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Single mother in need of explanation

Discussion in 'Electronic Repair' started by Dumb_Blonde, Mar 13, 2007.

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  1. Dumb_Blonde

    Dumb_Blonde Guest

    Thank you in advance for your time. I found a neat project to do with
    my 14 year old son, but would like to know the science behind it so it
    will be educational.

    Here is the video link.



    It is a fire cracker experiment, and I know he will love it, but I am
    clueless as to how this makes my car run.
     
  2. I assume the can is open on one end like a soup can, not a coke can. I
    think the water is there to provide an airtight, frictionless seal for
    more effect. Keeping the firercracker dry is tricky. This looks like a
    good use for the hundreds of firecrackers I have left over!

    What he is simulating is the explosion that happens in one of your cars
    engine cylinders. A car engine operates on a series of small controlled
    explosions. In your car, the explosive force drives a piston down,
    pushing a connecting rod which in turn rotates a crankshaft. A car
    engine has 4 to 8 cylinders which fire sequentially and smoothly. The
    links below illustrate this with a single cylinder like a lawnmower
    engine. These are "internal combustion engines".

    My sister did a similar science project years ago with a coffee can
    fitted with a spark plug and filled with a very small amount of gasoline
    or ether. A plastic lid was placed on top and an ignition coil made a
    spark which blew the plastic lid off. Not as dramatic as a fire cracker.

    http://www.keveney.com/otto.html
    http://en.wikipedia.org/wiki/Four-stroke_cycle

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  3. Their is no explosion in a properly operating internal combustion engine.
    The fuel merely heats the air. The expansion of the air pushes the piston.
    An explosion called detonation or knock can put a hole in the piston. Some
    engines require higher octane fuel to keep knock from occurring.
     
  4. Its a matter of semantics. A arguably a hydrogen bomb simply heats up
    surrounding air (and matter).

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  5. Arfa Daily

    Arfa Daily Guest

    That seems to me to be a misleading description of the principles of an
    internal combustion engine. The fuel is mixed with the air in a very
    carefully controlled ratio, highly compressed, and is then set light to,
    either by a spark in the case of a gasoline engine, or by self ignition from
    the rapid heating of the mixture during compression, in the case of a
    diesel. It burns or combusts, and what comes out of the exhaust, after the
    burning, is not air, but a fully reduced residue of the burning process. The
    burning of the mixture under such intense pressure, in what is essentially a
    fully contained space, takes place at such speed, it would usually be
    considered to be representative of a controlled explosion. Detonation knock
    is normally as a result of the timing of the ignition source not being ideal
    for the engine in question. The detonation process should be started just
    before the piston reaches top dead centre, so that by the time the burning
    has spread fully from the initiating point - ie the spark plug - through the
    entire mixture, and is thus at its fiercest, the piston has rolled over past
    its point of being momentarily stationary, and is just beginning on its way
    back down the cylinder. The rapidly burning ( exploding ? ) mixture will
    then deliver maximum thrust to the piston, driving it down the cylinder
    bore. If the mixture starts to burn too early, it will reach maximum energy
    output before the piston has reached the top, so will oppose the upward
    movement of the piston, which is still occuring, leading to the
    pre-detonation knock.

    Maybe it is just semantics, and some may disagree, but that has always been
    my take on how an engine works, ever since I was first rebuilding them as a
    kid, because I couldn't afford repair shop prices !!

    Arfa
     
  6. Arfa Daily

    Arfa Daily Guest

    Just as a matter of interest, I just looked up the word " explosion " at

    http://dictionary.reference.com/browse/explosion

    and interestingly, the first result, 5th definition, specifically mentions
    the internal combustion engine. The third result, definition 1a also seems
    to cover it neatly, as does the twelfth

    Arfa
     
  7. Arfa Daily

    Arfa Daily Guest

    Ah, it could be a question of semantics ! It's just occured to me what you
    were saying. It is the pressure wave from the burning ( although I still
    think " exploding " covers it also ) mixture that drives the piston down,
    and not the actual burning mixture ( flame front is it called ? ), which
    should not actually touch the top of the piston before it burns out, and can
    cause damage, if it does. Yep ! that's it I reckon. We're both on the same
    page now. Sorry ...

    Arfa
     
  8. I especially like this definition. In fact anyone who has watched a
    nitro fueled dragster can attest to the violent explosive manner of
    those engines exhaust. Those engine builders avoid "detonation" at all
    costs.

    1. A release of mechanical, chemical, or nuclear energy in a sudden
    and often violent manner with the generation of high temperature
    and usually with the release of gases.

    Most people don't think of the explosive process going on within an
    automobile engine because the process is very refined, by mufflers,
    flywheels and engine timing.

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  9. Sure there is. But you want it at the correct time in the cycle. Knocking is
    caused by misfiring.
     
  10. clifto

    clifto Guest

    To add to your excellent explanation, the byproducts of combustion, such
    as carbon dioxide, together occupy more volume than the fuel-air mixture
    did, and the heat generated by the rapid burn further increases the total
    volume.
     
  11. Detonation is all of the fuel burning at once(explosion). A proper flame
    path will happen relatively slowly to push the piston(burn). The beginning
    of the burn is timed to push the piston when the crank is in the proper
    position. How long the burn lasts and it's timing is dependent on engine
    design and application. If an explosion was acceptable there'd be no need
    for high octane fuel. Apparently you've never seen a piston with a hole in
    the crown. It's like the difference of flipping a light switch with your
    finger or hitting it with a hammer.

    Pinging is hot spots in the combustion chamber causing self ignition at the
    wrong time. The extra heat from this can cause detonation though.
     
  12. Detonation is all of the fuel burning at once(explosion). A proper flame
    tell me what is the change over point at which a "slow burn" turns to a
    explosion.
    u want the fuel to burn slow , so teh engine runs slower ?

    you are incorrect , dentonation is the IGNITING of fuel at the wrong time
    ..



    hmmm of course its a explosion, i`ll put u in a petrol vapour filled room
    with a sparkplug connected up to a engine , via a long plug lead, then i`ll
    crank the engine over KABOOM !!!!of course its gonna explode.
     
  13. Seems you are also incapable of understanding the difference between burning
    and an explosion too.
     
  14. The technical term is "High order reaction". The two options are:

    (1) A flame front moves across the gas, taking milliseconds. That
    what happen when you light a match, or a spark plug fires in a
    properly operating innternal combustion engine.

    (2) High order: The reaction starts instantly at many places throught
    the materinal, as it's heated to its iginition point throughout.
    Takes place in nano to microseconds. That's what most explosives do.
     
  15. flame> path will happen relatively slowly to push
    Bingo! And it produces a shock wave that combustion does not.
     


  16. Captain Midnight, huh? Tell me, what is the name of the street where
    the abandoned C-band uplink earth station that you used to jam HBO with
    ?


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  17. http://www.macdougallelectronics.com/bio.html
     

  18. I already know that, but where is the location of the earth station
    used to Jam HBO, or even the name of the company that built the
    equipment?


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  19. hi, read this "
    There are three rates of combustion; ordinary combustion, explosion (Rapid
    Combustion), and detonation..


    look around onthe net , hmmmmm rapid combustion , err COMBUSTION !!!!! OR
    EXPLOSION,.... i am right.
     
  20. no one challenging me .........
    ]
     
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