DE1094597B - Device for suppressing explosions - Google Patents

Description

The invention relates to a device for suppressing explosions with fragile, respectively a suppressant as well as a container containing an explosive charge, which is in the potentially explosive Zone are arranged and the explosive charge is detonated by means of photoelectric cells, that respond to the glow of a fire. In known devices of this type, the overlapping of a fire or an explosion from one potentially explosive zone to another potentially explosive Zone thereby prevents the fragile containers in connecting rooms and lines are arranged between the two zones and the photoelectric cells on the light a fire or an explosion in either zone.

Here, however, is the destruction of the zone in which the fire breaks out or the explosion takes place, inevitable. This is e.g. B. particularly disadvantageous in the case of aircraft fuel tanks, since the explosion a single tank, even if it prevents the explosion from spreading to neighboring tanks can lead to a total loss of the aircraft.

The invention aims to avoid these disadvantages of the known devices, and is based on the knowledge that a short time elapses from the instant of ignition of an explosive mixture until in a noticeable increase in pressure occurs in this mixture. The invention consists in that to take advantage of the Time interval between ignition spark and noticeable pressure increase each photoelectric cell by means of a electrical amplifier is designed so sensitive that already the light intensity of the ignition spark a An explosion in the process of igniting the explosive charges in the fragile containers is sufficient and the suppressant means before a noticeable increase in pressure in the potentially explosive area Zone is distributed. This results in an explosion that is about to occur is suppressed before it has developed, and thus the zone to be protected from destruction is preserved.

In the device according to the invention, the electrical amplifier of the photoelectric cell can be a photo-emission cell or a photo-multiplier, it being possible for the sensitivity of the photo-multiplier to be greater than one microampere per lux. A photo-multiplier should be understood to mean a combination, known per se, of a photo-emission cell with an electron multiplier. In the case of a photo multiplier, high voltages are required in a known manner for the operation of the multiplier dynodes, usually in a transformer
to suppress explosions

Applicant:
Gravin® [he Manufacturing Company

Limited

and The Wilkinson Sword Company
Limited, London

Representative: Dr.-Ing. K. Hoffmeister, patent attorney,
Hanover, Königstr. 23

Claimed priority:
Great Britain April 9, May 22 and September 11, 1953

Anders Mathisen, London,
has been named as the inventor

which is connected to the housing of the photo multiplier via high-voltage connections is. The high-voltage transformer and the high-voltage connections are useful in one Block of plastic insulating material embedded. This results in a particularly safe and compact design. By doing without the usual DC voltage supply of the dynodes, they can be used directly Alternating current can be fed. This precaution also primarily serves the operational safety of the System, since the rectification of high voltages can give rise to disturbances. Only in the second place is the cost savings matter.

In a particularly expedient embodiment of the invention, the electrical amplifier contains a cold cathode tube, a potentiometer that biases a control electrode of the tube indicates that the tube is normally non-conductive and one between the poles of a source of electrical power and storage capacitor connected in series with the tube and the ignition circuit. The output side of the photocell is between the

009 677/39

The anode and the control electrode of the tube are switched. AVenn now the photocell of the lighting effect mentioned is exposed, the photocell becomes conductive and the control grid of the tube receives positive potential, so that also the tube becomes conductive and thereby the capacitor discharges through the ignition circuit, whereby the explosive charge is detonated. Cold cathode tubes are special due to the lack of a filament reliable and have a long service life. The amplifier is practically one electronic container that is normally open but closed by exposure to light on the photocell is, whereby the storage capacitor discharges and thereby ignites the explosive charge. This ignition takes place very quickly due to the capacitor discharge.

In another embodiment of the invention, several photoelectric cells are connected in parallel, which respond to different spectral ranges. The maximum intensity of the light from an explosion introductory spark is at different wavelengths depending on the nature of the explosive mixture. The aforementioned photoelectric cells connected in parallel ensure almost the same responsiveness of the device over the entire spectral band in question.

The photoelectric cell or cells can also be designed as photo voltage cells, the output side are connected to an electromagnetic high-speed relay.

This relay switches the ignition circuit to a voltage source. Because of this design of the facility a particularly simple circuit is obtained.

Conveniently one in an aircraft fuel tank built-in device according to the invention, two photoelectric cells are provided, one of which is in an upper corner of the tank and the other in the diagonally opposite lower corner Corner of the tank is installed. This arrangement of the cells ensures that even when the aircraft is tilted at least one of the cells always remains uncovered or almost uncovered by the fuel and thus in responds with great sensitivity to a possible ignition spark. To reinforce the Light effect, the inner walls of the tank can be colored white.

To achieve a beneficial effect in suppressing a nascent explosion a substance, e.g. B. a flammable hydrocarbon is used, which suppresses the explosion by supersaturating the explosive mixture and has a boiling point of about 26 ° C at normal pressure.

