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Combustion of biodiesel

  1. Feb 1, 2006 #1
    Hey,

    I have to know how I am going to do this by tomorrow...I have to find out some way to measure the heat energy given off by the combustion of various batches of biodiesel that I have made for Physics/Chemistry. I can't just light the fuel, because it would explode and I wouldn't be able to measure the energy transfer.

    Any suggestions?

    Thank you!

    Edit: the fuel is in liquid form...
     
    Last edited: Feb 1, 2006
  2. jcsd
  3. Feb 1, 2006 #2

    Pengwuino

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    I don't see how you can measure the heat of combustion without initiating combustion. I think the trick might be just doing it on a small enough scale to contain the explosion.
     
  4. Feb 1, 2006 #3
    How would I measure the heat energy released? If I did it in a calorimeter I could measure the change in temperature...

    would one small combustion affect the temperature enough to determine a temperature change?
     
  5. Feb 1, 2006 #4

    Pengwuino

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    I believe what you're looking for is a "bomb calorimeter". I've heard that that is how you measure the heat of combustion of a hydrocarbon.
     
  6. Feb 1, 2006 #5
    Hmm...it seems a bomb calorimeter is what I am looking for, but they look to be big expensive devices...my high school physics lab doesn't have one:smile:

    I wonder if I could improvise. A bomb calorimeter basically causes the reaction to happen in a sealed container underwater, and then the heat of the reaction is transfered into the water and it's temperature change can thus be measured. A few simple calculations and your done.

    So I need to figure out a way to make the reaction happen in a sealed container underwater.
     
  7. Feb 1, 2006 #6
    I am just thinking out loud. Get a chamber, and an atomizer that can spray a fine mist. Get a chamber that is in a U shape, and make a hole in it at the bottom to insert the atomizer. Then put a spherical cover that will fit snug but not too snug over the opening, and is small and light weight. Then spray some fuel in and put a flame source. You should get a nice little pop, and you can measure the height at which the top flies up. All the chemical energy will go into kinetic energy, if you assume negligible loss to heating the air and incomplete combustion. I seriously doubt what I said would work.
     
  8. Feb 1, 2006 #7
    If I could create a spark inside the container at will, I could almost make my own combustion chamber. What do you think? If I put a fuel injecting device (a syringe?) attached to the "combustion chamber" (a tin can?) and then had metal leads that I could run electricity through inside the chamber to create a spark.........

    Possible? I just need the idea (materials, design, procedure etc) for tomorrow.
     
  9. Feb 1, 2006 #8
    That's awesome! Would something like a cleaner-bottle (one of those window spray cleaners) work as an atomizer?
     
  10. Feb 1, 2006 #9
    Probably would spray a nice mist for you. But the problem is that you need to have a good seal. You also need something to make a seal thats not too heavy to not go up enough to detect a change, but not so light that air resistance would factor in to its final height. Also, I just dont know if that would produce enough energy or not to make the sealer pop up at all! I guess its sort of like a potato gun.
     
  11. Feb 1, 2006 #10

    Pengwuino

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    Yah improvising with explosive materials sounds like a good idea...
     
  12. Feb 1, 2006 #11
    Its not going to explode. You are doing a controlled combustion, like what happens in your engine. A spritz from a spray bottle with air wont make anything explode pengwuino. You will get a 'POP' and the top flys in the air.
     
  13. Feb 1, 2006 #12

    Pengwuino

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    Like what happens in your engine? Your engine wasn't thrown together in a high school science class, the gas tank is like 8 feet from the engine, the engines made of steel/aluminum rated to withstand billions of cycles, the fuel injection is computer controlled.
     
  14. Feb 1, 2006 #13
    What does a gas tank have to do with anything? You are spraying a small amount of fuel into a closed chamber. You don’t need a steel or aluminum chamber. You are only doing one combustion. You won’t have much heat transfer from many cycles of repeated ignitions. Fuel injection has no significance hear. They used to be naturally aspirated by a carburetor, which does the same thing im telling him to do. (Fuel injection does the same thing as well actually, just electronically instead of through a venturi).
     
  15. Feb 1, 2006 #14
    My chemistry teacher built a "potato cannon" and has it in his office still I believe. It's not one of those compressed air ones, it uses explosive fuel (such as hairspray or something) and a tesla coil to light it.

    I could probably use that and launch it over the football field. I could control the amount of fuel, and the mass of the projectile. Then I could incorporate projectile motion from the kinematics unit into the thermodynamics study I'm doing. It would be great!
     
  16. Feb 1, 2006 #15
    It's not a great amount of fuel. We probably have only about 200mL of each type of biodiesel that we made. The reaction would be contained and small.
     
  17. Feb 1, 2006 #16
    Just be careful about measuring how much fuel you put in there. I would measure the mass of the bottle before and after filling the cannon with fuel on a very sensitive scale. You would want to spray about the same amount each time, and do a few trials to converge on the same range for one type of fuel. Then repeat the shooting with a different fuel trying to use the same amount of fuel as always. Make sure you use the same elevation of the cannon! Also, make sure the wind conditions are identical. But again, if your fuels have very small differences in the energy content, this experiment will fail horribly. That’s why something like a bomb calorimeter would give you better results if your fuel, which is most likely, has small differences in energy content between samples. (too small to see a big difference in the range the the projectile goes out of the cannon). But shooting something that far will also give you alot of error from air resistance, so its another draw back. Probably not the best way to do it, but the most fun.
     
    Last edited: Feb 1, 2006
  18. Feb 1, 2006 #17

    Pengwuino

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    Well, rule of thumb for these crazy people who like to use safety... oxygen + gasoline will find that spark eventually. 200ml... yah that'll kill you quite handedly if something happens.
     
  19. Feb 1, 2006 #18
    lol...i would definately not consider using all 200ml at once! That would certainly be suicide. Maybe like 5ml.

    Yea, I like the non-cannon idea for it's (better) accuracy...but the cannon would definately be fun. I'll propose both and see what happens I guess. Somehow I doubt my teachers will let me go ahead with the cannon idea.
     
  20. Feb 1, 2006 #19
    Yes, and we hope it does, or we wont have any ignition!

    No, what will happen is that you have too high a fuel air concentration ratio. Its called a rich mixture, and results in LESS power output. You dont want too much fuel, and be rich, or too little fuel, and be lean. If you talk to your teacher about the potato gun, let him put how much fuel he thinks it would need. But again, I don't think you should go that route, you wont see any variation between the fuels most likely. The bomb calorimeter seems like your best option.


    200mL is like 200 drops from an eyedropper. You wont cram all that fuel with such a small amount of air an explosion. You would need alot of air, alot of fuel.
     
    Last edited: Feb 1, 2006
  21. Feb 1, 2006 #20

    Pengwuino

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    Well keep the 200ml.... across the room. Explosions and gasoline containers need not spend much time within any small proximity.
     
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