CROSS-REFERENCE TO RELATED APPLICATION [0001]

This application is based on a Provisional Application Serial No. 61/170,325 filed on April 17, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention. [0002]

The present invention monitors the concentration level of a gas in a mixture of gasses and more particularly can measure the concentration level of a fire suppression agent in an engine nacelle Auxiliary Power Unit and/or cargo bay of an aircraft.

2. Description of Related Art. [0003]

The Federal Aviation Agency (FAA) has made requirements to mandate the use of fire suppression equipment in commercial aircraft including engines, auxiliary power units and aircraft cargo holds. There are a number of different fire suppression agents including Halon 1301, Halon 1211, HFC-125, NOVEC 1230 and FM 200 that can be used. NOVEC 1230 and FM 200 represent agents that are classified as non-ozone depleting.

[0004]

Fire suppression systems include a fire suppression agent distribution system that can distribute fire suppression agents under compression by providing a seal that can be pierced for an immediate release of a fire suppression agent to aircraft engine bays, engine nacelles, cargo compartments and auxiliary power units that can be a source of fire in an aircraft. The FAA requirements such as FAR Part 25 mandates that a fire extinguisher system be available to control fires in each fire zone of a turbine engine installation. The FAA AC20-100 Advisory Circular defines acceptable methodology and equipment for monitoring the amount of released fire extinguisher agent concentration in the fire zone. For example, a minimum concentration of Halon 1301 (CBrF3-bromotlifluoromethane) is necessary to extinguish a fire and to prevent its reoccurrence and should be delivered in at least 6% by volume throughout the fire zone space for at least a simultaneous half second (0.5 second) at all sampling points. Lower concentrations or shorter time periods will reduce the effectiveness and would not meet the FAA requirements. Conversely, Halons are a known ozone depleting chemical and higher concentrations at longer time periods would waste the fire suppression agent.

[0005]

Any fire suppression system that is installed on an aircraft generally undergoes a ground based certification or qualification testing procedure to confirm proper operation of the fire suppression system. It is desirable, however, to provide a monitoring system that can meet preflight certification testing of fire suppression systems and also is capable of being flown on the aircraft to monitor the concentration of a fire suppression agent released during flight in order to verify proper operation of the fluid fire suppression system when it is activated and/or to provide feedback data that could enable the level of the fire suppression system to be dynamically adjusted as required to ensure safe, effective, efficient and reliable operation of the fire suppression system. The utilization of relatively lightweight equipment that can monitor in-flight operations for example on aircraft take offs, landings and level flight would be advantageous, especially for FAA Part 23 aircraft.

[0006]

A presently available gas concentration measurement system that is used in preflight certification testing of fire suppression systems is provided by the Pacific Scientific Halonizer III and weighs approximately 400 pounds for a 12 channel system. The Pacific System Halonizer works on the basis of a differential pressure and is consistent with an original Statham Analyzer Design which measured a pressure drop of a binary gas mixture flowing across a porous plug at a known temperature. The Halonizer III system is only calibrated at Pacific Systems Duarte, California laboratory. Any change or repair of parts requires re- certification in the California laboratory.

[0007]

Walter Kidde Aerospace also supplies a derivative of the Statham Analyzer configuration. Thus, the two presently available gas concentration measuring systems both work on the basis of the differential pressures and are relatively bulky. Additionally, changes in ambient pressure, temperature and humidity are a concern in the measurement process. [0008]

U.S. Patent No. 6,181,426 described a system for monitoring fire suppression agents for aircraft based on an optical system that depends on an absorption of optical characteristic lines of select wavelengths by a photo detector at a selected optical absorption wavelength for the subject gas.

[0009]

There is still a need in the aircraft industry to provide, in a compact configuration at a low cost, reliable measurements of a gas concentration for monitoring a fire suppression agent.

SUMMARY OF THE INVENTION

[0010]

The present invention provides a monitoring system and method for determining a concentration of gas in an enclosed space, such as validating the performance of a fire suppression system in an aircraft. The monitoring system utilizes a plurality of separate modules of detector units, each containing a thermal conductor detector capable of outputting an electrical signal representative of a thermal differential due to a transmission of at least a portion of the monitored gas through the thermal conductor detector. Thus, a plurality of sampling locations can be provided as representative of the enclosed space. Additionally, a separate electrical power and vacuum module can power the detector modules.

