Power plants – Combustion products used as motive fluid – Combustion products generator
Patent
1994-09-20
1996-06-25
Thorpe, Timothy S.
Power plants
Combustion products used as motive fluid
Combustion products generator
F02C 7224
Patent
active
055289037
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a small gas turbine, in particular for propelling model aircraft, provided with a rotationally symmetrical casing, a compressor rotor at the fluid intake of the casing, a combustion chamber arranged within the casing and a turbine rotor with a stationary guide vane ring arranged forwardly thereof at the fluid outlet of the casing, the turbine rotor driving the compressor rotor by way of a shaft provided in a shaft tunnel extending through the combustion chamber, the tunnel being surrounded by a helical fuel feed and vaporizing tube arranged within the combustion chamber and feeding into it by means of nozzles.
A small gas turbine of this kind has been repeatedly disclosed by the present inventor: FMT Flug- u. Modelltechnik 405-10/89 pages 20/21; FMT Flug- und Modelltechnik 408-1/90 pages 52/53; FMT Flug- u. Modelltechnik Spezial Scale 89/90 pages 69/71; FMT Flug- u. Modelltechnik Spezial Scale Nr.1 90 pages 34/37 (all journals are published by Verlag fuer Technik und Handwerk, Baden-Baden, Germany). In accordance with the latest publications, the gas turbine designated "Strahlturbine FD3" (turbojet FD3) possesses the following technical specifications: The fuel used in flight operations is diesel fuel or a mixture of diesel fuel and gasoline. In a stationary operation, propane or butane, in gaseous or liquid state, may be used appropriately metered. The radial (centrifugal) compressor stage is provided with a rotor with backwardly curved blades and a cover plate. The turbine rotor is acting axially. Fuel is vaporized in a helical tube which also acts as a cooling coil for the shaft tunnel.
However, this state of the art still suffers from the following defects. In small gas turbines, the combustion of liquid fuel in a relatively small combustion chamber is especially problematical. Comparably sized small gas turbines, for instance for starting large turbo jet engines, preferably use reverse flow annular combustors or disc-shaped combustors. Either structure would, however, detrimentally increase mass and volume of a small gas turbine, particularly of the kind used for propelling model aircraft. An optimum combustor structure yielding uniform combustion with a stabilized flame front even under rapidly changing loads, has not yet been devised.
At the same time, there is the problem that the shaft tunnel in one way or another must extend through the combustion chamber, in order to drive of the antecedent compressor stage. This leads to thermal problems: In case of insufficient heat dissipation, the shaft tunnel supported by the guide vane ring at the turbine side, because of unavoidable temperature differences, causes deformation of the guide vane ring and, hence, an off-center displacement of the turbine rotor. To avoid any grinding contact, a relatively large free play of the turbine must be provided within the casing outlet, which results in a reduced internal efficiency of the turbine as well as the thrust/weight ratio. Furthermore, over-heating of the shaft tunnel often leads to a malfunction of the bearing of the turbine rotor supported in the outlet end of the wave tunnel and thus to a significantly reduced uniformity in the rotations of the turbine rotor as well.
Therefore, an optimum structure of the combustion chamber and its support must also take these thermal problems into consideration.
It is an object of the invention to provide a small gas turbine of the kind referred to at the outset, in which uniform stabilized combustion is attained even under rapid load changes and in which combustion heat is dissipated in a controlled manner.
Further objects of the invention reside in providing a gas turbine which for propelling model aircraft may preferably operated with diesel fuel; which in a stationary operation may optionally also be driven with gaseous fuels, preferably propane and/or butane gas, and which requires no adaptations or changes in the gas turbine when the kind of the fuel is changed; which attains a maximum thrust of about 30N at a thrust/weight ratio of at leas
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Society of Automotive Engineers; Johnson & Pedersen; Small Turbine Advanced Gas Generator . . .; Pub. No. 720831.
Hormann Karl
Schneider-Sanchez Ges.m.b.H.
Thorpe Timothy S.
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