Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
"Not baked goods, Professor; baked bads!" -- The Tick

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.

user:
pass:
register,


                                                   

Tuneable Naval Guns

Get rid of those inconvenient shells.... go liquid.
  (+4)
(+4)
  [vote for,
against]

After a bit of a read through the history of naval warfare, it’s clear that any warship taking a hit to the magazine is doomed. To counteract this, vast amounts of armor are used to protect these vulnerable areas. This is a shame because it could be used to protect the room in which the rum is stored. The problem here is that all those big shells constitute a ready-made ship-killing charge. This is because both fuel and oxidizer are carefully combined at their optimum ratios all the time. So, you have to make the oxidizer, carefully mix it, and assemble the shells without coughing too loudly…. Then, they’re stored in one or several armored magazines… waiting. Tedious and dangerous.

Let’s get rid of the oxidizer component, and those boring old explosives. They’re heavy and not-particularly-energy- dense (3-5 MJ/kg). Let’s use gasoline (47 MJ/kg… much better). We’re going to need a projectile… and behind this a chamber in which to detonate the gasoline…. Using compression ignition. Like a diesel engine, only diesel is slow. So, we open the breach, insert the projectile, close the breach, flood the chamber with compressed air, inject gasoline into the incoming compressed air stream, for nice mixing… then, set off a small charge, this raises the pressure inside the combustion chamber to the point where the gasoline/air mix detonates. Then BOOM! Off goes the projectile in the general direction of the enemy. The compressed air is used (200 Bar, nothing special) to bring the volume of the combustion chamber down.. and I believe that 200 Bar is well below the spontaneous detonation temp/pressure threshold for gasoline-air. Once the projectile has gone the chamber is depressurized, and a new projectile can be inserted…. No casing to worry about.

So, you can increase the ammo carried (or decrease weight), increase survivability in case of a direct hit AND you can tune the amount of gasoline. So you can go all out and have maximum velocity-ship piercing death-ensuring level, or you can dial it back and lob a projectile so it lands intact on their deck… with a note attached.

bs0u0155, Aug 02 2012

Petrol mortar http://www.youtube....r_detailpage#t=162s
Interesting comparison of petrol vs. gunpowder [mitxela, Aug 04 2012]

[link]






       Energy density is the problem, indeed.   

       You're right about the difference in energy density between propellants and volatile hydrocarbons… but there's a snag.   

       A kilo of propellant occupies about half a litre. Allowing a factor of 10 for efficiency (less than quoted), that kilo of propellant equates to 100g of octane.   

       However, that octane needs to be not only atomised, but in a stoic ratio with air.   

       Octane has a molecular weight of 114. So 114 g of octane (one mole) occupies 22 litres at STP. Close enough to 100g for this discussion.   

       Each mole of octane requires 13 moles of oxygen for combustion. That's 22 x 14 litres, except air is only 20% oxygen, so 13 x 5 x 22 litres of air; 1430 litres.   

       Compress that to 200 Bar and it's about 7 litres, a manageable volume.   

       That's for a stoic mixture, which will give you detonation; what you actually want is a nice steady "push", so actually your mixture needs to be on the weak side to give slower burning.   

       The difficult bit is going to be achieving the perfect dispersion of the fuel throught the chamber, which suggests that a gas such as ethane would be a better proposition.
8th of 7, Aug 02 2012
  

       //a stoic ratio with air// Is this the ratio at which the octane just resigns itself to the fact that it will burn?
MaxwellBuchanan, Aug 02 2012
  

       Natural gas/propane/butane all have better energy densities, and they're already on board in the galley.... I chose gasoline because there are baked solutions for safe storage... self-sealing tanks/bag etc.   

       Diesel would be ideal in many ways... fitting nicely with the whole single-fuel policy and not so dangerous. Perhaps the diesel detonation will give you a better 'push'? I thought it might be too slow.   

       Combustion chamber volume is fine I think, in the order of a metre or so.... volume goes up pretty quickly if you expand any dimension... I suspect the volume/shape would need careful optimization.
bs0u0155, Aug 02 2012
  

       //Is this the ratio at which the octane just resigns itself to the fact that it will burn?//   

       deep breath, shoulders back.... in the manner befitting a gentleman.
bs0u0155, Aug 02 2012
  

       //Tuneable Naval Guns// I was hoping for something more musical...
MaxwellBuchanan, Aug 02 2012
  

       well, if you like, there can be a very small bleed-off from the combustion chamber... leading to a whistle. naval guns tend to be in threes. You could have each turret toot out a full chord. A musical captain may be able to create pleasing tunes while visiting destruction upon whatever it is...
bs0u0155, Aug 02 2012
  

       //each turret toot out a full chord//   

       That would be cool. I'd like to hear the heavy artillery doing a walking bass while the smaller stuff runs through some nifty blues riffs.
MaxwellBuchanan, Aug 02 2012
  

       That would be the "riff of grapeshot", would it ?
8th of 7, Aug 02 2012
  

       "Also Sprach Zarathustra" as scored for battleship quartet.
FlyingToaster, Aug 02 2012
  

       "Right, boys, let's give 'em two verses of 'House of the Rising Sun' then seven bars of 'Blackberry Boogie' - and make it staccato."
MaxwellBuchanan, Aug 02 2012
  

       3 guns per turret, 4 turrets in total... so a Battleship, a cruiser and a couple of Destroyers should give you a very useful 4 octave range... The Admiral could fire the guns with a specially linked keyboard...   

