Gasoline
Gasoline (or Petrol) is a petroleum liquid mixture consisting primarily of hydrocarbons used as fuel in internal combustion engines. The term gasoline is primarily used in English-speaking North America to refer to such a mixture. People in other parts of the English-speaking world use the term petrol for such mixtures.
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The vast majority of hydrocarbon molecules present in gasoline are aliphatic compounds, meaning that they consist of chains of carbon atoms linked to hydrogen along the sides and at the ends. This contrasts with aromatic hydrocarbon molecules, which form rings of atoms. Most hydrocarbon chains in gasoline range in length from 6 to 12 carbon atoms. Typical gasoline also contains some other organic compounds: aromatic and other unsaturated hydrocarbons, organic ethers, amines and sulfoxides. Gasoline is a more volatile fuel than diesel or kerosene. The reason for this is not only the base constituents, but the additives that are put into it.
Many of the non-aliphatic hydrocarbons naturally present in gasoline (especially aromatic ones like benzene), as well as many anti-knocking additives, are carcinogenic. Because of this, any large-scale or ongoing leaks of gasoline pose a threat to the public's health should the gasoline reach a public supply of drinking water. The chief risks of such leaks come not from vehicles, but from gasoline delivery truck accidents and leaks from underground storage tanks. Because of this risk, most underground storage tanks now have extensive measures in place to detect and prevent any such leaks. Gasoline also readily evaporates, meaning that storage tanks on land and in vehicles must be properly sealed. However, certain measures must be in place to allow appropriate venting to prevent the buildup of pressure inside or outside.
The energy content of gasoline in the US is about 32 MJ/L (120 MJ/gallon).
It is possible to have octane ratings above 100, which seems confusing but merely reflects the fact that octane is not the most intensely burning substance available. Racing fuels and LPG typically have octane ratings of 110 or significantly higher.
It might seem odd that fuels with higher octane ratings burn less easily, yet are generally considered more powerful. Using a fuel with a higher octane allows the engine to be run at higher compressions, and not have problems with knock. Compression is directly related to power, so engines using higher octane deliver more power, explaining the common misconception. Some high-performance engines are designed to operate at the higher compression levels associated with high octane numbers, and thus demand high-octane gasoline.
Petrol pumps in Germany
Chemical Analysis
Octane rating
Gasoline typically carries an octane rating, which is a measure of how resistant gasoline is to premature detonation (knocking). It is measured relative to a mixture of isooctane (2,2,4-trimethylpentane) and n-heptane. So an 87-octane petrol has the same knock resistance as a mixture of 87% isooctane and 13% heptane. Petrol is typically separated from crude oil via distillation, so the mixture of the molecules in the resulting fuel is dependent on the oil used. Romania was a supplier of "light-sweet" crude oil, which, when distilled, resulted in a petrol with an 87 rating. 87 octane was the general benchmark for much of the world, and is the current standard rating for "normal" petrol in the US and Canada.History
Lead additives
Because the mixture known as gasoline has a tendency to explode early or "knock", lead additives were first blended with fuel in the 1920s. This practice continued through the 1980s. The most popular one was tetra-ethyl lead. However, with the recognition of the environmental damage caused by the lead, and the incompatibility of lead with catalytic converters, most countries are in the process of phasing out the sale of leaded fuel, and different additives to reduce knocking are now used. Among the most popular ones are aromatics, ethers and alcohol (usually ethanol or methanol). There are also additives to reduce internal engine carbon buildups, to increase oxidation, and to allow easier starting in cold climates.
WWII and Octane Story
One interesting historical issue involving octane rating took place during WWII. Germany received the vast majority of their oil from Romania, and set up huge distilling plants in Germany to produce petrol from it. In the US the oil was not "as good" and the oil industry instead had to invest heavily in various expensive boosting systems. This turned out to be a huge blessing in disguise. US industry was soon delivering fuels of ever-increasing octane ratings by adding more of the boosting agents, with cost no longer a factor during wartime. By war's end their aviation fuel was commonly 130 to 150 octane, which could easily be put to use in existing engines to deliver much more power by increasing the compression delivered by the superchargers. The Germans, relying entirely on "good" petrol, had no such industry, and instead had to rely on ever-larger engines to deliver more power. The result is that British and US engines consistently outperformed German ones during the war, playing no small part in the defeat of the Luftwaffe.See Also
External Links