LOL Drew, I know you would respond like that.
YOu keep your point of view and I go with mine, agree?
YOu keep your point of view and I go with mine, agree?
WILL 89 OCTANE CAUSE ANY PROBLEMS?
- Thread starter mossad
- Start date
- Status
Yo, Dude, Mr.Drew99GT.
I'm on your side regarding about useing 87 octane gas, but your statments that companies claim high octane (93 is the max for pump gas) causes more chamber deposites, need backing. Its not stated as an oppinion, you state this as a matter of fact in your last post.
I've owned a 916 Duc, and the manual actually stated to use 93 oct, ditto for my Tuono. (However, I still dont run 93) I've also owned many 80's and 90's Honda's, all of which clearly stated to use 85+ (80's) or 87+ (90's) octane fuel.
NEVER have I read a manual that says NOT to use 93 octane fuel.
So I gotta call you on that until you back it up with something. Point the way to prove your statements about Ford, Chevy and Ducati please.
I'm on your side regarding about useing 87 octane gas, but your statments that companies claim high octane (93 is the max for pump gas) causes more chamber deposites, need backing. Its not stated as an oppinion, you state this as a matter of fact in your last post.
I've owned a 916 Duc, and the manual actually stated to use 93 oct, ditto for my Tuono. (However, I still dont run 93) I've also owned many 80's and 90's Honda's, all of which clearly stated to use 85+ (80's) or 87+ (90's) octane fuel.
NEVER have I read a manual that says NOT to use 93 octane fuel.
So I gotta call you on that until you back it up with something. Point the way to prove your statements about Ford, Chevy and Ducati please.
Well, you already saw the Ford TSB but I guess that's a bunch of **
BTW - you all know all gas sold in America has a strict blend of required detergents and additives for ALL grades of gasoline, right?
And does anyone recall Amoco's "crystal clear" premium gas? Claimed to clean your motor and stop harmfull deposites? Here and gone real quick right? Yeah...see, its not the solely the octane level that is causing build up. Thats silly.
The only difference besides octane level of premuim fuels these days is SOME ...SOME ...SOME ... add a few more additives for marketing purposes. Today, you'll still find advertisements about premium fuel is "cleaner". Marketing my friends...marketing.
And does anyone recall Amoco's "crystal clear" premium gas? Claimed to clean your motor and stop harmfull deposites? Here and gone real quick right? Yeah...see, its not the solely the octane level that is causing build up. Thats silly.
The only difference besides octane level of premuim fuels these days is SOME ...SOME ...SOME ... add a few more additives for marketing purposes. Today, you'll still find advertisements about premium fuel is "cleaner". Marketing my friends...marketing.
I'm in a bad mood today, can't you tell? Just spent a thousand bucks to replace my hot water heater in new house.
There was a mention of it, I tried searching to no avail. There. you guys won this internet argument.
Don't worry Drew,
I'm not here to start a fight but to make things clear (also to learn from mistakes and misconceptions I have all these time):
Here are the myths of Octane and gasoline:
(1)higher octane gasoline contains more energy content.
Truth: no, in terms of actual BTU/calorie content, all ranges of pump gasoline sold in continental USA are pretty much the same. In other words: 87 Octane pump gas contains the same energy content as 91 Octane.
(2)higher octane rating gasoline "burns slower" than lower octane rating gasoline...
Truth: NOw this is the biggest internet misunderstanding (and would require some serious academic explanation to debunk this myth).
Many internet posters, car owners and enthusiasts discussion board pretty much "cut and paste" this higher octane gas "burns slower" part and repost them on their own board, and some may even go as far as deducing that higher octane gas-->burns slower-->leads to carbon deposits on engines that only calls for lower octane gas (87octane).