       'they're not responding to the radio Captain... perhaps a quick 'frere jacques' across the bows?'
bs0u0155, Aug 02 2012
  

       The aircraft carriers are going from steam to electromagnets to propel the deck aircraft catapult. Could you do something with water and electricity?
normzone, Aug 02 2012
  

       Throw in the new naval laser weapons, and a smoke screen, you get a light show. Like, to die for, I guess.
lurch, Aug 02 2012
  

       I read this as Tunable Gavel Nuns and was thinking, maybe it's the cobbles...   

       I remember reading about using an arc of current to flash water to steam to propel naval artillery, but on a recent google was unable to find out what had come of the work. IIRC it had the advantage of being both tunable and highly efficient through regulation of the current throughout the cycle. Anyone know any more on that?   

       Likewise I remember reading about experiments to "plasma boost" the propelant used for high velocity APFSDS rounds, but once again came up bubkis on Google. Like many things, you need to know the silly acronym they were using in order to make any headway.   

       [8th] - got any pointers for further reading?
Custardguts, Aug 02 2012
  

       We could tell you, but then we'd have to kill you. Not that we have a problem with that, mind ...
8th of 7, Aug 02 2012
  

       Try Googling "AMRTRR" andor "TASPOM".
MaxwellBuchanan, Aug 02 2012
  

       I'd like to see someone try to compress 1400 litres of octane fuel-air mixture down to 7 litres without it spontaneously combusting. Once you go past about 13:1 compression it detonates, causing "pinging" in gasoline engines.   

       Diesel will go to about 40:1 before it touches off.
UnaBubba, Aug 03 2012
  

       // I'd like to see someone try to compress 1400 litres of octane fuel-air mixture down to 7 litres without it spontaneously combusting. Once you go past about 13:1 compression it detonates, causing "pinging" in gasoline engines.   

       Diesel will go to about 40:1 before it touches off//   

       No, it doesn't. Diesel at 40:1 in an IC engine is at 40:1 AND it's been compressed to that point very rapidly and as a consequence is at several hundred celcius.... even so, you need a glow plug to get the whole process started.   

       Gasoline/air needs MUCH more pressure... which is why there are no compression-ignition gasoline engines... they'd have to be VERY well built.   

       'pinging' is caused by hot spots in an engine... chunks of still-burning carbon and the like. Gasoline engines don't detonate... they'd be more efficient if they did... they feature propagating conflagration originating at the spark.   

       The compression and temperature have been thought through.
bs0u0155, Aug 03 2012
  

       Would also be good for psy-ops, playing "Chopsticks" repeatedly would demoralise onshore populations, or playing "Stairway to Heaven", getting the same note wrong every time and then going back to the beginning as my neighbour used to do on his guitar...   

       Also, the idea of petrol powered guns is slightly baked in a tedious, naff short story some idiot wrote. I should know, it was me.
not_morrison_rm, Aug 04 2012
  

       A bit more on the energy density problem:   

       For a gasoline+air mixture to be combustable, it must be about 1.4 and 7.6% gas vapor by mass. The density of air at 1 atmosphere is about 1.2 kg/m^3, so there’s about .0168 to .106 kg gas/m^3. The specific energy of gas is about 47.2 MJ/Kg, so the energy density of the gas+air is about 0.793 to 5.02 MJ/m^3.   

       The maximum charge on a 16” (0.406 m) naval gun (might as well run the numbers for the biggest still around, no?) is around 250 kg smokeless powder. It’s specific energy varies, but 4.6 MJ/kg is a good one for a rough approximation like this, so its energy is about 1150 MJ.   

       Typical smokeless powder density is about the same as water (it’s milled into grains, so has a lot of air in it), so this pack into about 0.25 m^3, which stacks inside a 0.203 m radius cylinder about a manageable 2 m long.   

       The same about 1150 MJ of energy would take about from about 230 to 1500 m^3 of 1 atmosphere pressure gas+air mixture, about 900 to 6000 times the volume of an equivalent powder charge, which fills a 0.203 m radius cylinder about 1900 to 46000 m long, much too long to fit in a bun breach, even a gigantic naval one. You can compress the mixture, of course, but even if you manage something like 20 atmospheres (which you’d need to do with much care and refrigeration to keep it from igniting) you still need 95+ m long gun breech.   

       Gas+air mixtures work well for beer can and spud guns, but I don’t see how you could up their energy to what’s needed for a naval gun.
CraigD, Aug 07 2012
  

       Hot spots maybe but "pinging" or "knocking" is caused by local pockets of fuel/air burning outside of the flame front. It is more often due to lower octane rating fuel or to inconsistent heating in the combustion chamber.   

       Interestingly for this discussion, it can be readily reduced by adding a little water vapour into the chamber, to reduce the temperature of remianing gases in the cylinder and minimise hot spot propagation.
UnaBubba, Aug 07 2012
  

       Just a thought - what about Oxygen enriched liquid Air instead of compressed air?   

       I believe a mix of liquid air and fuel will not spontaneously ignite.
Custardguts, Feb 11 2016
  

       //believe//? I'd prefer a little more certainty in such matters.
bs0u0155, Feb 12 2016
  
      
[annotate]
  


 

back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle