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Water Injection in combustion spudguns.

A place to ask general spud cannon related questions.
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Water Injection in combustion spudguns.

Unread postAuthor: SPG » Mon Nov 12, 2007 8:33 am

I had this thought having seen the destruction of a diesel engine that had injested water during a river crossing. Remember that a diesel engine produces its power through combustion, not through detonation of the fuel air mixture, so is in many ways similar to a spudgun.

Water injection itself has been used in combustion engines since WWII. The initial injection of water cools the fuel-air mixture, which increases its density and hence the amount of mixture that enters the cylinder. But the greater effect comes later during combustion when the water takes in significant amounts of heat energy as it converts from liquid to gas (steam), increasing pressure in the cylinder.

It's this second part that we'd be most interested in in spudgunning. We're always looking at increasing chamber pressure in combustion guns. One way is to use different fuel/oxidiser mixes (propane and oxygen), one way is to increase fuel/air mix pressure (hybrid), but I don't think anyone's tried water injection. To give an example of possible incrreases in power available in 1942, the German Luftwaffe increased the horsepower of the Focke-Wulf 190D-9 fighter aircraft from 1776HP to 2240HP.

So can anyone see any problems?
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 12, 2007 9:07 am

Hey SPG, good to see you still occasionally browse the forums :)

As far as I know the Dora 9 used the MW50 system - Methanol Water injection, that delayed the ignition of the fuel mixture in the cylinder until it reached a higher compression - and since combustions and hybrids lack that compressive force, perhaps it wouldn't apply in this case?
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Unread postAuthor: ShowNoMercy » Mon Nov 12, 2007 9:17 am

Are you sure that you read that right? Water in any gas powered engine leads to misfires and rough running and I have never heard of any power gain from adding water to your fuel.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 12, 2007 9:19 am

ShowNoMercy wrote:Are you sure that you read that right? Water in any gas powered engine leads to misfires and rough running and I have never heard of any power gain from adding water to your fuel.


Not as far fetched as you think ;)
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Unread postAuthor: spanerman » Mon Nov 12, 2007 9:20 am

the water injection sprays a mist onto the intercooler if im not mistaken
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Unread postAuthor: ShowNoMercy » Mon Nov 12, 2007 9:26 am

Well, his post only stated water, not with an addition of methanol. And on a combustion gun, I doubt that the ~80 psi would be enough to vaporize water into steam, if it wasn't to early I would bust out the latent heat nonsense but I will refrain. Furthermore, the water/methanol combo is meant to lower the temperature range in a engine, isn't that against what a combustion gun needs?
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Unread postAuthor: SPG » Mon Nov 12, 2007 9:44 am

No that water doesn't cool the intercooler, and yes it can be done with 100% water, not with 50/50 MW mixes.

The basic idea is that the heat generated from combustion turns the water into water vapour (nothing to do with pressure here). The mass of the water doesn't change as its state changes, however its volume changes dramatically..

If that large volume is contained in a pressure vessel (spudgun) then what we have is increased pressure, and increased pressure = increased power.

Have a Google round there's plenty of info on 100% water injection.

PS, get water in a diesel engine and watch as it blows your pistons out of your crankcase, it's fascinating to see the power of steam drive engine parts through the hood of a car.
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Unread postAuthor: ShowNoMercy » Mon Nov 12, 2007 9:47 am

Not if you have a good water filter setup :wink: But yeah, we had a guy that got water in his fuel and he managed to shoot a rod straight out of the crankcase, cost him round 20 grand to fix the engine.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 12, 2007 10:05 am

Easy to check out - can someone with a spray-n-pray combustion spray some water with a deoderant atomiser into their chamber and see what happens :D
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Unread postAuthor: ShowNoMercy » Mon Nov 12, 2007 10:08 am

Would the combustion be long enough to vaporize water into steam before the projectile left the barrel? Or would you end up with a puddle of water in your chamber? Which would be fun to work with on a high voltage ignition system. :lol:
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Unread postAuthor: jimmy101 » Mon Nov 12, 2007 11:46 am

Folks are talking about two different things.

