Whats in petrol?

[Sojournerman]

Hi guys
this is more a curiousity question for me
What is in petrol? Say your average 95 octane rated go juice
I know benzene there some octane not sure what else
I have googled but not much on percentages wiki goes into it abit
As I say this is a curiosity question for me
Thanks

 

[LittleInch]

I sure hope there isn't much pure benzene in your petrol - though benzene is what petrol / gasoline / motor spirit is called some times in Africa.

"Petrol" is not a single substance. It is mainly hydrocarbons with a predominance of C6-C8 compounds, but a wide mix of others.

In Europe and the US there is up to 10% ethanol, though Brazil in particular has a min of nearly 30% to make use of the indigenous sugar crop which is distilled to ethanol.

Then there are a number of small volume additives to make the stuff actually usable in cars - anti knock agents, detergents, anti-foaming agents, TBE, anti icing etc etc.

Try searching gasoline

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Also: If you get a response it's polite to respond to it.

 

[romke]

petrol may vary in components somewhat dependent on local specifications and climate. generally speaking it is a mix of hydrocarbons with a boiling range of say about 30 deg C up to 160 deg C. in areas with very high temperatures the more volatile components may be left out somewhat, in very cold areas the highest boiling components may be left out and some more volatile compounds may be added to obtain cold weather startability.

to acquire the recommended knockrating most of the individual components need to meet or exceed that knockrating, which calls for predominantly branched alkane chains within the preferred boiling range. a knockrating of 95 means that the mixture has the same knockrating of a mixture of 95% 2.2.4-trimethylpentane and 5% n-octane

apart from the basefluid as described above petrol can contain small amounts of substances like detergents and dispersants to prevent fouling up of the fuel injection system or the carb used and to prevent deposits in the combustion chamber to prevent ignition by glowing deposits.

again, depending on the local specification, other components may be added in small amounts like bio-alcohol, anti-icing components, color dyes, ant-knock agents (as a substitute for the tetra-ethyl-lead as used in the past) etc. the amount and type of added components nowadays is restricted by the exhaust gas treatment system attached to the engine to prevent fouling up three way catalysts.

most times nowadays different makes of fuel are dispatched from the same depot. that does not mean all the fuels exactly the same. only the basefluid is the same and is stored in large tanks. when a tanker arrives to pick up a load, fuel is delivered from the large tanks via a blending station where the necessary proprietary "cocktail" of additives is added as per specification.

 

[LittleInch]

romke - spot on.

I would ony say that in your last para, it is different "brands" of petrol. The base 99% is exactly the same, but each "brand", whether it be an oil company or large retailer (supermarket) has it's own "pot" of additives which is switched on or off depending on which tanker is being loaded.

Some time ago, mid 1980's , this mixing fell down when at a more basic terminal, the extra additive for "Formula shell" was added by a bucket poured into the tanker compartment and "mixed" during filling and travelling to site. Someone got it wrong and added 10 x too much and consequently got bad publicity when a fleet of cars (Vauxhalls) started suffering premature engine failure....Formula shell was withdrawn and their expensive advertising gone to waste.

http://www.honestjohn.co.uk/forum/post/index.htm?t=8911

http://autoshite.com/topic/23896-qu...e-90s-that-damaged-engineswhat-was-it-called/

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sojournerman]

Thanks guys
Love the info especially about petrol brand mixing failures
Any more of those?

 

[georgeverghese]

Benzene in petrol adds to the octane number, but due to health reasons, its content in gasoline is restricted by legislation to an upper limit which varies depending on which country you are in. To make up for the loss in octane number due to this limitation in benzene content, isomerate is added. Isomerate is usually a straight run gasoline fraction, whose straight chain alkane fraction is partially converted to branched chain isomers in an isomerisation unit.