVER »</TD></TR><TR><TD CLASS="quote">I want to know if anyone is familiar with the term and if the explanation given in bold is valid. I dont need your guesses and assumnptions. If you are unfamiliar with the term then kindly bow out...</TD></TR></TABLE>Wow for someone who's asking a question that I tried to help answer you sure are an ******* buddy. 
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From: Looking for SloMofo....
Re: predetonation??? (Fkned)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Fkned »</TD></TR><TR><TD CLASS="quote">Wow for someone who's asking a question that I tried to help answer you sure are an ******* buddy.
</TD></TR></TABLE>
Exactly how did you try to help?? you say you have never heard of the term. You should have stopped there. At that point you became worthless to me...
</TD></TR></TABLE>
Exactly how did you try to help?? you say you have never heard of the term. You should have stopped there. At that point you became worthless to me...
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Re: predetonation??? (DCFIVER)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DCFIVER »</TD></TR><TR><TD CLASS="quote">
Exactly how did you try to help?? you say you have never heard of the term. You should have stopped there. At that point you became worthless to me...</TD></TR></TABLE>Your absolutely right I didn't try to help at all,good luck with the rest of your life sir.
I hope you enjoy sticking a sensor up a tail pipe for 40 or 50 yrs.
Exactly how did you try to help?? you say you have never heard of the term. You should have stopped there. At that point you became worthless to me...</TD></TR></TABLE>Your absolutely right I didn't try to help at all,good luck with the rest of your life sir.
I hope you enjoy sticking a sensor up a tail pipe for 40 or 50 yrs.
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Re: predetonation??? (Phil M)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF »</TD></TR><TR><TD CLASS="quote">I have never heard the term, so I am"out of here"</TD></TR></TABLE>
Thank you.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flyrod »</TD></TR><TR><TD CLASS="quote">From the context it sounds like "predetonation" = detonation. </TD></TR></TABLE> yeah i assumed so but i cannot find any pertinent information leading to this. Since the interweb is likley the largest collection of information available i tried searching but came up with nothing. From my years of lurking around honda-tech many have passed theirselves off as being knowledgable engine builders but either the term doesnt exist or they learned their craft in the "backyard".
Either way this thread is leading no where.
98VTEC do your thing please...
Thank you.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flyrod »</TD></TR><TR><TD CLASS="quote">From the context it sounds like "predetonation" = detonation. </TD></TR></TABLE> yeah i assumed so but i cannot find any pertinent information leading to this. Since the interweb is likley the largest collection of information available i tried searching but came up with nothing. From my years of lurking around honda-tech many have passed theirselves off as being knowledgable engine builders but either the term doesnt exist or they learned their craft in the "backyard".
Either way this thread is leading no where.
98VTEC do your thing please...
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Re: predetonation??? (DCFIVER)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF »</TD></TR><TR><TD CLASS="quote">I have never heard the term, so I am"out of here"</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DCFIVER »</TD></TR><TR><TD CLASS="quote">Thank you.</TD></TR></TABLE>WOW this guy doesn't even know sarcasm when it hits him over the head.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DCFIVER »</TD></TR><TR><TD CLASS="quote">Thank you.</TD></TR></TABLE>WOW this guy doesn't even know sarcasm when it hits him over the head.
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