MrBlunt
03-11-2004, 10:04 PM
First there are 2 different Octane rating numbers RON and MON. These are Research Octane Number and Motor Octane Number. THe RON is typically higher, but the importnat one for racing and performance is of course MON.
That is all that (R+M)/2 which is the minimum octane rating for the fuel.
Second, max possible octane rating is 120.6 for ANY gasoline. With the rating system, only straight toluene, with alot of TEL (Tetraethyl Lead) added. Which is a very good octane booster but will kill catylists. It comes in at 124 but more on this as a fuel later.
One consideration is the flame speed of the fuel, how fast it burns off. The reason this is important is if it all burns off in the first 25 or 30 degrees of crank rotation. Then the motor is just along for the ride. This is where other additives come in. Such as methanol, which is also a great octane booster. More over, it is an oxygenate, which just like it sounds provides O2 as it decomposes during combustion and provides additional oxidizer for that combustion.
Of course 10% alcohol is in some gas already, but the Feds say that anything that has more than 2.7% oxygen content by weight is not considered pump gas.
Pump gas, and many racing gases, because of restrictions on oxygenates are not high in oxygen content, but that is where the real power of fuel is at. Gasoline, has a very high heating value but requires alot of O2 to burn completely and have it's heat extracted and converted into mechanical energy.
Some of the other things that needs to be considered when adding things to gasoline is the way that they react both with the gas and with the car.
Toluene is a light aromatic (CH3C6H5) that is a common additive in pump gasoline, a boiling point of 231 degrees F. It is a common additive in unleaded gas that is not racing fuel. It's short coming is that although the higher octane number of toluene, it's burn speed, and low boiling point give it a tendency if used as a racing fuel to boil off ahead of the flame front during combustion. This can increase knock, and does not burn as well after being boiled off into a vapor.
Xylene is also a light aromatic C6H4(CH3)2 with a boiling point of 270 degrees. Used in all racing gasoline at a level of up to 30% (giving you a (R+M)/2 of 104 and a specific MON of 100.
The biggest consideration of all aromatics is the effects on the fuel system that they are being run through. All aromatics will have an adverse effect on rubber componets. And the increased burn rate of them. This directly relates to the RPM at which they are most effective of increasing power. When turning the motor at a low speed, the slower burning additives are better as they piston speed is slower and power is only created during the burn of the fuel. After the burn cycle has completed, gas expansion will soon cease. At a high RPM, with the piston moving at a high rate, the faster burn rate is ideal because the stroke time is much shorter.
This is a major reason that we are burning gasoline and not toluene or some other aromatic solvent for car fuel.
Methanol CH3OH has a combustion reaction of 2CH3OH + 3O2 -> 2CO2 + 4H2O. Methanol is converted down into MTBE which is a common additive in pump gas in small quanities, and is used as an octane increaser and oxygenate to decrease polution. (Gasohol)
Methanol, because of it's high oxygen content is a great additive, both to increase octane and fuel power, but requires additional fuel to produce the same power level (decreasing MPG because you have to run a richer mixture)
Has a slow burn speed that is idea in slow turning street motors and will also cool the intake charge considerably.
But it has its down sides too. It is corrosive to most metals, and some plastics. It is toxic, can enter the body through the skin and in pure form will burn without a visible flame. Although I can't seem to find anything specific about Methanols specific Octane number I do know that it is compatible in motors of up to 23 to 1 compression ratio. (Remember that supercharging an engine is compairable to increasing the compression ratio and I will provide the chart later for what boost level equates to what compression ratio change.)
So after all that here's the final skinny on this.
With an 80/20 mix of aromatic solvet to pump gas here are the final numbers
20% toluene with pump gas will get you a (R+M)/2 of 104
20% xylene wit pump gas will get you a (R+M)/2 of 110
Methanol, although being better than either of the two, is quite unsafe, draws moisture readily from the atmosphere and should only be considered as a race only fuel. I am going to try to do some more research on the mixing of Methanol and Gasoline to see where it might lead. The performance aspect, for pure performance use is promising but with costs being a real factor for Methanol it's not something to work well as an additive due to its high ratio requirement and the need to increase the fuel mixture in order to see an increase in power.
