This is the process that takes place in an engine (By the piston):
1- Input (Remember as “Suck”)
2- Compression (Remember as “Puff”)
3- Explosion (Remember as “Bang”)
4- Exhaust (Remember as “Blow”)
Knocking in engines occurs when a fuel with a low octane number is used.
Knocking is the pre-ignition of fuel.
Fuel’s ignitability must be in sync with the piston performance, otherwise knocking will occur, damaging the engine.
Measurements of pre-ignition. (How likely is it for a fuel to pre ignite)
The scale goes from 0 to 100, with some fuels being in the negatives, or even +100.
Example of a 100 is 2,2,4- trimethylpentane.
Example of a 0 is Heptane.
Fraction columns generally produce fuels of 40-60 octane numbers. While modern engines require 95-98. Therefore fuel must be manufactured in order to give it a greater Octane value.
Octane numbers increase as the Hydrocarbon chain becomes shorter, and/or more branched.
We can shorten hydrocarbon chains via Cracking.
E.g. C20 H42 à C8H18 + C12H24
We can increase branching via Isomerism.
We can also use reforming to create cycloalkanes from hydrocarbon chains.