GAS MONITORING SYSTEM AND AIRCRAFT COMPRISING A GAS MONITORING SYSTEM

Abstract

A gas monitoring system for detecting chemical substances in a gas comprising a Raman spectrometer comprising: an excitation source of light, a hollow core optical fiber having a longitudinal axis, a first longitudinal end, a second longitudinal end, an outer surface and an inner hollow core surface, the hollow core optical fiber being configured to: receive in its hollow core the gas to be monitored, receive at its first or its second longitudinal end light emitted by the excitation source of light, and transmit at its first or its second longitudinal end a Raman light when being illuminated by the received light. The system also includes a detector, and a transmission optical fiber coupled to the first longitudinal end and/or to the second longitudinal end of the hollow core optical fiber.

Claims

1. A gas monitoring system for detecting chemical substances in a gas, the system comprising: a Raman spectrometer comprising: an excitation source of light configured to illuminate a gas to be monitored, a hollow core optical fiber having a longitudinal axis, a first longitudinal end, a second longitudinal end, an outer surface and an inner hollow core surface, the hollow core optical fiber being configured to: receive in the hollow core optical fiber the gas to be monitored, receive, at the first or the second longitudinal end, a light emitted by the excitation source of light, transmit, at the first or the second longitudinal end, a Raman light generated in the hollow core optical fiber by the gas to be monitored when being illuminated by a received light, and a detector configured to receive a Raman light transmitted by the hollow core optical fiber; a transmission optical fiber coupled to the first longitudinal end, the second longitudinal end, or both longitudinal ends of the hollow core optical fiber and configured to guide light emitted by the excitation source of light to the hollow core optical fiber, or to guide the Raman light transmitted at the first or the second longitudinal end of the hollow core optical fiber towards the detector, or both.

2. The gas monitoring system according to claim 1, wherein the hollow core optical fiber comprises channels communicating the outer surface and the inner hollow core surface such that the hollow core optical fiber is configured to receive gas to be monitored through the channels.

3. The gas monitoring system according to claim 2, wherein the channels have a longitudinal axis perpendicular to the longitudinal axis of the hollow core optical fiber.

4. The gas monitoring system according to claim 1, wherein the transmission optical fiber is coupled to the inner surface of the hollow core optical fiber.

5. The gas monitoring system according to claim 1, wherein the transmission optical fiber and the hollow core optical fiber are coupled by gluing or splicing.

6. The gas monitoring system according to claim 5, wherein the transmission optical fiber and the hollow core optical fiber are spliced with direct fiber feed-throughs or fiber connectors, feed-through flanges, or optical windows.

7. The gas monitoring system according to claim 1, wherein the first longitudinal end of the hollow core optical fiber is configured to receive the light emitted by the excitation source of light and to transmit the Raman light generated by the gas to be monitored and a first transmission optical fiber is coupled to the first end of the hollow core optical fiber.

8. The gas monitoring system according to claim 7, further comprising: a second transmission optical fiber being coupled at one longitudinal end to the Raman probe and being coupled at its other longitudinal end to the excitation source of light, and, a third transmission optical fiber being coupled at one longitudinal end to the Raman probe and being coupled at its other longitudinal end to the detector.

9. The gas monitoring system according to claim 1, further comprising: a first transmission optical fiber coupled to the first longitudinal end of the hollow core optical fiber and configured to guide the light emitted by the excitation source of light to the hollow core optical fiber, and, a second transmission optical fiber coupled to the second longitudinal end of the hollow core optical fiber and configured to guide the Raman light transmitted at the hollow core optical fiber towards the detector.

10. The gas monitoring system according to claim 9, further comprising: a filter coupled between the second longitudinal end of the hollow core optical fiber and the second transmission optical fiber.

11. The gas monitoring system according to claim 1, wherein the gas to be monitored comprises N.sub.2, H.sub.2, O.sub.2, and combinations thereof.

