20 years away, and always will be

[paperburn1]

Fuel cell cars were mentioned earlier in this thread
now from toyota
http://www.toyota-global.com/innovation ... l_vehicle/

[GIThruster]

The troubles with hydrogen cars are that a) they have to tote around hydrogen in heavy tanks and b) the hydrogen comes from methane so they're not really any better than a very heavy, overly complex methane vehicle plus a lot of wasted infrastructure. Just not in the "good idea" category.

[paperburn1]

And C( no infrastructure in place or available to support it .

[D Tibbets]

...when it break-even fusion?

There is a minimum density, temperature, and confinement time needed for ignition (Q>=1) for a given reaction.....

FYI, while the Lawson criterion is absolute, ignition may be misleading. Some fusion schemes require it, as externally applied heating is insufficient to establish and maintain a net profitable fusion rate. But this is not always the case. If the heating is sufficient without self heating by the fusion products, then ignition is not necessary and may actually be undesired. The Polywell is the prime example of this, electrostatic heating- that is acceleration by the potential well does the job (relatively easily actually), is sufficient. And in the Polywell the fusion products are preferably removed from the system without further heating the fuel plasma, in fact the success of the system absolutely requires this. This is why Bussard used the term of power amplifier for the Polywell. With the Polywell, the question of ignition is inappropriate. It is a question of the cost of the heating directly, relative to the containment issues of course( Lawson criterion or triple product).

In an ignition dependent machine, the process is : heating a plasma to feeble fusion conditions (probably at net losses), the fusion product KE is conserved to a degree within the plasma, and this boosts temperature and fusion rate to adequate levels. Final net energy is then dependant on conversion of the eventual heat output to electricity and /or process heat.

In non ignition machines like the Polywell, the plasma is heated purely by input energy to adiquate levels for robust fusion rates. This is successful if the final fusion output exceeds the input energy. The end result is the same, but the process is more direct. There may be advantages with either approach. In an ignition machine, at least theoretically, once ignition was obtained, the other energy inputs could be shut down. In the Polywell, the input energy has to be maintained in order to continue fusing.

A comparison of the Polywell to a jet engine has been made. This is reasonable in the sense that you have to maintain combustion conditions (the compressor, etc) so that the fuel continues to burn and does work. An ignition machine is essentially a bomb, once ignition occurs, the reaction progresses under it's own internal power. All sorts of caveats can be made, but this is the basic difference.

Dan Tibbets

[prestonbarrows]

Yes, you're correct. I was sloppy with the use of the term 'ignition'. It is not strictly required for net gain, Q>1. An IEC style device would never reach ignition (nor would it need to).

[ladajo]

I agree, the Brayton comparison is probably most accurate.

The only "ignition" required would be the wiffleball startup, which like Brayton, requires an external "spark" or to be technically correct "ignitor" in Brayton terms. As we understand polywell, it is the filling and establishment of the plasma at useful energy and density to create fusion conditions. And furthermore, I do not know of any self starting Braytons, or what might be called a Diesel Brayton. The physics do not support it. In fact for turbines you not only have to spin it, you have to dump fuel into it and spark it. Once the burn starts, it will run itself. This is where polywell is different I think. You are not sparking the plasma, you are simply confining it, and doing so at a useful well depth to create conditions for collisions in the core. But for arguments sake, I guess we can say the establishment of the plasma requires input or "start up energy". It doesn't just appear out of thin air (pun intended).

[D Tibbets]

The jet turbine comparison to a Polywell is problematic, I admit. I used it because in Bussard's talk on a space forum, the commenter mentioned this and Bussard conceded that it could be compared in this fasion. For the comparison to work you have to assume that the compresser is powered externally, and once the fuel is added to the compressed air stream combustion occurs (with the help of a spark). An ignition machine might be more comparable to a,n internal combustion engine. Once compressed and sparked, the fuel burns and heats the gas till all of the fuel is consumed. No further compressed air or input is needed. Admittedly it is a foggy comparison.

I think Bussard in his Google talk liked to compare the Polywell to a power amplifier vacuum tube.

Dan Tibbets

[D Tibbets]

And C( no infrastructure in place or available to support it .

Not to mention that hydrogen gas does not exist as a energy source for practical purposes. It never seems to be mentioned by hydrogen fuel fans, but the hydrogen has to be produced from some feed stock such as natural gas. The laws of thermodynamics requires that it is a losing proposition from an energy perspective. There are various reasons hydrogen might be produced and used. Primarily this is pollution and CO2 issues. If natural gas is the source, you only gain if the carbon in the natural gas is sequestered- another energy drain.
The same applies if you electrolyze water. If you have to burn coal to produce the electricity, you are again losing ground. Only if the electricity comes from a fission, fusion reactor or hydroelectric, etc. do you gain from a mobile fuel source perspective, or an environmental perspective.

Dan Tibbets

[ladajo]

The jet turbine comparison to a Polywell is problematic, I admit. I used it because in Bussard's talk on a space forum, the commenter mentioned this and Bussard conceded that it could be compared in this fasion. For the comparison to work you have to assume that the compresser is powered externally, and once the fuel is added to the compressed air stream combustion occurs (with the help of a spark). An ignition machine might be more comparable to a,n internal combustion engine. Once compressed and sparked, the fuel burns and heats the gas till all of the fuel is consumed. No further compressed air or input is needed. Admittedly it is a foggy comparison.

