has anyone done a comparisons of the gas from different gas stations? I’m interested in combustable fuel. I realize that all stations have 87, 89 and 91 octane. But it seems to me that one could simply add more MTBE or ethanol or something to raise the octane. Thus have less combustable fuel for energy. Have there been any chemical analysis? Tests on dynos? etc. I ask this mainly because I personally do not use arco as I swear that I can feel the difference in my car.
Any scientific analysis done on those octane booster additives? Would the higher compression ratio required to ignite this fuel damage an engine not designed for the high compression ratio? I.e would using 91 in a car designed for 87 damage it?
how about fuel injection system cleaner? Does the additive itself affect octane at all? any negative effects to it?
Your engine’s compression ratio is the same no matter what fuel you use. Higher octane fuel does not require a higher compression ratio, since the fuel is ignited by the spark plug.
While you may use a higher octane fuel safely in a car designed for 87, you will receive no benefit from it.
You are aware that the gas from all the different gas stations probably comes from only 1 or 2 actual suppliers, right?
For example, here in Minnesota, all the oil comes into the state via 2 pipelines (Williams Bros. & Wood River) and goes to 2 refinery sites (Pine Bend & St. Paul Park), from which it is distributed to all the different gas stations around here. Each company claims to have their own ‘special’ additives that are added to ‘their brand’ of gasoline, but the basic product came up the same pipeline at about the same time as the competitors product. So I suspect comparisons between different gas stations would find only minor, if any, differences. Except maybe in the price, which I view as the major difference between gas stations.
I have a hard time believing that the difference between 87 and 91 is purely octane. Because it would seem to me that the MTBE/Ethanol that is added to raise octane will displace the more energy dense gasoline solution. Thus higher octane gasoline in this situation would contain less chemical energy, but more efficiently converted to mechanical energy. I just don’t see this as being correct.
I had always thought that higher octane fuel was purer, or contained more of whatever hydrocarbon was more energy dense and resistant to detonation (methanol?).
Please correct me if i’m wrong.
You’re probably right, but I had always thought there was a third step involved.
Major supplier -> franchise HQ(chevron, arco, shell etc) in the area -> local gas station.
Where franchise Hq could play with the fuel/octane boosters mixture. Because of this I see a possibility where the franchise HQ’s can add more octane boosters and less actual gas in order to reduce costs.
again, this is how I always pictured the chain of supply being. Am I wrong?
I meant to post this earlier but I was OBE (Overcome By Events – sounds much better than “I got busy and I forgot”.)
Gasoline with a higher octane rating has a lower energy density than gasoline with a lower octane rating. The energy density has no relation whatsoever to the efficiency with which it is converted to mechanical energy. That is purely a function of engine design.
Normal combustion in an engine’s cylinder, while rapid, is not an explosion, but simply very rapid combustion. Detonation can be caused by one of two different things happening inside the motor. I forget exactly what these two things are, but they can cause a shockwave within the cylinder. The shockwave, when it hits the inside of the cylinder, causes the “pinging noise”. ISTR that the shockwave whacking* the top of the piston can cause problems as well, increasing wear and possibly causing immediate damage, depending on the force of the whack and where the center of pressure impinges on the piston relative to the location of the connecting rod. (Correct me if I’m wrong, motorheads and engineers.)
–SSgtBaloo
*Note the use of jargon. Jargon makes or breaks any technical discussion. I hope you are all taking notes. There will be a test next period.
