100 Octane Gas
05-16-2015, 11:04 PM
#21
If the specific rate of combustion was the same for high oct as it is for low oct why would u need to increase ign timing to take advantage of the higher octane? Furthermore, why would u get detonation running that same increased timing with lower octane? I'm just sayin' 
05-17-2015, 12:09 AM
#22
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If the specific rate of combustion was the same for high oct as it is for low oct why would u need to increase ign timing to take advantage of the higher octane? Furthermore, why would u get detonation running that same increased timing with lower octane? I'm just sayin'
You adjust spark timing to MBT (maximum brake torque) that gives best power and best torque (depending on RPM) for your specific engine.
Pump gas, like 93 (or 91) is not suitable for finding MBT, it will preignite before you get there. That is when you need more octane.
If your engine makes best power with 25 degrees of spark timing and it pings on 93 octane at 17, you need better fuel/more octane. On the other hand, if it makes best power at 15 degrees and power drops off at 16 or 17, and you can run that on 93 safely without preignition/knock, then you won't benefit from more octane.
Corvettes on pump gas are not running at MBT spark. Not even close. GM knows this. They know our cars run on **** water pump gas.
Last edited by Higgs Boson; 05-17-2015 at 12:11 AM.
05-17-2015, 11:14 AM
#23
Burning Brakes
Not according to this site.
https://mn.gov/commerce/weights-and-...ctaneFacts.pdf
https://mn.gov/commerce/weights-and-...ctaneFacts.pdf
Glad you posted this--maybe everyone can learn something finally. Facts tend to kill old wives tales lol.
05-17-2015, 07:45 PM
#24
Not according to this site.
https://mn.gov/commerce/weights-and-...ctaneFacts.pdf
https://mn.gov/commerce/weights-and-...ctaneFacts.pdf
The "second definition" of octane was actually an attempt at the definition of octane rating. The first definition was for octane although it pretty much sucked. The following is n-octane which would be Octane C8H18:
...H..H.H..H.H..H.H.H
....l...l..l...l..l...l...l..l
H-C-C-C-C-C-C-C-C-H
....l...l..l...l..l...l...l..l
...H..H.H..H.H..H.H.H
Isomers of each normal member of the family have the same chemical formula as the normal member but with different molecular structure and properties. Isomers have the suffix "yl" added. For example, the name 2,2,4 trimethyl pentane is one specific isomer of octane. Tri means three and methyl means the radical CH3. So three methyl groups are attached to the pentane base (5 carbon atoms) at carbon atoms 2, 2, and 4 (numbered left to right) giving:
........CH3....CH3
....H....l...H....l...H
.....l....l....l....l....l
H--C--C--C--C--C--H
.....l....l....l....l....l
....H....l...H...H...H
........CH3
This is the structural formula for 2,2,4 trimethyl pentane or isooctane (you'll note it still has 8 carbon atoms and 18 hydrogen atoms just like n-octane). The isooctane and 2,2,4 trimethyl pentane terms are used synonymously since this particular isomer of octane is of importance in combustion engine work as you'll see below.
The critical compression ratio (or octane rating) of the paraffin family for audible knock in a spark ignition (SI) engine decreases rapidly as the length of the chain of the normal members is increased. The normal paraffins in the volatility range of gasoline are poor SI fuels due to very low octane ratings...remember n-octane has an octane rating of -17. Catalytically cracked fuels have branched paraffins (like above) making the carbon chain shorter resulting in higher critical compression ratios/higher octane ratings. The formula for the paraffin family is C(n)H(2n+2) giving methane (CH4), ethane (C2H6), propane (C3H8) etc.
Finally, the octane rating is a reference scale to measure SI knock and has been established by arbitrarily selecting two primary reference fuels. They are isooctane (2,2,4 trimethyl pentane) which has been arbitrarily assigned an "octane rating" of 100 and n-heptane which has been arbitrarily assigned an "octane rating" of 0. The "octane rating" of a fuel is found by comparing its knock intensity with various mixtures of n-heptane and isooctane. So an octane rating of 93 means a fuel has the same knock intensity in a standard CFR engine (google "astm CFR engine", you can vary compression ratio while it's running
) and at standard conditions is equivalent to a mixture of 93 parts isooctane and 7 parts n-heptane (by volume).Lead in the old days delayed the preflame reactions to increase self-ignition temperature/detonation resistance and get octane ratings higher than 100. Adding the fuel octane would have the opposite affect. Here's another link to get a better understanding of gasoline:
http://www.faqs.org/faqs/autos/gasoline-faq/part3/
From the end of paragraph 6.3:
"The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane."
