You'll have to forgive me for being pretty ignorant on the workings of engines but I'm a scientist and I like to understand why things work the way they do. Engines that are designed/ tuned to run on premium must compensate (some change in ignition timing?) for the above phenomenon? So I'm guessing that whatever compensation they have works in conjunction with more octane to burn, hence more compression and more torque/ HP?

 

Premium fuel basically just has a delay in combustion. If you have an engine that has been tuned to take advantage of this, it can lead to slightly more BHP. If not, you're just wasting money because your not getting the compression/spark/fuel/O2 at the ideal time.

Always run the lowest octane your engine will run smooth with. Only go to a higher octane if your engine knocks or pings with the lower octane.

 

If I understand it right a engine that has higher compression it needs the higher octane to keep from pre-igniting. The higher compresson would cause the heptane to become too unstable in regular range of gas.

I have a question now. Is the gas (fuel) used in regually aspirated aviation engines (100 LL) 100% Octane?

 

Gasoline is a complex mixture of C6-C12 hydrocarbons. Its quality as a fuel for internal combustion engines depends on how much it makes an engine "knock". Engine knocking occurs when some of the air-fuel mixture explodes prematurely and independently of ignition by the spark plug.

Two compounds were selected for rating gasoline quality. 2,2,4-Trimethlypentane (isooctane) has very good antiknock properties (the fuel-air mixture burns smoothly in the combustion chamber) and was assigned an octane rating of 100. Heptane, in contrast has poor antiknock properties and was assigned and octane rating of 0.

The octane rating of a particular gasoline is a number equal to the percentage of 2,2,4-Trimethlypentane in a mixture of 2,2,4-Trimethlypentane and heptane that has the same antiknock properties as the gasoline being rated. For example, the antiknock properties of 2-methlyhexane are the same as those of a mixture of 42% 2,2,4-trimethlypentane and 58% heptane; therefore, the octane rating of 2-methlyhexane is 42. Ethanol, which is added to gasoline to produce gasohol, has an octane rating of 105.
Octane itself has an octane rating of -20.

, Source: Introduction to Organic and Biochemistry; 5th edition


I just took and passed (with an A I might add ) Organic chemistry. We discussed this gas issue in class one day. Any alkane above decane (C10) really has a boiling point to high for use in gasoline. The octane rating of an alkane is determined by its degree of branching. Unbranched heptane has an octane rating of 0, but Isooctane that is highly branched has an octane rating of 100. To increase octane rating, other additives can be used. Tetraethlylead was once added to gas to increase octane. However, about 1g lead/gallon of gasoline was emitted into the environment, which caused serious health problems and as we all know lead was removed from gasoline in the 70's. Today unleaded gasoline contains other chemicals to help boost octane such as alcohols, ethers, and other metals.

*** I'm not an Organic Chemist, but I did stay at a Holiday Inn Express last night ***

 

Congrats on the A in organic, its a tough class! I loved organic chem in college and if I had it to do over again I would go into synthetic organic chem instead of molecular biology.

 

Better you than me! In regards to this octane stuff, I think the car manufacturers obviously have a deal worked out with the oil refineries. Just think about it, the lower the octane rating the faster a fuel will ignite and burn. So by requiring our trucks to run 87, Ford has the engine designed to consume as much fuel as possible. Ford must know that X% of the general population has no clear understanding of octane ratings, and the only thing that the majority of the public really understands about octane is that the lower the octane rating the cheaper the fuel. This make Ford out to be a winner in most consumers eyes leading them to think "hey Ford is on my side not the oil companies, if they wanted to help the oil company they would require their engines to burn 93 octane".

Or maybe I just have crazy ideas that knowone else understands

 

Taken from the Motor Trend website review on the F-150..
"...Intake and exhaust valves are timed to open and close in unison to optimize engine performance across the entire rev range while enabling a higher (9.8:1) compression ratio to operate with regular-grade gasoline..."
Initially, by having such high compression ratio I would have suggested to use Premium fuel to avoid preignition.
But after reading what ultramax21 says it makes perfect sense that this regular-grade gasoline thing might just be a marketing issue.