Gasoline, petrol (British English) or gas (American English) is a colourless petroleum-derived flammable liquid that is used primarily as a fuel in spark-ignited internal combustion engines.
In most parts of the world gasoline specifications are regulated. In Europe Test methods are those specified in EN 228:2004 while in the US are specified in 40 CFR Part 80.
On average, a barrel (42 US gallon or 160 litres) of crude oil yields about 19 US gallons (72 litres) of gasoline, though this varies based on the crude oil assay.
Gasoline is enhanced with a variety of additives to improve the characteristics of a particular blend to resist igniting too early (which causes knocking and reduces efficiency in reciprocating engines) and it is measured by its octane rating, one of the best rating being the research octane number (RON). Gasoline is produced in several grades of octane rating:
-
Straight-run gasoline, commonly referred to as naphtha, which is distilled directly from crude oil. Once the leading source of fuel, its low octane rating RON, required lead additives. The chemical properties (namely RON and Reid vapor pressure) of the straight-run gasoline can be improved through reforming and isomerisation.
-
Reformate, produced in a catalytic reformer, has a high octane rating with high aromatic content and relatively low olefin content. Most of the benzene, toluene and xylene (the so-called BTX hydrocarbons) are more valuable as chemical feedstocks.
-
Catalytic cracked gasoline, or catalytic cracked naphtha, produced with a catalytic cracker, has a moderate octane rating, high olefin content and moderate aromatic content.
-
Hydrocrackate (heavy, mid and light), produced with a hydrocracker, has a medium to low octane rating and moderate aromatic levels.
-
Alkylate is produced in an alkylation unit, using isobutane and olefins as feedstocks. Finished alkylate contains no aromatics or olefins and has a high MON.
-
Isomerate is obtained by isomerizing low-octane straight-run gasoline into iso-paraffins (non-chain alkanes, such as isooctane). Isomerate has a medium RON and MON, but no aromatics or olefins.
-
Butane is usually blended in the gasoline pool, although the quantity of this stream is limited by the RVP specification.
-
Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are different conventions for expressing octane ratings, so the same physical fuel may have several different octane ratings based on the measure used.
-
The octane rating of typical commercially available gasoline varies by country. In Europe 95 RON is the standard for regular unleaded gasoline and 98 RON is also available as a more expensive option.
-
Both Shell and BP produce fuel at 102 RON for cars with high-performance engines, and in 2006 the supermarket chain Tesco began to sell super-unleaded gasoline rated at 99 RON.
