Internal combustion engine similarities

[jamesr]

I have been thinking about the similarities between a plasma focus device and an internal combustion engine.

Both are a pulsed process in which a plasma is created in a metal container. The spark plugs in cars need to be able to cope with millions of repetitions without wearing down. The combustion chamber needs to be cooled externally to a level so that the internal surface temperature of the metal doesn’t get too high. etc.

Would it be sensible to add a piston onto the plasma focus vacuum chamber? The piston could withdraw after a pulse, expanding the plasma/gas cooling it. Then go back in just before the next pulse was set off to get the pressure & temperature quickly back to optimal conditions before discharging the capacitor bank through the overgrown sparkplug. The piston could also draw off some of the waste heat and make it into useful energy, albeit and insignificant amount, but maybe enough to power a coolant pump. Thus providing a secondary passive cooling circuit that would follow demand.

The alloys used for spark plug contacts have been refined over the years, such as Iridium Spark Plugs. These, however, contain heavy metals and would not be very conducive to the xray flux. However there must be a compromise between the physical robustness of the alloy and resistance to wear and the extra absorption & heating due to the X-rays.

Most of the diagrams show the cathodes as simple rods surrounding the anodes. Would there be an advantage in putting a couple of narrow spikes on the end of each cathode, made of something like the Iridium alloys used in spark plugs. These would then act as the point where the filament forms when the sheath reaches the end of the cathode. So whereas the rest of the cathodes may be copper or even beryllium. the area where the highest wear rate is tailored to be able to cope with the load.

[Aeronaut]

I doubt it would be beneficial, James, since the design is entirely about moving magnetic fields. ‘Sides, you know what more moving parts do to MTBF and profitability projections….

Otherwise, the similarities to the spark plug are one of FF’s strongest safety points- one spark, one cycle.

jamesr wrote: I have been thinking about the similarities between a plasma focus device and an internal combustion engine.

Both are a pulsed process in which a plasma is created in a metal container. The spark plugs in cars need to be able to cope with millions of repetitions without wearing down. The combustion chamber needs to be cooled externally to a level so that the internal surface temperature of the metal doesn’t get too high. etc.

Would it be sensible to add a piston onto the plasma focus vacuum chamber? The piston could withdraw after a pulse, expanding the plasma/gas cooling it. Then go back in just before the next pulse was set off to get the pressure & temperature quickly back to optimal conditions before discharging the capacitor bank through the overgrown sparkplug. The piston could also draw off some of the waste heat and make it into useful energy, albeit and insignificant amount, but maybe enough to power a coolant pump. Thus providing a secondary passive cooling circuit that would follow demand.

The alloys used for spark plug contacts have been refined over the years, such as Iridium Spark Plugs. These, however, contain heavy metals and would not be very conducive to the xray flux. However there must be a compromise between the physical robustness of the alloy and resistance to wear and the extra absorption & heating due to the X-rays.

Most of the diagrams show the cathodes as simple rods surrounding the anodes. Would there be an advantage in putting a couple of narrow spikes on the end of each cathode, made of something like the Iridium alloys used in spark plugs. These would then act as the point where the filament forms when the sheath reaches the end of the cathode. So whereas the rest of the cathodes may be copper or even beryllium. the area where the highest wear rate is tailored to be able to cope with the load.

[jamesr]

Aeronaut wrote: I doubt it would be beneficial, James, since the design is entirely about moving magnetic fields. ‘Sides, you know what more moving parts do to MTBF and profitability projections….

There will be moving parts in the system; coolant pumps, vacuum pumps etc. (multiples of each for redundancy). I was just thinking whether modulating the pressure in the chamber over the course of the cycle would reduce the wear and load on the inner surface and components inside exposed to the few thousand degree plasma that will exist between cycles. Do the benefits outweigh the disadvantages of mechanical parts and extra complexity?

There is a comprimise between cooling the waste heat out of the plasma in the bulk of the chamber between pulses, and letting it cool too far so the it starts recombining and leaving deposits.

[Aeronaut]

jamesr wrote:

I doubt it would be beneficial, James, since the design is entirely about moving magnetic fields. ‘Sides, you know what more moving parts do to MTBF and profitability projections….

There will be moving parts in the system; coolant pumps, vacuum pumps etc. (multiples of each for redundancy). I was just thinking whether modulating the pressure in the chamber over the course of the cycle would reduce the wear and load on the inner surface and components inside exposed to the few thousand degree plasma that will exist between cycles. Do the benefits outweigh the disadvantages of mechanical parts and extra complexity?

There is a comprimise between cooling the waste heat out of the plasma in the bulk of the chamber between pulses, and letting it cool too far so the it starts recombining and leaving deposits.

Yes, the system will probably always have moving parts. I’d recommend drawing up a timing chart of the current–> fields–>plasmoid–> beam processes before even trying to fit moving parts into a future design’s chamber dynamics. I suspect you’re going to encounter more energy required to move your parts far enough, fast enough, than first appears (ask me about my gravity engine, lol).

[jamesr]

I wouldn’t expect this sort of thing to be added to early prototypes. We need to prove it works & we can get the energy out first. But once we are upto the stage of wanting to pulse it at more than a few Hz then the cooling & wear rates become the next challenge.

at the 300Hz or so proposed, this equates to 18000rpm. Formula one car engines rev this high and produce stresses I would think of a similar order of magnitude. That is, the car engine produces around 1700kW of heat which is transformed into 500-700kW of useful power (source: wikipedia). A 5MW focus fusion device would be generating a similar amount of waste heat that is not in the ion beam or x-rays.

If we could take off a few hundred kW of waste heat mechanically, it will help in the whole break-even budget, and reduce the amount of heat that needs to be dumped in a heat exchanger.

At present an F1 car engine doesn’t last long, but it is experience from this kind of industry we will need to make a FF device last any sensible amount of time.

If the FF device was only pulsed at say 100Hz then the heat & rev rate will be similar to a normal road car, and these engines are built to last a long time. Basically the technology is already out there if we want it.

[Henning]

I’m wondering whether the pressure (about 7 torr, which is 10 mbar) would be big enough, so that any pistons are reacting at all. In the focus (a micrometer across) temperature and pressure is enormous, but outside? It’s a very small mass hitting the walls at high speed. Mechanics wouldn’t do much.

[jamesr]

Henning wrote: I’m wondering whether the pressure (about 7 torr, which is 10 mbar) would be big enough, so that any pistons are reacting at all. In the focus (a micrometer across) temperature and pressure is enormous, but outside? It’s a very small mass hitting the walls at high speed. Mechanics wouldn’t do much.

True – it was a silly idea really. The alloys used for spark plugs and chamber walls could still be useful though.

[Henning]

jamesr wrote: The alloys used for spark plugs and chamber walls could still be useful though.

Only for the spikes at the cathode’s end with extreme wear (I don’t know much about the DPF, but I was thinking about spikes too). The inner layers of the chamber itself needs to be beryllium (as I understand the the patent application), having a low Z (number of protons) for the photovoltaic x-ray conversion system.

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