4
« on: June 26, 2007, 11:10:12 PM »
There seems to be a lot of people hanging onto "octane" in this thread like it is the "be all, end all" in the world of power production. This is certainly not the case, or the extremely high octane (approx 130 points) of LPG and CNG would certainly create more power, but in real world application, everyone viewing this thread should be able to see that they do not.
Let's start with Aviation Fuel:
The octane of aviation fuel is not measured in exactly the same way as it is in automobile fuel.
The motor method of ASTM (which once stood for the American Society for Testing and Materials, but now is an internationally recognized standardization body) testing is used to determine the motor rating of aviation fuel. This differs from the R+M/2 methods used for traditional automotive gasoline.
Because of the different ways in which automotive and aviation gasoline octane is measured one must be very careful when comparing absolute numbers. 100 octane aviation fuel is not equal to 100 octane automotive gasoline, however, the lean number rating of aviation fuel will be close.
Now let's discuss Race Fuel:
The most talked about and most easily misunderstood characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to detonation and preignition (knocking). It is measured relative to a mixture of iso-octane and n-heptane. So an 87-octane gasoline has the same knock resistance as a mixture of 87% iso-octane and 13% n-heptane.
So how do we get gas over 100 octane?? Because iso-octane is not the most knock-resistant substance available, and when other additives or substances to enhance octane are used in the refining and manufacturing process, it skews the standard that was developed back when Jesus was still a teenager. Everyone familiar with high performance engines is aware that racing fuels and aviation fuels typically have octane ratings of 110 or higher.
It can be said that fuels with higher octane ratings burn less easily, yet they remain extremely popular because they are thought of as being a more powerful fuel. Manufacturers recommend using a fuel with a higher octane so that an engine can be run at a higher compression ratio without having problems with knock. Compression is directly related to power, so engines that require higher octane usually deliver more power. This is usually where the misnomer of higher octane = more power stems from. It cannot be stressed enough that the power output of an engine not only depends on compression (naturally) but also depends on the energy content of its fuel. Where the confusion sets in is that no simple correlation between octane rating and actual power derivation (energy content) of the fuel exists. Some people believe that adding a higher octane fuel to their engine will increase its performance, but this is not the case. Engines perform best when using fuel with the octane rating that allows for maximum power production without detonation or preignition. Given today's advanced refining processes and additive packages, this is typically easily obtained without the gargantuan octane numbers of yore.
Just my $0.02
Show Posts
. Mine went over 500, but we backed it off a bit. Nice to know what it'll do, but no reason to run the original block and heads on the ragged edge without reason.