I am considering some testing with model airplane fuel that is 80% methanol and 20% nitromethane. But Nitro is VERY suseptiable to knock, and no current additive seems to change that. More over adding it to gasoline it has been found to severly decrease the octane rating of gasoline, even though it's about 53% oxygen content and releases this oxygen very readily which would make it a wonderful gas additive except for the fact it kills MON quickly. Possibly blending it in small quanities, with Methanol as I am planning to do, will result in a good performance fuel. Although taking it to the track will get you throw out and its smell does leave something to be desired.
Somethng else that I am finding out. Octane does NOT make power. Higher Octane fuels than your motor actually require are not going to make more horsepower. So if you are getting into messing with fuels. Don't go overboard, becauser it's wasteful, and does nothing. The reason that fuels that are not high enough in octane don't make as much power is that power is reduced due to either spark knock, or the retarding of the timing to get rid of the spark knock.
Also don't get it in your head that high enough octane will allow you to run some silly spark advance, like 50 degrees in a small block chevy (yes I know that ford guys can do this) the maximum timing for a motor has to do with the shape of the combustion chamber and the way that effects the flame front and the speed at which the fuel burns, Not the octane of the gasoline running in it. If you switch fuels, then timing can be adjusted accordingly. Methanol, it burns slower, so it requires more advance than gasoline. Nitromethane on the other hand, or any aromatic solvent if you were to try to run it as a primary fuel would require much less timing because or the burn rate being faster than gasoline. This is also why, and here comes the nay sayers, a lower octane fuel, due to it's SLOWER burn time will make more power than a high octane fuel because the octane additives make it burn FASTER. We do not deal with motors that spin at a sufficent RPM to require a fast burn fuel. If this was Columbus Formula1racing.com then the prior statement would no apply due to the fact our motors would idle at what most of us consider to be redline for the motors we have (around 5000 RPM) and not start making real power until 9000 RPM. If any of you are spinning your motor up like that (12000 to 14000) other than the bike guys, I would really love to see that.
NOTE: This is the power of reading, some parts of this I knew, most I learned last night through reading and studying books on the subject.
So you noobs take heed. There is a wealth of information both on the web and in books. You want to learn about things like this, read, don't guess, if you are looking to get books on a specific subject, if its car related, look for books by David Vizard first, if he puts in in one of his books, it fact, not speculation
That is all that (R+M)/2 which is the minimum octane rating for the fuel.
Second, max possible octane rating is 120.6 for ANY gasoline. With the rating system, only straight toluene, with alot of TEL (Tetraethyl Lead) added. Which is a very good octane booster but will kill catylists. It comes in at 124 but more on this as a fuel later.
One consideration is the flame speed of the fuel, how fast it burns off. The reason this is important is if it all burns off in the first 25 or 30 degrees of crank rotation. Then the motor is just along for the ride. This is where other additives come in. Such as methanol, which is also a great octane booster. More over, it is an oxygenate, which just like it sounds provides O2 as it decomposes during combustion and provides additional oxidizer for that combustion.
Of course 10% alcohol is in some gas already, but the Feds say that anything that has more than 2.7% oxygen content by weight is not considered pump gas.
Pump gas, and many racing gases, because of restrictions on oxygenates are not high in oxygen content, but that is where the real power of fuel is at. Gasoline, has a very high heating value but requires alot of O2 to burn completely and have it's heat extracted and converted into mechanical energy.
Some of the other things that needs to be considered when adding things to gasoline is the way that they react both with the gas and with the car.
Toluene is a light aromatic (CH3C6H5) that is a common additive in pump gasoline, a boiling point of 231 degrees F. It is a common additive in unleaded gas that is not racing fuel. It's short coming is that although the higher octane number of toluene, it's burn speed, and low boiling point give it a tendency if used as a racing fuel to boil off ahead of the flame front during combustion. This can increase knock, and does not burn as well after being boiled off into a vapor.
Xylene is also a light aromatic C6H4(CH3)2 with a boiling point of 270 degrees. Used in all racing gasoline at a level of up to 30% (giving you a (R+M)/2 of 104 and a specific MON of 100.