12. An aircraft comprising: a hydrogen tank comprising an inner wall defining an inner chamber configured to house hydrogen and an outer wall which encloses the inner wall, the inner wall and the outer wall being separated by a vacuum gap configured to be kept at vacuum conditions, the gas monitoring system according to claim 1, the hollow core optical fiber located within the vacuum gap, the detector and the excitation source of light located outside the vacuum gap.

13. The aircraft according to claim 12, wherein the transmission optical fiber and the hollow core optical fiber are coupled at the outer wall of the tank.

14. The aircraft according to claim 12, wherein the hollow core optical fiber is coupled to a transmission optical fiber inside the vacuum gap.

15. The aircraft according to claim 14, wherein the transmission optical fiber is coupled at the outer wall of the tank to a transmission optical fiber located outside the vacuum gap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] To complete the description and to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate preferred embodiments of the invention. The drawings comprise the following figures.

[0065] FIG. 1 shows a schematic representation of a first embodiment of the invention.

[0066] FIG. 2 shows a schematic representation of a second embodiment of the invention.

[0067] FIG. 3 shows a cross section of a hollow core optical fiber with a metallic coating.

[0068] FIG. 4 shows a cross section of four photonic bandgap fibers and a revolver like hollow core optical fiber.

[0069] FIG. 5 shows a plan view of an embodiment of a portion of a hollow core optical fiber comprising channels along its longitudinal axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] As previously stated, the gas monitoring system object of the invention comprises a Raman spectrometer comprising: [0071] an excitation source of light (1) configured to illuminate the gas to be monitored, [0072] a hollow core optical fiber (6) having a longitudinal axis, a first longitudinal end (6.1), a second longitudinal end (6.2), an outer surface (6.4) and an inner hollow core surface (6.3), the hollow core optical fiber (6) being configured to: [0073] receive in its hollow core the gas to be monitored, [0074] receive at its first or its second longitudinal end (6.1, 6.2) the light emitted by the excitation source of light (1), [0075] transmit at its first or its second longitudinal end (6.1, 6.2) the Raman light generated by the gas to be monitored when being illuminated by the received light, and [0076] a detector (8) configured to receive the Raman light transmitted by the hollow core optical fiber (6).

[0077] In addition, the gas concentration monitoring system object of the invention further comprises a transmission optical fiber (2) coupled to the first longitudinal end (6.1) and/or to the second longitudinal end (6.2) of the hollow core optical fiber (6) and configured to guide the light emitted by the excitation source of light (1) to the hollow core optical fiber (6) and/or to guide the Raman light transmitted at the first or the second longitudinal end (6.1, 6.2) of the hollow core optical fiber (6) towards the detector (8).

[0078] Two embodiments of the invention are depicted in FIGS. 1 and 2. The embodiments are lens-less configurations.

[0079] FIG. 3 depicts a hollow core optical fiber (6) that comprises an outer surface (6.4) and an inner hollow core surface (6.3). It implements a reflecting metallic internal cylindrical hollow core which confines the light thanks to the metallic coating on the inner hollow core surface (6.3).

[0080] FIG. 4 depicts four embodiments of a photonic band gap optical fiber comprising a central hollow core surrounded by a complex silica structure that strongly limits propagation losses. A revolver channel hollow core fiber is also depicted on the right side of the figure.

[0081] In order to facilitate the diffusion of the analyte, these fibers could, but not necessarily need to, comprise channels (7), i.e., cuts or holes, of any size located along the longitudinal axis of the optical fiber. Channels (7) are depicted in FIGS. 1, 2 and 5. These channels (7) facilitate the diffusion of the gas inside the hollow core optical fiber (6), thus decreasing the detection time. Each channel (7) communicates the outer surface (6.4) and the inner hollow core surface (6.3) of the optical fiber such that the hollow core optical fiber (6) is configured to receive the gas to be monitored through the channels (7). Thus, the gas to be monitored may enter the hollow core optical fiber (6) at the first longitudinal end (6.1) and/or the second longitudinal end (6.2) and/or through the channels (7). Each channel (7) is being configured to allow the gas to enter the hollow core optical fiber (6) at different points along the longitudinal axis of the hollow optical fiber (6).

