Abstract:
A fuel circuit of an aircraft engine including a fuel tank; an engine fuel system including a low-pressure pump and a high-pressure pump, and a fuel recirculating pipeline connected to the engine fuel system; and a fuel recirculating valve arranged so as to switch between an open position and a closed position according to the pressure differential of the low-pressure pump, the valve being able to obstruct the fuel recirculating pipeline in the closed position, and to bring the fuel recirculating pipeline into communication with the fuel tank in the open position.

Description:
GENERAL TECHNICAL FIELD 
       [0001]    The invention concerns the general field of fuel circuit architectures of aircraft engines with motive flow tapping an engine fuel system. 
       PRIOR ART 
       [0002]      FIG. 1  illustrates a conventional fuel architecture of an aircraft engine. In such an architecture, an electrical pump  11 , known as the aircraft pump, embedded in a fuel tank  10  sends fuel into an engine fuel system  20  of the aircraft by way of a supply line  1 . 
         [0003]    The engine fuel system  20  makes it possible to produce hydraulic energy and supply fuel to the engine of an aircraft (not depicted) and to the variable—geometry vanes (not depicted.) 
         [0004]    This aircraft pump needs to be electrically powered. 
         [0005]    To avoid systematically employing this aircraft pump, a jet pump  12  operating by Venturi effect is also embedded in the tank  10  and can take over from the aircraft pump under certain conditions. 
         [0006]    This jet pump  12  needs a hydraulic power source which is, in a known manner, supplied by a fuel return line  2  tapping the engine fuel system  20 . 
         [0007]    This return line  2  makes it possible to send pressurized fuel taken from the engine fuel system  20  into the fuel tank  10 . 
         [0008]    It is however undesirable for the pressurized fuel to be sent arbitrarily to the tank  10  to power the jet pump  12 . 
         [0009]    To do this, a motive flow valve  30  can be positioned along the return line  2  in order to block it, under certain conditions dependent on the design and performances of the fuel system and in particular as a function of the rotation speed N2 of the aircraft engine. 
         [0010]    From the document FR 2 619 417, a fuel circuit of an aircraft engine is already known comprising a fuel tank, an engine fuel system equipped with a low-pressure pump connected to the fuel tank and a high-pressure pump connected to the low-pressure pump. The fuel circuit further comprises a mixer device comprising on the one hand a mixing valve and on the other hand a return valve. 
         [0011]    The mixing valve switches between an open position and a closed position, as a function of the pressure difference between a first and a second chamber, both supplied with a stream of hot fuel taken downstream of the high-pressure pump. The mixing valve further comprises a central chamber with a constant volume allowing a stream of cold fuel taken downstream of the low-pressure pump and a stream of hot fuel taken downstream of the high-pressure pump to mix together and be sent toward the fuel tank, when the mixing valve is in the open position. 
         [0012]    The return valve switches between an open position and a closed position, as a function of the opening and closing of an electrovalve which, when open, makes it possible to inject a stream of fuel taken downstream of the high-pressure pump into a first chamber and to cause the draining of a second chamber so that the return valve opens, and when closed, cause fuel to leak from the first chamber toward the second chamber so that the valve closes, thus blocking the passage of a stream of warm fuel from the mixing valve toward the fuel tank. 
         [0013]    In such a fuel circuit, the mixing valve and the return valve are therefore controlled as a function of the pressure of the stream of fuel downstream of the high-pressure pump. 
         [0014]    Thus such a fuel circuit does not allow the device to be controlled as a function of the rotation speed of the engine. 
         [0015]    There is therefore a need to control a motive flow valve under conditions of fuel system speed. 
         [0016]    Moreover, the motive flow valve  30  must be closed when the engine is stopped and open at speeds greater than or equal to a predetermined speed. 
         [0017]    However, it can happen that the valve exhibits a malfunction and remains jammed open so that it allows fuel to be sent from the engine fuel system  20  into the fuel tank  10  when this should not be the case. This impairs the engine performance since the operation of the fuel system is disturbed by the fuel stream taken in to be sent into the fuel tank. 
         [0018]    There is thus also a need to detect a failure of such a motive flow valve  30 . 
       PRESENTATION OF THE INVENTION 
       [0019]    According to a first aspect the invention proposes a fuel circuit of an engine of an aircraft comprising: 
         [0020]    a fuel tank; 
         [0021]    an engine fuel system comprising:
       a low-pressure pump connected to the fuel tank, the low-pressure pump being capable of raising the pressure of a low-pressure stream of fuel from the fuel tank by a variable pressure difference;   a high-pressure pump connected to the low-pressure pump capable of converting the low-pressure stream of fuel into a high-pressure stream of fuel;       
 