If you get a large amount of water in an engine cylinder the cylinder (or piston, or rod, or ...) will fail because water is not compressible. The engine tries to compress it during the compression stroke, can't, so something significant breaks.

Injecting small (as in very small) amounts of water into the intake stream of internal combustion engines has been done many times. I believe it is mostly done to cool the inlet stream, cooler inlet air lowers it's density so you get more sucked into the chamber. It really only helps an engine that is firing thousands of times a second, all that energy heats up the intake manifold and head, the water helps to cool them off so they don't heat up the incoming air stream.

In practice, water injection does not help a standard gasoline or diesel internal combustion engine, if it did cars would be using it.

Since a spudgun operates using ambient temperature air I wouldn't think adding water would help. If you used enough water to have liquid water in the chamber then some of the water will be vaporized. But how much? From click to bang is only about 50 milliseconds, not enough time for much of the water to vaporize. Ideally, you would probably want an aerosol of water (a mist of small enough drops of liquid water) that doesn't settle out of the air in the time it takes to fire the gun. This might give you enough contact between the liquid water and the hot combustion gases to get some of the water to vaporize.
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Unread postAuthor: SPG » Mon Nov 12, 2007 12:30 pm

Jimmy, yes, it cools down the air intake, as you've mentioned, but it was also and is still aslo used to increase the performance of an engine by vapourising the water in the cylinder during combustion, to produce steam.

There's plenty of fora dedicated to this which say all about the power increases available, and the technique goes back to the 1930's so there's plenty of research too.

Would combustion be long enough to vapourise the water? Well why not if it's long enough in a car doing 6000+ rpm I'm sure it's long enough in a spudgun.

It might be the case that it'd help to have a burst disk though.

I think I'll go buy some PVC and make up something simple to see what happens with and without water injection. That should tell us.

PS: Glad to be back, I drifted to the darkside and went airsofting, when I realised I had more ideas to build than expertise in building. But now I've got even more ideas to share.
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Unread postAuthor: homedepotpro » Mon Nov 12, 2007 12:59 pm

Is this sort of what you guys are thinking about, I read about it in popsci the other day.
http://www.popsci.com/popsci/technology/c1609351d9092110vgnvcm1000004eecbccdrcrd.html
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Unread postAuthor: williamfeldmann » Mon Nov 12, 2007 1:21 pm

People do use this in cars, but it is mostly in race or high performance cars. A buddy's dad owns a drag strip car and he uses a water atomizer. The engine doesn't run for long enough to get hot, but the extra output really makes a difference.

However, the fuel/air/water is atomized and under quite a bit of pressure in the engine. We are not talking simply ignition. Engines pressurize the fuel then ignite, like a hybrid gun. The increased pressure raises the temperature of the mix, making it easier for the water to go gaseous. I have a had time believing that in a simple combustion the water would go steam.

A hybrid this might work. IF you could add atomized water to the mix and pressurize the system fast enough to keep it from deatomizing. Those increased pressures, and increased temperatures from combustion would probably see a nice increase in outward pressure from the water addition. But I would suggest learning more about it before trying it your 11x hybrid, or...
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Unread postAuthor: jimmy101 » Mon Nov 12, 2007 1:24 pm

SPG wrote:Jimmy, yes, it cools down the air intake, as you've mentioned, but it was also and is still aslo used to increase the performance of an engine by vapourising the water in the cylinder during combustion, to produce steam.

There's plenty of fora dedicated to this which say all about the power increases available, and the technique goes back to the 1930's so there's plenty of research too.

But the basic fact that this technique it is not actually used in real engines is a very strong indication that, in practice, it does not work.

If a car manufacturer could increase fuel efficiency (or power) by just a couple of percent they would. Increasing efficiency (or power) by just 3% would have a huge affect on a manufacturers bottom line, just the affect on their CAFE rating alone would be worth hundreds of millions of dollars.

PopSci has been publishing about water injection in IE engines for decades. It still isn't used. It isn't because of the "big bad automakers are in collusion with the oil companies". It is because it just does not work.
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