Chemical composition of Kerosene

[18greens]

OK I've looked for this and I can't find the answer anywhere. ( I know my wife will say I haven't looked properly).

What is the chemical composition of Kerosene and why is it more stable than 100LL.

I understand, like diesel, if you chuck a match on it will not burn without a wick .



Anyone know what its made of?

[Legal Flyer]

Your best bet would be to look up one of the specifications on which kerosene (such as Jet A1) is sold, for example what used to be DERD 2494 now DEFSTAN 91/91.

Like most refined products it contains not only hydrocarbons but also other elements with specified min/max of those constituents to be on spec.

Incidentally whilst it may be (relatively stable) it carries its own risks, in particular the risk of static build up and explosion when rapidly fuelling a plane. That is why a special compound known as SDA (Static-Dissipator Additive) is added to jet fuel to reduce the risks. This is done either at the refinery or at the airport - though the practice is not universal and other measures can be taken (eg grounding the aircraft). Incidentally I believe I read somewhere that Concorde is fuelled without the use of SDA in the US it being though that grounding of the aircraft is the safest practice.

[Joe Phoenix]

http://www.galcit.caltech.edu/EDL/publications/reprints/flash.pdf

:confused:

[Mycroft]

For simple comparison
Jet A1 = Kerosene (Parafin)
Avgas 100ll = Gasoline (Petrol) (actually in old terms 5 star)

these equivalences should give the general idea to anybody, for a slightly more technical explanation all petroleum based fuels are a mixture of hydrocarbons selected by boiling point, that selected for kerosene having a higher boiling point than 100ll.
Any flammable liquid will ignite when a certain proportion of the liquid is in the gas phase (flash point). This is mainly dependent upon temperature, but is also effected by external pressure and surface area, therefore if you increase the surface area of kerosene (by using a wick) the flash point is greatly reduced.

[18greens]

Thanks Mycroft,

Can I take it a little further.

If 100ll is Octane (C8 H18) is kerosene Nonane( C9 H20)? Is it simply another carbon in the chain that raises its flash point.

[Gerard123]

The more carbons an alkane chemical has the stronger the bonds between the molecules are because there are more electrons present.The first four alkanes : methane , ethane , propane and butane are all gasses under standard room conditions. From pentane (5 carbons) up all are liquid and from 20 carbons on they are all waxy substances. Thus the less carbons an alkane chemical has the more volatile (ability to turn to a gas) the chemical is. So jet A-1 with 9 carbons (nonane) is less likely to turn to a gas and mix with the air. Since alkanes only burn in the presence of oxygen if the jet A-1 mixes with the oxygen in the air it is potentialy more explosive. So 18 greens is correct in his assumption that another carbon will lower the flashpoint.That's why it is safer to fly with full tanks. The only reason you have to ground an aircraft when refueling is because it is most likely to have empty tanks. Static build increases the risk of a spark which could cause the well mixed jetA-1 to explode. The same applies to 100lloctane or any petrol. I don't know if anyone remembers when cars had chains that dragged under them? It was for the same reason. Today of course we have SDA's added to petrol from the start to eliminate the need fo a chain. Grounding is not 100% proof since sometimes there is no actual metal to metal contact for reasons such as paint etc. To sum it up JetA-1 is more stable than 100ll , SDA's are the way of the future and no I am not from BP this is all 12'th year school chemistry !:ok:

[bookworm]

18greens

Because they are produced by distillation, fuels like kerosene are not pure alkanes but mixtures with a distribution of molecular weights. As far as I can see from a brief search, kerosene seems to be 10 to 14 carbons, with a peak around 11.

[Gerard123]

Of course they wouldn't be pure because there are all kinds of processes to create them and different additives. but to keep it simple I would have thought my description would be suitable . remember we are pilots here not scientists !

[bookworm]

No problem with what you wrote, Gerard123. You answered the question about stability, I tried to answer the question about what kerosene is.