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Octane number

Octane number. Internal Combustion Engine. Suck Squeeze Bang Blow. Straight chain alkanes auto-ignite When put under pressure they explode This causes “knocking” which means the engine runs less efficiently. Octane Number. The higher the octane number, the less knocking.

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Octane number

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  1. Octane number

  2. Internal Combustion Engine • Suck • Squeeze • Bang • Blow

  3. Straight chain alkanes auto-ignite • When put under pressure they explode • This causes “knocking” which means the engine runs less efficiently

  4. Octane Number • The higher the octane number, the less knocking. • •Increasing chain length decreases (worsens) octane number. Butane 94, pentane 62, hexane 25, heptane 0. • •Increasing branching increases (improves) octane number.

  5. Ways to process fuel fractions Cracking Isomerisation Reforming

  6. Cracking • Recap - • –the process of converting a long alkane into a shorter alkane(sometimes branched) and an alkene. • –This improves the octane number (and produces alkenes for polymerisation) • Produces branched hydrocarbons and aromatic hydrocarbons

  7. Aromatic hydrocarbons • Contain benzene rings

  8. Isomerisation • the process of converting a straight chain alkane into a branched isomer. • –This improves the octane number. • –The catalyst is aluminium oxide – alkanes heated, bonds broken and then new bonds made

  9. Zeolites • –Zeolites are used as molecular sieves to separate the isomers.

  10. Reforming • the process of converting a straight chain alkane into cycloalkanes and aromatic compounds. • –This improves the octane number. • –The catalyst is platinum. • –(During the process some of the hydrocarbons decompose to carbon, which decreases the efficiency of the catalyst. Excess hydrogen is added to suppress the formation of carbon.)

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