BATTERY ON AN AIRCRAFT FUEL LINE

Abstract

An accumulator (23) designed to dampen the pressure waves of water hammer originating from a downstream section (22) of the pipeline (2) is placed inside the pipeline, its orifice (28) preferably facing downstream. The absorption of the pressure wave is then excellent, and the circuit is protected from possible accumulations of air, water, or ice, provided there are no stagnant sections of the flow. Immersing the accumulator in the flow also ensures the protection of the equipment in case of fire.

Description

The subject of the invention is an accumulator on an aircraft fuel line. If an aircraft engine overspeed is detected, the control system quickly cuts off the flow of injected fuel. This can cause hydraulic water hammer, which can damage the fuel supply system upstream of the engine. This is why a hydraulic accumulator is often installed on the line to filter the pressure spike associated with this water hammer. Figure 1 schematically represents an existing configuration in which an accumulator 1 is connected to a pipe 2 between a fuel tank 3 upstream and a downstream portion of the fuel circuit, leading to injectors 4 belonging to the engine and comprising in particular a pumping unit 5 immediately downstream of the accumulator 1, a metering unit 6 downstream of the previous one, and a flow regulation unit 7 associated with the pumping unit 5. As shown more precisely in Figure 2, the accumulator 1 is usually connected to a transverse tapping 8 of the pipe 2 by a branch pipe 9 perpendicular to the fuel flow pipe 2, and the accumulator 1 is therefore located at some distance from the latter. It typically comprises an outer wall 10 in which a sealed bellows 11 and piston structure separates a gaseous volume 12 from a liquid volume 13, the latter communicating with the fuel flow through an orifice 14 in the outer wall 10 and the branch pipe 9. When a water hammer occurs and a pressure wave appears in the fuel, the bellows 11 contracts and the liquid volume 13 increases to absorb the pressure rise. Such accumulator arrangements have various disadvantages. When disassembly of the supply circuit is carried out, the accumulator 1 is completely emptied of liquid and must then be put back into service, by actuating a purge device 15 which evacuates the air then occupying the liquid volume 13 as well as the supply pipe 9. Another disadvantage is that the accumulator 1 is in a dead zone of the flow, where water can therefore accumulate and possibly freeze with various possible damages (disturbance of the flow, corrosion or proliferation of bacteria). The accumulator 1 must generally be fixed to adjacent structures of the aircraft by supports 16 which therefore complicate its installation. In the event of a fire, the static liquid content of the accumulator 1 is directly exposed to the temperature of the flames and is therefore likely to heat up excessively and vaporize, breaking the continuity of the flow.Finally, the absorption of pressure peaks produced by water hammer is not ideal, since it is carried out by an expansion of the fluid through the branch pipe 9 perpendicular to the main pipe 2, and which therefore involves significant pressure losses. The object of the present invention is therefore to achieve an improved arrangement of a hydraulic accumulator on a fuel supply circuit of an aircraft engine. A general aspect of the invention is then an aircraft fuel circuit, comprising a pipe extending between a fuel tank and an engine, and a hydraulic accumulator opening into the pipe, characterized in that the accumulator is surrounded by the pipe. By placing the accumulator in the pipe, accumulations of air and water are avoided, which are dissipated when the fuel flow resumes; the exposure of the accumulator to accidental high temperatures is greatly reduced, since it is bathed in fuel, in principle fresh, originating from tank 3 and which is renewed thanks to the flow; and it also becomes easy to arrange the accumulator so as to produce better absorption of the pressure peaks of water hammer. These various advantages and especially the last one are more present with a favorable orientation of the accumulator, according to which it has an external wall, arranged coaxially with the pipeline, and an orifice of the external wall, by which the accumulator communicates with the interior of the pipeline, is directed towards the engine: the pressure peaks rising in the pipe are then sent directly into the accumulator, without imposing a change of direction, nor therefore a significant loss of load on the wave. Good flow is achieved if the accumulator extends to a central position in the pipeline, and is supported by the pipeline by means of a bracket that connects them: the flow is then distributed evenly around the accumulator. A more moderate pressure loss in the flow can be expected if the support is then an openwork cylindrical partition, coaxial with the wall and the pipe. In a typical configuration, the accumulator is located in a widening of the pipeline, connected to an upstream section and a downstream section of smaller section, the widening, the upstream section and the downstream section being coaxial and in extension (curvilinear or in a straight line). In a preferred embodiment, a liquid chamber present in the accumulator communicates with the external volume, the seat of the flow, by a filtering external wall of the accumulator and by an opening fitted with a filter, to prevent the irruption of solid impurities or the permanence of gas bubbles. These aspects, characteristics and advantages of the invention, as well as others, will now be described by means of the following figures, attached for purely illustrative purposes, which represent a detailed embodiment: - Figure 1, already described, is a schematic representation of an aircraft fuel circuit; - Figure 2 illustrates a typical and known accumulator configuration; - and Figure 3 illustrates a modified configuration according to the invention. We move on to the commentary on Figure 3. The pipeline 2 now comprises a widening 20 of section between an upstream section 21 and a downstream section 22, which have the normal, smaller section of the pipeline 2. The widening 20, the upstream section 21 and the downstream section 22 are in extension and coaxial on the same straight line. The accumulator 23 of the invention is placed in the same place as the known accumulator 1 on the pipeline 2; it is similar in certain aspects to the known accumulator 1, and in particular comprises a wall external cylindrical filtering wall 24, a piston bellows 25 separating a gaseous volume 26 from a liquid volume Tl and an orifice 28 communicating the liquid volume Tl with the exterior of the accumulator 23. The accumulator 23 may be without a purge device, the orifice 28 is covered by a filter such as a strainer 29, and above all the orientation and arrangement of the accumulator 23 are different, since the accumulator 23 is arranged inside and in the center of the widening 20 of the pipe 2, with the cylindrical external wall 24 which is coaxial with the pipe 2 and the widening 20, thus leaving an annular clearance 30 with it. A support 31 connects the accumulator 23 to the wall of the enlargement 20 and consists of a cylindrical and perforated partition surrounding the orifice 28 coaxial with the external wall 24 and with the pipe 2. The bellows 25 is a reliable mechanism. The filtration strainer 29 stops impurities that could enter the accumulator 23, but is permeable to fluids, without significant pressure loss. The fuel flow from the upstream section 21 bypasses the accumulator 23 via the annular gap 30 before joining the downstream section 22. It is expected that a moderate pressure drop can be obtained, the inflections of the flow being quite small. There are no stagnant zones where humidity and air would be likely to accumulate. In the case of emptying of the pipe 2 followed by a resumption of the supply, the renewed fuel fills the liquid volume T1 by itself, expelling the air. The self-washable filtering outer wall 24 allows the fluid between the bellows and the outer wall 24 to enter or escape. It ensures, with the strainer 29, that no pollution can become blocked between the sections of the bellows 25, which would lead to a risk of piercing the bellows 25. And when a water hammer occurs, the pressure wave originating from the downstream section 22 is immediately projected inside the accumulator 23, the orifice 28 being in front of the downstream section 22, which guarantees good absorption of the overpressure. No significant pressure loss is in fact produced, according to the invention, on the path of this pressure wave leading to the accumulator 23. The outer wall 24 is advantageously of the self-washing type, in order to sweep the liquid volume 27. The surfaces of pipe 2 and accumulator 23 may be modified to reduce the pressure loss if necessary by reducing the abruptness of the 5 variations in section and flow direction. If moisture were to accumulate in the enlargement 20 and freeze at a temperature that would require it, the orifice 28 should still remain clear, since the flow passes in front of it before moving away, which maintains a circulation of fuel in front of it. 10 The invention can be designed with other types of accumulators hydraulic than bellows and piston hydropneumatic accumulators.

