Blending fuels

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.

Octane numbers

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.