If you read all of the FAQ in the link above, you'll see there are over 500 different hydrocarbons that make up gasoline. While I don't propose to know the "secret" formulas used by gas companies, it isn't a two component fuel comprised of "octane and heptane". If you go to the very end of the article, you'll find many excellent references used to write the article...there were no references in your state .gov link.
Here are a few links from Rockett Brand Racing Fuels:
http://rockettbrand.com/downloads/te...0&%20Power.pdf
From the link:
"Octane number is not related to flame (burn) speed either."
"As indicated above, flame speed and octane number both impact the amount of power that an engine will develop, but they are independent of each other."
http://rockettbrand.com/downloads/te...low%20Burn.pdf
http://rockettbrand.com/downloads/te...20Boosters.pdf
They have 100 octane gas that will allow a 9:1 engine make more power even though it'll run fine on 87 octane. How??? It's blended to have a faster burn.
So how does that make more power? Every engine has a MBT (mean best timing) at which it makes maximum power. With a 9:1 engine, 87 octane gas will allow you to run enough timing to achieve MBT. With the fast burn gas, your MBT is actually lower so you REDUCE timing. By starting the combustion event later in the compression stroke, the negative work done on the piston is reduced but the faster flame speed enables peak cylinder pressure to still occur at the optimum 11-15 degrees ATDC. So while we have the same BTU content, the same lbs/hr of fuel going into the engine, and the same IMEP, we've improved BSFC by reducing the height of the curve during the compression stroke on the pressure ordinate of the PV diagram which reduces FHP (BHP=IMEP-FHP)...in laymans terms, we reduced negative work so the engine makes more HP. I wonder what type of 100 octane gas people are getting at the race track and if it's a fast burn blend. If so, they may make more power by doing a tune and reducing timing. They may be reducing knock with the higher octane rating but the fast burn is increasing negative work and negating the power gains from no knock retard.Much is unknown as to exactly how MMT and TEL work but they do know the compounds increase the ignition delay of the fuel. This may be where confusion has come from as the term ignition delay does not refer to a time factor but the activation energy required to cause the reaction of oxygen and gas to complete (also referred to as combustion). The ignition delay term is just a fancy way of saying it takes a higher temperature to ignite the mixture, it has no time dimension associated with it.
Happy reading!
05-17-2015, 08:01 PM
#25
Actually, my minor at Georgia Tech was internal combustion engines and I was the teaching assistant my senior year. Our lab had a CFR engine like the one I mentioned in my post above...I may have run it once or twice.
I know the correct "key words" to put into a search engine to get the technically correct results and know a BS state .gov website when I see it.
05-17-2015, 08:32 PM
#26
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It looks like a real rocket scientist at the Minnesota State Department of Commerce wrote that article. There are many mistakes of which the least is in the last paragraph, "or" is spelled "ore"...pitiful. The worst transgressions are in the "technical" part, although I hesitate to call this article from a state .gov site a "technical article". Your link states in the "second definition" of octane that "pure octane" has a rating of 100. Pure octane (C8H18 also referred to as n-octane, a "normal" or straight chain member of the paraffin family) has an octane rating of -17.
The "second definition" of octane was actually an attempt at the definition of octane rating. The first definition was for octane although it pretty much sucked. The following is n-octane which would be Octane C8H18:
...H..H.H..H.H..H.H.H
....l...l..l...l..l...l...l..l
H-C-C-C-C-C-C-C-C-H
....l...l..l...l..l...l...l..l
...H..H.H..H.H..H.H.H
Isomers of each normal member of the family have the same chemical formula as the normal member but with different molecular structure and properties. Isomers have the suffix "yl" added. For example, the name 2,2,4 trimethyl pentane is one specific isomer of octane. Tri means three and methyl means the radical CH3. So three methyl groups are attached to the pentane base (5 carbon atoms) at carbon atoms 2, 2, and 4 (numbered left to right) giving:
........CH3....CH3
....H....l...H....l...H
.....l....l....l....l....l
H--C--C--C--C--C--H
.....l....l....l....l....l
....H....l...H...H...H
........CH3
This is the structural formula for 2,2,4 trimethyl pentane or isooctane (you'll note it still has 8 carbon atoms and 18 hydrogen atoms just like n-octane). The isooctane and 2,2,4 trimethyl pentane terms are used synonymously since this particular isomer of octane is of importance in combustion engine work as you'll see below.
