Patent Application
20230303224
The present disclosure pertains generally to Stirling cycle engines, and more particularly to submersible maritime propulsion systems incorporating the same.
Long endurance small submersible vehicles have long been needed for scientific and military operations. To date, however, the technical difficulties associated with their design have hindered their introduction. Since electric motors are typically used for propulsion in vehicles of this type, battery technology is a principle obstacle in this application.
Small submersibles employed by the military, or by universities for oceanographic research, are typically powered by electric motors which draw their electrical current from batteries. This limits the amount of “Bottom Time” a submersible can operate at depth. Additionally, the types of batteries commonly used in other fields present hazards in this application. In particular, if sea water floods a battery compartment containing lead acid batteries, chlorine and hydrogen gas may be released from the battery compartment, thus threatening the lives of a human crew. Similarly, lithium ion batteries present a risk of fire, which can lead the catastrophic failure of the pressure hull and the death of all of those on board.
Stirling Cycle engine designs have been recently employed in littoral class submarines, with a significant degree of success. Unfortunately, this design does not lend itself well to small submersibles. Air-independent submarines of the type represented in the littoral class could just as easily employ Ericson Cycle engine designs or Rankine Cycle engine designs, but these designs are also not suitable for use in small submersibles. In particular, in these engine designs, combustion takes place in a combustion chamber enclosure external to, or isolated from, the motive gas or working fluid. Thermal energy from combustion is then transferred to the motive gas or working fluid to drive the mechanisms of the engine. Typically, this thermal energy is transferred through the walls of an array of tubes making up the heater head or boiler, and may occur through both conductive and radiative thermal energy transfer.
During operation of the external combustion engine, thermal energy from combustion is transferred to the plurality of heater tubes (and subsequently to the mechanisms of the engine) at a nearly equal rate to ensure a balanced and sustained external combustion cycle. The combustion needed for a source typically requires oxygen. The oxygen can be liquefied, as in the case of the Air Independent Submarine, or drawn from the atmosphere itself, as with the Stirling Automotive Engine developed by NASA. These systems also rely on propellers to provide propulsion. Propellers may lead to cavitation when operated at high speeds of rotation, which can generate an acoustic signature detectable by passive sonar systems.
Information disclosed in this Background of the Invention section is only for enhanced and detailed understanding of the general background of the invention. It should not be taken as an acknowledgement, or any form of suggestion, that this information forms prior art to anything disclosed herein.
In one aspect, a watercraft, which may be a submersible or a submarine, is provided. The watercraft comprises a hull; a propulsion system for propelling the hull through water; and a power plant which powers the propulsion system, the power plant including a heat engine and a thermal energy source; wherein the thermal energy source includes at least one material selected from the group consisting of nuclear isomers and radioisotopes.
It has now been found that the aforementioned problems of combustion (as a heat source) and the sound generated by cavitation may be overcome with the systems and methodologies disclosed herein. In a preferred embodiment, a propulsion system for a long endurance submersible is provided that is equipped with a heat engine (such as, for example, a Stirling Cycle engine, Ericsson Cycle engine or equivalent engine design) which utilizes nuclear isomers for the heat source. Nuclear isomers have been shown to generate thermal energy through decay sufficient to power a Stirling engine in excess of 10,000 hours operation. The heat engine, drawing thermal energy from the nuclear isomer, may turn a generator to provide all the electrical power needed for the submersible to conduct military or scientific operations.
The outflow end of the conduit is equipped with a nozzle 113 and a quasi-conical housing 111. This housing 111 is preferably open to the sea at both ends, and acts to entrain sea water as the vortexual fluid flow exits the nozzle 109 to suppress cavitation. For reverse thrust of the system, the quasi-conical housing will maneuver to divert the flow from the nozzle 109 in a manner similar to the reverse thrust system on aviation jet aircraft engines commonly known as “bucket thrusters.” With the exception of operation in the reverse thrust mode, systems of this type may be configured to be exceptionally quiet, since there are no vibrations from reciprocating pumps or cavitation from propeller blades.
The propulsion system 121 is powered by a power plant that includes the heat engine 103 and a thermal energy source. The thermal energy source preferably comprises one or more nuclear isomer isotopes. Suitable isotopes for this purpose may include Americium (242Am), which has a half-life of 141 years and produces 49 keV; Hafnium (178m2Hf), which has a half-life of 31 years and can produce 2.4 MeV; and Molybdenum (93Mo). The use of these isotopes is advantageous in that they emit relatively small amounts of ionizing radiation. Rather, the decay energy is mostly in the thermal side of the equation, with only small amounts of beta particles emitted. To protect personnel in the submersible, the nuclear isomer pile may be coated with boron glass or obsidian glass ceramics.
The use of the foregoing types of isotopes as the fuel in a heat engine overcomes the limitations and hazards attendant to the use in submersibles of lithium or lead-acid batteries. Moreover, the endurance of the submersible may thus be based solely upon the human limitations of the operators.
Navigation and depth soundings may be augmented with blue lasers, depending on water clarity, as well as conventional systems of depth soundings and Inertial Navigation Systems. Since Stirling engines are scalable, the teachings disclosed herein may be applied to submersibles of any size, from ROVs to a submersible with more than a dozen occupants.
The above description of the present invention is illustrative and is not intended to be limiting. It will thus be appreciated that various additions, substitutions and modifications may be made to the above described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should be construed in reference to the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US21/46395 | 8/17/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63066321 | Aug 2020 | US |