         [0024]    a fuel return line connected to the engine fuel system, said line being capable of bringing the high-pressure stream into the fuel tank; 
         [0025]    a motive flow valve arranged to switch between an open position and a closed position, as a function of the pressure difference of the low-pressure pump, said valve being capable of blocking the fuel return line in the closed position, and of putting the fuel return line in communication with the fuel tank, in the open position. 
         [0026]    The invention is advantageously completed by the following features, taken alone or in any one of their technically possible combinations:
       the motive flow valve switches from the closed position to the open position as a function of a taring threshold of a spring of said valve;   it comprises an actuating line connected, on one hand, upstream of the low-pressure pump and on the other hand, downstream of the low-pressure pump, the motive flow valve being disposed in said actuating line and is arranged to switch between the open and closed positions as a function of the pressure difference prevailing in said actuating line;   the high-pressure pump is a positive displacement pump.       
 
         [0030]    The invention also proposes an aircraft comprising an engine supplied with fuel by a fuel circuit according to the first aspect of the invention. 
         [0031]    The actuating of the motive flow valve is passive, the opening and/or closing of the valve is commanded as a function of pressures (on either side of the low-pressure pump) of the fuel stream. 
         [0032]    Thus it is no longer necessary to put in place a dedicated path for controlling the valve and where applicable a second dedicated path that would make it possible to acquire the speed N2 and which would increase the complexity and cost of the fuel circuit. 
         [0033]    According to a second aspect the invention further proposes a fuel circuit of an aircraft engine, the fuel circuit including: 
         [0034]    a fuel tank; 
         [0035]    an engine fuel system connected to the fuel tank, said engine fuel system being capable of delivering a stream of fuel to the engine as a function of a speed of said engine; 
         [0036]    a fuel return line connected between the engine fuel system and the fuel tank; 
         [0037]    a motive flow valve arranged to switch between an open position and a closed position, said valve being capable of blocking, in the closed position, the fuel return line and of putting in communication, in the open position, the fuel return line with the fuel tank; 
         [0038]    a computer configured to implement the following steps: 
         [0039]    starting of the aircraft engine in such a way as to increase an engine speed from a zero speed to a minimum idle speed N0; and during the increase of said engine speed: 
         [0040]    measuring, for several values of the engine speed Ni, of a corresponding temperature Ti of the stream of fuel from the fuel tank. 
         [0041]    The invention is advantageously completed by the following features, taken alone or in any one of their technically possible combinations:
       the minimum idle speed N0 is at least equal to 50%N2;   the computer is further configured to implement a step of determining a variation in the temperature of the stream of fuel for an engine speed Ni&lt;35%N2 and if the determined variation is constant, a step of detecting a failure of the motive flow valve, the failure being a position locked open;   the computer is further configured to implement a step of determining a variation in the temperature of the stream of fuel for an engine speed Ni&lt;35%N2 and if the determined variation is constant and if the evolution of the temperature between 35%N2 and 50%N2 has no inflexion point, a step of detecting a failure of the motive flow valve, the failure being locked in the open position;   the measuring of the temperature Ti of the stream of fuel from the fuel tank is carried out by means of a temperature sensor disposed along a line connecting the fuel tank to the engine fuel system.       
 