[0082] The hollow core optical fiber (6) of the embodiments disclosed in FIGS. 1 and 2 comprises channels (7) along its longitudinal axis. Therefore, the gas to be monitored enters the core of the hollow core optical fiber (6) through the longitudinal open ends (6.1, 6.2) and through the channels (7).

[0083] The dimensions of the channels (7) depend on the internal diameter of the hollow core optical fiber (6) used, and the geometry of the channel (7). If the channel (7) has a circular cross-section, the diameter is generally less than 100 m. If the channel (7) has a rectangular cross-section, the long side can be up to 500 m.

[0084] In an embodiment, the channels (7) have a longitudinal axis perpendicular to the longitudinal axis of the hollow core optical fiber (6).

[0085] In an embodiment, the hollow core optical fiber (6) has a set of 50500 channels (7) placed between 0.1 cm and 10 cm between them along the longitudinal axis of the hollow core optical fiber (6).

[0086] Preferably, the channels (7) on the hollow core optical fiber (6) are performed in a large internal diameter, greater than 200 m. Generally, this method is only applied to hollow core fibers (6) with an internal diameter of less than 100 m. This greatly facilitates gas diffusion in the fiber, which greatly reduces detection times compared to conventional solutions.

[0087] The larger the section of the hollow core optical fiber (6), the larger the channel (7) diameter, which increases the gas diffusion velocity within the hollow core optical fiber (6) thus facilitating rapid detection of the analytes.

[0088] The first embodiment, depicted in FIG. 1, comprises the following elements: [0089] the excitation source of light (1), [0090] the hollow core optical fiber (6) having the first longitudinal end (6.1) and the second longitudinal end (6.2). The hollow core optical fiber (6) receives at its first longitudinal end (6.1) the light emitted by the excitation source of light (1) and also transmits the Raman light, [0091] the detector (8), [0092] a first transmission optical fiber (2.1) coupled to the first end (6.1) of the hollow core optical fiber (6).

[0093] In addition, it comprises a Raman probe (3), for instance, placed close to the excitation source of light (1). The Raman probe (3) includes a set of optical components, for instance mirrors, filters, dichroic mirror, that allows to separate the laser source from the Raman signal, so that only the latter reaches the detector (8).

[0094] Thus, the gas concentration monitoring system disclosed in FIG. 1 further comprises: [0095] a Raman probe (3), [0096] a first transmission optical fiber (2.1) coupled to the first end (6.1) of the hollow core optical fiber (6) and to the Raman probe (3), [0097] a second transmission optical fiber (2.2) being coupled at one end to the Raman probe (3) and being coupled to the excitation source of light (1) at its other end, and, [0098] a third transmission optical fiber (2.3) coupled to the Raman probe (3) at one end being and being coupled to the detector (8) at its other end.

[0099] The application object of the invention and shown in FIG. 1 discloses a vacuum gap (5) of a double-wall liquid hydrogen. Said vacuum gap (5) is the enclosure to be monitored.

[0100] In an embodiment, the transmission optical fiber (2) and the hollow core optical fiber (6) are coupled inside the vacuum gap (5). In an alternative, the transmission optical fiber (2) and the hollow core optical fiber (6) are coupled at the outer wall of the vacuum gap (5).

[0101] In FIG. 1, the hollow core optical fiber (6) is placed inside the vacuum gap (5) and the transmission optical fiber (2) is coupled to the hollow core optical fiber (6) inside the vacuum gap (5).

[0102] In addition, in the embodiment of FIG. 1, the transmission optical fiber (2.1, 2.2) is coupled at the outer wall of the vacuum gap (5) or tank to a transmission optical fiber (2) located outside the vacuum gap (5).

[0103] In an embodiment, the transmission optical fiber (2) is coupled to the inner surface of the hollow core optical fiber (6) by splicing or gluing, thus enabling a lens-less coupling.

[0104] Thus, an effective coupling is achieved by fiber optic splicing, or by gluing, among others, so that the optic fiber transmitting the excitation and/or emission light is joined to the inner surface of one of the two ends of the hollow core fiber (6).