Claims

CLAIMS 1) Aircraft fuel circuit, comprising a pipe (2) extending between a fuel tank (3) and an engine (4), and a hydraulic accumulator (23) opening into the pipe, characterized in that the accumulator is surrounded by the pipe, has a filtering outer wall (24), the outer wall and the pipe are coaxial, and an orifice of the accumulator is directed towards the engine (4). 2) Aircraft fuel circuit according to claim 1, characterized in that the accumulator extends at a central position of the pipe, and is supported by the pipe by means of a support (31) which connects them. 3) Aircraft fuel circuit according to claim 2, characterized in that the support (31) is an openwork cylindrical partition coaxial with the wall and the pipe. 4) Aircraft fuel circuit according to any one of the preceding claims, characterized in that the accumulator is located in an enlargement (20) of the pipe, connected to an upstream section (21) and a downstream section (22) of smaller section, the enlargement, the upstream section and the downstream section being coaxial and in extension. 5) Aircraft fuel circuit according to any one of the preceding claims, characterized in that a liquid chamber (27) present in the accumulator is separated from an external volume of the accumulator by a filter (29) and the external wall (24) of the accumulator. 6) Aircraft fuel circuit according to any one of the preceding claims, characterized in that the accumulator is a hydropneumatic accumulator. 7) Aircraft fuel circuit according to claim 6, characterized in that the hydropneumatic accumulator is bellows (25).

Images