Method for controlling the purity/flow rate relationship of an inert gas injected into a fuel tank, an inerting system for carrying out the method

Abstract

An inerting system of a fuel tank of an aircraft includes an air separation module supplied at the inlet with air at a certain pressure to generate at the outlet an inert gas to be injected into the fuel tank comprising a certain flow rate and a certain oxygen concentration. A control method includes, at a given instant and at a constant air temperature and atmospheric pressure, (1) reducing the inert gas flow rate to a determined value, and (2) reducing the air pressure in order to cause an increase in the oxygen concentration from an initial value to a determined value. Decreasing the inert gas flow rate is performed by compensating for a loss of inert gas flow caused by the air pressure reduction, and decreasing the air pressure is performed by compensating for a reduction in the oxygen concentration caused by the inert gas flow rate reduction.

Claims

1. A method for controlling an inerting system of at least one fuel tank of an aircraft, the inerting system comprising at least one air separation module supplied at the inlet with air at a certain pressure in order to generate at the outlet an inert gas to be injected into the fuel tank comprising a certain flow rate and a certain oxygen concentration, wherein the method comprises, at a given instant and at constant temperature and atmospheric pressure: an operation whereby the inert gas flow rate is reduced to a determined value; an operation whereby the air pressure is reduced in order to cause an increase in the oxygen concentration from an initial value to a determined value; and wherein: the operation of reducing the inert gas flow rate is performed by compensating for a loss of inert gas flow caused by the air pressure reduction operation; the operation of reducing the air pressure is performed by compensating for a reduction in the oxygen concentration caused by the inert gas flow rate reduction operation.

2. A method according to claim 1, wherein the determined inert gas flow rate value corresponds to a value determined as a function of an actual inert gas flow rate requirement at the given instant.

3. A method according to claim 1, wherein the determined oxygen concentration value corresponds to a value determined as a function of an actual oxygen concentration requirement at the given instant.

4. A method according to claim 1, wherein the determined oxygen concentration value corresponds to the initial oxygen concentration value before the operation of reducing the inert gas flow rate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features will become more apparent from the following description, given by way of a non-limiting example, of a control method for a fuel tank inerting system, from the attached drawings wherein:

(2) FIG. 1 schematically illustrates a first embodiment of an inerting system, particularly with regard to the arrangement of the controller, the air separation module and the various valves and sensors;

(3) FIG. 2 is a schematic view similar to that of FIG. 1, illustrating a second embodiment of an inerting system.

DETAILED DESCRIPTION

(4) With reference to FIGS. 1 and 2, an inerting system (1) is illustrated, intended for injecting a flow of inert gas into at least one fuel tank of an aircraft during the flight of the aircraft.

(5) The inerting system (1) comprises at least one air separation module (2) supplied at the inlet (2a) thereof with air at a given pressure, in order to generate an inert gas at the outlet (2b) that is depleted in oxygen, to be injected into the fuel tank at a certain flow rate and with a certain concentration of oxygen.

(6) The inerting system (1) comprises a motorized air pressure regulating valve (3) positioned at the inlet (2a) of the air separation module (2) and a motorized inert gas flow rate regulating valve (4) and a flow meter (5) positioned at the outlet (2b) of the air separation module (2). The motorized flow rate control valve (4), the flow meter (5), and the motorized pressure control valve (3) are connected to an electronic controller (6) supplied by an electrical power supply (7).

(7) The electronic controller (6) integrates software (8) for managing the various elements of the inerting system (1) as described below, and implements a flow rate control law in order to decrease the inert gas flow rate to a determined value, and in order to decrease the air pressure at the inlet (2a) of the air separation module (2) in order to cause an increase in the oxygen concentration, from an initial value to a determined value.

(8) Specifically, the operation for decreasing the inert gas flow rate is performed by compensating for a loss of inert gas flow caused by the air pressure reduction operation, and the operation for decreasing the air pressure is performed by compensating for a reduction in the oxygen concentration caused by the inert gas flow rate reduction operation.

