Novel Microcombustor for Highly Efficient Generation of Electric Power from Fuel Microcombustor

 

This technology is a microcombustor a compact, submillimeter device that burns hydrocarbon fuels homogeneously as a source of power. It efficiently converts heat generated by combustion into electric power, and has the potential to replace batteries in portable applications requiring long-term power. This device is actually the burner, and will eventually form the core of a system that includes peripheral technologies, such as thermal isolation.

This microcombuster is designed to burn hydrocarbon fuels homogeneously and to convert generated heat into electric power, on a compact, submillimeter scale. While this technology provides the burner, it will ultimately be developed as the central element in a suite of peripheral technologies, such as thermal isolation, enabling it to be functional on a practical scale (i.e., be worn by military personnel).

This technology burns hydrocarbons in homogeneous combustion. It has attained temperatures over 1,000 C. The higher the temperature, the more efficient the conversion to electric power will be (the higher the practical power density). The development of the microcombustor addresses two essential technological problems: the need for a wall material that retards/prevents radical formation; and, a wall material that can withstand very high temperatures. Various materials are being tested for the microcombustor and the underlying physics of the device are being determined. The wall material of this device required a chemistry that does not force recombination of radicals at the wall, as by catalysis (a process that would quench the flame).

This technology uses a combination of silica, alumina, and magnesium to create a wall that disallows recombination and also rejects the radicals, returning them to the gas phase to continue to react. These materials also can tolerate high temperatures, an important factor in solving the second problem. The walls of the microcombustor must be able to tolerate very high temperatures-more than 1,000 C-to preserve efficiency.

As an alternative to thick walls, which would make the device rather large, a thermal isolation technology is under development that will enable thin walls to be hot on the inside while their outsides remain cool. This will allow the microcombustor to be worn in close proximity to a user.

The microcombustor gives a very high practical power density. Batteries that produce high energy density are often too heavy and, typically, have low power density (and vice versa). They cannot provide the energy density required for many high-power applications, for light weight, for any extended period. Compared to the highest possible energy density battery, which may someday provide 2,000 kwh/kg, homogeneous combustion yields up to 18,000 kwh/kg, a nine-fold enhancement.

The microcombustor, due to its very small size and weight, can deliver extremely high power density for extended periods of time, which cannot be matched by batteries of any type. If used as a heat source for microchemical reactors, the system would involve sandwiching the microcombustor between microreactors and then insulating the package. This type of microreactor can then be used to generate a wide range of chemicals, on the spot, for various applications in industry.

This is particularly true for chemicals that are difficult to make and store, or are expensive, unstable, or toxic, thus requiring only very small quantities. For power generation, the reactor can be used to generate hydrogen gas for fuel cells, on demand, without requiring hydrogen to be stored, thereby increasing safety. By itself, if the microcombustor was used in a thermophotovoltaic system, it would be the alternative to solar cells and thermoelectricity, which are inefficient and not popular.

Applications:

The microcombuster is designed for applications where a lot of power is needed quickly, in a small package.

  • Military portable systems: Future military personnel will require a high power source for portable electronic devices.
  • Consumer portable systems: Portable consumer electronics (e.g., laptop computers) will benefit from a device offering higher power and energy densities and less recharging than batteries.
  • Microreactors: Devices that must control chemical reactions in a small space (e.g., fuel cells) will benefit from a high-temperature heat source that can be stacked to larger sizes.

Benefits:

  • Greater energy and power density: As a portable power source, the microcombuster will offer higher energy and power densities than are possible with batteries.
  • Higher temperatures: By initiating homogeneous combustion, the microcombustor achieves higher temperatures than are normally possible with heterogeneous (catalytic) combustion.
  • Greater efficiency as a heat source: The microcombustor achieves high efficiencies in chemical reactions (e.g., in decomposition of ammonia) via its generation of temperatures over 1,000 C.

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