Question on increasing Compression

[Trevor]

Originally Posted by svxistentialist

Hi Trevor

That is very informative, and thank you

My descriptions used terminology that does not agree/match with what is commonly used by engine people to describe the phenomena. Well, I did say at the start I am not an engineer.

Essentially I was describing and dealing with pre-ignition detonation only.

Rather strangely, the term detonation in the Google article is restricted to spontaneous detonation that happens after the spark has fired. Almost as if what the spark had already triggered off a fraction earlier was not a detonation at all!!

In my defense I can only say that these terms are incorrect and imprecise use of English, even if they are understood by engineers.

The word "preignition" refers to a state or to a time. It does not describe an event, which is the process of spontaneous detonation I was describing.

Likewise the term "detonation" as used in that article would be more correctly described as post-ignition spontaneous detonation.

Rant/

Thank you for pulling up the article, I will study it carefully.

Joe

Joe,

Please be sure that it not my intent to raise an argument, but it is desirable that the facts are made clear, so that others reading this stuff do not become misled.

It would appear that you are currently claiming that the dictionary is incorrect. -----

-----“In my defense I can only say that these terms are incorrect and imprecise use of English, even if they are understood by engineers.”

“The word "preignition" refers to a state or to a time. It does not describe an event, which is the process of spontaneous detonation I was describing.”-----

N.B. The word “preignition”, pasted from my computer dictionary --- noun the premature combustion of the fuel–air mixture in an internal combustion engine. The word IS a noun covering an EVENT.

Furthermore, the two words “pre” and “ignition”, together as a verb and noun, can be used to describe a relative point in time, but do not, and can not a be used in describing a certain state.

You also know say:-

“Essentially I was describing and dealing with pre-ignition detonation only.”

Therefore you have confirmed that you were previously dealing only with “pre-ignition/preignition” , i.e. a state resulting from of combustion being initiated prior to the intended point of ignition. (Ignition. Noun, the action of setting something on fire or starting to burn.)

Therefore you were not dealing with detonation. (Dictionary ---Combustion of a substance that is initiated suddenly and propagates extremely rapidly, giving rise to a shock wave.)

Finally you say:-

“Likewise the term "detonation" as used in that article would be more correctly described as post-ignition spontaneous detonation.”

An addendum could be applied to assist those not exactly acquainted with English. However the article is exactly correct. Again as per my computer dictionary. (Combustion of a substance that is initiated suddenly and propagates extremely rapidly, giving rise to a shock wave.)

I too found it a good article as it precisely sums up a subject which confuses many.

Cheers, Trevor.

[Trevor]

Originally Posted by TomsSVX

I have oil?? I will agree that a denser charge is less likely to detonate. BUT only if the amount of air stays equal. For exampel a turbo car runs no itnercooler making 14psi of boost. An intercooler is added and he continues to make 14psi because of his wastegate adjustment. The denser charge is like running twice the boost so it has to be done in respect to the limitations. If you were detonating on 6 psi so lowered it 14.... You are going to more than likely detonate on 14 now and lower the boost pressures would be recomended. Thats how I see it and if I am wrong, please do correct me

Tom

Tom, thanks for oiling a crossed thread.

There has been some confusion within the thread because, within the terms or reference applied in describing the subject being discussed, NA, SC and Turbo charging have become rather intwined.

In any event, there are so many aspects involved that it has been difficult to define which comes first, the chicken or the egg.

Confusion also exists regarding preignition as opposed to detonation. It is to be hoped that all interested, will scroll back on the complete thread, so that real oil is wasted.

Cheers, Trevor.

[svxistentialist]

Originally Posted by Trevor

Joe,

Please be sure that it not my intent to raise an argument, but it is desirable that the facts are made clear, so that others reading this stuff do not become misled.

It would appear that you are currently claiming that the dictionary is incorrect. -----

-----“In my defense I can only say that these terms are incorrect and imprecise use of English, even if they are understood by engineers.”

“The word "preignition" refers to a state or to a time. It does not describe an event, which is the process of spontaneous detonation I was describing.”-----

N.B. The word “preignition”, pasted from my computer dictionary --- noun the premature combustion of the fuel–air mixture in an internal combustion engine. The word IS a noun covering an EVENT.

