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Diesel+Autoignition idea

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Diesel+Autoignition idea

Unread postAuthor: auxiliary » Wed May 20, 2009 8:38 am

The concept of igniting a fuel in a combustion chamber using just pressure is pretty widely used. This is a video of a guy that uses the diesel effect with oxyacetylene:
[youtube]http://www.youtube.com/watch?v=mGRKYcsTImo[/youtube]

And this guy uses a small amount of 5W 30 motor oil:
[youtube]http://www.youtube.com/watch?v=gLzEqfRVeOA[/youtube]

I was wondering if I could use diesel itself. The problem I see is that in a typical diesel engine, the diesel is injected while the piston is at top dead center and the pressure is 600psi. So this means that the diesel is introduced to an already high pressure atmosphere. My question is, If I sprayed a little diesel into a pellet gun with a strong enough spring before I shot it, would it ignite when I release the piston? Instead of timing it perfectly.
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Unread postAuthor: jeepkahn » Wed May 20, 2009 8:45 am

Yes, there's been a few who've done it... a drop of oil in the skirt of a pellet... I'm sure someone can link to the thread...
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Re: Diesel+Autoignition idea

Unread postAuthor: Technician1002 » Wed May 20, 2009 9:13 am

auxiliary wrote:The concept of igniting a fuel in a combustion chamber using just pressure is pretty widely used. This is a video of a guy that uses the diesel effect with oxyacetylene:

I was wondering if I could use diesel itself. The problem I see is that in a typical diesel engine, the diesel is injected while the piston is at top dead center and the pressure is 600psi. So this means that the diesel is introduced to an already high pressure atmosphere. My question is, If I sprayed a little diesel into a pellet gun with a strong enough spring before I shot it, would it ignite when I release the piston? Instead of timing it perfectly.


The engine used injectors for timing. They have no throttle body to vary the air to compensate for elevation, temperature, etc. To prevent engine knock and produce a controlled burn instead of a detonation, the fuel is sprayed for a short time and it burns as it mixes with air instead of going bang if it was a mist mixture. Fuel in a liquid which isn't sprayed should still burn, but may burn partially and burn slow depending on how much gets blown into mist on compression.

For compression ignition, a compression ratio of over 15:1 is typical. Glow engines use lower compression ratios.

More info is here.
http://autorepair.about.com/cs/generalinfo/a/aa102001a.htm
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Unread postAuthor: qwerty » Wed May 20, 2009 10:43 am

you could do it. But when the fuel ignites it can totally wreck you piston chamber by making a huge bulge in it. Search it on youtube then read peoples comments.
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Unread postAuthor: Moonbogg » Wed May 20, 2009 1:26 pm

Dieseling in a springer is something people try to avoid (if they care about their gun). It can diesel by just using oil in the chamber for lubrication. So use a crappy old gun for this. I bet it works great for power though.
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Unread postAuthor: far_cry » Wed May 20, 2009 5:41 pm

try gasoline or any light fuel (be careful)

diesel and oil is almost the same
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Unread postAuthor: irisher » Wed May 20, 2009 5:59 pm

Diesel and gasoline are very different in combustion behavior and should not considered the same.
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Unread postAuthor: jonnyboy » Wed May 20, 2009 6:15 pm

dieseling is a bad thing in air guns. :? It's pretty much unavoidable though the first couple shots you take in a brand new gun because the lube the use is combustible. In fact last night when I first shot my quest it dieseled the first couple times.

If your doing this for a power boost you might gain a little power but your accuracy will crumble because the pellet is probably supersonic and when it slows down it will begin to tumble.
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Unread postAuthor: Ragnarok » Wed May 20, 2009 7:02 pm

As has been said, dieseling is not a good thing. Indeed, I take every possible precaution to avoid it happening in my air rifle, even down to using non-combustible silicon based lubricants.

Preventing it is good for several reasons:
1) Dieseling damages the air gun.
2) Dieseling reduces consistency.
3) Dieseling increases noise.

I don't want any of those things to happen and my rifle's got quite enough power already, so no thank you.

Anyway, if I wanted more power than I was getting from an air rifle, then I wouldn't be modifying them to diesel. Bear in mind, my launchers are many dozens of times the power of my air rifles and far more destructive.
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Unread postAuthor: POLAND_SPUD » Wed May 20, 2009 11:29 pm

well it might be bad in commercial airguns but this thread is obviously not about them.... my idea to inject acetylene into a deadspace of a normal pneumatic should work (given how reactive acety is and that it can burn in wide range of mixes)
but I don't think it'll work as easily with gasoline or propane
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Unread postAuthor: Ragnarok » Wed May 20, 2009 11:35 pm

POLAND_SPUD wrote:well it might be bad in commercial airguns but this thread is obviously not about them...

Which would of course be why both videos linked show commercial airguns, would it?
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Unread postAuthor: inonickname » Thu May 21, 2009 3:47 am

Acetylene is easy to do this with. It's dissolved into acetone because of it's high instability and tendency to go bang around 20 psi.
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Unread postAuthor: CpTn_lAw » Thu May 21, 2009 6:00 am

There are several ways of increasing the power of your pellet springer. Dieseling is fun if you do not care about your airgun.
As rag said, it's bad for many reasons. I broke mine by dieseling too much.

Now if you want to use the same principle in a homemade 20$ airgun, feel free to try it ( in a relatively safe way). You can have a high pressure chamber, have the air released in a smooth pipe pushing a heavy-weight piston, this piston will compress gas between itself and the smaller caliber barrel, with a airtight projectile in.
You'd still need some calculation done to estimate the amount of force acting on the piston, both sides. The suden ignition of a flammable gas/ air mix will create a pressure spike. The pressure behing the piston must be calculated to counter balance this pressure spike. Otherwise, the piston will either slam in the small caliber barrel, or slam back at your valve assembly.

I tried something like that 2 years ago, but it wasn't satisfactory.
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Unread postAuthor: POLAND_SPUD » Thu May 21, 2009 9:10 am

@ rag ohhh yeah it's not that he already knew it's not a good thing...
it seems that he actually wanted to use it in a commercial air gun.. sorry


but still it would be a good idea to experiment with acetylene to increase power of a pneumatic... but, similarly, it might cause inconsistencies in power and, as a resultof it, in accuracy

@cptn_law
psycix and my idea is to use compressed air to compress and ignite acetylene.... in theory there is no need to add a piston as acety is very sensitive...
one would have to inject acety into the deadspace between the valve and the projectile... the air released by the main valve would first compress and then provide oxygen for combustion
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Unread postAuthor: Technician1002 » Thu May 21, 2009 10:02 am

POLAND_SPUD wrote:one would have to inject acety into the deadspace between the valve and the projectile... the air released by the main valve would first compress and then provide oxygen for combustion


Unfortunately the first air after it to hit it will be very cold and turbulent. It may dilute it too much before ignition. Maybe a premix would be better with some kind of super light piston, such as a sheet of paper or paper cup.
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