TECHNICAL FIELD

The disclosure herein relates to an inerting system for an aircraft, a method for supplying an inert gas in an aircraft and an aircraft in which is such an inerting system is arranged, as well as an aircraft in which a corresponding inerting system is used.

BACKGROUND

In airplanes (termed “aircraft” below), air enriched with nitrogen is conducted into an aviation fuel tank and/or a trim tank to reduce the risk of explosion. Air with a normal oxygen and nitrogen content can create a highly flammable mixture together with aviation fuel vapours. Nitrogen-enriched air is also used in extinguisher systems, in order to smother any fire sources by increasing the nitrogen content, with a resultant reduction in the oxygen content. The nitrogen-enriched air is produced by inerting systems. These are also termed inert gas systems, Inert Gas Generation Systems (IGGS) or On Board Inert Gas Generation Systems (OBIGGS). Cooled bleed air from jet engines or auxiliary turbines (so-called auxiliary power units, APUs) is used as an air source for the inert gas production. However, this bleed air has a temperature of roughly 200° C. and must therefore be cooled to a temperature tolerable for the IGGS. Furthermore, the air supplied to the IGGS must also have a certain pressure, and must be compressed or expanded, therefore. Systems that supply air with these predetermined temperature and pressure characteristics are described as a CSAS (Conditioned Service Air System).

FIG. 1illustrates a known CSAS, which represents an air supply for an IGGS100. The bleed air110branched off from an engine is supplied to a compressor120or even an expansion device. InFIG. 1, a motor-operated compressor120is shown, which supplies the bleed air110at the pressure required for operating the IGGS100. Bleed air110that has a pressure higher than that required can also be routed past the compressor by a valve125and supplied, suitably expanded, to the IGGS. Since the bleed air usually has a temperature that is too high for use in the IGGS100, or the bleed air110is additionally heated by the compressor120, it has to be cooled with the help of a heat exchanger130. The bleed air110can optionally be pre-cooled before entering the compressor120in an upstream heat exchanger135. For finer control of the temperature required in the IGGS100, the CSAS comprises a bypass line with a suitable control valve140. Finally, other regulating elements, such as e.g. regulating valves150and160, are provided in the air lines of the CSAS. An ozone converter165can also be optionally integrated, which removes the ozone that is detrimental to the IGGS. The cooling in the heat exchangers130/135, thus their heat sink, is effected by an air stream. This is produced by outside air, which is made available in flight mode as ram air of a ram air channel180and in ground operation by an additional conveying device, such as e.g. a ventilator or blower170.

The present disclosure has recognized that the tapping of bleed air of an engine and the fitting of ram air channel inlets and outlets in the outer skin of an aircraft entail disadvantages for an IGGS. For example, the tapped bleed air is no longer available to the engine itself, which leads to increased fuel consumption. The fitting of ram air channel openings produces vortices on the outside of the aircraft, which likewise increase the aircraft's fuel consumption.

SUMMARY

An object of the disclosure herein, therefore, is to specify an inerting system and a corresponding method for supplying an inert gas in an aircraft, which reduces the overall consumption of fuel.

This object is achieved by an inerting system such as described herein.

An inerting system according to one aspect of the present disclosure comprises an inert gas generation apparatus for generating inert gas and an air supply line. Furthermore, a compressor is provided, which supplies the inert gas generation apparatus with air from the air supply line at a pressure required for the operation of the inert gas generation apparatus. The inerting system also comprises an inert gas line, which conducts inert gas generated by the inert gas generation apparatus to an inert gas consumer. The air supply line of the inerting system is advantageously connected to an exhaust air system of the aircraft.

The connection of the air supply line to an exhaust air system of the aircraft can be provided at a point that limits the length of the air supply line to a minimum. The inert gas generation apparatus (IGGS) is advantageously arranged in an area of the aircraft in which other air conditioning systems are also present. It is particularly advantageous if the IGGS is fitted in direct proximity to an exhaust air system for discharging consumed air from areas of the aircraft that require fresh air. Weight can be saved by the shortest possible air supply line.

Alternatively, the inerting system can even be integrated directly into an exhaust air line of an exhaust air system of the aircraft, provided that the exhaust air line has suitably large cross sections or can be realised with the necessary cross sections.