Furthermore, the two words “pre” and “ignition”, together as a verb and noun, can be used to describe a relative point in time, but do not, and can not a be used in describing a certain state.

You also know say:-

“Essentially I was describing and dealing with pre-ignition detonation only.”

Therefore you have confirmed that you were previously dealing only with “pre-ignition/preignition” , i.e. a state resulting from of combustion being initiated prior to the intended point of ignition. (Ignition. Noun, the action of setting something on fire or starting to burn.)

Therefore you were not dealing with detonation. (Dictionary ---Combustion of a substance that is initiated suddenly and propagates extremely rapidly, giving rise to a shock wave.)

Finally you say:-

“Likewise the term "detonation" as used in that article would be more correctly described as post-ignition spontaneous detonation.”

An addendum could be applied to assist those not exactly acquainted with English. However the article is exactly correct. Again as per my computer dictionary. (Combustion of a substance that is initiated suddenly and propagates extremely rapidly, giving rise to a shock wave.)

I too found it a good article as it precisely sums up a subject which confuses many.

Cheers, Trevor.

Full well I understand that you have no wish to propagate an argument, and merely wish to clarify for those who want to understand the processes involved with internal combustion. Never the less, I have to take you to task on the use of the English language as it is employed by those who would be quite happy correcting the majority of us in what is correct, absolute and proper.

"The dictionary is incorrect."

Exactly what dictionary?

If your computer dictionary is describing the term preignition as a noun, it can only be doing so by accepting the meaning of the term as that which is commonly applied to the phenomenon of premature localised detonation pre ignition in an internal combustion engine.

To define this as the commonly accepted meaning of the phrase is quite acceptable.

However, there is a radical difference between accepting this phrase as commonly defining a specific event and the actuality in English of the term pre ignition, which precisely and absolutely defines a state or a time, not an event. Not even in Middle Earth English does the term pre ignition define an event.

As regards the use of the term "detonation", here in Ireland, once upon a time Bomb Central, we are only too well aware of what exactly the REAL word "detonation" means.

To suborn the use of this noun to merely describe a pretty unusual and little understood in-cylinder phenomenon is totally asking for confusion in the minds of non-engineers.

So if your intention is to enlighten, and I have no doubt this is your intention, then perhaps it would actually help if the misuse of these words in this context was actually recognised and explained, and the specific meaning in the context of the internal combustion process was explained clearly, and without the acceptance of such mental shorthand that engineers might use while usurping older and more correct definitions of certain nouns, words and phrases.

Joe

[Trevor]

Originally Posted by svxistentialist

Full well I understand that you have no wish to propagate an argument, and merely wish to clarify for those who want to understand the processes involved with internal combustion. Never the less, I have to take you to task on the use of the English language as it is employed by those who would be quite happy correcting the majority of us in what is correct, absolute and proper.

"The dictionary is incorrect."

Exactly what dictionary?

If your computer dictionary is describing the term preignition as a noun, it can only be doing so by accepting the meaning of the term as that which is commonly applied to the phenomenon of premature localised detonation pre ignition in an internal combustion engine.

To define this as the commonly accepted meaning of the phrase is quite acceptable.

However, there is a radical difference between accepting this phrase as commonly defining a specific event and the actuality in English of the term pre ignition, which precisely and absolutely defines a state or a time, not an event. Not even in Middle Earth English does the term pre ignition define an event.

As regards the use of the term "detonation", here in Ireland, once upon a time Bomb Central, we are only too well aware of what exactly the REAL word "detonation" means.

To suborn the use of this noun to merely describe a pretty unusual and little understood in-cylinder phenomenon is totally asking for confusion in the minds of non-engineers.

So if your intention is to enlighten, and I have no doubt this is your intention, then perhaps it would actually help if the misuse of these words in this context was actually recognised and explained, and the specific meaning in the context of the internal combustion process was explained clearly, and without the acceptance of such mental shorthand that engineers might use while usurping older and more correct definitions of certain nouns, words and phrases.

Joe

Please Joe,

Read accurately what I stated lest there be cause for expletives here.