         [0046]    The invention also proposes an aircraft comprising an engine supplied with fuel by a fuel circuit according to the second aspect of the invention. 
         [0047]    Using the invention according to its second aspect, the detection of the failure of the motive flow valve does not require a dedicated position sensor to be put on the valve. 
         [0048]    Specifically, the inventors have established that the temperature of the stream of fuel from the fuel tank is a parameter that is robust enough to the effect of opening the motive flow valve not to risk flagging up failures that do not exist. 
         [0049]    The first aspect and the second aspect of the invention can advantageously be combined. 
     
    
     
       PRESENTATION OF THE FIGURES 
         [0050]    Other features, aims and advantages of the invention will become apparent from the following description, which is purely illustrative and non-limiting and which must be read with reference to the appended drawings wherein, besides  FIG. 1  already discussed, 
           [0051]      FIG. 2  illustrates an operation of a fuel circuit according to a first aspect of the invention in a closed position of a motive flow valve; 
           [0052]      FIG. 3  illustrates an operation of a fuel circuit according to the first aspect of the invention in an open position of a motive flow valve; 
           [0053]      FIG. 4  illustrates an architecture of a fuel circuit according to a second aspect of the invention; 
           [0054]      FIG. 5  schematically illustrates the steps of a method according to the second aspect of the invention; 
           [0055]      FIG. 6  illustrates an evolution of a temperature of a stream of fuel from a fuel tank according to the second aspect of the invention as a function of an engine speed supplied by the fuel circuit according to the invention. 
       
    
    
       [0056]    In all the figures, similar elements bear identical reference numbers. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0057]      FIGS. 2 and 3  illustrate an operation of the fuel circuit according to a first aspect of the invention in two positions of the motive flow valve. 
         [0058]    The fuel system  20 ′ comprises a low-pressure pump  21 ′ capable of raising the pressure of the stream of fuel from the tank  10 ′ by a variable pressure difference ΔP. The low-pressure pump  21 ′ is connected to the fuel tank  10 ′ by the supply line  1 ′. 
         [0059]    The low-pressure pump  21 ′ is followed directly downstream by a high-pressure pump  22 ′ capable of raising the pressure of the stream of fuel from the low-pressure pump  21 ′ in order to have a high-pressure stream of fuel at the outlet of this high-pressure pump. The high-pressure pump  22 ′ is connected to the low-pressure pump  21 ′ by way of a line  1   a ′. Advantageously, the high-pressure pump  22 ′ is a positive displacement pump. 
         [0060]    Note there that the term “low pressure” is understood to mean a pressure upstream of the high-pressure pump  22 ′ and “high pressure” a pressure downstream of the high-pressure pump  22 ′. 
         [0061]    The stream of fuel from the high-pressure pump is then directed on one hand toward the engine (not depicted) and on the other hand toward the variable-geometry vanes (not depicted) by way of the respective lines  3   a ′,  3   b′.    
         [0062]    Of course, the fuel circuit includes other known components such as filters, heat exchangers, flow rate controllers etc. which do not need to be described here for the invention to be understood. 
         [0063]    The fuel circuit also includes a motive flow valve  30 ′ disposed on an actuating line  4 ′ a first end of which  4   a ′ is connected upstream of the low-pressure pump  21 ′ and a second end of which  4   b ′ is connected downstream of the low-pressure pump  21 ′. 
         [0064]    The motive flow valve  30 ′ is arranged to switch between a closed position (see  FIG. 2 ) and an open position (see  FIG. 3 ) as a function of the pressure difference prevailing between the first and second ends  4   a ′,  4   b ′ of the actuating line  4 ′. 
         [0065]    In the open position, the valve  30 ′ makes it possible to put the fuel return line  2 ′ in communication with the fuel tank  10 ′ in order for the high-pressure stream to be sent into the jet pump of the fuel tank  10 ′. 
         [0066]    In the closed position, the valve  30 ′ blocks the fuel return line. The actuating of the valve  30 ′ is advantageously implemented by means of a spring  30   a ′ the taring threshold of which is dimensioned for a value of a set pressure difference ΔP=ΔPO. 
         [0067]    Specifically, the applicant has shown that the pressure difference applied by the low-pressure pump  21 ′ is variable and depends:
       on the rotation speed of the low-pressure pump  21 ′ of the fuel system mechanically connected to the rotation speed N2 of the engine of the aircraft;   of the flow rate of the stream of fuel at the engine inlet;   on the manufacturing tolerances of the low-pressure pump;   on the inlet temperature of the low-pressure pump.       
 
