Fuel Octane?
All Star
Joined: Jan 2007
Posts: 982
Likes: 0
From: Connecticut
RE: Fuel Octane?
ORIGINAL: Duso02
OOOOHHH!!! Somebody referred the same site as you did!!! Are you sure you aren't brothers? LOL J/K
ORIGINAL: FFMedic1479
Here, I just googled this page, kinda of blurry but a good explination of the principles of octane: http://chemistry.about.com/cs/howthi...a070401a_2.htm
Please tell me I don't sound like someone else on this site...
Here, I just googled this page, kinda of blurry but a good explination of the principles of octane: http://chemistry.about.com/cs/howthi...a070401a_2.htm
Please tell me I don't sound like someone else on this site...
All Star
Joined: Jan 2007
Posts: 982
Likes: 0
From: Connecticut
RE: Fuel Octane?
ORIGINAL: bdhuntr
If I remember correctly, the octane rating number indicates the resistance to anti-detonation (autoignition, also known as the anti-knock quality) of that fuel as if it contained that percentage of iso-octane (an isomer of octane, C8 H18) with the remainder heptane. This does not mean that 89 octane fuel contains 89% percent octane or iso-octane and 11% heptane, but it has the anti-knock qualities of such a fuel. In reality, most automotive (motor grade) gasoline contains iso-octane, heptane and other petrochemicals, including ethanol and other additives.
Octane ratings and the grade of fuel specified for a specific engine are mostly based upon the compression ratio of the engine, and the ambient air pressure that engine will be used in. At high altitudes, engines that require 87 octane at sea level can safely use 85 octane due to the lower amounts of air that is drawn into the cylinders; less air reduces compression in the cylinders, which deters knock.
Just think what it was like back in the day of supercharged and turbocharged multi-banked radial aircraft engines like Pratt & Whitney’s 28 cylinder, 4,363 cubic inch, 3,870 pound R-4360 Wasp Major radial engines that burned 115/145 octane gasoline to generate 21,000 teeth-rattling, heart-throbbing horsepower.
Don't put THAT in your gas tank! BTW, the 115/145 octane rating of AVGAS is not the same as the (R+M)/2 rating of motor grade gasoline (MOGAS). The 115 octane rating is for a lean mixture and the 145 is for a rich mixture and it is determined via a different testing procedure. Plus, it's a leaded fuel. They still manufacture 115/145 once a year for the air races in Reno.
ORIGINAL: FFMedic1479
Does the higher octane screw things up? I am not talking the 93 but the 110+.
Now, I definatly don't think that I am a chemist by any means (I got an "R" in high school chem... worse then an F, kinda like them telling you not to bothertaking it again, EVER), but I took this blue collared type class called Chemistry of Haz Mat for the firehouse. From what I remember, the word octane (8) comes from the chemical composition of C8H18... and the properties of the octane are based on the amount of carbon inside the chemical compound... more carbon more stable,and yields a higher amount of energy (propane has 3 carbons in the chain, resulting in a lower molecular weight being a gasand a lower boiling point, thus giving energy off earlier but not as much). So, the octane rating is the amount of octane compounds attached in the gasoline chemical compound (don't ask me what it is) and relates its properties to that compound. Soooo... if there are more octane compounds attached then there should be more energy and a higher ignition temp. I really need to stop drinking.
I hope there is a chemist on this site that will set me straight because I am probably wrong.
Does the higher octane screw things up? I am not talking the 93 but the 110+.
Now, I definatly don't think that I am a chemist by any means (I got an "R" in high school chem... worse then an F, kinda like them telling you not to bothertaking it again, EVER), but I took this blue collared type class called Chemistry of Haz Mat for the firehouse. From what I remember, the word octane (8) comes from the chemical composition of C8H18... and the properties of the octane are based on the amount of carbon inside the chemical compound... more carbon more stable,and yields a higher amount of energy (propane has 3 carbons in the chain, resulting in a lower molecular weight being a gasand a lower boiling point, thus giving energy off earlier but not as much). So, the octane rating is the amount of octane compounds attached in the gasoline chemical compound (don't ask me what it is) and relates its properties to that compound. Soooo... if there are more octane compounds attached then there should be more energy and a higher ignition temp. I really need to stop drinking.
I hope there is a chemist on this site that will set me straight because I am probably wrong.
Octane ratings and the grade of fuel specified for a specific engine are mostly based upon the compression ratio of the engine, and the ambient air pressure that engine will be used in. At high altitudes, engines that require 87 octane at sea level can safely use 85 octane due to the lower amounts of air that is drawn into the cylinders; less air reduces compression in the cylinders, which deters knock.
Just think what it was like back in the day of supercharged and turbocharged multi-banked radial aircraft engines like Pratt & Whitney’s 28 cylinder, 4,363 cubic inch, 3,870 pound R-4360 Wasp Major radial engines that burned 115/145 octane gasoline to generate 21,000 teeth-rattling, heart-throbbing horsepower.
Don't put THAT in your gas tank! BTW, the 115/145 octane rating of AVGAS is not the same as the (R+M)/2 rating of motor grade gasoline (MOGAS). The 115 octane rating is for a lean mixture and the 145 is for a rich mixture and it is determined via a different testing procedure. Plus, it's a leaded fuel. They still manufacture 115/145 once a year for the air races in Reno.
Veteran
Joined: Jun 2007
Posts: 387
Likes: 5
From: Bel Air, MD
RE: Fuel Octane?
Organic chemistry was one of my favorite subjects in HS, and I seriously thought of becoming a chemical engineer until I decided to join the military and found myself in the aviation maintenance field. It is hard to believe that just by adding one atom of carbon and a few atoms of hydrogen how quickly the properties change. If we could just figure out a way of burning iso-octane and heptane 100% complete, lf we would produce would be CO2, H2O and heat energy. But Al Gore would still be upset!
Yes, leaded fuel in your engine is bad. At the least it will coat your O2 sensors with lead deposits.
Originally Posted by Hellbilly1
yeah the 110 racing fueli used was leaded? is that bad?
Captain
Joined: Apr 2007
Posts: 566
Likes: 2
From: Western PA
RE: Fuel Octane?
Yep, as said, the higher the compression ratio, the higher the octane you should be burning. Ten plus years ago when I bought a Jeep 4.0 I was pissed that it required 91 octane! Them things had some high-compression!