IMHO this is far from truth. For interpretation's sake, higher octane gas resists detonation better than lower octane gas during the compression stroke (before ignition, and even before piston's TDC) or sudden, uncontrolled ignition of the fuel-air mixture during power stroke. In a properly designed, tuned water-cooled (thermally controlled) automotive gasoline engine, everything that has to do with combustion of fuel-air mixture is supposed to be precisely controlled for optimal power output, low exhaust emissions and such.
higher octane rating gas does not prematurely ignite during the course of compression stroke. During the ignition phase, high octane rating gasoline also comes with a much more controlled flame propagation pattern, meaning that there shall be no "uncontrolled", premature ignition to the fuel-air mixture to cause "kickbacks" before the spark flies(during compression stroke), and similarly, no "uncontrolled" ignition during flame propagation post sparking to abruptly disrupt the expected flame propagation behaviour and pattern during power stroke.
At the end of this "controlled" burn, fuel/air mixture shall be properly consumed so as to maximise power output.
To the "eye" of the combustion chamber during compression stroke and also during the course of ignition(power) stroke, higher octane rating gasoline ignites and flame propagates in a much more controlled manner(when compared to lower octane gasoline which may have the tendency to pre-ignite during those aforementioned phase). At the end of all these, the fuel/air mixture is spent and gets out by means of exhaust stroke.
Bottomline: octane rating has everything to do with "controlled" burn of automotive gasoline.
So, where on earth does "slower burning" of higher octane gasoline falls into this picture may I ask? (one of the greatest misconception since the dawn of the internet)
Last biggest myth typical to internet posting RE: higher octane rating gasoline is: don't run gasoline with higher octane rating than needed. Because of the "slow burning" of higher octane gasoline, you might get unburned gasoline into your emissions system (catalytic converter), overwhelms it which subsequently cause it to fail prematurely.
Analysis: A properly tuned, well controlled water-cooled 4-stroke gasoline engine, be it carbed or EFI, shall be able to consume air-fuel mixture properly irregardless of the octane rating of your fuel. during the end of the exhaust stroke, these spent fuel shall come w/o any raw (remember, it is absolutely impossible to get raw fuel, letting alone any high concentrations of unconsumed gasoline vapour in the exhaust stream before it hits the cat (with the exception of an engine that is in a mechanically-questionable state).
Also: for those EFI freaks like me, there shall always be an O2 sensor pre cat during the exhaust downstream to constantly monitors any residual Oxygen that hasn't been successfully consumed during the combustion process.
With the advancements of EFI control, now most cars with the latest generation of EFI control comes with 1 o2 sensor up the exhaust stream, one post cat down the exhaust stream to finely adjust the F/A ratio so as to achieve even higher efficiency and optimal power output.
The only thing I could see that has to do with higher octane rating gasoline on a car that runs on basic 87 octane gas, given all else equal, is that you'll be wasting your $$$, and that's it. All others are myths, housewive's tale or urbanlegand that needs scientific analysis or debunking.
lastly, like I said before: there are some manufacturers TSB that aimed at fixing the real root cause of a mechanical issue, and then there are some TSBs that are for legal reasons or beancounter's cause.
I'm not here to start a fight but to make things clear (also to learn from mistakes and misconceptions I have all these time):
Here are the myths of Octane and gasoline:
(1)higher octane gasoline contains more energy content.
Truth: no, in terms of actual BTU/calorie content, all ranges of pump gasoline sold in continental USA are pretty much the same. In other words: 87 Octane pump gas contains the same energy content as 91 Octane.
(2)higher octane rating gasoline "burns slower" than lower octane rating gasoline...
Truth: NOw this is the biggest internet misunderstanding (and would require some serious academic explanation to debunk this myth).
Many internet posters, car owners and enthusiasts discussion board pretty much "cut and paste" this higher octane gas "burns slower" part and repost them on their own board, and some may even go as far as deducing that higher octane gas-->burns slower-->leads to carbon deposits on engines that only calls for lower octane gas (87octane).
IMHO this is far from truth. For interpretation's sake, higher octane gas resists detonation better than lower octane gas during the compression stroke (before ignition, and even before piston's TDC) or sudden, uncontrolled ignition of the fuel-air mixture during power stroke. In a properly designed, tuned water-cooled (thermally controlled) automotive gasoline engine, everything that has to do with combustion of fuel-air mixture is supposed to be precisely controlled for optimal power output, low exhaust emissions and such.
higher octane rating gas does not prematurely ignite during the course of compression stroke. During the ignition phase, high octane rating gasoline also comes with a much more controlled flame propagation pattern, meaning that there shall be no "uncontrolled", premature ignition to the fuel-air mixture to cause "kickbacks" before the spark flies(during compression stroke), and similarly, no "uncontrolled" ignition during flame propagation post sparking to abruptly disrupt the expected flame propagation behaviour and pattern during power stroke.
