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Very High Efficiency Generator

Use a pulse detonation engine combined with micro-electromechanical turbines to generate large amounts of power in a small space.
  [vote for,

Pulse detonation engines (or PDE's) http://www.aardvark.co.nz/pjet/pde.shtml are extremely powerful and efficient jet-like combustion engines. Essentially they work like a pulse-jet, rapidly combusting a fuel many times a second to generate a powerful gas flow, except they are designed to cause the fuel to explode, rather than burn. This results in a whole lot more power, noise, and efficiency. Micro-electromechanical systems (or MEMS) http://www.memsnet.org/mems/what-is.html are microscopic scale machines that are etched just like the individual transistors of computer chips, they operate very fast and are highly controllable.

Now one of the big problems with PDE's is valving. To cause detonation of the fuel, you need to close off the combustion chamber somehow when you ignite the explosion, then open it very quickly to let the exhaust out. I propose a solid block of hundreds of thousands of microscopic, switchable MEMS turbines to act as a valve, simultaneously harnessing the exhaust to generate electricity.

There are several obvious problems with this idea. First is the durability of the MEMS components. I believe current MEMS prototypes are etched on silicon substrate, which would either break, or melt, or both, under the intense pressure and heat of detonation. I envision a sandwiched block of hundreds of lithographed MEMS sheets, each containing an array of thousands and thousands of microscopic turbines and generators, along with their associated cooling and power conduits. Each turbine is covered by a shutter which can flip open or closed at computer chip speeds, in the khz or Mhz range. Clearly to act as an effective valve the MEMS would have to be etched on a very durable material indeed, probably a ceramic or other tight carbon substance.

Another obvious problem is the exotic fuel required to run today's prototype PDE's. Hydrogen is very difficult to transport and store, and we'd want a generator this compact and efficient to run off more common fuels, ideally a range of hydrocarbons like gasoline, kerosene, and diesel. I can see this as possible if you take full, dynamic control over the geometry of the detonation chamber. Electromechanical actuators or magnetic fluids could be used to change the shape of the interior engine on the fly to maintain detonation. MEMS sensors imbedded in the metal of the combustion chamber provide real-time data on temperature and pressure with a very high resolution, and a computer decides how best to adjust the geometry.

chronophasiac, Feb 28 2004

Pulse Detonation Engines http://www.aardvark.co.nz/pjet/pde.shtml
From the main article. [jutta, Oct 04 2004, last modified Oct 21 2004]


       A note on cooling and power: I imagine a simple series of channels etched into the MEMS turbine substrate, and hooked up capillary-style into larger pipes would be sufficient for cooling so long as you can feed enough water through it. A similary capillary-like series of conductive layers (like how copper is deposited on CPU's) would work to gather energy from the multitude of turbines. So basically a MEMS turbine block would look like a piece of porous ceramic, with a large cooling pipe sticking out of each end and power leads snaking out from a central interface.
chronophasiac, Feb 29 2004

       [xc], a bunch of tiny turbines would be less efficient than one large one, in general. The losses of transmitting that power, be it mechanical, electrical, etc. would be a more significant percentage of the output power of each individual turbine, since each has a tiny output. Also, lots of turbines = lots of points of friction / resistance to transmit power from multiple source points, vs one turbine and one source point and therefore only one point where friction would occur. Note that friction is not necessarily proportional to output size.
RayfordSteele, Feb 29 2004


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