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RJB: thoroughly mixing the air/fuel will lead to a quicker, cleaner burn. In basic combustion gas guns, a quicker burn is very beneficial, and cleaner burns tend to be hotter and more energetic (the ratio for maximum pressure generation is typically somewhat greater than stoichiometric, but not by much - think 4.5% fuel vs. 4% fuel. You can find this to a very good approximation using GasEq, a tool which I'm sure a student of "advanced" science such as yourself will have no trouble using). Our use of fans in combustion guns aids both in mixing and decreasing burn time (by inducing turbulence), and has been shown to noticeably improve performance in typical designs. I must question how you have determined the performance of your combustion gun to be "good" without comparing it against an identical one using a fan.
If you're going for aesthetics and want to build your own fuel tanks to fit that, then gasoline may well be a better option. Just remember the greatly increased issues with proper mixing for an aerosolized fuel over a gaseous one.
I wouldn't go so far as to say that working with drops of gasoline is more practical - the system will be somewhat lighter and occupy a bit less volume, but, as I mentioned above, mixing is more difficult.
Controlling the variation in muzzle energy requires more consistent procedures in fueling and loading - more accurate gauges on fuel meters, electrically operated valves for injection, consistent mixing times, projectiles with consistent masses and good tolerances on diameter, loading to the same distance down the barrel before each shot, and, of course, round and smooth barrels. The rest is down to temperature and humidity, factors which are largely beyond our control. As a student of "advanced" science like you surely knows, the initial mixing and combustion processes are also quite chaotic, so even the best instrumentation won't guarantee consistency anywhere near what the instruments are capable of.
Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.
How old are you?
who said i didnt compare? is the same shot really
and please dont be ironic with the "advance science"
please show me your best cannon...
I'm going to clear this up for you quicklike since no one else will;
we[the members that have been here for a while] generally have a pet peeve about people that show up with other trade experience and think that automatically makes them a veteran cannon builder.
Now, if you come here and actually post a nice cannon out of the blue, you'll find it'll get you instant respect.
Another pet peeve here is shameless self/company promotion. Honestly, if you hadn't mentioned the word "spudgun" or "cannon" in you first post I might have thought you were a spambot. You work at RJB, we get it!
Anyway... if you want useful comments or suggestions try not to be so vague. We only keep our projects in obscurity when asking for advice if there's a contest, or when the finished product is almost done.
There's nothing wrong with posting a "teaser", but you should at least include a picture or rough diagram of your build.
Oh, and I wouldn't really argue with DYI if you can avoid it. It's a pretty safe bet you will lose.
He likes to troll a little when annoyed... most of us do.
Last edited by Fnord on Sun Sep 11, 2011 6:33 pm, edited 1 time in total.
i will put more pictures and reduce the number of words i use...
but could you tell me your age...?
RJB, he's DYI, just look around. I'm certain you'll change your attitude if you see what he does.
Volumetric measurement of fluids on a practical scale is quite difficult. How do you intend to integrate a customized volumetric pipette into your build? Keeping aerosolized fluids aerosolized is not that simple presuming the fluid isn't exccedingly volatile.
I think that'll do for the moment.
Some of us have taken the time and effort to compare results. Everything from a shooting chronograph, high speed photography, strobes, home made speed detection etc are used. The advantage of a fan are well documented. It is true that spray and pray cannons do shoot projectiles, they don't win performance contests.
Photo below is a composite from high speed video shot at 1.000 frames/second. The video validated the shooting chrony reading. The projectile is a rolled up t shirt. The measure in back is 5 feet long. Yes. the shirt is traveling almost .5 foot/msec. Every other frame is shown.
IIRC, I did a calculation a while ago that showed that it's actually possible to run an atmospheric combustion at room temp on octane. I actually once fueled a spray 'n' pray with gasoline, 'tis certainly possible, but why? You have to measure exceedingly low pressure values, which necessitates either chamber fueling with an extremely accurate gauge, by which point you might even conserve space by switching back to propane.
In any case, some basic wikipedia searching and unit conversions tell you that good 'ol benzene beats out octane for energy density, based on the enthalpy of combustion (36.72kJ/cm<sup>3</sup> vs 31.23kJ/cm<sup>3</sup>).
So if you're so interested in conserving space, why not build a benzene-fueled combustion? Toluene would perform almost exactly as well (energy density off by .06kJ/cm<sup>3</sup>, within error), and is far easier to find (at any nearby paint shop, there's one near me that sells it by the litre) and far less toxic.
Saefroch, if you use benzene you'll have a cancer gun. Now, where did I put those infra-violet baby seeking boolits
I'm such a post harlot
You'll be locating a certain foot to a certain mouth if DYI indulges you with a reply.
There's spudding, advanced spudding and then there's DYI.
I assume you're still talking about DYI? He can answer the question himself but I will say that he is studying at University (IIRC) and when it comes to DYI, his age is largely irrelevant if you're trying to estimate his intelligence or experience.
i am not trying to estimate his intelligence or experience but you talk as you are afraid of him...
I don't really post much in his threads, mostly because they are wayyyyy over my head(and tl;dr).
e.g: http://www.spudfiles.com/forums/al-h2o- ... 22347.html
'' To alcohol... The cause of, and solution to, all of life's problems.”
Add me on ps3: wannafuk, 8/11/11 cant wait
Congratulations DYI very good in fact the "Al H2O reactions"...
please tell me what all of you think of screwing after pasting, the parts of my PVC cannon?
Not sure how my message conveyed fear and not some degree of reverence.
DYI would have to build an awfully big cannon to make me afraid as I'm a mere ~12,000km away.
Good point on both accounts, and toluene would be better suited in any case for an atmospheric combustion.
DYI builds probably the most advanced launchers on the site (that is to say that they require machining and rather esoteric materials and are difficult to understand, if simple in operation).
"screwing after pasting"? Neither are terms normally applied to PVC.
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