At the end of this "controlled" burn, fuel/air mixture shall be properly consumed so as to maximise power output.
To the "eye" of the combustion chamber during compression stroke and also during the course of ignition(power) stroke, higher octane rating gasoline ignites and flame propagates in a much more controlled manner(when compared to lower octane gasoline which may have the tendency to pre-ignite during those aforementioned phase). At the end of all these, the fuel/air mixture is spent and gets out by means of exhaust stroke.
Bottomline: octane rating has everything to do with "controlled" burn of automotive gasoline.
So, where on earth does "slower burning" of higher octane gasoline falls into this picture may I ask? (one of the greatest misconception since the dawn of the internet)
Last biggest myth typical to internet posting RE: higher octane rating gasoline is: don't run gasoline with higher octane rating than needed. Because of the "slow burning" of higher octane gasoline, you might get unburned gasoline into your emissions system (catalytic converter), overwhelms it which subsequently cause it to fail prematurely.
Analysis: A properly tuned, well controlled water-cooled 4-stroke gasoline engine, be it carbed or EFI, shall be able to consume air-fuel mixture properly irregardless of the octane rating of your fuel. during the end of the exhaust stroke, these spent fuel shall come w/o any raw (remember, it is absolutely impossible to get raw fuel, letting alone any high concentrations of unconsumed gasoline vapour in the exhaust stream before it hits the cat (with the exception of an engine that is in a mechanically-questionable state).
Also: for those EFI freaks like me, there shall always be an O2 sensor pre cat during the exhaust downstream to constantly monitors any residual Oxygen that hasn't been successfully consumed during the combustion process.
With the advancements of EFI control, now most cars with the latest generation of EFI control comes with 1 o2 sensor up the exhaust stream, one post cat down the exhaust stream to finely adjust the F/A ratio so as to achieve even higher efficiency and optimal power output.
The only thing I could see that has to do with higher octane rating gasoline on a car that runs on basic 87 octane gas, given all else equal, is that you'll be wasting your $$$, and that's it. All others are myths, housewive's tale or urbanlegand that needs scientific analysis or debunking.
lastly, like I said before: there are some manufacturers TSB that aimed at fixing the real root cause of a mechanical issue, and then there are some TSBs that are for legal reasons or beancounter's cause.
for Credits and credentials on my postings, one may be able to reference to most of the URLs and links I posted on this topic:
In addition to most of the SAE past papers on the internal combustion engines and such, another academic field research that would be of interest shall be COMODIA (Symposium on Diagnostics & Modelling of Combustion in International Combustion Engines).
***********************************************
Harold H. Schobert - The Chemistry of Hydrocarbon Fuels - Butterworth-Heinemann Ltd.
Keith Owen, Trevor Coley - Automotive Fuels Reference Book - SAE - R151
H.P. Lenz - Mixture Formation in Spark-Ignition Engines - Springer-Verlag
Jeff Hartman - Fuel Injection - Motorbooks International
Germane, Wood, Hess - Lean Combustion in Spark-Ignited Internal Combustion Engines - A Review - SAE paper 831694
Z. Warhaft - An Introduction to Thermal Fluid Engineering - Cambridge University Press
COMODIA 2001
In addition to most of the SAE past papers on the internal combustion engines and such, another academic field research that would be of interest shall be COMODIA (Symposium on Diagnostics & Modelling of Combustion in International Combustion Engines).
***********************************************
Harold H. Schobert - The Chemistry of Hydrocarbon Fuels - Butterworth-Heinemann Ltd.