The critical compression ratio (or octane rating) of the paraffin family for audible knock in a spark ignition (SI) engine decreases rapidly as the length of the chain of the normal members is increased. The normal paraffins in the volatility range of gasoline are poor SI fuels due to very low octane ratings...remember n-octane has an octane rating of -17. Catalytically cracked fuels have branched paraffins (like above) making the carbon chain shorter resulting in higher critical compression ratios/higher octane ratings. The formula for the paraffin family is C(n)H(2n+2) giving methane (CH4), ethane (C2H6), propane (C3H8) etc.
Finally, the octane rating is a reference scale to measure SI knock and has been established by arbitrarily selecting two primary reference fuels. They are isooctane (2,2,4 trimethyl pentane) which has been arbitrarily assigned an "octane rating" of 100 and n-heptane which has been arbitrarily assigned an "octane rating" of 0. The "octane rating" of a fuel is found by comparing its knock intensity with various mixtures of n-heptane and isooctane. So an octane rating of 93 means a fuel has the same knock intensity in a standard CFR engine (google "astm CFR engine", you can vary compression ratio while it's running ) and at standard conditions is equivalent to a mixture of 93 parts isooctane and 7 parts n-heptane (by volume).
Lead in the old days delayed the preflame reactions to increase self-ignition temperature/detonation resistance and get octane ratings higher than 100. Adding the fuel octane would have the opposite affect. Here's another link to get a better understanding of gasoline:
http://www.faqs.org/faqs/autos/gasoline-faq/part3/
From the end of paragraph 6.3:
"The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane."
If you read all of the FAQ in the link above, you'll see there are over 500 different hydrocarbons that make up gasoline. While I don't propose to know the "secret" formulas used by gas companies, it isn't a two component fuel comprised of "octane and heptane". If you go to the very end of the article, you'll find many excellent references used to write the article...there were no references in your state .gov link.
Here are a few links from Rockett Brand Racing Fuels:
http://rockettbrand.com/downloads/te...0&%20Power.pdf
From the link:
"Octane number is not related to flame (burn) speed either."
"As indicated above, flame speed and octane number both impact the amount of power that an engine will develop, but they are independent of each other."
http://rockettbrand.com/downloads/te...low%20Burn.pdf
http://rockettbrand.com/downloads/te...20Boosters.pdf
They have 100 octane gas that will allow a 9:1 engine make more power even though it'll run fine on 87 octane. How??? It's blended to have a faster burn. So how does that make more power? Every engine has a MBT (mean best timing) at which it makes maximum power. With a 9:1 engine, 87 octane gas will allow you to run enough timing to achieve MBT. With the fast burn gas, your MBT is actually lower so you REDUCE timing. By starting the combustion event later in the compression stroke, the negative work done on the piston is reduced but the faster flame speed enables peak cylinder pressure to still occur at the optimum 11-15 degrees ATDC. So while we have the same BTU content, the same lbs/hr of fuel going into the engine, and the same IMEP, we've improved BSFC by reducing the height of the curve during the compression stroke on the pressure ordinate of the PV diagram which reduces FHP (BHP=IMEP-FHP)...in laymans terms, we reduced negative work so the engine makes more HP. I wonder what type of 100 octane gas people are getting at the race track and if it's a fast burn blend. If so, they may make more power by doing a tune and reducing timing. They may be reducing knock with the higher octane rating but the fast burn is increasing negative work and negating the power gains from no knock retard.
Much is unknown as to exactly how MMT and TEL work but they do know the compounds increase the ignition delay of the fuel. This may be where confusion has come from as the term ignition delay does not refer to a time factor but the activation energy required to cause the reaction of oxygen and gas to complete (also referred to as combustion). The ignition delay term is just a fancy way of saying it takes a higher temperature to ignite the mixture, it has no time dimension associated with it.
Happy reading!
