Method for regulating a supply circuit

Abstract

A method of regulating a feed circuit including at least a first pump and an upstream duct leading to the first pump, the method including the steps of: determining the gas content of a flow in the upstream duct feeding the first pump; and, when the value of the gas content in the upstream duct, as determined in the determining step, is greater than or equal to a predetermined threshold value, modifying the flow rate of the flow feeding the first pump.

Claims

1. A method of regulating a feed circuit comprising at least a first pump and an upstream duct leading to the first pump, the method comprising the steps of: determining a gas content of a flow in the upstream duct feeding the first pump; and when a value of the gas content in the upstream duct, as determined in the determining step, is greater than or equal to a predetermined threshold value, increasing a flow rate of the flow feeding the first pump so as to obtain supercavitation conditions in the upstream duct.

2. A method according to claim 1, wherein the increase in the flow rate feeding the first pump is greater than 2% and less than 15% of the flow rate.

3. A method according to claim 1, wherein the feed circuit comprises a downstream duct downstream from the first pump and at least a first branch channel branching from the downstream duct and enabling a certain quantity of fluid to be bled from the downstream duct, and wherein the modification of the flow rate of the flow feeding the first pump is performed by modifying the certain quantity of the fluid bled from the downstream duct at least via the first branch channel.

4. A method according to claim 3, wherein the flow rate of the flow feeding the first pump is increased by decreasing the quantity of the fluid bled from the downstream duct at least via the first branch channel.

5. A method according to claim 1, wherein the gas content of the flow is determined by a phase measurement tool suitable for determining the gas content of a two-phase flow and arranged in the upstream duct.

6. A method according to claim 1, wherein the predetermined threshold value for the gas content lies in the range 50% to 80% of the flow as a whole.

7. A feed circuit comprising at least a pump and an upstream duct leading to the pump, a phase measurement tool disposed in the upstream duct, a flow rate adjustment device, and a calculation unit, said calculation unit being configured, when a gas content value measured by the phase measurement tool in the upstream duct is greater than or equal to a predetermined threshold value, to control the flow rate adjustment device so as to increase a flow rate feeding the pump and to obtain supercavitation conditions in the upstream duct.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages can be better understood on reading the following detailed description of an embodiment of the invention given in non-limiting manner. The description refers to the accompanying figures, in which:

(2) FIG. 1A shows in modeled manner a pipe in which a fluid is flowing in a pocket cavitation mode;

(3) FIG. 1B shows in modeled manner a pipe in which a fluid is flowing in a turbulent cavitation mode;

(4) FIG. 1C shows in modeled manner a pipe in which a fluid is flowing in a supercavitation mode;

(5) FIG. 2 shows an aircraft including a feed circuit of the present disclosure;

(6) FIG. 3 is a diagram of such a feed circuit; and

(7) FIG. 4 shows a phase measurement tool.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) FIG. 2 shows an aircraft 9 having an engine 1 and a tank 2 located in a wing of the aircraft 9. The engine 1 has a feed circuit 10, which is fed by fuel taken from the tank 2. On its path from the tank 2 to the engine 1, the fuel flows initially in a first tank pipe 2a coming from the tank 2 and forming part of the aircraft 9, and then in a pipe 10a forming part of the feed circuit 10 of the engine 1. The junction between these two pipes 2a and 10a constitutes an interface I between the aircraft 9 and the engine 1.

(9) The feed circuit 10 is shown diagrammatically in FIG. 3. It comprises pump equipment for pressurizing the fuel before it is fed to the combustion chamber 20. This pump equipment comprises a first pump 12 (low pressure pump) and a second pump 14 (high pressure pump). The arrows in FIG. 3 show the flow direction of the fuel. The pipe 10a is an upstream duct in which the fuel coming from the tank 2 flows and it leads to the first pump 12. The first pump 12 delivers to a downstream duct 13 in which the fuel flows until it reaches the second pump 14 to which the downstream duct 13 is connected. The fuel leaving the second pump 14 is then delivered to a meter unit 19 and then to the combustion chamber 20 of the engine 1. A heat exchanger 16 is arranged on the downstream duct 13 between the first pump 12 and the second pump 14. It serves to regulate the temperature of the flow by exchanging heat between the fluid flowing in the downstream duct 13 and the fluid taken by the meter unit 19 downstream from the second pump 14 and taken to the heat exchanger 16 by a metering pipe 19a.

(10) The feed circuit 10 also has a first branch channel 13a and a second branch channel 13b. The first and second branch channels 13a and 13b serve to take a certain quantity of fuel from the downstream duct 13. The first branch channel 13a branches from the downstream duct 13 between the first pump 12 and the heat exchanger 16. The second branch channel 13b branches from the downstream duct 13 between the heat exchanger 16 and the second pump 14.

(11) A bleed device 18 is provided on the first and second branch channels 13a and 13b. The bleed device 18 has a first bleed valve 18a provided on the first branch channel 13a and a second bleed valve 18b provided on the second branch channel 13b. The degree to which the bleed valves 18a and 18b are open serves to regulate the quantity of fuel that flows in the first and second branch channels 13a and 13b, and thus the quantity of fuel that is bled from the downstream duct 13. The bleed device 18 is also connected to a return duct 10b in which the fuel that has been bled from the downstream duct 13 flows back towards the tank 2. The return duct 10b is itself connected to a second tank pipe 2b at the interface I. The fuel coming from the feed circuit 10 flows to the tank 2 via this second tank pipe 2b.

