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Developing fuels

Developing fuels. DF 3 Petrol is popular. Petrol and Crude Oil. Petrol is a mixture of many different compounds blended to give the right properties 30% - 40% of each barrel of crude oil goes to make petrol Thick black liquid with gases and solids dissolved inside

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Developing fuels

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  1. Developing fuels DF 3 Petrol is popular

  2. Petrol and Crude Oil • Petrol is a mixture of many different compounds blended to give the right properties • 30% - 40% of each barrel of crude oil goes to make petrol • Thick black liquid with gases and solids dissolved inside • Crude oil is a mixture of hydrocarbons (molecules made of a chemical combination of carbon and hydrogen atoms)

  3. Petrol and Crude Oil • Crude oil is separated by fractional distillation • works because the molecules have different boiling/condensation points • many of these hydrocarbons are alkanes, and are sorted into fractions • each fraction has a range of boiling points in the distillation • narrow boiling ranges of limited carbon number (eg petrol is C5 to C7 boiling point 25C -75C) Gasoline and gas oil fractions are sources of petrol components Naptha used for high grade petrol and chemical feedstocks

  4. Petrol and Crude Oil

  5. Petrol and Crude Oil • 'straight run' gasoline from primary distillation doesn't make good petrol, most needs further treatment • supply and demand - surplus of high boiling hydrocarbons which need to be cracked to make more volatile hydrocarbons suitable for petrol etc. (AND in the process making valuable alkenes - important secondary chemical feedstock for a huge number of other chemicals including plastics) • the 'refinery's job' is to convert the crude oil fractions into useful products - wide range of hydrocarbons • Alkanes converted into other types of hydrocarbon cycloalkanes (containing carbon rings) arenes (containing benzene rings)

  6. What’s left over? • After distillation there is a residue left over • Can be used to make useful products • First is distilled again under reduced pressure • Vacuum distillation avoids high temps that would be needed at atmospheric pressure (which would crack the hydrocarbons) • More volatile oils distils • Oils are used as fuel oils in power stations or ships • Others are used as base for lubricating oils

  7. Winter and summer petrol • Not as simple as sending straight run gasoline to the pump. Petrol has to be blended to get the right properties – Volatility • In a car engine mixture of petrol vapour and air is ignited • When weather is cold petrol is difficult to vaporise – car difficult to start How do petrol blenders solve the problem?

  8. Winter and summer petrol • Petrol companies make different blends for different times of year • Winter – more volatile compounds vaporise more easily, more small molecules such as butane and pentane • Summer – in hot weather you don’t want too many volatile compounds – petrol would vaporise to easily and you would lose petrol from the tank – costly and polluting • Different blend for different countries How would petrol blends differ in Russia and Egypt ?

  9. Octane rating of petrol is important characteristic petrol blenders must take into consideration This is a measure of the tendency of the petrol to cause a problem known as ‘Knock’ The problem of knocking Figure 12 How a four-stroke petrol engine works. The compression stroke is shown here. The piston compresses the petrol–air mixture, then a spark makes the mixture explode, pushing the piston down and turning the crankshaft.

  10. Octane number • The tendency of a fuel to auto ignite is measured by its octane number. • 2,2,4 – trimethylpentane is a branched alkane with a low tendency to auto-ignite – given an octane number of 100 • Heptane- straight chain alkane - auto-ignites easily and is given an octane number of 0 • The octane number of any fuel is the percentage of 2,2,4 – trimethylpentane in a mixture of 2,2,4 – trimethylpentane and heptane which knocks at the same compression ratio as a given fuel • For example 4-star petrol has an octane number of 97 and knocks at the same compression ratio as a mixture of 97% 2,2,4 – trimethylpentane and 3% heptane CH3 CH 3 l l CH3-C-CH2-CH-CH3 l CH3 2,2,4 – trimethylpentane Low tendency to auto ignite scores 100 CH3-CH2-CH2-CH2-CH2-CH2-CH3 Heptane High tendency to auto ignite scores 0

  11. In a petrol engine, the petrol-air mixture has to until at the right time As the fuel air mixture is compressed it heats up Many hydrocarbons auto-ignite in these conditions The fuel air mixture catches fire as it is compressed When this two explosions happen one due to compression and one with the spark This causes a knocking sound Engine performance is lowered and cylinder can be damaged The problem of knocking

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