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Combustion Engine Questions...

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Combustion Engine Questions...

Unread postAuthor: THUNDERLORD » Sat Feb 28, 2009 1:17 pm

Hello all, Hope my bad sense of humor lately hasn't offended anyone too badly. :)

Anyway, I'm wondering what pressure small combustion engines can typically handle? (can't find info and limited time now...)

Also, just wondered, but if anyone knows what type mixes they could handle in normal gas (hybrid) use?

I was thinking of using a 20 something cc up to maybe 50cc cylinder and piston as blow-forward bolt components for a pneumatic (unregged co2 design).
And it will only move around 1" or 1.5" forward (To chamber rounds).

All the other components of this design are really available and coming together. (muzzle-loader barrel for barrel and chamber, seamless hydraulic pipe for piston housing, bulk co2 tank, co2 pistol for pilot valve etc....) But this part has me wondering.

Oh, thinking of the components (rather than create another post),
I even found dry-ice for $1 a pound very nearby !!!....
Is there a chart anyone knows of or info on what volume and pressure co2 gas can be obtained from solid dry ice???

If noone has info I'll figure it out soon I hope.
But especially for any info on the engine questions, it will save me time. thanks very much in advance!!! :D :wink: 8)

EDIT:Cool VidBTW!!!
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Unread postAuthor: jrrdw » Sat Feb 28, 2009 2:36 pm

What do you mean by "what pressure can they handle"? The only pressure in them is in the cylinder and if you let it out, the engine will stop running. Compression that is. Whats coming out of the exhaust would build up to the cylinder compressed pressure then the engine would stall.
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Unread postAuthor: Hotwired » Sat Feb 28, 2009 4:55 pm

It would be interesting to see what you'd need to do to tap the high pressure combustion gases.

They can handle whatever pressure they create with the fuel they're meant to use, few hundred to a few thousand psi at peak pressure. Not very large volumes of course.

The exhaust pressure is nothing like that however, by the time it's being exhausted it's expanded a great deal from the point where it was combusting and also cooled down somewhat.

The theory I'm currently imagining is:

To use the combustion pressure you'd have to have a projectile or burst disk connected directly to the top of the cylinder which would hold back pre-ignition pressure, only give way and fire when the mix ignites and still provide enough resistance for the combustion to drive the piston down to cycle the engine properly.

Which sounds like some serious tinkering would need to happen.
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Unread postAuthor: jeepkahn » Sat Feb 28, 2009 5:08 pm

Actually, small engines like scooters and dirtbikes will make about 200-250 psi, larger bikes are normally somewhere between 95-160psi, now this is without firing, air/fuel ratio for gas engines is about 14:1, so you should be able to do the mathe from there to figure th xfactor and fueling ratios....

Engines I know, I am a service manager at a Motorcycle(honda/yamaha/can-am) dealership...
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Unread postAuthor: Hotwired » Sat Feb 28, 2009 5:14 pm

Eh, I missed the "small" part and went for "general" while rummaging, also the numbers are with combustion. Still if you get hold of a full size car racing engine then that several thousand psi peak pressure is still good :)
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Unread postAuthor: psycix » Mon Mar 02, 2009 3:15 pm

Actually, a combustion engine is a 10-20x hybrid so they should be able to withstand quite much. Especially diesel engines should be able to handle alot of pressure.
Though I believe that these parts are far too heavy to be used for a blow forward bolt.
Only option I see is a hybrid chamber (with built-in valves! yay!)
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Unread postAuthor: THUNDERLORD » Tue Mar 03, 2009 8:36 pm

Thanks for the replies fellas,

@psycix, I was thinking of one with a small diameter something like the smallest weed-whacker engines (20 something cc)...so the piston diameter would be like 1.25-1.5" inch.
For the pneumatic application, the cast cooling fins would be mostly removed.
The piston would have a hole dead center (probably .50"inch)
And the piston rod would be removed.
BTW, the main advantage is the factory piston ring, but that also seems to be the weak point when engines get over pressured, heated or wrong type fuels. So (Hmmm.?)
The cylinder head would be bored out to accept a pipe the same inside diameter or larger than the cylinder (blow-forward bolt housing now)

A pipe w/ flange(shaped like a top hat) would slide through the cylinder heads and be bolted on by using the cylinder head and gasket.
That would be the piston housing.
That way the piston is accessable by removing the cylinder head.
There would be less constriction since the pison diameter is slightly larger than the cylinder.
It may have sounded over-kill to use a thick factory made muzzle-loader barrel. But the advantage is that it can be bored into considerably for the pipe on the front of the blow-forward bolt. Giving less restriction of flow also since the inside diameter can be the same as the bullet diameter that way.
Seemed like a good idea and readily available, but my mechanical ability is still a little clouded from the flu to be certain. :roll: :(

...What do you mean by "what pressure can they handle"?.. .


Just if anyone had an estimate of thier bursting pressure, but I suppose it would vary greatly from size and manufacture so perhaps like a minimum they need to withstand in thier normal operation I was looking for is all.

Thanks for all the replies, I'm getting a mssg. 2 minutes left online :cry: :wink: 8)
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Unread postAuthor: psycix » Fri Mar 06, 2009 2:16 pm

Thats a lot of work...
Too much IMO.

There are many other ways to achieve the same thing.
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Unread postAuthor: THUNDERLORD » Tue Mar 10, 2009 11:40 am

psycix wrote:Thats a lot of work...
Too much IMO.

There are many other ways to achieve the same thing.


Yeah, I've always stated that a design is as good as the amount of time someone is willing to put into it.

For a 800+ psi .50 cal. or so design,with accessable Blow-forward bolt AND piston valve ,I for one would be willing to put much time forth.

Besides, it's one thing to design something feasible ,But another to have the components and complete it.

Besides I am a steel worker/machinist most of all, so for me it's actually fun. :)

But as far as another way to achieve the same thing, I've been thinking of a revolving loading mechanism (possibly a cloud chamber magazine and revolving mechanism), connected to an electric solenoid piloted qev piston valve(Contact when inline), so when the round is in line with the muzzle, an electronic curcuit will activate the solenoid QEV pilot.
But that idea involves "fiddly" electronics. so IDK.... :roll: :wink: 8)
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-----SPEED,STRENGTH, AND ACCURACY.-----
"Procrastination" is five syllables for "Sloth".
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