[0105] The splicing may be achieved by means of direct fiber feed-throughs, through fiber connectors, feed-through flanges, optical windows of any type compatible with any wavelength from UV to infrared, or any other means to facilitate the transmission of light through the wall of the enclosed volume to be analyzed.

[0106] In the embodiment disclosed in FIG. 1, the transmission optical fiber (2) enters the vacuum gap (5) by means of a fiber-to-fiber feedthrough (4) (MM/MM) which allows breaching the vacuum gap (5) by the diameter of the transmission optical fiber (2).

[0107] Preferably, outer diameter of the transmission optical fiber (2) is smaller than the diameter of the inner surface of the hollow core optical fiber (6) so that the end of the hollow core fiber (6) serves as entrance for both the excitation light and the gas to be monitored.

[0108] In an embodiment, the outer diameter of the hollow core optical fiber (6) is greater than 200 m.

[0109] In the embodiment of FIG. 1, the hollow core fiber (6) has an internal diameter of 500 m, so that this of the fiber allows both light transmission and analytes diffusion.

[0110] In the shown embodiment, the collected light is transmitted using the same 200 m MM transmission fiber (2) used for the transmission of the excitation light. The Raman probe (3) filters the residual signal of the laser (Rayleigh emission) and guides the Raman emission through the collection optical path. The collected light is analyzed by the detector (8), for instance, a transmission spectrometer with CCD detector cooled to 60 C.

[0111] A multimode MM fiber of similar diameter to the hollow core optical fiber (6) may be used to maximize the light collection even if there are some additional losses in the excitation.

[0112] The development of a detection system based on single channel detectors (8) allows to obtain a more robust and more sensitive system towards the detection of specific analytes (H.sub.2, N.sub.2 and O.sub.2).

[0113] The second embodiment, depicted in FIG. 2, would use both ends (6.1, 6.2) of the hollow core optical fiber (6), one for excitation and another one for transmission of the Raman light, thus optimizing the collection of the Raman signal and decreasing detection times. For both embodiments, a long transmission optical fiber (2) is used to connect the hollow core optical fiber (6) to the excitation source of light (1) and to the detector (8), so that these two embodiments can be placed far away from the hollow core fiber (6) performing the monitoring of the gas.

[0114] Thus, the second embodiment, depicted in FIG. 2, comprises the following elements: [0115] the excitation source of light (1), [0116] the hollow core optical fiber (6) having the first longitudinal end (6.1) and the second longitudinal end (6.2). The hollow core optical fiber (6) receives at its first longitudinal end (6.1) the light emitted by the excitation source of light (1) and transmit the Raman light at its second longitudinal end (6.2), [0117] the detector (8), [0118] a first transmission optical fiber (2.1) coupled to the first end (6.1) of the hollow core optical fiber (6). [0119] a second transmission optical fiber (2.2) coupled to the second end (6.2) of the hollow core optical fiber (6).

[0120] It further comprises a filter (9) coupled between the second end (6.2) of the hollow core optical fiber (6) and the second transmission optical fiber (2.2). The aim of the filter (9) is to prevent the radiation source and the Rayleigh scattering to reach the detector, so that only the Raman scattering is measured.

[0121] By proposing the use of hollow core optical fibers (6) with channels (7), gas diffusion issues are addressed improving the detection capabilities of the system. It will also facilitate the coupling of the hollow core optical fiber (6) to the transmission optical fiber (2) not impairing the gas diffusion capabilities thanks to the diffusion through the channels (7).

[0122] The application object of the invention and shown in FIG. 2 also discloses a vacuum gap (5) constituting a thermal insulation of a double-wall hydrogen tank. The transmission optical fibers (2) and the hollow core optical fiber (6) are coupled inside the vacuum gap (5). The hollow core optical fiber (6) is placed inside the vacuum gap (5) and the transmission optical fibers (2) are coupled to the hollow core optical fiber (6) by means of a fiber-to-fiber feedthrough (4) which allows breaching the vacuum gap (5) by the diameter of the transmission optical fiber (2).