Keith Owen, Trevor Coley - Automotive Fuels Reference Book - SAE - R151
H.P. Lenz - Mixture Formation in Spark-Ignition Engines - Springer-Verlag
Jeff Hartman - Fuel Injection - Motorbooks International
Germane, Wood, Hess - Lean Combustion in Spark-Ignited Internal Combustion Engines - A Review - SAE paper 831694
Z. Warhaft - An Introduction to Thermal Fluid Engineering - Cambridge University Press
COMODIA 2001
Typo: it should be "Symposium on Diagnostics & Modelling of Combustion in Internal Combustion Engines".
My bad.
My bad.
I have to disagree with a couple of things said:
1) Ethanol does not lower the octane rating of gasoline. Ethanol's octane is much higher than regular grade 87 octane gasoline. Ethanol lowers the productivity (output BTUs) of the gasoline.
2) Not only is compression and cam duration a factor, but so is timing and air/fuel ratio. A tuner can make an engine produce more HP and get better MPG by tuning a car spec'd for 87 octane to run on 93, without any compression or cam changes but with timing and fuel management adjustments. I've seen it done and I've seen dyno results to prove it. Of course, after the tune, 87 octane can no longer be used but the tune usually pays for itself based upon the increase in fuel mileage, even taking in to consideration the cost difference of premium gas.
1) Ethanol does not lower the octane rating of gasoline. Ethanol's octane is much higher than regular grade 87 octane gasoline. Ethanol lowers the productivity (output BTUs) of the gasoline.
2) Not only is compression and cam duration a factor, but so is timing and air/fuel ratio. A tuner can make an engine produce more HP and get better MPG by tuning a car spec'd for 87 octane to run on 93, without any compression or cam changes but with timing and fuel management adjustments. I've seen it done and I've seen dyno results to prove it. Of course, after the tune, 87 octane can no longer be used but the tune usually pays for itself based upon the increase in fuel mileage, even taking in to consideration the cost difference of premium gas.
This one is for you Drew:
http://www.eric-gorr.com/techarticles/Fuel_Basics.htm
Enjoy the reading ;^>
Q.
p.s. air-cooled, 2-stroke engines tend to behave differently than air-cooled, 4-stroke bike engines or even water-cooled, 4-stroke bike engines. ****,in fact, technical observations based on water-cooled 4-stroke automobile engines does not often apply to bike engines these days!
http://www.eric-gorr.com/techarticles/Fuel_Basics.htm
Enjoy the reading ;^>
Q.
p.s. air-cooled, 2-stroke engines tend to behave differently than air-cooled, 4-stroke bike engines or even water-cooled, 4-stroke bike engines. ****,in fact, technical observations based on water-cooled 4-stroke automobile engines does not often apply to bike engines these days!
Dude, I don't need to read your little shindig about octane. I'll stand by my, as well as Ford's, Chevy's, and Ducatis statements that high octane fuel can cause combustion chamber deposits. It's even widely accepted in the pushrod Mustang community; many guys only run 87 octane in their built 302 based motors for these very reasons!
Wow. You talked all around it but don't quite see it.
The reason that higher octane resists knock and controls the burn is because it burns slower. That is why you can ignite the fire earlier (increase ignition timing) with higher octane fuel. If it didn't burn slower you could not increase the ignition timing lead (before top dead center).
Believe what you want, but I spent too much time as a tuner to be swayed by your incomplete understanding.
With all due respect,Big Jim-
When it comes to Octane rating of gasoline, I'm always referring to "anti-knock" capability, or the ability for gasoline to resists uncontrolled, pre-ignition (sudden pressure rise)during the course of compression stroke and also post-ignition power stroke when the air-fuel mixture (has to be reasonable on this part, you simply cannot throw something that is unrealistically "rich or lean" in air-fuel ratio).
And all these time my postings in response to "higher Octane rating gasoline burns slower...", I've been holding onto the following variables static:
(a) the automobile engine in discussion is a stock unit stright out of the factory assembly line, with stock compression ratio, factory program control engine management control (timing, cloosed loop operating temperature, N/A, factory set stoichiometric ratio (air-fuel mixture)and profile, etc.), minimum octane rating is set to be 87 (standardised (RON+MON)/2)
(b) straight swap of 87 octane gas on this said vehicle while holding all the aforementioned factors static with Octane rating of 89 or higher
Question: will this increase of octane rating on the said car going to cause carboning up due to your said "slower burning" properties of higher octane rating gasoline?
