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Fusion idea that I've always had. Why can't we scale up a something like a car engine's piston and cylinder to be 1000's of times bigger and explode hydrogen b
by tocomment 15y ago
Fusion idea that I've always had. Why can't we scale up a something like a car engine's piston and cylinder to be 1000's of times bigger and explode hydrogen bombs in it to move the piston up and down?
I know it sounds kind of absurd to think about but it seems like it would work to me. Can anyone explain why it wouldn't work? Is it just a cost issue?
- bradleyland 15y agoLots of great answers here, but only a couple really get down to brass tacks. TGFlynn answers the question of why we can't use fusion bombs: "Thermonuclear bombs require a fission explosion to trigger them (in fact I believe most produce more energy from fission than from fusion)." So in short, even setting off "fusion" bombs produces lots of bad byproducts. The other part of your question is, "why not a big piston and cylinder?" Car engines are heat engines as well. They convert heat in to kinetic energy (motion). The problem is that they're relatively inefficient when compared to the typical means of heat/motion conversion used in a power plant. They're also far more complex and require more maintenance than other, simpler designs. The design of a car engine has advantages that suit it well to use in an automobile. Namely that it's power output is easily variable. You don't need peak horsepower when sitting at a stoplight, so you throttle the engine back and generate far less power. This requirement is almost nonexistent in power plants. There is some variability, but you're dealing with average power consumption from thousands of households. The rate of increase/decrease is much, much slower than you find in an automobile. Because of this, power plants use heat engines that might require a lot of energy to get started, but are more efficient once operating. Steam generators coupled with turbines are most common. The heat is used to boil water, which creates steam, which is used to drive some type of turbine. Turbines are wildly efficient if they're designed properly. The primary inefficiency in a steam/turbine power plant is startup and shutdown, but plant operators try to minimize this impact by employing operation strategies that distribute load in a way that can scale up and down minimally. So, why not use a large piston in cylinder design? Because it's less efficient, more complex, requires more maintenance, and requires more materials to construct.
- rbarooah 15y agoWhat use would this have?
- GiraffeNecktie 15y agoSounds great except for the absurdly impractical parts (i.e. exploding hydrogen bombs to move a giant piston). Where would you propose expelling the radioactive gases after the first stroke of the engine?
- tocomment 15y agoGood point about the radioactive gas. I wonder if there is some way to mitigate that?
- tocomment 15y agoFunny this was down voted on the same day we have this article on the front page: Bill Gates: We need crazy energy entrepreneurs Perhaps we're part of the problem? We should discuss radical energy ideas, teach others what wouldn't work, and how to change them, not poo poo them.
- silon3 15y agoSee project Orion.
- dbcooper 15y agoThe coulomb barrier (electromagnetic force derived) for hydrogen nuclei is not overcome until a temperature of about 120 million kelvin. Obviously, no metallic materials can operate at this temperature. Controlled magnetic fields are required to contain a plasma above the coulomb limit.
- arethuza 15y agoOne idea that was actually investigated was to explode atomic bombs underground and use the heat released to produce steam that could be user to generate power. The Project Gnome test used a relatively small bomb (3.1kt) which created a 20m wide cavity - which people eventually entered (!): http://en.wikipedia.org/wiki/Project_Gnome http://en.wikipedia.org/wiki/Project_Gnome http://www.wipp.energy.gov/science/ug_lab/gnome/gnome.htm http://www.wipp.energy.gov/science/ug_lab/gnome/gnome.htm
- mseebach 15y agoI think that combustion engines are mainly good for their scalability in terms of output: You can make a combustion engine go from cold to pulling a tractor trailer up a mountain in seconds. For sustained loads (electricity generation), the steam pressure and turbines setup is much more efficient.
- huxley 15y agoAre there actually any materials which could withstand repeated contained hydrogen bomb explosions in the same manner as a piston? No point having a 1000x sized piston you only use 2 or 3 times.
- alphaBetaGamma 15y agoNuclear fusion needs high temperature (so that the hydrogen nuclei have enough energy to get close together). "High" means ~10 million kelvin, several orders of magnitude higher than the fusion/evaporation point of any material. So your giant piston will melt and evaporate long long long before you get fusion.
- tocomment 15y agoI'm talking a really giant piston and cylinder so that the piston and cylinder walls are far enough away from the blast that they don't experience destructive levels of heat. (You'd explode the bomb in the middle of the cylinder (during freefall))
- huxley 15y agoIn most pistons, the chamber is completely contained until the release cycle so I think you'd still need to deal with the heat. I don't know what the Mach stem effect of a contained cylinder would be, but the materials might also need to deal with that.