The computer (Appleworks) dictionary is CORRECTLY defining the word “preignition”. You clearly state preignition is a PHRASE which is quite acceptable. Then you inexplicably insert the word “premature” and you derive the words “pre ignition”, in lieu of the subject matter, i.e. the single word “preignition”. Twisting my statements in an effort to score points, does not impress.

As I have pointed out there are two subject matters relative to the debate. Each is separate and spelled in common plain English, "preignition" and "pre ignition". Arguing otherwise is frankly stupid.

I have considerable in-depth experience draughting technical specifications which must stand up in law, and state with absolute confidence, that real engineers never use “mental shorthand”. What is more when speaking, they say what they mean, and mean what they say.

According to Funk and Wagnalls Standard Dictionary. Detonate, verb. --- To cause to explode suddenly and with violence. (i.e. Not combust slowly.) Detonation, noun. Detonator, noun.

Webster Pocket Dictionary. Detonate, To cause to explode. Detonation,
noun, explosion.

Examples illustrating similar nouns:-

The preignition resulted from carbon deposits.

The prefix enabled understanding.

The prescription was prepared.

The precaution was warranted.

You state that in Ireland you all are exactly aware of what the real term detonation means. I state that what you have set down is an Irish joke.

My intention IS to enlighten and I reject your sarcastic suggestion that I should alter any of that which I have accurately described. In fact I am annoyed that I have had to expend so much time, in order to make sure that readers are not advised in error, as a result of continuing absurdity.

With due respect, Trevor. *<)

[svxistentialist]

I think not.

If there is "confusion" here to begin with it is because there are terms in use by the engineering community that use words or conjoined words in this context that may have other meanings in common English.

Establishing and explaining the fact that these words may have other meanings is important to those who wish to understand what is going on, but are not engineers and could not be expected to be familiar with or understand that the words mean something particular and different when used in an internal combustion context.

The word "detonation" is a particular point in this respect.

And the word "preignition" as a noun now has a different meaning from the phrase pre ignition, from which it is derived.

These things need to be made clear, Trevor, so that people not only understand what is taking place but the imprecise nature of the language that is used to describe the situation.

And while I am yielding the point [and did in my last post!] that the engineering terminology is commonly accepted, and thus "correct", I stand by my original contention that the use made of these terms is incorrect and imprecise English.

Arguing these points and explaining the use of these words in this context is not a waste of time. We are not explaining for a third level group of engineering students here, who have already accepted the mental shorthand. We are trying to explain to a group of SVX owners [including me!] who may not realise that the words and terms used in this context may mean something different from other possible dictionary definitions.

So there is absolutely no need for expletives. I genuinely thank you for explaining the use of these terms and enlightening me and for finding that great article. However, lighten up, the words used may be perceived to have different meanings to non engine people, and as you are always saying, it is important that the explanations we give make it clear exactly what these words are commonly taken to mean in engineering language [not English!!] when describing these phenomena.

Joe

[svxistentialist]

I have just read that SRS article through.

Twice.

That is a fabulous description of the process, the causes, the cures and adjustment strategy.

Thanks a million Trevor I'm in your debt.

[Hey, I still think the word detonation is not properly descriptive of what is happening, but now at least I know what's being described in this context]

I vote we coin a phrase here and call it "postignition".

[Trevor]

Originally Posted by svxistentialist

The word "detonation" is a particular point in this respect.

And the word "preignition" as a noun now has a different meaning from the phrase pre ignition, from which it is derived.

These things need to be made clear, Trevor, so that people not only understand what is taking place but the imprecise nature of the language that is used to describe the situation.

And while I am yielding the point [and did in my last post!] that the engineering terminology is commonly accepted, and thus "correct", I stand by my original contention that the use made of these terms is incorrect and imprecise English.

Joe

Joe, you have clearly indicated that in your opinion readers here are unable to understand correct plain English, and do not have the wit to comprehend the meaning of the words --- detonation, pre ignition, pre-ignition and preignition. You claim that these terms are both incorrect and imprecise English.

I claim that any person able to read, possessing a normal understanding of the language and a reasonable level of intelligence, will be able to understand all of that which I have posted. However, provided that they have the patience to sort and bypass the confusing asides. No special or obscure engineering words have been included, all is plain exact English.

