METHOD FOR DETERMINING CHARACTERISTICS OF A FUEL SUPPLIED TO AN AIRCRAFT ENGINE

Abstract

On board an aircraft, a method is perform in which the following steps are implemented in the following order: measuring a first density value, a first dielectric constant value and a first temperature value of the fuel at a first time, measuring a second density value, a second dielectric constant value and a second temperature value of the fuel, determining parameters of a function for calculating a density from a temperature or a dielectric constant, measuring a volume flow rate value and at least one of a third temperature value and a third dielectric constant value of the fuel in a fuel injection duct in the engine, and determining a density value of the fuel and a mass flow rate of the fuel in the injection line.

Claims

1-10. (canceled)

11. A method, the method comprising determining properties of a fuel supplying an engine of an aircraft, in which method, on-board the aircraft, the following steps are implemented in the following order: a first density value, a first dielectric constant value and a first temperature value of the fuel are measured at a first time, a second density value, a second dielectric constant value and a second temperature value of the fuel are measured at a second time, chosen so that the first and second temperature values are different; on the basis of the first and second values, parameters are determined of at least one function for calculating a density from a temperature or from a dielectric constant; a volume flow rate value and at least one from among a third temperature value and a third dielectric constant value of the fuel in a fuel injection line into the engine, are measured; by taking account of the third value or at least one of the third values, and at least one of the functions, a density value of the fuel is determined, and on the basis of the values for volume flow rate and density, a mass flow rate of the fuel in the injection line is determined.

12. The method according to claim 11, in which the first and second density values are measured by means of a same density sensor, the first and second dielectric constant values by means of a same dielectric constant sensor, and the first and second temperature values by means of a same temperature sensor.

13. The method according to claim 11 in which, after the first time and before the second time, a step is implemented causing a temperature change of the fuel in a chamber where the measurements are performed at the first and second times.

14. The method according to claim 11, in which the two first steps of claim 1 are implemented in a fuel tank.

15. The method according to claim 11 in which, by means of the first and second values, parameters of a function for calculating a dielectric constant as a function of a temperature are determined.

16. The method according to claim 11, in which a fourth temperature value of the fuel in the injection line is measured.

17. The method according to claim 11, in which: on the basis of the respective third values and by means of the functions, calculating test values of the density; for the or each pair of test values considered, two-by-two, determining whether a difference between the test values exceeds a predetermined threshold, and determining the density value of the fuel as a function of a result of determining whether a difference between the test values exceeds a predetermined threshold.

18. The method according to claim 17, in which, at the end of the first two steps of the preceding claim, the density value is determined without taking account of one, two or three of the test values.

19. The method according to claim 11, in which the density value is determined by taking account of at least one other value obtained during the implementation of the method according to claim 1 for another engine of the aircraft, or by taking account of at least one other predetermined function.

20. The method according to claim 13, comprising introducing into the chamber fuel coming from a system for injecting fuel into the engine.

21. The method according to claim 16 comprising determining whether a difference between the third and fourth temperature values exceeds a predetermined threshold.

22. The method according to claim 19, in which the density value is determined by taking account of at least one other predetermined function without taking account of the test values.

23. An aircraft comprising: at least one engine, at least one fuel tank, a system for injecting fuel into the engine, devices for measuring a density, a dielectric constant and a temperature of the fuel, and a control device configured to control an execution of the steps of the method according to claim 11.

Description

DESCRIPTION OF THE FIGURES

[0076] An embodiment of the invention will now be described by way of a non-limiting example with support of the drawings, in which:

[0077] FIG. 1 is a diagram showing an injection circuit of an aircraft and one of its tanks, in an embodiment of the invention,

[0078] FIG. 2 is a more detailed view of the injection circuit of the aircraft of FIG. 1,

[0079] FIGS. 3 to 5 show curves representing functions connecting the density and the dielectric constant as a function of the temperature and the density, and

[0080] FIG. 6 is a point cloud showing a test result of the method of the invention.

[0081] FIG. 1 shows an aircraft according to an embodiment of the invention, such as an airplane 2. This airplane comprises a plurality of engines 4, for example turbojet engines. It is assumed, for example, that the airplane has at least one engine on each side of a fuselage of the airplane.

[0082] The airplane also comprises fuel tanks, one of which 6 is illustrated in the figures. It is also equipped with a system 8 for injecting fuel into the engine, which also ensures a heat exchange with a cooling fluid formed by the oil circulating from an oil tank 10. Hence, as illustrated in FIG. 1 by the dashed-line arrows, the oil 12 passes from the oil tank 10 into the engine 4 in order to cool it, then into the injection system 8 to heat the fuel which passes through the latter in order to supply the engine 4. Finally the oil returns to its tank 10. This figure provides a summary illustration of the fuel circuit.

