Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is n-heptane really explosive?

  1. Apr 12, 2018 #1
    Is n-heptane really explosive? Why is it chosen to be the lowest value (zero) for the octane number? Is it because it is really explosive? and why should n-heptane be so explosive (if that is the case)?

    Thanks
    Ric
     
  2. jcsd
  3. Apr 12, 2018 #2

    Borek

    User Avatar

    Staff: Mentor

    Please google for octane number, almost everything you wrote is incorrect.
     
  4. Apr 12, 2018 #3
    Octane number measure "the tendency of a fuel to resist self-ignition" (quoted from Wikipedia to avoid misunderstandings).

    If a fuel has octane number ##n##, it behaves like a mixture of n-heptane and iso-octane with ##n##% of iso-octane. This means that a fuel with octane number 100 behaves like pure iso-octane and a fuel with 0 octane number behaves like pure n-heptane.

    Also an octane number of 0 means the fuel is likely to self-detonate.

    I don't understand what I wrote wrong in the previous post
     
  5. Apr 12, 2018 #4

    Borek

    User Avatar

    Staff: Mentor

    You are mistaking being an explosive with tendency of an fuel/air mixture to ignite during an adiabatic compression, these are fundamentally different things.
     
  6. Apr 12, 2018 #5
    I'm sorry, may fault. Let me rephrase my question: Why is a mixture of n-heptane and iso-octane chosen to be the reference to establish the tendency of a fuel to resist self-ignition? Why n-heptane and not other substances ?

    I hope the English is correct
     
  7. Apr 13, 2018 #6

    jbriggs444

    User Avatar
    Science Advisor

    If you want to quantity how an atomized liquid fuel resists self-ignition then a scale with one pure liquid fuel on the one end and a different pure liquid fuel on the other seems a reasonable way to go. The choice of those standard fuels is more or less arbitrary, though you do want the range between to cover the fuels and fuel mixtures that you are interested in classifying.
     
  8. Apr 13, 2018 #7
    High purity n-heptane was readily available when the heptane/octane rating system was conceived.
     
  9. Apr 13, 2018 #8
    Ok so I guess it's just an arbitrary decision based upon historical circumstances, there is not a scientific explanation for this.
     
  10. Apr 13, 2018 #9

    jbriggs444

    User Avatar
    Science Advisor

    [joke]And resublimated thiotimoline is finicky when dissolved in iso-octane.[/joke]
     
  11. Apr 13, 2018 #10
    I don't understand
     
  12. Apr 13, 2018 #11

    jbriggs444

    User Avatar
    Science Advisor

  13. Apr 13, 2018 #12
    I googled it and found out Resublimated Thiotimoline is an invented chemical compound that should "start dissolving before it makes contact with water" (Wikipedia), but I still don't get the joke. Anyway thank you all for the replies.
     
  14. Apr 13, 2018 #13
    n-heptane (C7) and iso-octane (C8) are both in the mix of what constitutes gasoline (C4 through C9). A major difference between the two is n-heptane has a straight chain structure while iso-octane is branched, and it turns out that straight chain HCs are more prone to causing detonation. You'd have to research this further, but my suspicion is these things in combination make n-heptane and iso-octane good proxies for how much 'knock' to expect from a particular gasoline formulation.
     
  15. Apr 13, 2018 #14
    Ok thanks.

    Yeah, I really want to know why is that
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Loading...