(12) A phase measurement tool 30 is arranged in the upstream duct 10a, downstream from the interface I. As shown in FIG. 4, the phase measurement tool 30 comprises a cylindrical shell 30a having a plurality of cylindrical electrodes 30b, 30c, 30d, and 30e arranged therein, which electrodes are coaxial with one another and with the cylindrical shell 30a. The fluid flowing in the upstream duct 10a flows into the phase measurement tool 30 along these electrodes. The electrodes serve to measure electrical capacitance, which presents a value that is representative of the gas content of the fluid flowing through the phase measurement tool 30.

(13) A calculation unit 40 is connected to the phase measurement tool 30 and to the bleed device 18. By way of example, the control unit 40 may be of the full authority digital engine control (FADEC) type. The gas content of the fluid flowing in the upstream duct 10a, as measured by the phase measurement tool 30, is transmitted to the calculation unit 40. As a function of this gas content value, the calculation unit 40 controls the degree to which the first and second feed valves 18a and 18b are opened, using a method as described below.

(14) A gas content threshold value that is characteristic of the appearance of turbulent cavitation conditions is predetermined. In this example, the predetermined threshold value corresponds to a gas content of 10%. When the calculation unit 40 determines that a gas content value in the upstream duct 10a as measured by the phase measurement tool 30 is greater than the predetermined threshold value, the calculation unit 40 deduces that turbulent cavitation conditions are present in the downstream duct 13, and consequently it controls the degree to which the first and second feed valves 18a and 18b are opened.

(15) In the above example, the existence of a predetermined threshold value makes it possible to deduce that turbulent cavitation conditions are present. Nevertheless, other means could be used. For example, turbulent cavitation conditions in the downstream duct 13 could be detected in the event of the phase measurement tool 30 measuring a variation of at least 5% in the gas content in less than 1 second.

(16) Partially closing the first and second feed valves 18a and 18b serves to reduce the quantity of fuel bled from the downstream duct 13 by means of the first and second branch channels 13a and 13b. This reduction in the quantity of fuel bled from the downstream duct 13 leads to an increase in the flow rate of fuel in the upstream duct 10a.

(17) On this topic, the main manufacturers of aviation pumps assume that all of the quantity of gas is compressed on passing via the blades of the inducer and the impeller (first pump 12 in this example). Unfortunately this need not be true, since traces of cavitation can be found in the HP stage of the main pumps (second pump 14 in this example). This indicates that a certain quantity of gas is not compressed at the outlet from the first pump 12 and consequently is to be found in the downstream duct 13. This is even more true since “supercavitation” is considered as being in a saturated state for gas content, and as mentioned above, the total volume fraction of the gas phase in the fluid as a whole over a portion of the duct increases even more. As a result, the total mass of fluid in the duct is weighted by the liquid and gas phase masses, respectively. The volume of the duct remains constant in an engine configuration, so the total mass of fluid is weighted by the densities of each of the phases. The density of kerosene at ambient temperature is about 780 kilograms per cubic meter (kg/m.sup.3) and the density of kerosene vapor is about 4.5 kg/m.sup.3, thereby giving a ratio of about 170 between those two values, it being understood that the acceptable gas content in the low pressure pump (first pump 12 in this example) according to the ARP492C standard is 45%. Furthermore, the mass flow rate requirement of the first pump under particular conditions of speed of rotation, altitude, and temperature remains constant. Furthermore, it is impossible to filter the liquid bled from the downstream duct 13, which would imply returning a two-phase flow back towards the tank 2 and consequently reducing the total mass of the fluid upstream from the second pump 14. The two-phase mixture that is to be found in the tank 2 is thus sucked out once more by the first pump 12. For this purpose, the bleed device 18 needs to be in its new position in order to limit the bleed two-phase flow. Another effect present in fuel systems is an increase in the temperature of the kerosene as a result of its compressibility on the liquid passing through the first pump 12. More precisely, the temperature of the flow returned to the tank 2 is weighted by a mixture of “hot” fuel with “cold” fuel. The presence of gas at the outlet from the first pump 12 reduces the quantity of liquid present, thereby increasing the mean temperature of the fuel that has been bled off. Consequently, its return to the tank 2 also results in an increase in the mean fuel temperature. This increase has a beneficial effect, since cavitation is retarded as a result of the latent heat of the fluid, given that cavitation is an endothermal phenomenon (transforming liquid into vapor consumes energy and that energy is taken from the liquid, thereby creating local cooling in the pocket made up of liquid and vapor). With kerosene, the saturated vapor pressure increases at higher temperature, thereby retarding the appearance of cavitation. Consequently, the first pump 12 will suck in more liquid than two-phase mixture.

(18) In the present example, the control unit 40 controls the degree of opening of the first and second feed valves 18a and 18b so as to enable the flow rate to be increased by 5% in the upstream duct 10a. This increase in flow rate serves to pass from a turbulent cavitation mode in the upstream duct 10a (shown in FIG. 1B), to a “supercavitation” mode (shown in FIG. 1C). The term “supercavitation” is used to designate a flow mode that is more stable and more regular, and thus more favorable to proper operation of the first pump 12 than is a turbulent cavitation mode, and that therefore serves to reduce the risk of damaging the first pump.

(19) Although the present invention is described with reference to specific embodiments, it is clear that modifications and changes can be undertaken to those embodiments without going beyond the general ambit of the invention as defined by the claims. In particular, individual characteristics of the various embodiments shown and/or mentioned may be combined in additional embodiments. Consequently, the description and the drawings should be considered in a sense that is illustrative rather than restrictive.

(20) It is also clear that all of the characteristics described with reference to a method can be transposed singly or in combination to a device, and conversely that all of the characteristics described with reference to a device can be transposed, singly or in combination to a method.