[0083] The airplane has a fuel filler port 14 for supplying the tank with fuel from outside the airplane. It communicates with a filling line 16 extending outside and inside the tank 6 to a terminal end 18 of the line opening into the tank. A measurement line 20 extends from a centre portion of the filling line 16 and diverts part of the fuel flow from the latter to a measurement chamber 22 extending inside the tank 6 and communicating with the latter so that the fuel can pass freely from the chamber to the rest of the tank and vice versa. This chamber 22 is equipped with sensors for measuring the properties of the fuel in the tank. In the present example, this respectively involves a density sensor 24, a dielectric constant sensor 26 and a temperature sensor 28.

[0084] The fuel circuit is illustrated by the solid lines in FIG. 1. Hence the fuel passes from the tank 6 to the injection system 8, then is injected by the latter into the engine 4 via the injection line 57. Since excess fuel frequently arrives in the injection system 8, part of it is sent back to the tank 6 via a reintroduction line 30 which opens directly into the tank.

[0085] In the present example, this reintroduction line is equipped with a bypass line which forms an introduction line 32 which places it in direct communication with a central part of the measurement line 20. The introduction line is connected to the reintroduction line in a region located between the system 8 and the tank 6 in the present example. In this way, the fuel passing from the introduction line 32 into the measurement line 20 is directly introduced into the chamber 22 without passing via the general volume of the tank and without mixing with the rest of the fuel located there. The measurement line 20 is equipped with a non-return valve 34 in order to prevent the fuel rising in the filling line 16 on this occasion. The non-return valve 34 only opens during filling of the tank from outside the aircraft. Finally, the introduction line 32 is equipped with a valve 36 which can interrupt the passage of fuel therein when desired.

[0086] The chamber 22 is produced, for example, as described in document WO 2018/002682 in order that the modification of the fuel circuit in order to implement the invention can be mainly limited to the addition of the line 32 with its valve 36.

[0087] A more detailed version of the injection system 8 is illustrated in FIG. 2. The fuel coming from the tank 6 passes through a low-pressure centrifugal pump 40 then a heat exchanger 42 with the oil, a filter 44 and a high-pressure pump 46. In the remainder of the circuit, which is at high pressure, the fuel passes through a fuel meter 48 then a cut-off valve 50, a flow meter 52 and then arrives in the injectors 54. The oil passes from the tank 10 to exchanger 58 then to exchanger 42 in order then to be directed to the engine 4.

[0088] Downstream of the pump 46 and upstream of the metering device 48, a part of the fuel is diverted to a heat exchanger 58 with the oil, then to cylinder servo valves 59 in order to be finally reintroduced into the low-pressure circuit upstream of the pump 46. These cylinders are cylinders of the engine in which the fuel is used as hydraulic fluid (it involves for example air bleed control cylinders).

[0089] A part of the fuel located in the metering device 48 is sent via the reintroduction line 30 to the tank 6. The line 30 is at low pressure and is also referred to as a fuel recirculation line. It is used to return the excess pumped fuel to a point upstream of the high-pressure pump 46 since, according to the operating phases of the engine, a more or less significant part of the flow supplied by this pump is in excess compared to the flow rate which must be supplied from the metering device to the combustion chamber of the engine. The fuel returned upstream of this pump can be entirely reintroduced into the circuit downstream of the low-pressure pump 40, but it is also possible to reintroduce all or part of this fuel return into the fuel tank 6, as is the case here.

[0090] The injection line 57 bearing the flow meter 52 is also equipped with two temperature sensors 54, 55 and a dielectric constant sensor 56.

[0091] In this case the fuel is kerosene but it could also be a mixture of kerosene with biofuel, or even 100% biofuel.

[0092] Finally the airplane comprises computer control means 60 comprising processing means and one or more memories, connected to the various elements of the airplane. These means are configured so as to implement, on-board the airplane, the method comprising the steps which are now described.

[0093] In a first step, at a first time, measurement is made of: [0094] a first density value D.sub.1, [0095] a first dielectric constant value K.sub.1 and [0096] a first temperature value T.sub.1.

[0097] These measurements are performed by means of the sensors 24, 26 and 28 of the chamber 22 and concern the fuel located in the chamber, inside the tank 6. They are performed when the fuel return valve 36 is closed.

[0098] Then, the fuel coming from the injection system 8 is introduced into the chamber 22. For this purpose, valve 36 is opened, which causes a flow of fuel into the introduction line 32 then directly into the measurement line 20 and to the chamber 22. Since this fuel comes from the injection system 8, it is at a temperature higher than that of the fuel initially found in the chamber 22. This therefore causes a temperature change of the fuel in the chamber 22. The above-mentioned replacement mode is implemented here with, in addition, a small amount of mixing and heat exchange.