You claim that the use I have made of words/terms is incorrect and imprecise English. I claim that all words used have been carefully chosen as being exactly correct and precise. Damn it all the words are in common use, included in dictionaries, are not confined to engineering, exactly as I have already detailed.

Please, precisely, briefly in plain English, exactly indicate and in the context in which I have used them, (your words) “ that the use made of these terms, is incorrect and imprecise English.” The three terms in dispute being the words --- detonation, pre-ignition, or pre ignition.

I regret that my understanding must now be, that you are trying to justify your own misunderstandings and subsequent incorrect comment, regarding that which has been written carefully, logically and with due respect those reading.

You instruct me to “lighten up”. For the good of others, the issue here is the need for only accurate facts to be presented. This is the aspect which I take very seriously. N.B. My objective is objective.

Sincerely, Trevor.

P.S. Unfortunately the above was 'saved' before I had read your last sincerely appreciate post. Even so the content is valid and I trust that my motives are understood. *<)

[Dessertrunner]

So guys do we understand why the SC or turbo can run at a higher final compression then a NA?

[svxistentialist]

Originally Posted by Trevor

I regret that my understanding must now be, that you are trying to justify your own misunderstandings and subsequent incorrect comment, regarding that which has been written carefully, logically and with due respect those reading.

I agree with this statement by and large.

And as I am logical and not unintelligent my quest for clarity on the definitions of the words used by engine builders came from the fact that although you seem to see the words as unambiguous, clearly they are not.

We will have to agree to disagree here Trevor.

What do you think of my better word "postignition" as a substitute for "detonation". eh??

Joe

[svxistentialist]

Originally Posted by Dessertrunner

So guys do we understand why the SC or turbo can run at a higher final compression then a NA?

Tony, as I said at the start I do not have access to the numbers on this, but if you read that article Trevor linked in his post, it very clearly explains what the problem is.

You are quite correct when you said that the NA engine gets its fuel charge pumped in by atmospheric pressure. Using a supercharger aka blower, or a turbo pumps in the mixture under pressure in order to get more oxygen in the cylinder.

If you look at pages 4 and 5 of the article it explains really well why higher efficiency engines [usually with higher CRs] are more prone to this detonation lark.

You have to remember that when the piston compresses the gas mix down to approx one tenth of its original volume this causes very high pressures and some heat in the cylinder, even in a naturally aspirated engine.

So when you add extra pressure [and more gas] using forced feeding by SC or turbo, you are only adding a percentage of extra pressure and heat to the equation.

However this extra pressure and heat is enough to push the combustion process beyond the safe limits the engine was designed at, and into the zone where this post ignition detonation is caused.

Bottom line, if you bolt on a supercharger or turbo, you need to lower the compression ratio to keep your engine safe.

Just as a rough guide, and this is not engineering gospel, mind, our SVX engines can probably manage 5 to 6 lbs boost without falling apart, at least in the short term. At 12 lbs boost you would need to be at about 9:1 CR for safety, and at 18 lbs boost you would need to be at 8:1 or so.

This latter [rough guide!!] figure I'm quoting here is tried and tested, it is the level Subaru uses for the turbo EJ20 engine.

Naturally you would have to change other things, like using colder plugs and so on, I assume you are aware of these things.

Does that even partly answer your question?

Joe

[Dessertrunner]

Joe I agree with what you are saying and the artical was good. I am still not sure any one has explain why the NA motor gets problems at 12:1 up. May be I am missing some thing isn't it correct that when you talk 8 or 9:1 on boasted engines this is before you boast. If you then put a SC or Turbo on the engine the new actual compression a lot higher. 9:1 with 19# boast would be over 18:1 final compression.
Have I got the whole thing wrong.
Tony

[Trevor]

Originally Posted by Dessertrunner

Joe I agree with what you are saying and the artical was good. I am still not sure any one has explain why the NA motor gets problems at 12:1 up. May be I am missing some thing isn't it correct that when you talk 8 or 9:1 on boasted engines this is before you boast. If you then put a SC or Turbo on the engine the new actual compression a lot higher. 9:1 with 19# boast would be over 18:1 final compression.
Have I got the whole thing wrong.
Tony

Tony,

Joe has explained:-

“So when you add extra pressure [and more gas] using forced feeding by SC or turbo, you are only adding a percentage of extra pressure and heat to the equation.”