Arguments:
if you hold the fuel-air mixture ratio and ignition timing advance profile along the entire said stock engine profile static (factory spec.) and simply vary the octane rating, I do not think your "slow burning" of higher octane rating gasoline can be applied here for the flame speed shall remains the same throughout the entire experiment (remember: we are trying higher octane gas w/o changing other variables here).
***********************************************
My argument has always be the controlled "flame propagation" here, not the generalised "slower burn" terms here.
As a tuner I understand you have pretty much all the variables available to your manipulation (e.g. on a stock engine with stock combustion chamber, stock cam profiles, stock fuel injectors, no "tricking" add-ons, factory set coolant temperature,etc.) you still get to manipulate the mixture richness and timing advancing profile to accommodate your specific needs, to say the least.
Knowing that these 2 variables go hand in hand and can be manipulated to outside of the design confines of a said factory engine, naturally, octane rating of gasoline can be put into good use so as to achieve the goal a tuner would like to get (e.g. higher power output, etc.)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >>>>>
Your point of argument:
"...The reason that higher octane resists knock and controls the burn is because it burns slower...."
My argument:
(*using higher octane gas, while the aforementioned operational variables on a factory stock engine (designed for use of min 87 octane rating gasoline)pretty much remained static*)
Normal flame speed is pretty consistent for all gasoline hydrocarbons, and this has no correlation to octane rating.
The increase in octane rating is to control the "uncontrollable" sudden pressure rise, and no correlation to the flame propagation speed here (or what you would refer to as "spped of burning"). It's more like suppressing any sudden, abnormal misbehaviour(uncontrolled sudden pressure increase) during the compression stroke and also throughout the entire air/fuel combustion stage after the spark flies.
All gasoline engines coming straight out of the assembly line comes with somewhat conservative operational margin on all aspects, with one of them being the ignition timing advance. One can simply raise the ignition advance further (BTDC, which is highly dependent to the flame propagation behaviour in a combustion chamber design, and stoichiometric ratio of the said engine designs) beyond factory spec and tries to compensate with higher octane rating gasoline to correct any abnormal behaviour throughout the course of timing manipulation. That being said however, you manipulation of timing advance away from factory spec. has more to do with flame propagation speed, which can also be further compensated with stoichiometric change (richening of the mixture) to complete the task. But then again: additives that used for increasing octane rating is for the suppression of abnormal behaviour during the course of mixture compression, and also during the flame propagation stage and has nothing to do with flame propagation speed (or what you referred to as "relative fast/slow burning").
Ok, let me put it in another way: octane rating is like a race track with guard rails to keep the race dog in check: lower octane rating is like a race track with very, very wide guard rails across where race dogs can run all over the place, not all of them goes straight from the start to the finishing line.
Higher octane rating is like a very narrow, confined guard rails that would keep the race dogs from running astray. As a consequence, all race dogs go relatively straight from start to the finish line in a consistent manner.
*************************************************
My argument has always been "controlled flame propagation behaviour" associated to increased octane rating of gasoline and NOT "flame speed" (relative fast/slow burning").
You may spend too much time as a tuner but you missed the fundamentals of:
(1)
The normal flame speed is fairly consistent for most gasoline HCs, regardless of octane rating,
and
(2) the flame speed is also affected by stoichiometry (or air-fuel mixture ratio).
Oh well, so much for my posting for one day. Good nite everyone.
**************************************************
Further proofs and reading materials cited from Gasoline FAQ.
http://www.faqs.org/faqs/autos/gasoline-faq/
The specific point I used during this argument comes from part 3 of the FAQ section, about 60% from top down:
.......
The actual ignition timing to achieve the maximum pressure from normal
combustion of gasoline will depend mainly on the speed of the engine and the
flame propagation rates in the engine. Knock increases the rate of the
pressure rise, thus superimposing additional pressure on the normal
combustion pressure rise. The knock actually rapidly resonates around the
chamber, creating a series of abnormal sharp spikes on the pressure diagram.