The biggest consideration of all aromatics is the effects on the fuel system that they are being run through. All aromatics will have an adverse effect on rubber componets. And the increased burn rate of them. This directly relates to the RPM at which they are most effective of increasing power. When turning the motor at a low speed, the slower burning additives are better as they piston speed is slower and power is only created during the burn of the fuel. After the burn cycle has completed, gas expansion will soon cease. At a high RPM, with the piston moving at a high rate, the faster burn rate is ideal because the stroke time is much shorter.
This is a major reason that we are burning gasoline and not toluene or some other aromatic solvent for car fuel.
Methanol CH3OH has a combustion reaction of 2CH3OH + 3O2 -> 2CO2 + 4H2O. Methanol is converted down into MTBE which is a common additive in pump gas in small quanities, and is used as an octane increaser and oxygenate to decrease polution. (Gasohol)
Methanol, because of it's high oxygen content is a great additive, both to increase octane and fuel power, but requires additional fuel to produce the same power level (decreasing MPG because you have to run a richer mixture)
Has a slow burn speed that is idea in slow turning street motors and will also cool the intake charge considerably.
But it has its down sides too. It is corrosive to most metals, and some plastics. It is toxic, can enter the body through the skin and in pure form will burn without a visible flame. Although I can't seem to find anything specific about Methanols specific Octane number I do know that it is compatible in motors of up to 23 to 1 compression ratio. (Remember that supercharging an engine is compairable to increasing the compression ratio and I will provide the chart later for what boost level equates to what compression ratio change.)
So after all that here's the final skinny on this.
With an 80/20 mix of aromatic solvet to pump gas here are the final numbers
20% toluene with pump gas will get you a (R+M)/2 of 104
20% xylene wit pump gas will get you a (R+M)/2 of 110
Methanol, although being better than either of the two, is quite unsafe, draws moisture readily from the atmosphere and should only be considered as a race only fuel. I am going to try to do some more research on the mixing of Methanol and Gasoline to see where it might lead. The performance aspect, for pure performance use is promising but with costs being a real factor for Methanol it's not something to work well as an additive due to its high ratio requirement and the need to increase the fuel mixture in order to see an increase in power.
I am considering some testing with model airplane fuel that is 80% methanol and 20% nitromethane. But Nitro is VERY suseptiable to knock, and no current additive seems to change that. More over adding it to gasoline it has been found to severly decrease the octane rating of gasoline, even though it's about 53% oxygen content and releases this oxygen very readily which would make it a wonderful gas additive except for the fact it kills MON quickly. Possibly blending it in small quanities, with Methanol as I am planning to do, will result in a good performance fuel. Although taking it to the track will get you throw out and its smell does leave something to be desired.
Somethng else that I am finding out. Octane does NOT make power. Higher Octane fuels than your motor actually require are not going to make more horsepower. So if you are getting into messing with fuels. Don't go overboard, becauser it's wasteful, and does nothing. The reason that fuels that are not high enough in octane don't make as much power is that power is reduced due to either spark knock, or the retarding of the timing to get rid of the spark knock.
Also don't get it in your head that high enough octane will allow you to run some silly spark advance, like 50 degrees in a small block chevy (yes I know that ford guys can do this) the maximum timing for a motor has to do with the shape of the combustion chamber and the way that effects the flame front and the speed at which the fuel burns, Not the octane of the gasoline running in it. If you switch fuels, then timing can be adjusted accordingly. Methanol, it burns slower, so it requires more advance than gasoline. Nitromethane on the other hand, or any aromatic solvent if you were to try to run it as a primary fuel would require much less timing because or the burn rate being faster than gasoline. This is also why, and here comes the nay sayers, a lower octane fuel, due to it's SLOWER burn time will make more power than a high octane fuel because the octane additives make it burn FASTER. We do not deal with motors that spin at a sufficent RPM to require a fast burn fuel. If this was Columbus Formula1racing.com then the prior statement would no apply due to the fact our motors would idle at what most of us consider to be redline for the motors we have (around 5000 RPM) and not start making real power until 9000 RPM. If any of you are spinning your motor up like that (12000 to 14000) other than the bike guys, I would really love to see that.
NOTE: This is the power of reading, some parts of this I knew, most I learned last night through reading and studying books on the subject.
So you noobs take heed. There is a wealth of information both on the web and in books. You want to learn about things like this, read, don't guess, if you are looking to get books on a specific subject, if its car related, look for books by David Vizard first, if he puts in in one of his books, it fact, not speculation