[0011]

The thermal conductive detectors use a tungsten-rhenium filament that can be operated at a high temperature of 275°C. Current flows through the filament causing it to heat to a fixed temperature, any gas that flows across the filament will remove heat at a characteristic constant rate (such as a mixture of ambient air and Halon) so that concentrations of the specific gas components from 100% down to only 300 parts per million can be ascertained. An output of millivolts, discloses a thermal differential based on the heat absorption as a representative signal of the volumetric amount or concentration of the desired gas in the flow stream. The thermal conductor device can serve the function of a universal detector since it detects all molecules and it is possible to determine the heat absorption characteristics of such molecules as representative of a desired gas at different concentration levels. [0012]

A probe unit is operably connected to the desired monitored enclosure space such as an engine nacelle, cargo space, or auxiliary power unit. The probe unit can be mounted, for example, on the housing of an engine nacelle at predetermined locations to permit an adequate number of samplings to determine the gas concentration rate throughout the enclosed space as required by FAA regulations. The probe units include a first communication conduit that can be connected to a probe member inserted into an interior space of the housing, with the first communication conduit being secured to the surface of the engine nacelle, for example, by an adhesive tape.

[0013]

A plurality of probe units can be utilized, each with individual first communication conduits to isolate the drawing of sample gas at specific locations. A micro filter ensures that only a gas is transmitted and a second communication conduit downstream of the micro filter, having a substantially smaller cross-sectional area, can withdraw a portion of the gas flow for testing purposes.

[0014]

For example, the second communication conduit can support a maximum of lOccs per minute flow rate. A vacuum pump with a capacity of 1.1 cubic feet per minute can be connected to the first communication conduit. The second communication conduit is indirectly connected to a third communication conduit that connects to a common vacuum manifold which is in turn connected to the vacuum pump or vacuum source and also to the first communication conduit.

[0015]

A flow meter is mounted in each of the third communication conduits downstream of each of the thermal conductive detectors. The flow meters can be set for each of the plurality of detector units to provide a maximum flow rate of lOccs per minute.

[0016]

The second communication conduit can be connected to a predetermined length of a metal conduit such as coiled heat conducting metal tubing which in turn is connected to the thermal conductive detector for delivering the sample gas. Means for heating each of the thermal conductive detectors can include a thermal manifold housing enclosure with a resistance heater that can be set at a desired temperature, such as 54°C to heat both the coiled metal conduit of the second communication conduit and the individual housings of the thermal conductive detectors.

[0017]

The vacuum pump draws the sample gas portions through the probes from the monitored enclosed space. Electrical outputs of the individual thermal conductive detectors are attached to a data acquisition system in the detector modules, for processing measured millivolts of each channel to provide input signals to a processor such as a notebook PC at a scan rate, for example of 20 scans per second. The data acquisition system is capable of calculating and displaying relative volumetric concentrations based on a sample gas calibration and can be set at a scan rate from 0 to 50 scans per second. A graphic display of the signal outputs from each channel or probe unit can be visually disclosed by a Peak Simple software program on a display screen.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings.

[0018]

Figure 1 is a partial perspective view of an engine nacelle set up for a certification test;

[0019]

Figure 2 is a schematic diagram of a detector module connected to a vacuum pump;

[0020]

Figure 3 is a diagram of a volumetric concentration over time for a 12 probe/channel monitoring system;

[0021]

Figure 4 is a schematic representation of a pair of six channel detector modules and a vacuum pump/AC power supply; and [0022]

Figure 5 is a schematic illustration of a two modules, six channel monitoring of an aircraft nacelle with a power supply unit.