[0099] It is also observed that, then, when the entry of the fuel via the line stops, i.e. with the valve 36 closed, the fuel from the tank pushes on that in the chamber in order to take its place. This enables a cyclic operation for the alternating measurement of the properties of the fuel in the tank and of that returning from the injection system.

[0100] Then, at a second time, the same sensors are used to measure, in the chamber: [0101] a second density value D.sub.2, [0102] a second dielectric constant value K.sub.2 and [0103] a second temperature value T.sub.2 of the fuel.

[0104] This second time follows the arrival of the heated fuel so that the first and second temperature values T.sub.1, T.sub.2 are different. The same applies for the other first and second values.

[0105] As can be seen, in this example, the first and second density values D.sub.1, D.sub.2 are therefore measured by means of the same density sensor 24, the first and second dielectric constant K.sub.1, K.sub.2 by means of the same dielectric constant sensor 26, and the first and second temperature T.sub.1, T.sub.2 by means of the same temperature sensor 28.

[0106] In a following step, the parameters of the functions f.sub.1, f.sub.2 and f.sub.3 are determined on the basis of the first and second values, as:

D=f.sub.1(T),D=f.sub.2(K) and K=f.sub.3(T)

[0107] making it possible to calculate, respectively: [0108] a density D from a temperature T, [0109] a density D from a dielectric constant K, and [0110] a dielectric constant K as a function of a temperature T.

[0111] These three functions are those which have been described above. f.sub.1 and f.sub.3 have a classical affine linear equation of type y=cx+e. Their graphs are illustrated in FIGS. 3 and 4 respectively for various types of fuel used in airplane engines.

[0112] The second function f.sub.2 is that of the above-mentioned formula derived from the so-called generic “Clausius-Mossotti” formula and has an equation of type:

D=(K−1)/[A+B(K−1)]

[0113] If it is assumed that x=K−1 and that y=(K−1)/D as is the case in document US2016/0123860, an affine linear formula is obtained of type y=cx+e, the graph of which is illustrated in FIG. 5.

[0114] It is important to note that the use of affine equations in the present case for the three formulas is a choice, and that other types of formulas are possible.

[0115] Under these conditions, knowing the first and second measured values, the computer is able to determine the parameters c and e for each of the two functions f.sub.1, f.sub.3 and the parameters A and B for function f.sub.2. In this way, the three functions or laws governing the relations between the properties of the fuel are determined. Hence the three quantities measured at two different temperatures enable the fuel to be precisely characterised and to predict the change in one of the quantities over time on the basis of one of the others, using the three functions.

[0116] In a following step, in the line 57 for injecting fuel into the engine, a measurement is made by means of the flow meter 52 and sensors 54, 55 and 56, with regard to the fuel in the line, of: [0117] a value of volume flow rate DV, [0118] third and fourth temperature values T.sub.3, T.sub.4, and [0119] a third dielectric constant value K.sub.3.

[0120] It is then determined whether the absolute value of a difference T.sub.3−T.sub.4 between the third and fourth temperature values exceeds a predetermined threshold. This threshold is chosen, in this case, as being equal to twice the tolerance interval associated with each temperature sensor 54, 55. However, it is possible to take into account another threshold value.

[0121] Furthermore, on the basis of the respective values T.sub.3, T.sub.4 and K.sub.3 and by means of functions f.sub.1, f.sub.2 and f.sub.3, test values D.sub.a, D.sub.b, D.sub.c of the density are calculated as follows:

D.sub.a=f.sub.1(T.sub.3)D.sub.b=f.sub.2(T.sub.4)D.sub.c=f.sub.3(K)

[0122] Then, for each pair of test values considered, two-by-two, it is determined whether a difference in absolute value between the test values exceeds a predetermined threshold. Then |D.sub.a−D.sub.b|, |D.sub.a−D.sub.c| and |D.sub.b−D.sub.c| are successively compared to this threshold.

[0123] The result of these four tests is then taken into account in order to determine the density value D.sub.3 to be considered in the rest of the method.

