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TURBOSHAFT ENGINE WITH PARALLEL SHAFTS

Time:2018-12-28 04:12Turbochargers information Click:

Turboshaft Engine with PARALLE

The field of the present invention is that of aeronautic propulsion, and in particular that of turboshaft engines with gas generator and free turbine.

Turbine engines are commonly used for aircraft propulsion and in particular for propulsion and lift for rotary-wing aircraft or helicopters. These engines comprise a gas generator consisting of a compressor, an annular combustion chamber and a turbine known as a generator turbine which drives the compressor by means of a shaft, known as a generator shaft. The gas generator is generally a single spool gas generator, that is to say it comprises just one compressor and a single turbine, both connected by a single shaft, but it may also be a multi-spool gas generator, that is to say it may comprise a plurality of compressors and a plurality of turbines, each compressor being connected to a turbine by a specific shaft. The gases leaving the gas generator are then sent to a second turbine, known as a free turbine, which is associated with a power shaft, distinct from the shaft(s) of the generator, which provides the power needed for propulsion. This shaft drives a reduction gearbox connected to the main gearbox of the helicopter (or MGB), which drives the hub of the main rotor and the anti-torque rotor. This reduction assembly is generally integrated into an accessories gearbox for the equipment necessary for good operation of the engine or the aircraft.

For reasons of structural simplicity, the free turbine is generally positioned downstream of the last generator turbine and the shaft which it drives is coaxial with the shaft of the gas generator. This power shaft may exit towards the rear of the engine or alternatively, as is more usually the case, be concentric with the shaft of the gas generator and return towards the front. With the objective of compactness and/or ease of access, this configuration makes it possible to position the reduction gearbox and the accessories gearbox on a level with the air inlet of the gas generator.

These engines with concentric shafts, such as, for example that described in British Patent GB 594207, have the drawback of being complex to produce, which makes it somewhat difficult to produce them at relatively low cost. To this is added the complexity of the combustion chamber, due to its annular shape, which likewise hinders the reduction of production costs; this annular shape requires a large number of injection points, which, in small engines, complicates the introduction of devices for reducing nitrogen oxide (NOx) emissions.

The object of the present invention is to remedy these drawbacks by proposing a small turboshaft engine which does not display certain problems of prior art turboshaft engines and which is of simple design to reduce its production costs, while allowing the incorporation of devices for reducing NOx emissions.

To this end, the invention provides a turboshaft engine with free turbine comprising on the one hand a gas generator comprising at least one compressor supplied with air, a combustion chamber receiving the compressed air leaving said compressor, and at least one generator turbine connected mechanically to said compressor by a drive shaft and driven by the gases arising from fuel combustion carried out in said combustion chamber, and further comprising a free turbine supplied with the gases arising from said combustion after passage thereof through said generator turbine and which drives a power shaft oriented non-coaxially with the drive shaft of the gas generator and supplying the turboshaft engine power via a reduction gearbox, characterized in that the combustion chamber is a substantially cylindrical or frustoconical chamber, coaxial with the axis of the generator turbine and comprising a single injector.

Coaxial shafts mean two shafts which are situated in the extension of one another, whatever their relative direction of rotation.

This arrangement of the shafts provides great flexibility for the arrangement of the two parts of the engine and makes it possible to select a “single can” combustion chamber, that is to say one that is substantially cylindrical or frustoconical in shape with a single injector placed at the center of said cylinder or truncated cone, which allows easy integration of an injection system enabling reduced formation of nitrogen oxides. A combustion chamber coaxial with the axis of the generator turbine has the advantage of not creating excessive bulk, which would not be compatible with one of the objectives sought, namely of producing a small turboshaft engine. Furthermore, the gases leaving the combustion chamber are sent directly to the turbine of the generator, which prevents the presence of a chamber bottom which would otherwise be necessary for regulating the flow thereof and which would require cooling. In the light of the very high temperature of the gases leaving the combustion chamber in modern engines, the claimed configuration avoids this operation, which would be particularly difficult to implement.

The power shaft is preferably oriented parallel to said drive shaft. This arrangement makes the engine very compact. Even more preferably, the reduction gearbox is associated with an accessories gearbox, the two being positioned in the longitudinal direction substantially on a level with the air inlet of the compressor. Compactness is improved further in this way and the reduction gearbox/accessories gearbox assembly is situated in a relatively cool zone.

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