The compressor is advantageously a motor-driven compressor. For example, the compressor can be driven by an electric motor.

The inerting system can also comprise a heat exchanger, which cools air supplied by the compressor to a temperature required for the operation of the inert gas generation apparatus. Alternatively, the heat exchanger can also heat the air supplied by the compressor to a required temperature. Usually, however, heat is introduced into the supply air by the compressor, so that the supply air mostly has to be cooled.

Air from an area inside the aircraft advantageously serves the heat exchanger as a heat sink. Due to this, a ram air channel for the inerting system (IGGS) and corresponding openings in the outer skin of the aircraft can be eliminated. At least, existing ram air channels and openings that are necessary for other systems in the aircraft can be of smaller dimensions.

A blower can optionally be included in the inerting system. The blower produces an air stream from the air surrounding the inerting system, wherein the air stream flows through the heat exchanger and acts as a heat sink. The blower can be implemented by a ventilator or other fan, such as e.g. an impeller fan. Alternatively, another air stream, which is already present in the vicinity of the inerting system for other reasons, can also be used. Provided that such an air stream has a velocity and volume necessary for the operation of the heat exchanger, any other air stream can be used without the additional deployment of a blower.

According to one aspect of the present disclosure, the inerting system is arranged in an area of the aircraft that is not pressurized during flight operation of the aircraft. Usually at least one area of the aircraft, such as e.g. the cockpit, a passenger cabin and/or a cargo hold, is acted upon during flight operation by an increased pressure compared with the ambient air outside the aircraft, in order to create an environment necessary for life for persons and living beings in the aircraft at relevant flight altitudes. The inerting system is advantageously arranged in an area of the aircraft that lies outside this pressurized area, but naturally still within the aircraft. In this case the inerting system comprises a branch line, which branches off from the air supply line upstream of the compressor and supplies air serving as a heat sink to the heat exchanger. In other words, a branch line branches off from the air supply line, which leads from the exhaust air system of the aircraft to the compressor, ahead of the compressor. This branch line is arranged such that it carries air from the air supply line to the heat exchanger and flows through this. Due to a pressure difference between the exhaust air system and the unpressurized area, air now flows through the branch line. The branched-off air can thus be used as a heat sink in the heat exchanger. Furthermore, a shut-off valve can be arranged in the branch line to control the flow (flow rate) of the air supply through the branch line.

Floor areas in the aircraft fuselage, apex or roof areas of the fuselage, or also the tail of the aircraft can be considered as an area that is not pressurized. To guarantee an adequate supply of air for the IGGS, the exhaust air system is an exhaust air system of a passenger cabin, a cargo hold and/or another area of the aircraft that is pressurized during flight operation, such as e.g. a cockpit or sleeping areas for the crew arranged in the roof of the aircraft. Due to the pressure difference between these areas of the aircraft and thus within the exhaust air system from these areas and the area in which the inerting system is arranged, the noted advantages can be achieved.

In addition, the inerting system can comprise a control device, which controls the shut-off valve and the blower in such a way that the shut-off valve is open during flight operation, and air that flows through the branch line owing to the pressure difference between the exhaust air system and the unpressurized area acts as a heat sink of the heat exchanger. During ground operation, the control device can control the shut-off valve and the blower in such a way that the shut-off valve is closed and the air stream produced by the blower acts as a heat sink of the heat exchanger. In other words, the blower can be turned off during flight operation and the heat exchanger only cooled by air that flows through the branch line. During ground operation of the aircraft, the blower can be used to produce an air stream as a heat sink for the heat exchanger.

The blower can also be used optionally if the aircraft is flying at low altitudes. For this the control device can be configured to control the shut-off valve and the blower in such a way that a first air stream is created through the branch line on account of the pressure difference between the exhaust air system and the unpressurized area, and a second air stream is produced by the blower. Both air streams together act as a heat sink for the heat exchanger. The control device controls the second air stream produced by the blower for this, so that the cooling requirements to be met by the heat exchanger are achieved.