DETAILED DESCRPTIOON OF THE PREFERRED EMBODIMENTS

[0023]

Reference will now be made in detail to the preferred embodiments of the invention which set forth the best modes contemplated to carry out the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

[0024]

The present invention described below is based upon the principles of a fire extinguisher gas chromatograph system that can be represented by three inter connectable modular containers that can be mountable in an aircraft. In the embodiment shown herein, a monitoring gas system is used for an engine, auxiliary power unit and cargo compartment certification by measuring a fire suppression agent such as Halon, for concentration of a discharged extinguishant at 12 measuring points within the fire zone of a desired enclosed space. Examples of enclosed spaces can be an engine nacelle, a cargo bay of an aircraft, or an auxiliary power unit. The present invention only utilizes 12 measuring points within the enclosed space for a fire zone, as an example. An additional or lesser number of measuring points can be accommodated within the parameters of our present invention to meet the requirements of each aircraft. [0025]

A vacuum source such as a vacuum pump 38, with a capacity of 1.1 cubic feet/min., can be used to draw the discharge of Halon gas through capillary tubes connected to predetermined probe points for the enclosed space. Alternative capacity vacuum pumps could be used. A discharge gas will be basically a combination of ambient air and Halon that would be filtered and a small portion of gas in each individual channel will be conducted to a dedicated thermal conductive detector that is maintained at a set temperature with the flow rate controlled to be constant for each channel.

[0026]

Differential thermal signals from the filament of the thermal conductive detectors, due to varying concentrations of the fire extinguishing gas will be output to a data acquisition system that can prepare data for a processor unit to convert the thermal changes to represent a concentration of Halon in the gas flow for each respective channel. The data acquisition system will record the volumetric concentration of Halon as a function of time. Visual display can also be provided to the operator showing the output of each channel as a function of time and fire suppressant concentration.

[0027]

Figure 1 discloses a rear portion of an aircraft 2 with an engine nacelle 4 having a series of probe members 6 mounted for communication with the interior of a desired monitored enclosed space within the nacelle 4. Each of the probe members 6 are connected to a flexible tube conduit 8 such as polyethylene or vinyl tubes with 1/8" ID. Adhesive tape 10 can be applied to hold the tube conduit 8 on the surface of the engine nacelle 4.

[0028]

While only six probes 6, which can be polyethylene, are disclosed in Figure 1, it can be appreciated that the other side of the engine can have additional probes that provide additional channels or sampling locations within the desired enclosed space, see Figure 5. The importance of having multiple sample locations is to validate the requirement of meeting the FAA requirements of a concentration level of 6% by volume for at least one-half second throughout the entire monitored enclosed space within the engine nacelle 4. The conduits 8 can form a first communication conduit, having a 1/8 inch inside diameter, and can be ganged together as shown in Figure 2 to provide a quick common connection to a port 56 on a detector module housing 12. Figure 2 schematically discloses only one of the detector units and it should be appreciated that the detector module housing 12 can accommodate six or more detector units 14. The conduits 8 represent a first communication conduit for each respective detector unit 14. A micron filter 16 ensures that the gas sample does not contain any solid debris.

[0029]

A second communication conduit 18 having a 1/32 inside diameter can be connected in a perpendicular manner to the first communication channel and can comprise a flexible Tygon™ resin tube. The resin tube can be connected to a metal tube of the same size with an appropriate length that can be coiled or bent to extend the surface area within a heated manifold 22 or box that will house the coiled tubing 20 to act as a heat exchanger before connection to a thermal conductor detector 24. Within the housing of the thermal conductor detector 24 is a filament of, for example, tungsten rhenium 26, that can be heated by the flow of current to operate at a temperature of approximately 275°C. A flow meter 28 is connected to the gas sample discharge from the thermal detector housing whereby an operator can adjust the flow meters 28 for each of the respective channels to ensure a constant sample volume flow through the respective thermal conductor detectors. The flow meter 28 is shown in Figure 4 in a ganged arrangement on the exterior surface of the detector module. The respective lengths of the first and second communicator conduits from the probes 6 to the thermal conductor detectors 24 are equal to ensure a simultaneous measurement at the same time for all locations of the enclosed space.

[0030]

A third communication conduit 32 includes a check valve 34 that permits a discharge of the sample gas flow through the channel from its respective probe to a vacuum manifold 36. The vacuum manifold 36 is connected to the vacuum pump 38 which has a capacity of at least a pump flow rate of 1.1 cubic feet per minute. The first communication conduit 8 is also connected to the common vacuum manifold 36 for exhausting the specimen of gas flow.