A measurement of forced pressure can not be considered as a ratio in conjunction with a measurement in respect of compression, as there is no common denominator. Each measurement is in a different ball park and do not relate on equal terms. Therefore one can not relate a NA engine on 12:1 with a SC engine in the way you describe.

Compression ratio measurement, illustrates a ratio in respect of maximum cylinder volume, as opposed to combustion chamber volume and indicates how much the charge becomes compressed prior to ignition. The same scale/description/denominator, applies in respect of both measurements.

Forcing the charge into the cylinder of an engine with a lower compression ratio does not increase pressure of the charge, prior ignition to the same degree as an increase in compression ratio. What is more the two measurements are unrelated, as they are not recorded by means of a similar scale.

On the basis of overall estimation/view as you describe, things are rather cock-eyed.

Got it?

I hope that I have correctly identified the point in respect of your confusion. If not, do not hesitate to again shout out loud.


What about an article on your experiences, as I mentioned twice in the thread on tyres.

Cheers, Trevor.

[Dessertrunner]

Trevor I will stop talking compression ratio and talk head pressure at the time of ignition. Would it be correct to say that at that time the maxium NA pressure would be lower then the boasted engine?

[Trevor]

Originally Posted by Dessertrunner

Trevor I will stop talking compression ratio and talk head pressure at the time of ignition. Would it be correct to say that at that time the maxium NA pressure would be lower then the boasted engine?

In respect to lower or higher, you must state what is being compared.

If a NA engine and boosted engine have the same cylinder capacity and compression ratio, the boosted engine must have higher pressure at the point of ignition. Obviously there will be a greater volume of air forced into the combustion chamber to become compressed. What is more forced induction, will result in a small positive pressure at the moment compression commences, although this will have a very limited affect.

[svxistentialist]

Originally Posted by Dessertrunner

Joe I agree with what you are saying and the artical was good. I am still not sure any one has explain why the NA motor gets problems at 12:1 up. May be I am missing some thing isn't it correct that when you talk 8 or 9:1 on boasted engines this is before you boast. If you then put a SC or Turbo on the engine the new actual compression a lot higher. 9:1 with 19# boast would be over 18:1 final compression.
Have I got the whole thing wrong.
Tony

Yes, Tony, you are slightly mislead here in what you are saying, and Trevor has already answered.

Your idea on compression ratio is being distorted by your idea on the added pressure the turbo gives.

The CR, or compression ratio, is the ratio between the volume of the cylinder when the piston is at its lowest point over the volume when it's at TDC, the highest point just when ignition happens.

Once the engine is built, this ratio is fixed.

The in-cylinder pressures can go up if you add extra fuel/oxygen to the mixture, which is what the turbo is designed to do in order to give you more power. Our MAFs measure the amount of air the NA engine is taking in, and the computer can use this measurement to decide what the optimum timing may be for the required burn.

With engines that are turbo'd, they often use a MAP sensor. This measures Manifold Absolute Pressure, rather than the amount of air sucked in. It is a better measurement device for these force fed engines because the heat the turbo makes can vary[reduce] the density of the charge going in, and the intercooler if fitted cools and increases the density of the charge. So the MAP sensor gives an absolute measure of the pressure in the manifold which is a more accurate reading of how much oxygen is getting in there.

So when we say vary the compression ratio to suit the turbo, this requires engine work and will remain fixed when the engine is built.

Adding different higher boost pressures from the turbo will not change the CR on the engine. As you correctly suspect it will add more gas to the cylinder and because there is more in there, when the piston compresses this new denser mix, there will be higher pressures at maximum compression, just before spark.

To partly answer your question about high CR naturally aspirated engines, the following is the problem encountered; the very high CR, 12:1 as you mentioned, compresses the charge into a space 1/12th of original atmospheric pressure volume. This makes the mixture hotter and more pressurised than in a lower tune engine. These two factors create the environment where spontaneous detonation [pinking] will occur in the engine, so the easiest solution to counter the pinking is to use fuel [gasoline] that is resistant to detonation with a higher octane rating.

Joe