Depending on the design of the exhaust air system, the air stream through the air supply line and the branch line can also be produced by a conveying device in the exhaust air system. The areas such as the passenger cabin, the cargo hold and/or another area of the aircraft that is pressurized during flight operation, for example, are supplied with an adequate quantity of fresh air on the one hand, and on the other hand, a certain quantity of consumed air is removed from the area. Conveying devices such as blowers or fans are provided for this. These can already produce a sufficiently strong air stream, which is necessary for the operation of the heat exchanger. The control device can thus (even in ground operation) control the blower also as a function of the air stream already present from the exhaust air system. The blower can possibly even be dispensed with completely.

In addition, the area in which the inerting system is arranged can have openings in the outer skin of the aircraft. These serve for aeration or air ventilation of the area. These openings are advantageously used in ground operation to supply ambient air from outside the aircraft, which is conducted by the blower through the heat exchanger. It is likewise advantageous if the openings in the outer skin are arranged in such a way that an air stream can be created between an (inlet) opening, the blower, the heat exchanger and another (outlet) opening. It is also advantageous if these openings can be closed in flight operation of the aircraft, so that no vortices of the outer skin arise due to the openings.

In another configuration of the inerting system, the heat exchanger is cooled only by the blower. In other words, only the ambient air of the inerting system acts as a heat sink. The inerting system advantageously comprises an opening in the outer skin of the aircraft for this as well as a flap for closing and opening the opening. A control device of the inerting system can control the flap in such a way that the flap is closed during flight operation, and during ground operation of the aircraft the flap is open. In ground operation and when the flap is open, the blower can be arranged in such a way that it conveys ambient air from outside the aircraft through the opening and produces the air stream from this.

The blower is advantageously arranged directly behind or close to the flap, so that on the suction side of the blower, air is aspirated predominantly through the opening in the outer skin. The air is supplied to the heat exchanger on the pressure side of the blower by suitable mechanisms, such as e.g. pipes or other air ducting devices. Thus in ground operation and when the flap is open, air outside the aircraft can be used as a heat sink for the heat exchanger.

In addition or alternatively, the inerting system also comprises an air ducting device, which is arranged between the opening in the outer skin and the blower. The flap is arranged in this case in such a way that when the opening in the outer skin is closed, it opens an opening in the air ducting device into the interior of an area in which the inerting system is arranged, and when the opening in the outer skin is opened, it closes the opening in the air ducting device into the interior of the area in which the inerting system is arranged.

It is also advantageous if the outer skin of the aircraft in the area in which the inerting system is arranged can be used as a heat sink to the ambient air outside the aircraft. This is possible in areas of the aircraft in particular in which no (or only very little) heat insulation is arranged on the outer skin. For example, in a floor area of the aircraft or the tail area of the aircraft, the temperature falls during flight operation at a great altitude. Here temperatures of 10° C. maximum often prevail inside the aircraft. Cooling takes place exclusively via the outer skin in this area of the aircraft. In other words, the outer skin of the aircraft forms a heat exchanger to the ambient air outside the aircraft. In addition, this effect can be amplified by an outer skin heat exchanger. For example, a heat exchanger can be arranged in the outer skin at a certain point of the outer skin. Passive heat exchangers, which consist of lamella-shaped elements attached to the outside and/or inside of the outer skin, are especially advantageous for this. It is likewise advantageous if the suction side of the blower is arranged close to or above such an outer skin heat exchanger. In flight operation the air inside the aircraft in the area of the inerting system can thus be used exclusively for cooling the air supply for the IGGS. No other openings in the outer skin are necessary for this. Existing openings, which guarantee an adequate supply of (cooler) outside air in ground operation, for example, can be closed during flight operation. Vortices due to openings in the outer skin are thus avoided, due to which the fuel consumption of the aircraft falls.

The inerting system can also comprise a bypass line, which branches off from the air line downstream of the compressor and supplies the inert gas generation apparatus with compressed air from the compressor, circumventing the heat exchanger. The bypass line is brought back together with the air line leaving the heat exchanger, therefore. Control of the temperature of the air supplied to the inert gas generation apparatus can be realised by a control valve inside the bypass line. By merging of the air line downstream of the heat exchanger and of the bypass line, the temperature of the air for the IGGS can be controlled with a suitable degree of opening of the control valve. The use of such a control valve permits much finer temperature control than would be possible only by the heat exchanger. Even by controlling the blower or the air stream that flows through the heat exchanger as heat sink, the temperature of the air leaving the heat exchanger is not controlled as quickly and precisely as by a bypass line and control valve.

