Joesmoe
IMOKUR2
Bunch of myths out there about fuel. In the early early days, engines were made low compression because that was all the technology could support - cylinder walls, pistons, seals, valves, oil, and so on, and the fuel was short-chained hydrocarbons - principally hexane - obtained by simple distillation. As research moved into high gear ahead of World War II, and there came the realization that higher compression could yield higher power to weight, the need arose for fuel able to handle the higher compression, and so was a standard to measure it.
Those who have taken organic chemistry somewhere along the way may recall there is an international system for naming hydrocarbons, and there is a simple series to start:
A single carbon and four hydrogen atoms is methane -- or the primary constituent of natural gas.
Two carbons and six hydrogen atoms is ethane - also a gas
Three carbons = propane - loved by barbecue grills and others - a gas
Four carbons = butane - found in lighters - gas/liquid
Five carbons (where the international naming convention comes in) = pentane - liquid
Six carbons = hexane - principal component of early gasoline - liquid and so on
Seven carbons = septane
Eight carbons = octane
So when "they" were looking at increased performance, they arbitrarily decided that a laboratory engine running on a fuel of pure octane would be rated "100". And all other fuels would be compared to that.
In short order, chemists found that longer chained hydrocarbons resisted detonation better - to a point. Branched hydrocarbons resisted detonation still more. And certain additives really boosted the "octane" rating - the most well known was tetraethyllead (TEL).
Refineries were built that "cracked" the oil to both increase the fraction of gasoline and increase the occurrence of branched chain hydrocarbons.
Midway through World War II, one mixture of fuel and TEL was rated 140 octane, and many high performance aviation engines were designed to take this fuel.
So higher octane rating these days is achieved primarily the old fashioned way -- by increasing the proportion of longer and branched chained hydrocarbons in the fuel. The trade off is one gets fewer gallons of higher octane fuel from a barrel of oil - so more expensive.
Those who have taken organic chemistry somewhere along the way may recall there is an international system for naming hydrocarbons, and there is a simple series to start:
A single carbon and four hydrogen atoms is methane -- or the primary constituent of natural gas.
Two carbons and six hydrogen atoms is ethane - also a gas
Three carbons = propane - loved by barbecue grills and others - a gas
Four carbons = butane - found in lighters - gas/liquid
Five carbons (where the international naming convention comes in) = pentane - liquid
Six carbons = hexane - principal component of early gasoline - liquid and so on
Seven carbons = septane
Eight carbons = octane
So when "they" were looking at increased performance, they arbitrarily decided that a laboratory engine running on a fuel of pure octane would be rated "100". And all other fuels would be compared to that.
In short order, chemists found that longer chained hydrocarbons resisted detonation better - to a point. Branched hydrocarbons resisted detonation still more. And certain additives really boosted the "octane" rating - the most well known was tetraethyllead (TEL).
Refineries were built that "cracked" the oil to both increase the fraction of gasoline and increase the occurrence of branched chain hydrocarbons.
Midway through World War II, one mixture of fuel and TEL was rated 140 octane, and many high performance aviation engines were designed to take this fuel.
So higher octane rating these days is achieved primarily the old fashioned way -- by increasing the proportion of longer and branched chained hydrocarbons in the fuel. The trade off is one gets fewer gallons of higher octane fuel from a barrel of oil - so more expensive.