- bradleyland 15y agoThe efficiency of a piston-in-sleve design is reduced, drastically, as you introduce free space in to the combustion chamber. Keep in mind that converting heat to motion can be easily expressed a math problem. You have a specific amount of heat that is output by the nuclear reaction. The units that are used to measure heat can be directly converted to the units that measure motion energy and electromagnetic energy. So, let's assume that you have built a massive piston engine that has a target thermal efficiency of other piston engines in common use. A highly efficient diesel ship engine (some of the most efficient made) will reach 50% thermal efficiency. Most car engines are around 35%. Because of the intense heat of the fusion reaction, you must make some design compromises. Namely, the massive distances required to protect your materials. Your materials must be far enough away that the heat reaching them is below their thermal design limit. This means that all the heat energy between the temperature of the actual thermonuclear reaction and your material design limits must be dissipated somehow. In your design, you propose to use an air-gap, which means the heat will dissipate in to the air, which will be discharged during the exhaust cycle. There's a big loss in efficiency. You'll also have the problem of heat soak. As you repetitively detonate thermonuclear bombs in your combustion chamber, some of the energy will transfer in to the materials that make up your engine. You'll have to carry this wasted heat energy away some how. In cars, this is a water cooling jacket and radiator. In power plants, this heat energy is normally used to boil water in what is called a "combined cycle" generator. You could apply the same principle here. But let's look at the piston-in-sleve side of things, because that's your primary design idea. The combined cycle side of the equation is irrelevant, because thermonuclear reactions generate heat that is easily converted to steam without the intermediary piston engine mechanicals. Inefficiency scales with size, so it doesn't matter that we're generating insane amounts of energy, we're still facing losses here due to design compromises. The losses due to the massive air gaps required cannot be overstated. The compression ratio in a car engine has a lot to do with its efficiency. A car engine that loses even 20% of it's compression can fail to sustain operation. That is, the energy created by the fuel-air explosion isn't sufficient to overcome the parasitic forces present in the engine. So let's make a wild guess and say that your engine is one-tenth (optimistic) as efficient as an optimally efficient diesel engine; around 5% thermal efficiency. Ouch. So what is the thermal efficiency of a thermonuclear power plant that simply uses the heat energy from the reaction to generate steam? Current designs are limited to around 30% because of materials limits. In a typical nuclear reactor, the rods are actually inside the pressure vessel, which must be actuated to regulate the reaction, as well as accessible for servicing. Keep in mind that I have a very limited understanding of these principles, but much of it is hands-on. I used to be a small-engine mechanic. I worked for a retired Army power plant engineer, who taught me more than I'll ever need to know that a gigantic piston-in-sleve design is a monumental waste of time.
- shingen 15y agoA working piston of this sort would generate extraordinary sums of energy in a relatively short period of time, you'd need a storage device so the energy could be distributed when needed. Any breakthrough in output will need equal or greater breakthroughs in transmission and storage. Makes the whole equation that much harder: it's not enough to just crack one of them.
- aqme28 15y agoDespite their name, hydrogen bombs are primarily uranium fission bombs[1]. What you've described is just another kind of fissile nuclear reactor, though surely far less stable and likely far less efficient. The other problem is that materials weaken and swell (as in gain actual volume) when bombarded with radiation. It would be pretty difficult to make a piston that changes shape throughout its life. [1] http://en.wikipedia.org/wiki/Teller%E2%80%93Ulam_design http://en.wikipedia.org/wiki/Teller%E2%80%93Ulam_design
- tgflynn 15y agoIf I understand what you're suggesting I think it addresses only the aspect of how to convert the energy released by fusion reactions into useful work (ie. mechanical or electrical energy). This is not actually the difficult part of building a practical fusion reactor. Even if your design could work you need a way to produce pure fusion explosions. There is currently no sufficiently energy efficient way of doing this. Thermonuclear bombs require a fission explosion to trigger them (in fact I believe most produce more energy from fission than from fusion). The laser based inertial confinement schemes actually are designed to produce tiny pure fusion explosions. If such a system could be built that produced more fusion energy than the driving lasers consume there would be many ways to convert that energy into electrical energy (photovoltaics, steam generators/turbines, etc.). I suspect an internal combustion engine would not be the most practical of these methods from an engineering point of view.
- tocomment 15y ago> (in fact I believe most produce more energy from fission than from fusion). If this is true, then that puts a kink in my design. I assumed the vast majority of energy output was from fusion. (why else would they build them?) I mainly suggest my design because it seems so difficult to trigger fusion without fission using current technology.
- tgflynn 15y agoI mainly suggest my design because it seems so difficult to trigger fusion without fission using current technology. How does your design address that ? Are you saying the fusion reactions would be triggered by the mechanical compression of the pistons in the cylinder ?
- tocomment 15y agoI don't seem to be allowed to reply to the comment below: > How does your design address that ? Are you saying the fusion reactions would be triggered by the mechanical compression of the pistons in the cylinder ? I'm saying fusion reactions are triggered by the detonation of a hydrogen bomb (fission triggers fusion inside the bomb).
- bradleyland 15y agoThere's a greater lesson in all this discussion. Great ideas can be stifled by the limitations of knowledge. That is to say, if you "know" that an idea cannot work, you may not explore it. However, if you know nothing about the principles that limit a field, you can't even begin to postulate solutions, because you can't see that an idea is as absurd as putting the cart in front of the horse.