The "second definition" of octane was actually an attempt at the definition of octane rating. The first definition was for octane although it pretty much sucked. The following is n-octane which would be Octane C8H18:
...H..H.H..H.H..H.H.H
....l...l..l...l..l...l...l..l
H-C-C-C-C-C-C-C-C-H
....l...l..l...l..l...l...l..l
...H..H.H..H.H..H.H.H
Isomers of each normal member of the family have the same chemical formula as the normal member but with different molecular structure and properties. Isomers have the suffix "yl" added. For example, the name 2,2,4 trimethyl pentane is one specific isomer of octane. Tri means three and methyl means the radical CH3. So three methyl groups are attached to the pentane base (5 carbon atoms) at carbon atoms 2, 2, and 4 (numbered left to right) giving:
........CH3....CH3
....H....l...H....l...H
.....l....l....l....l....l
H--C--C--C--C--C--H
.....l....l....l....l....l
....H....l...H...H...H
........CH3
This is the structural formula for 2,2,4 trimethyl pentane or isooctane (you'll note it still has 8 carbon atoms and 18 hydrogen atoms just like n-octane). The isooctane and 2,2,4 trimethyl pentane terms are used synonymously since this particular isomer of octane is of importance in combustion engine work as you'll see below.
The critical compression ratio (or octane rating) of the paraffin family for audible knock in a spark ignition (SI) engine decreases rapidly as the length of the chain of the normal members is increased. The normal paraffins in the volatility range of gasoline are poor SI fuels due to very low octane ratings...remember n-octane has an octane rating of -17. Catalytically cracked fuels have branched paraffins (like above) making the carbon chain shorter resulting in higher critical compression ratios/higher octane ratings. The formula for the paraffin family is C(n)H(2n+2) giving methane (CH4), ethane (C2H6), propane (C3H8) etc.
Finally, the octane rating is a reference scale to measure SI knock and has been established by arbitrarily selecting two primary reference fuels. They are isooctane (2,2,4 trimethyl pentane) which has been arbitrarily assigned an "octane rating" of 100 and n-heptane which has been arbitrarily assigned an "octane rating" of 0. The "octane rating" of a fuel is found by comparing its knock intensity with various mixtures of n-heptane and isooctane. So an octane rating of 93 means a fuel has the same knock intensity in a standard CFR engine (google "astm CFR engine", you can vary compression ratio while it's running
) and at standard conditions is equivalent to a mixture of 93 parts isooctane and 7 parts n-heptane (by volume).Lead in the old days delayed the preflame reactions to increase self-ignition temperature/detonation resistance and get octane ratings higher than 100. Adding the fuel octane would have the opposite affect. Here's another link to get a better understanding of gasoline:
http://www.faqs.org/faqs/autos/gasoline-faq/part3/
From the end of paragraph 6.3:
"The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane."
If you read all of the FAQ in the link above, you'll see there are over 500 different hydrocarbons that make up gasoline. While I don't propose to know the "secret" formulas used by gas companies, it isn't a two component fuel comprised of "octane and heptane". If you go to the very end of the article, you'll find many excellent references used to write the article...there were no references in your state .gov link.
Here are a few links from Rockett Brand Racing Fuels:
http://rockettbrand.com/downloads/te...0&%20Power.pdf
From the link:
"Octane number is not related to flame (burn) speed either."
"As indicated above, flame speed and octane number both impact the amount of power that an engine will develop, but they are independent of each other."
http://rockettbrand.com/downloads/te...low%20Burn.pdf
http://rockettbrand.com/downloads/te...20Boosters.pdf
They have 100 octane gas that will allow a 9:1 engine make more power even though it'll run fine on 87 octane. How??? It's blended to have a faster burn.
So how does that make more power? Every engine has a MBT (mean best timing) at which it makes maximum power. With a 9:1 engine, 87 octane gas will allow you to run enough timing to achieve MBT. With the fast burn gas, your MBT is actually lower so you REDUCE timing. By starting the combustion event later in the compression stroke, the negative work done on the piston is reduced but the faster flame speed enables peak cylinder pressure to still occur at the optimum 11-15 degrees ATDC. So while we have the same BTU content, the same lbs/hr of fuel going into the engine, and the same IMEP, we've improved BSFC by reducing the height of the curve during the compression stroke on the pressure ordinate of the PV diagram which reduces FHP (BHP=IMEP-FHP)...in laymans terms, we reduced negative work so the engine makes more HP. I wonder what type of 100 octane gas people are getting at the race track and if it's a fast burn blend. If so, they may make more power by doing a tune and reducing timing. They may be reducing knock with the higher octane rating but the fast burn is increasing negative work and negating the power gains from no knock retard.Much is unknown as to exactly how MMT and TEL work but they do know the compounds increase the ignition delay of the fuel. This may be where confusion has come from as the term ignition delay does not refer to a time factor but the activation energy required to cause the reaction of oxygen and gas to complete (also referred to as combustion). The ignition delay term is just a fancy way of saying it takes a higher temperature to ignite the mixture, it has no time dimension associated with it.
Happy reading!