The drawing shows two diagrams that are characteristic of an explosion, as well as various exemplary embodiments of the invention, namely shows

1 shows a pressure-time diagram of the explosion of a hydrocarbon-air mixture,

2 shows an aircraft fuel tank in plan,

3 shows a cross section through the tank according to FIG. 2,

4 shows a circuit diagram for a photoelectric cell with a photo multiplier,

Fig. 5 is a circuit diagram for a photoelectric cell with a simple photo-emission cell in connection with cold cathode tubes,

6 shows a further example of a circuit diagram with a simple emission cell in connection with a thyratron tube,

7 shows a fourth example of a circuit diagram with a photo-emission cell in connection with a Hot cathode tube and a magnetic relay and

8 shows a diagram of the approximate energy distribution over the visible spectrum for characteristic Explosion flames.

The diagrams and exemplary embodiments shown relate primarily to devices for Suppressing explosions in aircraft fuel tanks. However, the invention is not to use restricted in airplanes but can be used wherever there is a possibility of explosions is given, for example for crankcases of diesel engines, in catalytic chemisehen Process for electrostatic precipitators, grinding and pulverizing systems, air classifiers, filters, d. H. so in systems in which finely divided explosive dust and powder are handled.

1 shows a characteristic curve of the pressure increase in pounds per square inch (Pr) as a function of the time after ignition in milliseconds (f) in a test explosion in an aircraft fuel tank which was filled with 200 l of a hydrocarbon-air mixture.

The diagram shows that the time required to reach an explosion pressure of about 5 psi (= 0.35 kg / cm ² ) is only about 50 msec. The diagram also shows that there is a short time between ignition and the onset of a noticeable rise in pressure, which is probably due either to the time required to build up the energy of the ignition source or to the time required to ignite the fuel.

To utilize the time interval between the ignition spark and the onset of the noticeable increase in pressure photoelectric cells are used according to the invention, each by means of an electrical amplifier are made so sensitive that the light intensity of the spark of an explosion sufficient to ignite the explosive charges in the fragile containers.

However, the sensitivity of the photoelectric cells alone is generally not sufficient.

<5 more is in many cases an extremely fast one Distribution of suppressant required. Since the top speed of the spark is about up to 3 m / sec, it is desirable to run the suppressing means at a speed of at least 46 m / sec up to a radius of at least 65 cm within a period of time no more than 10 msec after ignition. For such a rapid distribution of the suppressant are known suppressant container in hemispherical shape particularly suitable, which an explosive charge to smash the Containers as well as the suppressant. But it can also be spherical, tubular or other shaped suppressant containers can be used. However, the prerequisite is that when the explosive charge is ignited, practically the entire container and the contents of the container shattered the necessary speed is given.

Referring to Figures 2 and 3, the aircraft fuel tank 10 illustrated is made of rubber and is within a tank carrier, not shown, directly on the outer skin of the aircraft fuselage or a Arranged wing of the aircraft. In one of the upper corners and in the diagonally opposite one lower corner of the tank 10 is a photoelectric

I 094 597

Irish cell 11 α or 11 b attached. With such an arrangement of two photoelectric cells 11a, 11 b is ensured that also in an inclined position of the aircraft is always only one cell is immersed in the fuel, while the other cell is always located above the combustion mirror or immersed in the worst case by little.

The suppressant tanks are as two

In the device according to the invention, the required sensitivity of the photoelectric Cells can be achieved by amplifiers which electronically increase the output current take, causing an almost simultaneous detonation of the explosive charges in the suppressant containers is reached with the ignition pulse.

In the circuit diagram according to FIG. 4, a photo-multiplier 20 is used as an amplifier for a photoelectric cell

arranged through the entire length of the tank 10 passed io, which is illustrated by its closure cap and on and on its end faces attached cylindrical locking pins. The tubes 12a, 12b are formed on the pin 0. The ignition circuits are connected to the photocathode, while the two to 9 of the multiplier dynodes are connected in parallel to the pins 1 of the suppressant container and the collector anode is connected to the pin 10 photoelectric cells 11 a, 11 b. As can be seen from the drawing, the connecting wires 13 preferably being within the 15 drawing, the pin 0 is arranged on a clamp half of the rubber wall of the tank 10. The suppression transformer 21 can be connected to the secondary winding of a voltage-increasing transformer instead of a tubular shape, the primary winding element container of which is also connected to an alternating current source 22 in a spherical configuration, for example. be educated. Such spherical suppression The alternating current can generally be taken from the central medium tank 20 are shown in dashed lines of the aircraft frequency network, so and designated 14. When using half the normal voltage of 115 V and 400 Hz of the spherical containers, these are expediently attached to the aircraft network through the transformer 21 in one of the walls of the tank 10. Voltage of about 600 V can be converted.

