Chemistry AS DF DF3 DF4
- Created by: A.B.
- Created on: 01-12-13 12:13
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- DF Auto-Ignition and Octane Numbers SL DF3 and DF4
- Definition
- Auto-ignition is the explosion of a fuel without a spark.
- The octane number is a measure of the tendency of petrol to auto-ignite.
- High number, low tendency
- Auto-ignition in a petrol engine causes:
- A knocking sound
- Reduced engine performance
- Engine damage
- Octane Numbers
- 2,2,4-trimethylpentane = octane number 100
- 80% 2,2,4-trimethylpentane with 20% heptane = octane number 80
- Heptane octane number 0
- 80% 2,2,4-trimethylpentane with 20% heptane = octane number 80
- Comparing octane numbers
- Short chain compounds have a higher octane number than long-chain compounds
- Branched-chain compounds have a higher octane number than the corresponding unbranched-chain compounds
- Cycloalkanes have higher octane numbers than the corresponding straight-chain alkanes
- Arenes have higher octane numbers than cycloalkanes
- Oxygenates have higher octane numbers than the corresponding alkanes and are added to petrol to increase the octane number.
- The photochemical industry uses a number of different chemical reactions to increase the octane numbers of the components in petrol.
- Cracking
- Reforming
- Isomerisation
- 2,2,4-trimethylpentane = octane number 100
- Definition
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