gasoline

Burning Gasoline
To burn gasoline, you mix it with air, compress it, and ignite it with a spark. Roughly speaking, it takes about 3.5 pounds of oxygen for each pound of gasoline you want to burn. Air is about 23% oxygen, so it takes about 15 pounds of air for each pound of gasoline. A gallon of gasoline weighs about 6.25 pounds, and requires 95 pounds of air to burn. 95 pounds of air is about 11,500 gallons of air. So we see why internal combustion engines are often called air pumps. Five gallons of gas will use up all the oxygen in almost 60,000 gallons of air. This is all the oxygen in a room 20' x 20' x 20', more or less a typical two stall garage. When you're burning the gasoline, you mix it with air and compress it. The horsepower your engine makes is directly proportional to the compression ratio - the more you can compress the mixture, the more horsepower you get. Unfortunately, at higher compression ratios the fuel / air mixture has the rather annoying habit of burning on its own rather than waiting patiently for the spark plug. When the mixture self-ignites there will be more than one flame front in the cylinder. When these flame fronts collide, the pressure in the cylinder increases very dramatically resulting in a knocking sound and the likelihood of engine damage. If your engine is knocking, it's very important you do something to fix the problem. To fix engine knocking, you can lower the compression ratio, which will lower the engine's power output. Or, you can use different gasoline which is formulated to burn slower and be harder to ignite. We have a number to tell us how slowly the gasoline ignites - it's called the octane rating. It would more properly be called the anti-knock rating. Higher octane ratings mean slower burning. Slower burning will prevent the knocking, but will also cost us horsepower. In the US it's well known that bigger numbers = more money = better. But with gasoline, lower octane ratings mean less money and often more horsepower. You want to run the lowest octane rating you can run without detonation or knocking. The story of gasoline is the story of finding ways to increase the octane rating, so that car manufacturers can make engines with higher compression ratios and more power.

Density
The specific gravity (or relative density ) of gasoline ranges from 0.71–0.77 ( 719.7 kg / m 3 ; 0.026 lb / in 3 ; 6.073 lb/ US gal ; 7.29 lb/ imp gal ), higher densities having a greater volume of aromatics. Gasoline floats on water; water cannot generally be used to extinguish a gasoline fire, unless used in a fine mist.

Chemical analysis and production
Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specifications for modern engines (in particular octane rating; see below), but will form part of the blend.    Some of the main components of gasoline: isooctane, butane , an aromatic compound , and the octane enhancer MTBE. The bulk of a typical gasoline consists of hydrocarbons with between four and 12 [|carbon] atoms per molecule (commonly referred to as C 4 -C 12 ). The various refinery streams blended to make gasoline have different characteristics. Some important streams are: The terms above are the jargon used in the oil industry but terminology varies. Overall, a typical gasoline is predominantly a mixture of paraffins ( alkanes ), naphthenes (cycloalkanes), and olefins (alkenes). The actual ratio depends on: Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such regulations led to increasing preference for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce benzene content. Gasoline can also contain other organic compounds, such as organic ethers (deliberately added), plus small levels of contaminants, in particular organosulfur compounds, but these are usually removed at the refinery.
 * **straight-run gasoline** is distilled directly from crude oil . Once the leading source of fuel, its low octane rating required lead additives. It is low in aromatics (depending on the grade of crude oil ), containing some naphthenes ( cycloalkanes ) and no olefins . About 0-20% of gasoline is derived from this material, in part because the supply of this fraction is insufficient and its RON is too low.
 * **reformate**, produced in a catalytic reformer with a high octane rating and high aromatic content, and very low olefins ( alkenes ). Most of the benzene, toluene , and xylene (the so-called BTX ) are more valuable as chemical feedstocks and are thus removed to some extent.
 * **cat cracked gasoline** or **cat cracked naphtha **, produced from a catalytic cracker, with a moderate octane rating, high olefins (alkene) content, and moderate aromatics level.
 * **hydrocrackate** (heavy, mid, and light) produced from a hydrocracker, with medium to low octane rating and moderate aromatic levels.
 * **alkylate** is produced in an alkylation unit, involving the addition of isobutane to alkenes giving branched chains but low aromatics.
 * **isomerate** is obtained by isomerizing low octane straight run gasoline to iso-parafins (like isooctane).
 * the oil refinery that makes the gasoline, as not all refineries have the same set of processing units;
 * crude oil feed used by the refinery;
 * the grade of gasoline, in particular, the octane rating.