The normal flame speed is fairly consistent for most gasoline HCs, regardless
of octane rating, but the flame speed is affected by stoichiometry.
.......
When it comes to Octane rating of gasoline, I'm always referring to "anti-knock" capability, or the ability for gasoline to resists uncontrolled, pre-ignition (sudden pressure rise)during the course of compression stroke and also post-ignition power stroke when the air-fuel mixture (has to be reasonable on this part, you simply cannot throw something that is unrealistically "rich or lean" in air-fuel ratio).
And all these time my postings in response to "higher Octane rating gasoline burns slower...", I've been holding onto the following variables static:
(a) the automobile engine in discussion is a stock unit stright out of the factory assembly line, with stock compression ratio, factory program control engine management control (timing, cloosed loop operating temperature, N/A, factory set stoichiometric ratio (air-fuel mixture)and profile, etc.), minimum octane rating is set to be 87 (standardised (RON+MON)/2)
(b) straight swap of 87 octane gas on this said vehicle while holding all the aforementioned factors static with Octane rating of 89 or higher
Question: will this increase of octane rating on the said car going to cause carboning up due to your said "slower burning" properties of higher octane rating gasoline?
Arguments:
if you hold the fuel-air mixture ratio and ignition timing advance profile along the entire said stock engine profile static (factory spec.) and simply vary the octane rating, I do not think your "slow burning" of higher octane rating gasoline can be applied here for the flame speed shall remains the same throughout the entire experiment (remember: we are trying higher octane gas w/o changing other variables here).
***********************************************
My argument has always be the controlled "flame propagation" here, not the generalised "slower burn" terms here.
As a tuner I understand you have pretty much all the variables available to your manipulation (e.g. on a stock engine with stock combustion chamber, stock cam profiles, stock fuel injectors, no "tricking" add-ons, factory set coolant temperature,etc.) you still get to manipulate the mixture richness and timing advancing profile to accommodate your specific needs, to say the least.
Knowing that these 2 variables go hand in hand and can be manipulated to outside of the design confines of a said factory engine, naturally, octane rating of gasoline can be put into good use so as to achieve the goal a tuner would like to get (e.g. higher power output, etc.)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >>>>>
Your point of argument:
"...The reason that higher octane resists knock and controls the burn is because it burns slower...."
My argument:
(*using higher octane gas, while the aforementioned operational variables on a factory stock engine (designed for use of min 87 octane rating gasoline)pretty much remained static*)
Normal flame speed is pretty consistent for all gasoline hydrocarbons, and this has no correlation to octane rating.
The increase in octane rating is to control the "uncontrollable" sudden pressure rise, and no correlation to the flame propagation speed here (or what you would refer to as "spped of burning"). It's more like suppressing any sudden, abnormal misbehaviour(uncontrolled sudden pressure increase) during the compression stroke and also throughout the entire air/fuel combustion stage after the spark flies.
All gasoline engines coming straight out of the assembly line comes with somewhat conservative operational margin on all aspects, with one of them being the ignition timing advance. One can simply raise the ignition advance further (BTDC, which is highly dependent to the flame propagation behaviour in a combustion chamber design, and stoichiometric ratio of the said engine designs) beyond factory spec and tries to compensate with higher octane rating gasoline to correct any abnormal behaviour throughout the course of timing manipulation. That being said however, you manipulation of timing advance away from factory spec. has more to do with flame propagation speed, which can also be further compensated with stoichiometric change (richening of the mixture) to complete the task. But then again: additives that used for increasing octane rating is for the suppression of abnormal behaviour during the course of mixture compression, and also during the flame propagation stage and has nothing to do with flame propagation speed (or what you referred to as "relative fast/slow burning").
Ok, let me put it in another way: octane rating is like a race track with guard rails to keep the race dog in check: lower octane rating is like a race track with very, very wide guard rails across where race dogs can run all over the place, not all of them goes straight from the start to the finishing line.
Higher octane rating is like a very narrow, confined guard rails that would keep the race dogs from running astray. As a consequence, all race dogs go relatively straight from start to the finish line in a consistent manner.
