Burning petrol:• Petrol vapour and air are
mixed and compressed.
• The mixture is ignited by a spark.
Pollution:
• Inefficient burning produces carbon monoxide.
• The spark produces nitrogen oxides.
LO: I understand how a petrol engine works.
The standard for the quality of a petrol fuel is measured against iso-octane:
The higher the number the more smoothly the petrol burns.
2,2,4-trimethylpentane
Iso-octane burns smoothly and is given an octane number of 100.
H C C C C C H
H
H
C
C
H
H
C
H H
H
HHH
HH
H
HHH
LO: I understand what is meant by the octane number of a fuel.
The octane number can be increased by:
• decreasing the carbon chain
LO: I understand what is meant by the octane number of a fuel.
• increasing the branching
• using aromatics
If the octane number is too low the fuel will auto ignite at the wrong point in the engine cycle.
This can damage the engine.
Petrol is made from 3 fractions of crude oil:
Reforming the naphtha fraction:
LO: I understand how petrol is made.
• changes the shape of the molecules without changing the number of carbon atoms
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