CO2 combustion

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Postby spuzi14 » Wed Feb 01, 2006 9:51 pm

Eric(friend of mine) and I were talking and he suddenly outta nowhere comes up with a CO2 combustion engine. No CO2 doesnt combust but he meant running CO2 through the engine with an air compressor. I came up with this idea and I dont just randomly have an old engine laying around or an air compressor so I told him Id ask here:

Lets say one chamber area(where the valves and piston are) has a pressure rating of 100PSI but normally with a compresser the air runs through at 14.8 PSI. Now connect the exhaust valve to the entrance valve. If you added a small computer fan in front of the entrance valve and then pumped in enough air to fill up twice the volume of the chamber it should keep moving after the pistons get going. Now you have constant pressure and a fan to move the air.

Thats just a 30 second brain blast. He wants to do this with a lawn mower engine. My theory is acting like the engine is air tight with a constant flow of air. I was also thinking that the fan might not really work to well since if the pistons arent sealing by even the smallest bit the air will just cycle through. My terminology might not be right either but Im still learning so please forgive me.

Can this be done?
If not why wont it work?
How can he make it work if its possible?

Thanks for the help
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Postby benstern » Wed Feb 01, 2006 10:08 pm

No, it is not possible CO2 is not combustable in any way. (think CO2 fire extinguishers)
I don't quite get what you are saying.
Do you mean moving the pistons with the pressure?
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Postby Freefall » Wed Feb 01, 2006 10:38 pm

It sounds like you're treating the engine as a pump running backwards.
If you redesign the camshaft so that the intake opens on every downstroke and the exhaust opens on every upstroke, you basically have an active-valve pump (as opposed to one with one-way valves to control the flow). If you force air from the low pressure side to the high pressure side, you should be able to force the pump to turn. Basically, it's now no longer a pump, but an "air motor".

To drive an air motor, you'll need much more pressure than you could provide with a computer fan.

With a two-stroke lawnmower engine, there is pretty much no way to do this.
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Postby Mr.Plow » Wed Feb 01, 2006 10:46 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by benstern
[br]No, it is not possible CO2 is not combustable in any way. (think CO2 fire extinguishers)
I don't quite get what you are saying.
Do you mean moving the pistons with the pressure?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Ben, please read more than the title of the topic. From the SECOND sentence:
<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">No CO2 doesnt combust but he meant running CO2 through the engine with an air compressor.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
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Postby plasticex009 » Thu Feb 02, 2006 1:35 am

An issue when using CO2 will be keeping the gas flowing into the engine warm enough to prevent solid CO2 from forming in the intake lines. You could get around this by using compressed air, but you would need a to either increase the source pressure or tank capacity to get enough "fuel" to power the engine for even moderate durations.
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Postby TurboSuper » Thu Feb 02, 2006 7:09 am

Soooo.... this is basically a steam engine running on air?
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Postby spuzi14 » Thu Feb 02, 2006 9:39 pm

Heh yeah pretty much. I couldnt think of a attracting title except CO2 combustion so make sure you read more than that. I knew a computer fan wouldnt do it but that was just to get the point across. I dont see why it wouldnt work. Solid CO2 could be a problem but I know we can get our hands on an air compressor. At least we could get one for the time the motor runs.

I thought that having a compressed amount of air in the motor at all times would get rid of an air compressor. But as I type this I understand what you meant(at least I think I do)by solid CO2. Does it cool as it moves around under pressure in the engine?
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Postby plasticex009 » Fri Feb 03, 2006 12:36 am

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Does it cool as it moves around under pressure in the engine? - spuzi14<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

When CO2 expands it cools and the heat of nearby objects is absorbed by the gas. If the flow rate of CO2 through the engine is high enough, the engine won't warm fast enough for the gas to stay a gas and either liquid or solid CO2 will form depending on the pressure. By looking at a phase diagram for CO2 you can find the points at which each scenereo will occur if you know the pressures at work in the engine.

If you use compressed air you will probably need a dryer to get the water vapor out of the air. Otherwise, there could be a chance that this water will condense in the engine and freeze.
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Postby Darth Tater » Fri Feb 03, 2006 1:53 pm

ever play with an originial air hogs plane ?

i had one of those, i wish i still did :-\, but anyway, you pump the tank up with air, and spin the prop, and a custom "engine" with spring-loaded valves with little bumpers on the pistons was how it worked.

piston comes down towards bottom valve by you spinning the prop, pitson bumper opens valve, air from the tank forces piston back up, causing the prop to continue rotating, this causes the piston to come back towards the valve again, valve opens again from the force of the piston, and gets shoved back up while the prop is still rotating....this turns into a cycle, and the prop continues to turn, under power from the plane itself, you throw plane into the air, plane keeps going, you get lots of enjoyment.

i seriously wish i still had that thing, because later downt he road i wanted to (still do) replace the tank with something else, like a pop bottle or something, and pressurize it with an air compressor to like 80 PSI and then flick the prop and let it go haha.

anyway, there is a way to make an engine that uses air pressure to run, as i described above, but there really is no point, there is no feasable reason to do so. other than just to prove you can do it lol.
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Postby spuzi14 » Fri Feb 03, 2006 11:37 pm

Well the kid found directions for a good sized RC tank. He wanted to build one a little bigger so he could fit(barely) in it. The plans used electric motors and even though they were a good size they didnt look like they had the power. Thats where this idea came from. Ill worry about accomplishing it if he can get the RC part setup. And even then maybe Ill make a very small one, just to prove I can do it because I like doing things for that reason.
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