[0031]

The plurality of individual thermal conductor detectors 14, such as but not limited to, an SRI Instruments of Torrance, California P/N 8670-9120 TCD are sealingly connected to the second communication conduit 18 of a smaller cross-sectional flow than the first communication conduit 8, so that an untainted gas sample is appropriately heated in the coil 20 and delivered into the sealed thermal conductor detector housing 24 to flow in a controlled manner across the tungsten-rhenium filament 26. The molecules of the fire suppressant agent will cool the filament 26 thereby causing an increase in voltage with appropriate current flow to be drawn to maintain the desired temperature setting for the filament. Thus, the millivolts that are drawn are representative of the concentration of a fire suppressant agent. This output signal is directed to a data acquisition unit 40 which accumulates the data from each of the respective thermal conductor detectors 14 and provides signals that can be processed by a processor unit 42 such as a notebook PC running a Peak Simple Software Program. Thus, each of the channels are representative of a probe sampling at particular locations of the enclosed space and can be visually displayed as a function of a volumetric concentration of the fire suppressant fluid such as Halon 1301 over a period of time represented in seconds in Figure 3. This can be displayed on the display 44 connected to the processor unit 42.

[0032]

As can be seen in Figure 3, 12 channels were measured as representative of 12 different locations on the enclosed space within the engine nacelle 4. A fire suppressant volumetric concentration of 6% were achieved over a period of time of 1.416 seconds indicating a Pass Result for the system.

[0033]

Advantageous features of our invention permit a heated container or manifold 22 that can maintain a constant temperature, for example 54 ⁰ C, for each of the respective thermal conductor detectors within the manifold 22. This ensures a uniformity of monitoring conditions. Additionally, the adjustable flow meter 28 for each of the respective sampling channels ensures a constant flow rate for each of the respective thermal conductor detectors 24. Therefore, a uniform measurement is made across the entire enclosed space that is being monitored. The concentration of fire suppressant gas would be mixed with ambient air so that a binary flow mixture is passed in a controlled manner at a controlled temperature across the thermal conductor detectors 24 to enable an accurate thermal differential to be measured. A scan rate or data interval of 20 scans per second can be realized to provide sufficient data points to enable an appropriate measurement for verification of our sampling.

[0034]

The means for heating each thermal conductor detector can be conventionally realized, for example through resistance heaters 53, see Figure 5, to maintain a constant temperature within the manifold 22. Metal coils 20 act as a heat exchange component to ensure an appropriate even heating of the respective gas samples to equalize the temperatures in each sample for each channel before the gas samples are applied to their respective tungsten-rhenium filaments 26. As mentioned above, each of the thermal conductor detectors are driven to a predetermined temperature, such as 275 ⁰ C so that when the controlled flow rate of heated gas specimens for each channel flows across their respective filaments, they can remove heat at a constant rate and the subsequent adjustment of the electric current can compensate for the thermal differential due to the presence of the binary gas mixture and can be an accurate thermal differential measurement representative of the desired monitored gas. Additionally, since a thermal differential is being utilized, it is representative of the amount of sample gas concentration.

[0035]

Our system is designed to be relatively free from potential errors relating to variances in pressure differentials associated with the altitude of the measurement site, the ambient humidity and air temperature. This enables calibration in the field and the ability to replace any defective module at the measurement site. The thermal conductive detectors are calibrated by drawing ambient air through each thermal conductor detector to determine a base line, and subsequently drawing a predetermined concentration amount of a fire suppressing gas through each thermal conductor detector to adjust for the base line. The processor unit provides an output signal in accordance with the calibration. For example, a measurement at a location such as Denver, will produce pressure differences different from that at sea level or at other elevations. Since we are measuring a thermal differential, our system can be free of potential errors based upon variations in pressure in the ambient air.

[0036]

In calibrating our instrument, the FAA Regulations require a field calibration with a calibration verification using 100% volumetric concentration of the fire suppressant agent prior to any certification demonstrations. Accordingly, our gas monitoring system can be initialized by activating the vacuum pump 38 to initially draw a baseline of only ambient air through our thermal conductor detectors 24. Any moisture content in the air is, therefore, factored into the calibration process with baseline measurements. A charge of 100% of the fire suppressant gas such as Halon can be drawn through the vacuum pump into the respective conduits or channels to provide relative readings for calibration purposes of 100% of the thermal differential of the gas to be monitored. [0037]

As can be appreciated, it is also possible to provide calibration results for a series of different percentages of mixtures of air and the sample gas such as 5% Halon mixture, 10% Halon mixture, 15% Halon mixture, 20% Halon mixture. As known in the industry, calibration curves can be computed based upon these measurements to provide a correction for each individual monitoring system.