[0123] Again, a laser is used as excitation source of light (1). The excitation light is transmitted using a conventional single mode (SM) glass transmission fiber (2), with a diameter of, for example, 9 m, towards the vacuum gap (5) to be monitored. The excitation light is coupled inside the hollow core optical fiber (6) placed inside the vacuum gap (5) by means of a fiber-to-fiber feedthrough (4) (SM/SM) which allows breaching the vacuum gap (5) by the diameter of the fiber.

[0124] The SM transmission fiber (2) is joined to the inner surface of the hollow core optical fiber (6) of the first end (6.1) of the hollow core optical fiber (6) by splicing or gluing, thus enabling a lens-less coupling.

[0125] The hollow core optical fiber (6) has an internal diameter of 500 m, so that this fiber allows light transmission and maximize analytes diffusion. The hollow core optical fiber (6) has a set of 50500 microns channels (7) placed between 0.1 and 10 cm along the longitudinal axis of the hollow core optical fiber (6).

[0126] A MM transmission optical fiber (2), with for instance, an inner core of 400 m, is coupled to the second end (6.2) of the hollow core optical fiber (6) by splicing or gluing thus enabling an in-line, lens-less filtering of the residual signal of the laser (Rayleigh emission). The Raman emission is guided to the exterior of the vacuum gap (5) by means of a fiber-to-fiber feedthrough (MM/MM) (4) which allows breaching the vacuum gap (5) by the diameter of the fiber. The collected light is transmitted using a conventional MM glass fiber towards the detector (8). The collected light is analyzed by the detector (8), a transmission spectrometer with a cooled CCD detector (8) cooled to 60 C.

[0127] In the second embodiment single mode transmission fibers (2) are used so that excitation is maximized thanks to a better numerical aperture match, while collecting at the other end with a suitable diameter.

[0128] As previously stated, solutions known in the state of the art achieve low detection limits with long acquisition times, for instance of the order of minutes. The system of the invention allows equivalent detection limits to be achieved but in shorter times, specifically in the order of seconds. This represents an enormous advantage for aeronautical applications where gas detection has to be carried out as quickly as possible. The reduction of acquisition times is achieved by a combination of multiple technological solutions, including the perforation of the hollow core fiber (6) and the use of more efficient detection systems compared to conventional CCDs.

[0129] By proposing the use of alternative detection systems for ad hoc applications using Single Channel Detectors (SCD) such as photomultipliers Tubes (PMTs) instead of multi-channel detectors such as Charged Coupled Devices (CCDs), the overall sensibility of the proposed detection system can be increased while reducing its demand for resources (weight, power). The use of such a system in combination with hollow core fibers (6) provides detection advantages compared to existing solutions.

[0130] The systems and devices described herein may include a controller or a computing device comprising a processing and a memory which has stored therein computer-executable instructions for implementing the processes described herein. The processing unit may comprise any suitable devices configured to cause a series of steps to be performed so as to implement the method such that instructions, when executed by the computing device or other programmable apparatus, may cause the functions/acts/steps specified in the methods described herein to be executed. The processing unit may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof.

[0131] The memory may be any suitable known or other machine-readable storage medium. The memory may comprise non-transitory computer readable storage medium such as, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory may include a suitable combination of any type of computer memory that is located either internally or externally to the device such as, for example, random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. The memory may comprise any storage means (e.g., devices) suitable for retrievably storing the computer-executable instructions executable by processing unit.

[0132] The methods and systems described herein may be implemented in a high-level procedural or object-oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of the controller or computing device. Alternatively, the methods and systems described herein may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems described herein may be stored on the storage media or the device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein.

[0133] Computer-executable instructions may be in many forms, including modules, executed by one or more computers or other devices. Generally, modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Typically, the functionality of the modules may be combined or distributed as desired in various embodiments.

[0134] It will be appreciated that the systems and devices and components thereof may utilize communication through any of various network protocols such as TCP/IP, Ethernet, FTP, HTTP and the like, and/or through various wireless communication technologies such as GSM, CDMA, Wi-Fi, and WiMAX, is and the various computing devices described herein may be configured to communicate using any of these network protocols or technologies.

[0135] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.