None.
The present invention relates generally to a gas turbine engine, and more specifically to a small gas turbine engine for a Unmanned Aerial Vehicle (UAV) with a high turbine inlet temperature.
In a gas turbine engine, a gas turbine drives a compressor to supply compressed air to a combustor where a fuel is burned to produce a hot gas flow that is passed through the gas turbine to drive the compressor and a fan to propel the vehicle. The efficiency of the engine can be increased by passing a higher temperature gas flow into the turbine. However, the turbine inlet temperature is limited to what the turbine materials can withstand. Nickel super alloys are typically used as a material for the gas turbine. Turbine airfoil cooling is performed to allow for even higher turbine inlet temperatures. However, for a small gas turbine engine of the type used to power a UAV, the airfoils of the gas turbine are too small for cooling passages.
A small gas turbine engine for a UAV, where the engine includes a radial flow gas turbine and rotor shaft both made as a single piece and from a ceramic material so that an increased firing temperature can be used that will allow for a power to weight ratio of the engine to be more than double that from an all-metal gas turbine engine.
A metallic shaft thrust runner forms an annular cooling passage with the ceramic shaft to pass cooling air. A compliant spacer star centering ring is located adjacent to the radial flow gas turbine between the ceramic shaft and the metallic shaft thrust runner.
The present invention is a small gas turbine engine used to power an unmanned aero vehicle (UAV) in which the gas turbine is a radial flow gas turbine made of a ceramic material along with a ceramic shaft connected to a metal compressor, where the ceramic radial flow gas turbine is without cooling and the ceramic shaft includes an metal outer sleeve that forms a cooling passage for the turbine shaft. The ceramic radial flow turbine and the ceramic shaft are formed as a single piece. The ceramic radial turbine and ceramic shaft of the present invention will allow for a combustor firing temperature (T4) of around 2,400 degrees F. which will more than double the power to weight capability of the engine over a prior art all metal gas turbine engine.
The small gas turbine engine includes a radial flow compressor 11 and a radial flow gas turbine 12 both supported by air foil bearings. A reverse flow combustor is integrated within the structure of a high effectiveness recuperator. The engine powers a high speed electric generator that is also supported on air foil bearings. The electric generator can be directly driven by the shaft of the engine, or can be driven through an oil-less gearbox for shaft drive applications. Use of the integrated recuperator with this engine will allow for a compressor pressure ratio of 5 to 6 which will avoid the historic issues of environmental effects causing ceramic surface degradation seen in APU (Auxiliary Power Unit) applications and stationary industrial gas turbines.
The radial flow gas turbine 12 and ceramic shaft 13 are both formed as a single piece and from Si3N4 monolithic ceramic material. With this monolithic ceramic material, it is feasible to increase the relative rotor inlet temperature to 2,250 degrees F. equivalent to around 2,400 degrees F. firing temperature (T4).
The radial flow compressor 11 made from a non-ceramic material is secured to the ceramic shaft 13 using the threaded split ring retainer 21 held in place by the single piece threaded retention nut 17. At the compressor end, the ceramic shaft 13 is ground with a double conical recess where the threaded split ring retainer 21 is inserted and compressed by a retention nut 17. Small flats are ground on the ceramic shaft 13 that interface with corresponding flats on the interior of a split retention ring 21.
On the ceramic turbine shaft 13, a metallic shaft runner 14 is positioned with an interference fit compliant spacer star centering ring 23 situated between the shaft runner 14 and the ceramic turbine shaft 13. The centering ring 23 provides for a tight fit between the metal thrust runner 14 and the ceramic shaft 13 so that a tight fit is formed even when the metallic thrust runner 14 expands with respect to the ceramic shaft 13 under high temperatures. An annular cooling flow passage 15 is formed between the ceramic shaft 13 and the metallic thrust runner 14 in which cooling air is passed through the annular passage 15 and through the compliant spacer star centering ring 23.
This Application claims the benefit to U.S. Provisional Application 62/688,819 filed on Jun. 22, 2018 and entitled CERAMIC RADIAL TURBINE.
Number | Name | Date | Kind |
---|---|---|---|
4786238 | Glaser | Nov 1988 | A |
4915589 | Gessler | Apr 1990 | A |
5020932 | Boyd | Jun 1991 | A |
5169297 | Mizuno | Dec 1992 | A |
Number | Date | Country |
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58220901 | Dec 1983 | JP |
Number | Date | Country | |
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62688819 | Jun 2018 | US |