*************************************************
My argument has always been "controlled flame propagation behaviour" associated to increased octane rating of gasoline and NOT "flame speed" (relative fast/slow burning").
You may spend too much time as a tuner but you missed the fundamentals of:
(1)
The normal flame speed is fairly consistent for most gasoline HCs, regardless of octane rating,
and
(2) the flame speed is also affected by stoichiometry (or air-fuel mixture ratio).
Oh well, so much for my posting for one day. Good nite everyone.
**************************************************
Further proofs and reading materials cited from Gasoline FAQ.
http://www.faqs.org/faqs/autos/gasoline-faq/
The specific point I used during this argument comes from part 3 of the FAQ section, about 60% from top down:
.......
The actual ignition timing to achieve the maximum pressure from normal
combustion of gasoline will depend mainly on the speed of the engine and the
flame propagation rates in the engine. Knock increases the rate of the
pressure rise, thus superimposing additional pressure on the normal
combustion pressure rise. The knock actually rapidly resonates around the
chamber, creating a series of abnormal sharp spikes on the pressure diagram.
The normal flame speed is fairly consistent for most gasoline HCs, regardless
of octane rating, but the flame speed is affected by stoichiometry.
.......
Lastly a bit of long-winded reading (again, from the gasoline faq section):
......
7.4 What is the effect of changing the ignition timing?
The tendency to knock increases as spark advance is increased. For an engine
with recommended 6 degrees BTDC ( Before Top Dead Centre ) timing and 93
octane fuel, retarding the spark 4 degrees lowers the octane requirement to
91, whereas advancing it 8 degrees requires 96 octane fuel [27]. It should
be noted this requirement depends on engine design. If you advance the spark,
the flame front starts earlier, and the end gases start forming earlier in
the cycle, providing more time for the autoigniting species to form before
the piston reaches the optimum position for power delivery, as determined by
the normal flame front propagation. It becomes a race between the flame front
and decomposition of the increasingly-squashed end gases. High octane fuels
produce end gases that take longer to autoignite, so the good flame front
reaches and consumes them properly.
The ignition advance map is partly determined by the fuel the engine is
intended to use. The timing of the spark is advanced sufficiently to ensure
that the fuel-air mixture burns in such a way that maximum pressure of the
burning charge is about 15-20 degree after TDC. Knock will occur before
this point, usually in the late compression - early power stroke period.
The engine management system uses ignition timing as one of the major
variables that is adjusted if knock is detected. If very low octane fuels
are used ( several octane numbers below the vehicle's requirement at optimal
settings ), both performance and fuel economy will decrease.
The actual Octane Number Requirement depends on the engine design, but for
some 1978 vehicles using standard fuels, the following (R+M)/2 Octane
Requirements were measured. "Standard" is the recommended ignition timing
for the engine, probably a few degrees BTDC [38].
Basic Ignition Timing
Vehicle Retarded 5 degrees Standard Advanced 5 degrees
A 88 91 93
B 86 90.5 94.5
C 85.5 88 90
D 84 87.5 91
E 82.5 87 90
The actual ignition timing to achieve the maximum pressure from normal
combustion of gasoline will depend mainly on the speed of the engine and the
flame propagation rates in the engine. Knock increases the rate of the
pressure rise, thus superimposing additional pressure on the normal
combustion pressure rise. The knock actually rapidly resonates around the
chamber, creating a series of abnormal sharp spikes on the pressure diagram.
The normal flame speed is fairly consistent for most gasoline HCs, regardless
of octane rating, but the flame speed is affected by stoichiometry. Note that
the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1
CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s,
and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds
are also very dependent on stoichiometry.
......
......
7.4 What is the effect of changing the ignition timing?
The tendency to knock increases as spark advance is increased. For an engine
with recommended 6 degrees BTDC ( Before Top Dead Centre ) timing and 93
octane fuel, retarding the spark 4 degrees lowers the octane requirement to
91, whereas advancing it 8 degrees requires 96 octane fuel [27]. It should
be noted this requirement depends on engine design. If you advance the spark,
the flame front starts earlier, and the end gases start forming earlier in
the cycle, providing more time for the autoigniting species to form before
the piston reaches the optimum position for power delivery, as determined by
the normal flame front propagation. It becomes a race between the flame front
and decomposition of the increasingly-squashed end gases. High octane fuels
produce end gases that take longer to autoignite, so the good flame front
reaches and consumes them properly.