(9) In practice, the software (8) transmits a decrease flow rate command to the motorized valve (4) controlling the inert gas flow rate, depending upon the inert gas flow rate determined by the flow meter (5), in order to decrease the inert gas flow rate to a determined value that corresponds, as a function of the implemented inerting strategy, to a flow rate value determined as a function of an actual inert gas flow rate requirement determined at a given instant.

(10) According to a first embodiment shown in FIG. 1, the inerting system (1) operates in a closed loop based upon the oxygen concentration value and comprises an oxygen sensor (9) positioned at the outlet (2b) of the air separation module (2) and connected to the controller (6) in order to determine the oxygen concentration within the inert gas.

(11) According to this first embodiment, the software (8) also transmits a decrease air pressure command to the motorized valve (3) controlling the air pressure, depending upon the inert oxygen concentration determined by the oxygen sensor (9), in order to increase the oxygen concentration from an initial value to a determined value.

(12) According to a second embodiment, illustrated in FIG. 2, the inerting system (1) operates in a closed loop based upon the air pressure value and in a closed loop based upon the oxygen concentration value, and comprises an air pressure sensor (10) and a temperature sensor (11) positioned at the inlet (2a) of the air separation module (2) and connected to the controller (6).

(13) According to this second embodiment, the software (8) transmits a decrease air pressure command to the motorized valve (3) controlling the air pressure, depending upon the air pressure value determined by the air pressure sensor (10), and upon a pressure regulation setpoint in order to increase the oxygen concentration from an initial value to the determined value. The pressure regulation setpoint is obtained from a conversion table integrated into the software (8) of the controller (6). The conversion table is particularly designed in order to convert an oxygen concentration regulation setpoint to a pressure regulation setpoint. This conversion is performed based upon the inert gas flow rate value supplied by the flow meter (5), the inert gas temperature supplied by the temperature sensor (11), the ambient atmospheric pressure supplied by the atmospheric pressure sensor or recovered directly from data (12) supplied by the aircraft, and technical and performance characteristics of the air separation module (2) integrated into the software (8).

(14) With both embodiments the decrease flow rate command is defined in order to compensate for a loss of inert gas flow caused by the decrease in air pressure and the decrease air pressure command is defined in order to compensate for a reduction in the oxygen concentration caused by the inert gas flow rate reduction.

(15) The inert gas flow rate and air pressure control laws are combined and converge such that the air pressure and inert gas flow rate are adjusted to the values determined by the inerting strategy.

(16) Depending upon the chosen inerting strategy, the concentration of oxygen within the inert gas can be adjusted, regardless of the value of the inert gas flow rate, to a determined value, for example based upon an actual inert gas flow rate requirement determined at a given instant, or else the oxygen concentration is increased in line with the reduction in the flow of inert gas in order to be constantly maintained at an initial value.

(17) In a known manner, the inert gas is then conveyed to means for distributing the inert gas, such as distribution pipes, valves, and injection nozzles, for injection as such into the fuel tank(s) of aircraft for safety reasons in order to reduce the risk of explosion of said tanks. The injected inert gas allows the level of oxygen present within tank(s) to be reduced, and notably to maintain this level below a certain threshold, for example, less than 12%.

(18) It is apparent from the foregoing that the present embodiments make it possible to significantly reduce the flow of air consumed by the air separation module (2) by overcoming the constraint of dependence between the inert gas flow rate and the purity of the inert gas that is inherent in the use of the air separation module (2). The presently described embodiments thus indirectly make it possible to reduce fuel consumption, to reduce the ecological footprint of the aircraft and the costs associated with the operation of the inerting system (1).

(19) Reducing the consumption of incoming air also makes it possible to reduce the wear on the filters and membranes used within the inerting system (1), and thus to increase the service life thereof. The maintenance intervals are therefore elongated, decreasing the cost of ownership of the inerting system (1).