Posted:

**Tue Mar 13, 2007 6:48 pm**Well, I recently made a long, complicated post on spudfiles (intended as a joke; yes, it did have a punchline)...

It's here because I thought you guys might aprecciate both the joke and the concepts behind it; I welcome serious discussion of it.

Here's the origional post. (interpret in the context of a thread asking "which do you think is cooler: pneumatics or combustions?"

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I felt like making a useless post:

Well, you lazy person, go use the GGDT. You'll find that the gasses, on exit, are significantly below the freezing point of water - to the tune of -50 to -100*F

We then note that any degree of research will show that combustions derive their pressure from temperature.

A bit more research will lead you to write this formula:

(V<sub>p</sub>P<sub>0</sub>T<sub>0</sub>) / (V<sub>0</sub>P<sub>f</sub>) = T<sub>p</sub>

Where V<sub>0</sub> is the initial volume, V<sub>p</sub> is the volume at the optimum (perfect) ratio, P<sub>0</sub> is the initial particle count (in the case of propane-air, 26), P<sub>f</sub> is the post-reaction particle count at (27), T<sub>0</sub> is the initial temperature in absolute units, and T<sub>p</sub> is the temperature at the optimum ratio.

This is based on the assumption that the pressure at the optimum ratio is equal to the starting pressure. This is not true for hybrids - but you should be able to figure out how to account for that factor.

We substitute the values like so:

(2.25L*26p*293K)/(1L*27p) = T<sub>p</sub>

...and solve to find that T<sub>p</sub> equals 635K.

Now, we note that this calculation ignores any evaporation of potato juices, but the optimum ratio for the latke tests using the sabot slugs suggest that this, at least up to the optimum ratio, is at most minor effect.

Also, you might note that this is the temperature when the pressure equals zero PSIG, and that the gasses might further cool off due to their momentum or such. I will not dispute that these effects might exist, but I doubt their seriousness.

So, I feel reasonably secure in saying that the exhaust gasses of a combustion spudgun are significantly hotter, on average, than the exhaust gasses of a pneumatic launcher, or, as you put it, that pneumatics are cooler.

(that was fun)

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(get the joke? See, it's a pun: he ment "which do you find more exciting?", but I answeared "which one is colder?". The long technical discussion of something which you expect to be a matter of taste is also somewhat amusing.)

It's here because I thought you guys might aprecciate both the joke and the concepts behind it; I welcome serious discussion of it.

Here's the origional post. (interpret in the context of a thread asking "which do you think is cooler: pneumatics or combustions?"

**********************************************************

I felt like making a useless post:

Well, you lazy person, go use the GGDT. You'll find that the gasses, on exit, are significantly below the freezing point of water - to the tune of -50 to -100*F

We then note that any degree of research will show that combustions derive their pressure from temperature.

A bit more research will lead you to write this formula:

(V<sub>p</sub>P<sub>0</sub>T<sub>0</sub>) / (V<sub>0</sub>P<sub>f</sub>) = T<sub>p</sub>

Where V<sub>0</sub> is the initial volume, V<sub>p</sub> is the volume at the optimum (perfect) ratio, P<sub>0</sub> is the initial particle count (in the case of propane-air, 26), P<sub>f</sub> is the post-reaction particle count at (27), T<sub>0</sub> is the initial temperature in absolute units, and T<sub>p</sub> is the temperature at the optimum ratio.

This is based on the assumption that the pressure at the optimum ratio is equal to the starting pressure. This is not true for hybrids - but you should be able to figure out how to account for that factor.

We substitute the values like so:

(2.25L*26p*293K)/(1L*27p) = T<sub>p</sub>

...and solve to find that T<sub>p</sub> equals 635K.

Now, we note that this calculation ignores any evaporation of potato juices, but the optimum ratio for the latke tests using the sabot slugs suggest that this, at least up to the optimum ratio, is at most minor effect.

Also, you might note that this is the temperature when the pressure equals zero PSIG, and that the gasses might further cool off due to their momentum or such. I will not dispute that these effects might exist, but I doubt their seriousness.

So, I feel reasonably secure in saying that the exhaust gasses of a combustion spudgun are significantly hotter, on average, than the exhaust gasses of a pneumatic launcher, or, as you put it, that pneumatics are cooler.

(that was fun)

*****************************

(get the joke? See, it's a pun: he ment "which do you find more exciting?", but I answeared "which one is colder?". The long technical discussion of something which you expect to be a matter of taste is also somewhat amusing.)