According to another configuration of the inerting system, the blower can be configured further to ventilate the area in which the inerting system is arranged. To avoid the accumulation of gases or other substances, the area in which the inerting system is arranged should be ventilated. Usually other components of the aircraft that require ventilation or also cooling by a (light) air stream are also arranged in this area. For example, tanks with liquids, such as e.g. a trim tank or a tank for holding aviation fuel for the APU, can be arranged in this area. Permanent ventilation of the area is thus prescribed, so that openings are already present in the outer skin. By dimensioning the blower and corresponding air ducting devices appropriately, the blower can not only supply the heat exchanger with air, but also achieve ventilation of the area in question. A separate ventilation blower can thus be eliminated. Furthermore, the aircraft can have closable and/or permanent openings in the outer skin in the area in which the inerting system is arranged to ventilate the area. Openings already present in the outer skin of the aircraft that are used to ventilate the area can thus also be used to supply ambient air to cool the heat exchanger during ground operation.

The inerting system can also have air ducting devices that are suitable to conduct the air heated in the heat exchanger to outlet openings in the outer skin of the aircraft. In particular, if the area in which the inerting system is arranged requires permanent ventilation, it is sensible to discharge the air heated by the heat exchanger to the outside. Openings already present in the outer skin can be used for this. The air stream after the heat exchanger must only be conducted accordingly to these openings. Closed lines or also guide plates can be used for this. In the case of the implementation variant in which air from the exhaust air system is used to cool the heat exchanger, it is also necessary to route this exhaust air out of the aircraft to the outside.

Alternatively, the air can be supplied following heating by the heat exchanger also to an air conditioning system of the aircraft. The heated air can thus also be routed back to an aircraft cabin or other area of the aircraft in some cases, due to which heating of the fresh air is at least partially eliminated. The fuel consumption can be reduced further by this.

The inert gas consumer can be an aviation fuel tank or a trim tank, from which air containing oxygen is displaced by inert gas. In addition or alternatively, a fire extinguishing device can be the inert gas consumer. To suppress sources of fire, inert gas can be introduced into the affected areas, so that the seat of a fire can be extinguished due to the reduction in oxygen.

According to another aspect of the disclosure herein, a method is provided for supplying an inert gas in an aircraft. The method comprises the tapping of air from an exhaust air system of the aircraft, compression of the tapped air and production of inert gas from the compressed air in an inert gas generation apparatus. By dispensing with bleed air for the production of inert gas, the fuel consumption is reduced, as less air is tapped from the engine.

In one configuration of the disclosure herein, the method also comprises cooling of the compressed air to a temperature necessary for the operation of the inert gas generation apparatus. The method also comprises, during flight operation of the aircraft, branching of air from the air tapped from the exhaust air system prior to compression, and use of the branched-off air as a heat sink to cool the compressed air, wherein the branched-off air flows due to a pressure difference between the exhaust air system and the air surrounding the inert gas generation apparatus. During ground operation of the aircraft, on the other hand, the method comprises production of an air stream by a blower from the air surrounding the inert gas generation apparatus, and use of the air stream as a heat sink for cooling the compressed air.

By using air from an area inside the aircraft, such as e.g. air from the exhaust air system or air that surrounds the inert gas generation apparatus, a ram air channel with corresponding opening in the outer skin can be dispensed with. By dispensing with another opening in the outer skin, a vortex on the outer skin is avoided or reduced. The fuel consumption of the aircraft is reduced by this.

In addition or alternatively, the method can also comprise control of a flap for closing and opening an opening in an outer skin of the aircraft and cooling of the compressed air to a temperature necessary for the operation of the inert gas generation apparatus. In this case, the method comprises, during flight operation of the aircraft, closing of the flap, production of an air stream by a blower from the air surrounding the inert gas generation apparatus, and use of the air stream as a heat sink to cool the compressed air. During ground operation of the aircraft, on the other hand, the method comprises opening of the flap, production of an air stream by the blower from the air surrounding the aircraft through the opening and use of the air stream as a heat sink for cooling the compressed air.

According to another aspect, an aircraft is provided in which an inerting system as explained above is arranged. In addition or alternatively, an inerting system can be used in the aircraft according to one of the methods described above.