The ignition advance map is partly determined by the fuel the engine is
intended to use. The timing of the spark is advanced sufficiently to ensure
that the fuel-air mixture burns in such a way that maximum pressure of the
burning charge is about 15-20 degree after TDC. Knock will occur before
this point, usually in the late compression - early power stroke period.
The engine management system uses ignition timing as one of the major
variables that is adjusted if knock is detected. If very low octane fuels
are used ( several octane numbers below the vehicle's requirement at optimal
settings ), both performance and fuel economy will decrease.
The actual Octane Number Requirement depends on the engine design, but for
some 1978 vehicles using standard fuels, the following (R+M)/2 Octane
Requirements were measured. "Standard" is the recommended ignition timing
for the engine, probably a few degrees BTDC [38].
Basic Ignition Timing
Vehicle Retarded 5 degrees Standard Advanced 5 degrees
A 88 91 93
B 86 90.5 94.5
C 85.5 88 90
D 84 87.5 91
E 82.5 87 90
The actual ignition timing to achieve the maximum pressure from normal
combustion of gasoline will depend mainly on the speed of the engine and the
flame propagation rates in the engine. Knock increases the rate of the
pressure rise, thus superimposing additional pressure on the normal
combustion pressure rise. The knock actually rapidly resonates around the
chamber, creating a series of abnormal sharp spikes on the pressure diagram.
The normal flame speed is fairly consistent for most gasoline HCs, regardless
of octane rating, but the flame speed is affected by stoichiometry. Note that
the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1
CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s,
and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds
are also very dependent on stoichiometry.
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Feel like taking on more? Here's one more:
http://www.eric-gorr.com/techarticles/Fuel_Basics.htm
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It's a commonly held misconception that higher Octane fuel slows down the flame speed which keeps the engine from knocking. Flame speed is a function of fuel chemistry, not the Octane rating. The component make up of the fuel will determine the flame speed whether it's a high octane fuel or not. . Racing fuels designed for high rpm applications tend to have higher flame speeds than normal to help reduce burn time. There isn't much time available to complete the combustion cycle at 10,000rpm, so choosing the right fuel can really make a difference. Choosing a faster burning fuel will allow you to run less ignition advance, and ultimately make more power at higher revs.
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This pretty much sums up my point that "higher octane" gasoline is not "slower burning".
http://www.eric-gorr.com/techarticles/Fuel_Basics.htm
......
It's a commonly held misconception that higher Octane fuel slows down the flame speed which keeps the engine from knocking. Flame speed is a function of fuel chemistry, not the Octane rating. The component make up of the fuel will determine the flame speed whether it's a high octane fuel or not. . Racing fuels designed for high rpm applications tend to have higher flame speeds than normal to help reduce burn time. There isn't much time available to complete the combustion cycle at 10,000rpm, so choosing the right fuel can really make a difference. Choosing a faster burning fuel will allow you to run less ignition advance, and ultimately make more power at higher revs.
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This pretty much sums up my point that "higher octane" gasoline is not "slower burning".
I really think that you are trying to "split a hair" on an issue that only someone with an interest in fuel chemistry can understand.
The basic definition of octane rating is the measure of a gasoline's ability to resist detonation.
Pre-detonation is the uncontrolled air/gas mixture flashing ahead of the advancing flame front.
A controlled flame front will burn the mixture at a slower rate, hence the analogy that a correct octane to compression ratio match is a slower burn rate.
The basic definition of octane rating is the measure of a gasoline's ability to resist detonation.
Pre-detonation is the uncontrolled air/gas mixture flashing ahead of the advancing flame front.
A controlled flame front will burn the mixture at a slower rate, hence the analogy that a correct octane to compression ratio match is a slower burn rate.
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