I think Bussard in his Google talk liked to compare the Polywell to a power amplifier vacuum tube.

Dan Tibbets

Why does the compressor have to be powered externally? Polywell could power its own fields and guns once start up is complete.

In a gas turbine the ignitor is only run during the start cycle. Once flame is detected and RPMs are sufficient (idle speed 4500rpm for an LM-2500), it is turned off. At this point the engine only requires fuel and air and is self sustaining.

[D Tibbets]

....

Why does the compressor have to be powered externally? Polywell could power its own fields and guns once start up is complete.

In a gas turbine the ignitor is only run during the start cycle. Once flame is detected and RPMs are sufficient (idle speed 4500rpm for an LM-2500), it is turned off. At this point the engine only requires fuel and air and is self sustaining.

I stress external power to run the compressor to fit the Polywell. This is of course internally powered by the turbine in the Jet engine. . In the Polywell the system is driven by the injection of high energy electrons- this is my compressor analogy (a poor one). The fuel then burns just like in a jet engine and produces excess energy. This excess energy can be fed back into the system through electrical conversion and creating new high energy electrons. An extra step, but similar to the turbine in the jet engine. The machine maintains itself but it is external to the actual burning process, it is less tightly coupled than an ignition machine, and while the comparison in this regard is vague, in actual fusion reactors the differences in goals and design between an ignition and a non ignition machine are fundamentally different. Ignition implies that the fusion products must thermalize with the fuel and this requires that relative long confinement times are essential, thermalization cannot/ must not be avoided. Non ignition requiring machines avoids this absolute requirement for thermalization. It allows (if possible) more monoenergetic fuel ion populations, minimizes some Bremsstruhulung consequences, and perhaps even allows for helpful ion energy distributions across the machines that can be maintained over the lifetimes of the fuel ions (things like edge annealing, central confluence, etc.). All of this is much more difficult, if not impossible in fully thermalized- ignition machines.

Dan Tibbets

[CharlesKramer]

The troubles with hydrogen cars are that a) they have to tote around hydrogen in heavy tanks and b) the hydrogen comes from methane so they're not really any better than a very heavy, overly complex methane vehicle plus a lot of wasted infrastructure. Just not in the "good idea" category.

Fuel cells have bigger problems than that.

Many fuel cell chemistries use Platinum as a catalyst. It's expensive to start, and doesn't last long without needing to be replaced. They have worked well in trial cars for many years (GM has been especially diligent in working with them), but they're not practical. PLUG POWER's dream of using natural gas for local electricity generation failed for the same reason -- stack expense, and stack duration.

There are ongoing attempts at solutions:

-- substitutes for platinum

-- storing hydrogen in hydrides instead of gas/liquids

-- reformer to allow fuel cells to run on gasoline and other standard hydrocarbons (reforming into hydrogen as needed)

But GM's experiments with fuel cell vehicles go back at least to the 1960s (I believe it used alkaline chemistry in a fuel cell Covair van).

So.... might work one day, but so far 20 years away (and always will be -- maybe). Not everything close becomes practical. For now, fusion remains a very expensive laboratory curiousity.

- CBK

[CharlesKramer]

Not to mention that hydrogen gas does not exist as a energy source for practical purposes. It never seems to be mentioned by hydrogen fuel fans

Yep. No hydrogen mines anywhere. And hydogen is very challenging to store. The atoms slip through just about any containment.

Your comment reflects the bigger problem in science stories -- that people don't understand systems. You've probably been amused (and horrified) by the awe the press sometimes expresses for "exhaust free, totally green" electric cars. DUH. I would expect everyone here to see through that one (even without considering the system cost for lithium batteries).

Systems analysis sometimes leads to surprising conclusions. I was suprised to read that comparing three methods of coffee delivery:

-- real cup, clean to reuse
-- paper cup, dispose
-- styrofoam cup, dispose

that one that uses the least resources is unrecyclable styrofoam!

- Charles

[ltgbrown]

I think of hydrogen not as an energy source, but as an energy storage mechanism. Developing more efficient ways to create it and store it are what will lead to a hydrogen (vice fossil fuel) based economy. Of course, if you can generate and store electricity efficiently (solar/wind/fusion and capacitors/batteries), then hydrogen is not needed. So, hydrogen is just another mechanism for storing electricity. The common man benefit is that you can treat hydrogen like gasoline (got to a service station and pour it into your car!).

[ladajo]

And hydogen is very challenging to store

If you try and store it as pure Hydrogen.
Given how easily it bonds with things, it can be readily stored as "something else".

Like "Water".

[CharlesKramer]

Hydrogen.
Given how easily it bonds with things, it can be readily stored as "something else".
Like "Water".

water + electricity = o2 and h2 (no doubt there is a more formal way to express that)

Fuel cells reverse that equation: o2+h2 = water and electricity

So you can' t use water as a fuel to make... water. You would require at least the same energy to electrolyze water into gases as you could hope to get by combining the gases.

There has been hope (20 years away, and maybe always will be) that reforming other things (gasoline, methanol, alcohol) to release hydrogen might be practical. Not very efficient apparently (a lot of the energy is released as heat).

There's lot of talk about cars running on water, thanks to magic catalysts. Great stuff. Fusion could use it too -- add a little magic to a Polywell or LENR and presto! Even better than 20 years away (and always will be); it would be here now, only no one could see it.