[0124] In the present example, a truth table is predetermined in order to respond to all the cases encountered. The names given to these tests and the table are presented below:

[0125] T_valid=If (|T−T′|<=authorised deviation) then OK (1/true) else NOK (0/false)

[0126] Dab_valid=If (|D.sub.a−D.sub.b|<=authorised deviation) then OK (1/true) else NOK(0/false)

[0127] Dac_valid=If (|D.sub.a−D.sub.c|<=authorised deviation) then OK (1/true) else NOK(0/false)

[0128] Dbc_valid=If (|D.sub.b−D.sub.c|<=authorised deviation) then OK (1/true) else NOK(0/false)

TABLE-US-00001 Truth table D Dac_Valid Dbc_Valid used 00 10 01 11 00 Dc (D.sub.a + D.sub.c)/2 (D.sub.b + D.sub.c)/2 D.sub.c 10 D D.sub.a D.sub.b D.sub.c default T_Valid 01 D D.sub.a D.sub.b D.sub.c Dab_Valid default 11 (D.sub.a + D.sub.b)/2 (D.sub.a + D.sub.b)/2 (D.sub.a + D.sub.b)/2 (D.sub.a + D.sub.b + D.sub.c)/3

[0129] Each box of the table contains the density value D which will be taken into account for the rest of the method as a function of the test results. (Some values are underlined for reasons explained below). For example, at the intersection of row “10” and column “01”, the density value used for D.sub.3 is D.sub.b. This is a situation in which the following results are cumulated: [0130] the test on the temperatures gives the value “true”, [0131] |D.sub.a−D.sub.b| exceeds the threshold, [0132] |D.sub.a−D.sub.c| exceeds the threshold, and [0133] |D.sub.b−D.sub.c| does not exceed the threshold.

[0134] As can be seen, in certain cases, it is one of the following values which is used for D.sub.3: D.sub.a, D.sub.b, D.sub.c, (D.sub.a+D.sub.b)/2, (D.sub.a+D.sub.c)/2, (D.sub.b+D.sub.c)/2, or (D.sub.a+D.sub.b+D.sub.c)/3.

[0135] In the other cases, which correspond to the degraded mode in the presence of at least two failures, it is the default value which is used. This is primarily another value obtained during the implementation of the method of the invention on the other engine of the aircraft located on the other side of the fuselage. If this is no longer available, it is a value calculated on the basis of a default function giving the properties of a standard fuel and stored in the memory of the computer without taking account of the results of the sensor measurements in the chamber 22. Alternatively, this latter value can be used directly by default, without using the value given for the other engine. The default value takes into account the margins necessary to guarantee reliability and safety.

[0136] As can be seen in this table, in certain cases, the density value D.sub.3 is determined without taking account of one, two or three of the test values D.sub.a, D.sub.b and D.sub.c.

[0137] In the present embodiment, the measurement of two temperature values T.sub.3 and T.sub.4 and of a dielectric constant value K.sub.3 in the injection line 57 enables a redundancy which makes it possible, in return, to detect the occurrence of an anomaly or a failure, or even a complete failure corresponding to the delivery of an erroneous measurement by a sensor. The complete failure case is that illustrated in the three underlined boxes which are cases (00, 10), (00, 01) and (11, 00). It can also be seen that only the last box at the bottom right of the table is associated with the absence of any anomaly and takes into account the three values D.sub.a, D.sub.b and D.sub.c for the calculation of the density. The detection of an anomaly or a failure makes it possible to dismiss the suspect value or values for the remainder of the method as originating from an erroneous measurement.

[0138] In a last step, a mass flow rate DM of the fuel in the injection line 57 is determined on the basis of the thus determined values of volume flow rate DV and density D.sub.3.

[0139] This knowledge of the mass flow rate of the fuel under the conditions of injection into the engine 4 enables a more precise metering without compromising the performance, reliability and safety, and while reducing the margin of overconsumption.

[0140] The arrangement illustrated in FIG. 1 is particularly well suited to the determination of the properties of the fuel on the basis of the measurements performed in the tank 6 in order to take them into account for the determination of its properties in the injection line 57, which is advantageous for a precise metering of the injected fuel.

[0141] FIG. 6 illustrates the result of a simulation of the method of the invention implementing 100 random selections of the values T.sub.3, T.sub.4 and K generating errors on the latter with respect to the values expected for a fuel of predetermined density D.sub.p. A density value D.sub.d was obtained by implementing the above method and was compared with this predetermined value D.sub.p. It is the difference between these two values which is illustrated on the ordinate in the figure, with the random number appearing on the abscissa. It is seen that the difference in absolute value never exceeds 2/1000, which demonstrates the reliability of the method of the invention.

[0142] Of course, numerous modifications could be made to the invention without going beyond its scope.

[0143] Many different strategies are possible for determining the density of the fuel on the basis of the quantities measured in the injection line 57. If a table is used, this could be different from the table presented above. For example, in certain cases, it could be possible to use the default value in a place where it is not currently used, or other values than those which appear there. It is also possible to dispense with calculating an average of certain values or all the values as is the case in some boxes and simply substitute one of the values there.

[0144] Some redundancies could be dispensed with.

[0145] By way of example also, the value of the dielectric constant obtained by calculation on the basis of the measured temperature is not used in the strategy presented above for determining the density to be taken into account. However, it could be used in another strategy, for example by comparing this calculated value with the measured value of the constant.