         [0072]    Furthermore, the applicant has shown that the engine inlet flow rate, the manufacturing tolerances of the low-pressure pump, and the inlet temperature of the pump have an effect in the order of 2 in relation to the rotation speed of the pump on the pressure difference applied by the low-pressure pump such that this pressure difference is an indicator of the rotation speed N2 of the engine. 
         [0073]    Specifically, it is not desirable for the motive flow valve  30 ′ to send a high-pressure stream of fuel for certain rotation speeds N2 of the engine. These speeds can be defined by a range of aircraft engine rotation speeds N2, for example greater than 50% and strictly less than 50%. 
         [0074]    As will be understood, the actuating of the motive flow valve  30 ′ is a hydraulic and not an electrical device and therefore does not require any auxiliary provision to actuate it. It is a passive device. 
         [0075]    In connection with  FIG. 4 , an architecture of a fuel circuit according to a second aspect of the invention comprises, besides the elements described in connection to  FIG. 1 , an “Engine Fuel Temperature” (EFT) sensor  400  disposed along the line  1 ″ connecting the fuel tank  10 ″ to the fuel system  20 ″. Such a temperature sensor  400  makes it possible to make sure of the temperature of the stream of fuel sent into the fuel system  20 ″. 
         [0076]    Furthermore, such a sensor is conventionally in connection with a device for generating an alarm (not depicted) to raise an alarm if conditions of temperatures at the engine inlet depart from the specified range (not described.) 
         [0077]    It will be recalled that the fuel system  20 ″ makes it possible to supply an engine  60  by way of the line  3   b ″ and makes it possible to supply a hydraulic force to displace the various valves kinetically linked, on one hand to the variable-geometry vanes and on the other hand to the doors for evacuating the excess air downstream of the low-pressure compressor (not depicted) by way of the line  3   a″.    
         [0078]    The fuel tank  10 ″ comprises a stream of fuel at a first temperature and the fuel system  20 ″ is adapted to deliver a stream of fuel as a function of a speed of said engine at a second temperature greater than the first temperature. 
         [0079]    The fuel circuit in  FIG. 4  further comprises a computer  50  which is configured to implement a method for detecting a failure of the motive flow valve  30 ″ described below. 
         [0080]    The method for detecting the motive flow valve  30 ″ in accordance with the second aspect of the invention consists in observing the temperature of the stream of fuel at the inlet of the fuel system  20 ″ at the start-up of the aircraft engine. 
         [0081]    In connection with  FIG. 5  a method for detecting a failure of the motive flow valve  30 ″ comprises a step E 0  of starting the engine aircraft during which the speed goes from a zero speed to a minimum idle speed NO (around 50% of the maximum speed N2). During this starting phase, the method comprises a measurement E 1  for several values of the engine speed Ni of the temperature Ti of the corresponding stream of fuel. 
         [0082]    The measurement of the engine speed is, in this case, taken by means of a speed sensor  200  of the engine fuel system  20 ″. 
         [0083]    Thus, the method makes it possible to obtain a variation in the temperature T of the stream of fuel at the inlet of the fuel system  20 ″ as a function of the engine speed N2. 
         [0084]    Advantageously, the method comprises a step E 2  of determination of a variation of the temperature of the stream of fuel for an engine speed of less than 35%N2. 
         [0085]    If a constant increase in the temperature is observed, the method comprises a step E 3  of detection of a failure of the motive flow valve  30 ″, the failure being in the locked open position. 
