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Automatic Dieseling Air Gun

Use Diesel effect to recock gun
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First, I should mention that this idea is more of a firearm than an airgun.

Imagine you've got the following components, from back to front: An air intake. A carburetor. A checkvalve that lets air move from the carberator to the spring chamber, but not backwards. An airtight chamber with the spring in it. A piston with a checkvalve in it. The check valve lets air move through the piston to the combustion chamber. The combustion chamber. The bullet. The gun barrel.

When the trigger is squeezed, the spring pushes the piston forwards, simultaneously drawing a fresh fuel/air mixture from the carburetor into the spring chamber, and compressing the mix in the combustion chamber.

When the pressure and temperature in the combustion chamber get high enough, the fuel/air mixture combust, creating a large increase in temperature and pressure.

The hot gasses simultaneously press the bullet forward and the piston backward. As the piston moves back, the fuel air mix behind it compress. After the pressure in the spring chamber matches the pressure in the compression chamber, the additional backwards motion of the piston will force the fuel air mixture through the piston's check valve into the combustion chamber.

Once the piston is all the way back, it would either be caught by a latch (if the gun is in semiautomatic mode) or be allowed spring forward (the gun is in full automatic mode).

Meanwhile, a small portion of the high pressure exhaust gas is used to load a new bullet. The new bullet prevents the air/fuel mix in the combustion chamber from dissipating out the barrel.

There are a couple of obvious benefits over a regular gun: Firstly, a wide variety of fuels could be used, probably even regular diesel fuel. Secondly, since the bullets don't need shells, the weight of ammunition could be vastly reduced. Thirdly, it might be possible to make the gun's power adjustable by varying the air/fuel ratio.

goldbb, May 03 2009

New Gun that Shelled Dunkirk http://query.nytime...AC0A9639C946496D6CF
A similiar gun from WWII. [Aristotle, May 03 2009]

Fuels used for miniature engines http://modelenginenews.org/faq/fuels.html
Note the "Miniature Diesel Fuels" part [goldbb, May 10 2009]

[link]






       Potentially not original, see link.
Aristotle, May 03 2009
  

       //A carberator//
Is that anything like a "carburettor" ? (or "carburetor" for the Atlantically-challenged)
AbsintheWithoutLeave, May 03 2009
  

       Aristotle, Nothing in the dunkirk gun article suggests any kind of repeating action, which is the main feature of my idea.   

       AbsintheWithoutLeave, thanks, fixed.
goldbb, May 04 2009
  

       I wonder what the maximum muzzle velocity for an airgun might be. I am remainded of Colonel Moran's nefarious airgun from the Sherlock Holmes stories, although I am sure his did not run on diesel as it would have sounded like a chainsaw and probably defeated the stealthiness of it.
bungston, May 04 2009
  

       Hmm. I have full scuba tanks in my closet. I wonder what propulsive fun I could have with 80 cubic feet of 3000 PSI air.
normzone, May 04 2009
  

       [normzone], I'm sure you'll have a blast.
shapu, May 05 2009
  

       I cannot find any reference to diesel engines in the desired size-range (you are talking about hand-held guns, are you?) - and i suspect this is for a reason (although i do not grasp enough of the internal combustion principles to say why this should be so)
loonquawl, May 07 2009
  

       loonquawl, this isn't a conventional diesel engine that's been modified to fit into a handgun... it doesn't have a crank or crankshaft. A better comparison might be to a single cylinder, single piston, free piston engine.   

       As for being handheld ... yes, I expect that this idea could be implemented as something about the same size as a conventional automatic machine gun.
goldbb, May 07 2009
  

       Hmmm, methane would be good.   

       [goldbb]: i understood the way you wanted this to work - what i wanted to point out was the lack of miniature diesel engines, which for me points to some problem with miniaturizing the Diesel prinicple. Otto motors, turbines, steam engines, all have miniature working models... Diesel seemingly does not.
loonquawl, May 08 2009
  

       Very small engines have a high ratio of surface area to volume. Because of that, conventional diesel fuel won't ignite unless the engine is hot [see the link], or unless something is mixed in to lower the self-ignition point (such as ethyl ether).   

       However, the pressures (and therefor temperatures) generated in a spring air gun are higher than those generated in a conventional diesel engine. This is why it is common in high powered air guns for some of the lubricant to ignite due to the heat of air compression while firing... even when that lubricant is something which you wouldn't expect to work in a diesel engine.
goldbb, May 10 2009
  

       Very cool link. Thanks!
loonquawl, May 11 2009
  
      
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