[0038]

Referring to Figure 4, a pair of detector modules 46 and 48 can supply 12 separate channels of monitoring of the desired enclosed space. The number of channels could be lesser or greater, for example 24. A vacuum pump/ AC power supply module 50 is also provided for connection to each detector module. Above the flow gauge 30 is a temperature sensor gauge 52 for monitoring the temperature within the sealed manifold housing 22. An emergency stop button 54 is provided on each of the units to stop the operation. A six channel disconnect connector 56 is provided on the top of the respective detector modules 48 and 46 for ease of connection of the first communication conduits 8. Additionally, a connector 58 is provided to enable a vacuum connection with the vacuum pump 38 to provide a source of vacuum by attaching conduits 64 to each detector module 46, 48. Also, a power connection port 60 permits power from module 50 to be supplied to the detector modules 48 and 46.

[0039]

Referring to Figure 5, the present invention is shown with 12 channel thermal conductor detector units installed on a nacelle with disclosed representations of measurements shown in Figure 3. A schematic overall view of the connections between the vacuum pump/AC power supply 50 and the respective detector modules 46 and 48 are shown.

[0040]

The present monitoring system is designed to be mountable within the aircraft. The aircraft can provide the desired electrical power directly to module 50. Six channel connectors 56 can engage complementary connectors from the first communication conduits that are ganged for a quick disconnect mounting. Additionally, a vacuum conduit 64 can be connected to the respective vacuum connection ports 58 on each of the detector modules 46 and 48. [0041]

Our present gas monitoring system utilizes a different principal for analyzing the fire suppressant gas concentration than that of the known prior art monitoring systems. Our system uses a thermal conductivity detector that works on the concept of a thermal conductivity principle based upon a premise that all specific gas molecules are defined by a specific thermal conductivity. For example, Halon (refrigerants in general) have a lower thermal conductivity than ambient air. Thus, we use a vacuum pump 38 to draw a sampling of either the ambient air during calibration or a fixed amount of the fire suppressant agent such as Halon 1301 across the filament bridge 26 of our thermal conductive detector 24. Since a lower thermal conductivity is created as compared to the carrier air gas, the filament will be cooled and the thermal conductive detector 24 will be driven by a measurable current change and corresponding voltage change which can be connected to an electronic data acquisition unit 40 capable of recording variations. The pre-heating of the gas samples in the detector modules equalizes the condition of the gas samples before measurements. Real time monitoring of the sampling process of the present invention is accomplished with the use of a PC based data acquisition software.

[0042]

A processor unit 42 can provide visual representations on a display 44 of the results of a measurement. The measurement can be taken when the aircraft is on the ground or due to its relative light weight of about 190 pounds, can be taken when mounted in the aircraft during flight, for example during take offs, level flights and landings. Our thermal conductive detectors 24 can be mounted within a sealed heated manifold 22 to ensure a constant temperature across each of the detectors. Each of the channels or gas sampling conduits can have flow meter adjustment valves 28 to ensure a uniform gas flow through the detectors. Communication conduits from the probes 6 on the enclosed space will be of equal length to ensure that a simultaneous measurement of each of the spaces are provided by each of the respective thermal conductive detectors 24. The second conduit line 18 has a coiled tubing forming a heat exchanging coil 20 to ensure uniform heat transfer to the sample gas before entering the thermal conductor sensor chamber 24 and passing across the filament 26.

[0043]

The data acquisition system software calculates and displays the volumetric concentration of the resulting fire suppression discharge test while taking into account the initial calibration specific to our monitoring system and its location relative to both relative humidity and pressure variations depending upon the altitude of the measuring site. The scan rate of a data acquisition interval is adjustable up to 20 scans per second to ensure sufficient data sampling for verifying a 6% concentration by volume of a fire suppressant agent throughout the entire enclosure of the tested portion of the aircraft. The data system software is capable of displaying real time dynamic profiles of volumetric concentration versus time for the fire suppressant agent.

[0044]

Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the amended claims, the invention may be practiced other than as specifically described herein.