         [0086]    Alternatively, besides the constant variation of the temperature, the detection of the failure E 3  is carried out if the evolution of the temperature does not comprise any inflexion point in the range of the engine speed 35%N2 and 50%N2. This allows more robust failure detection. 
         [0087]    Specifically, the motive flow valve  30 ″ is commanded to open for an engine speed between 35 and 50% of N2 when the engine starts and to be closed outside this range. 
         [0088]    Thus, from the opening of the motive flow valve, a stream of fuel from the fuel system  20 ″ to act as hydraulic energy for the jet pump  12 ″ (see  FIGS. 1 and 4 ) is sent into the fuel tank  10 ″. At the outlet of the jet pump  12 ″ and therefore at the outlet of the fuel tank  10 ″ and at the inlet of the fuel system  20 ″ there is a mixture between the stream of fuel present in the fuel tank  10 ″ and the stream of fuel from the fuel system  20 ″. 
         [0089]    The stream of fuel at the outlet of the fuel tank  10 ″ is therefore a mixture between a stream at the temperature of the fuel tank and a stream at a higher temperature, since it comes from the fuel system as it is heated inside the fuel system by way of a heat exchanger (not depicted) and the fuel pump (not depicted.) The result of this is that the stream of fuel sent to the inlet of the fuel system  20 ″ sees its temperature increase upon opening of the motive flow valve  30 ″. 
         [0090]    Thus, in the situation where the motive flow valve  30 ″ is operational and therefore closed before the opening range of 35-50%N2, one observes by way of the temperature sensor  400  a temperature of the stream of fuel that is constant at the inlet of the fuel system  20 ″ until it reaches the speed range of opening of the motive flow valve  30 ″ then as soon as the motive flow valve  30 ″, is open, one observes an increase of the fuel temperature at the inlet of the fuel system  30 ″. There is therefore an inflexion point of the temperature of the stream of fuel from the fuel tank, at the inlet of the fuel system, upon the opening of the motive flow valve  30 ″. 
         [0091]    If, on the contrary, the motive flow valve  30 ″ is in a failure locked in the open position then the heating of the stream of fuel from the fuel tank  10 ″ is effective from the beginning of the increase in speed and therefore before the speed range of opening of the motive flow valve  30 ″ (i.e. for an engine speed N between 35%N2 and 50%N2). One therefore no longer observes the inflexion point of the temperature of the stream of fuel from the fuel tank, but a constant increase from the beginning. It is this phenomenon shown by the inventors that makes it possible to detect the failures of the motive flow valve. 
         [0092]      FIG. 6  illustrates the evolution of the temperature T (in degrees Celsius) of the stream of fuel from the fuel tank as a function of the engine speed in terms of %N2 supposing here that the fuel valve opens for an engine speed from 45%N2 onwards. 
         [0093]    As explained previously, at the nominal speed (curve C 1 ) the evolution of the temperature is constant within the range for which the motive flow valve is closed (for an engine speed of less than 35%N2) and increases gradually within the range for which the motive flow valve is open (for an engine speed between 35 and 50%N2). 
         [0094]    On the other hand, in a situation of a failure locked in the open position (curve C 2 ) of the motive flow valve  30 ″, the temperature increases constantly within the range for which the motive flow valve is closed (for an engine speed of less than 35%N2) and with no inflexion point within the range for which the motive flow valve is open (for an engine speed between 35 and 50%N2). 
         [0095]    The first and second aspects of the invention can advantageously be combined. Thus, the method for detecting a failure of a motive flow valve according to the second aspect of the invention can be applied to a motive flow valve  30 ′ according to the first aspect of the invention, and the engine fuel circuit according to the second aspect of the invention can comprise a motive flow valve  30 ′ according to the first aspect of the invention.