The suppression agent container containing a is the second terminal of the secondary winding via suppressant partly by chemical WIR 25 a l, 5-megohm-W ^T esistance to ground and to the effect and partly becomes effective by cooling, examples pin 8 and a 7 picofarad capacitor of, for example, methyl bromide or dibromodifmomethane. connected to pin 9. The collector anode is over. A burning pin 10 and a 1 megohm resistor with the liquid hydrocarbon, e. B. Isopan, connected to the positive pole of a direct current source of 125 V, to which the explosion caused by supersaturation 3 ° whose negative pole is connected to earth. The Verdes suppressed explosive mixture. The large preamplifier tube is a cold cathode triode 23, part of which is connected to a control grid such as this, oversaturated with the explosive mixture, to pin 9. The lowering liquid is connected to earth by means of the suppressing means 3 to explosive charges 24 acting through the cathode of the tube 23 via the ignition circuits of the cooling, whereby these are 3.5 times lower specific weight. In addition, 35 circuits either one behind the other or in parallel cannot be connected to one another with liquids of this type. Between the corrosion and permeability problems of the 125 V power source, there is a storage condenser of the suppressant reservoir, such as a 4 microfarad capacitor. One 7 and one 11 megohms for methyl bromide. On the other hand, when using a resistor, there is a voltage divider of the 125 V connection of a 4 ° current source that supersaturates the explosive mixture and gives the control grid of the liquid the risk of post-ignition by a 23 such a bias voltage that the tube normally creeping ignition source, especially in the Fall when wise does not guide. If light falls on the photocathode, so the aircraft has to fly down very quickly, the 7-megohm resistance is practical because of the increased air flow and the explosive mixture of electricity between the last dynode and the collector may return to the critical ratio of 45 anode short-circuited, and which can bring to the. Higher voltage lying on the control electrode,

Of considerable importance is the boiling point that the tube 23 becomes conductive, whereupon the foldes used suppressant, since it causes the discharge of the 4 microfarad capacitor the different vapor pressures within the detonates depending on the explosive charge. The task of the 1.5 megohmdem Purpose of use is the specific temperature 5 ° resistor and the 7 picofarad capacitor depend on the area. The suppressant must, the unwanted internal capacity of the photo ver

aiso be so volatile that it is still effective at low temperatures while its vapor pressure on the other hand, at high temperatures, it must again not be so high that the suppressant 55 container a great strength is required. In this regard are isopentane and dibromodifluoromethane most suitable as their boiling point is around 26 ° C at a pressure of 760 mm of mercury amounts to.

The minimum distance between the suppressant tanks at which a certain concentration of the suppressant - based on the tank content - is achieved, depends on the size of the

To compensate many times, the impedance at the supplied frequency over the upper branch of the Voltage divider considerably reduced.

The risk of having a voltage source on the order of 1000 V in or next to it the fuel tank 10 can be by installing the transformer 21 in close proximity to the photoelectric Cell and by isolating transformer 21, multiplier pins 0-10, and the Interconnections by potting these parts in a plastic block from which the photosensitive Part of the photoelectric cell protrudes, weaken it. Such embedding in plastic is used

separate containers. The smaller the container, the more at the same time as protection against the ingress of

The suppressant is consumed more evenly. Fuel and water vapor.

Splits. However, this advantage must be used because of the input

number of containers required due to a responsive photoelectric cell because of cold cathode tubes

complex structure of the device because of the lack of a filament and because of it

will be bought. 70 greater mechanical strength are preferred,

7 8

so can of course also the usual incandescence sensitivity is the circuit with the circuit according to cathode tube amplifiers can be used. Comparable to Fig. 4. However, it has the disadvantage that like amplifiers, however, increase the effective reception of a filament and especially the ins Sensitivity of the photoelectric cell is not due to the weight-bearing property that any inadvertent output current in very weak light incidence with 5 visible interruption of the circuit the small random fluctuations in the output - closing the relay contacts and igniting the explosive current is comparable to the cell, which would then also handle pre-charges 33 in the suppressant containers are when the cell is in complete darkness - making it unsuitable for use in airplanes is located. This random output current continues is appropriate. For other purposes where this the disadvantage that can be accepted with simple photoelectric cells, it forms incidence of light a lower limit. On the other hand, however, it is an attractive example of its use gives the use of electron multipliers - a photo multiplier.

as with the photo multiplier, stage an amplification from a hydrocarbon ignition spark

without increasing the dark current of the cell. radiated light energy is neither on a specific

If the high sensitivity of a photomultiplier is limited to a wavelength or a waveband, but multiple is not necessary, a simple one can also have the same energy content for all wavebands. Photo-emission cell can be used, which can be designed as the spectral distribution of the energy is a combined vacuum cell, preferably any configuration which, depending on the type of ignition spark, has a gas filling, since gas-filled cells are sensitive to different properties of all individual elements are more than equivalent Vacuum cells. Like 20 components of the spark. The decisive factor in the circuit diagram according to FIG. 5 is the question of whether free carbon particles, the photoelectric cell 30 over the upper branch of a mainly supersaturated mixture, are formed from two resistors of 15 and 18 megohms or are present not. The presence of this deten voltage divider connected. As in the case of the carbon particles, the increased radiation energy in the circuit according to FIG. 4 causes a voltage increase in the control infrared region on the cell 30 from the visible wavebands to the falling light. The photocells with the highest sensing electrode of a cold cathode triode 31, which means that they are in the infrared area, however, are precisely the ones that become conductive. The triode 31 is in turn parallel to which, at temperatures above 20 ° C., a verdem upper branch of a resistor of 140 has reduced sensitivity, so that only photocells are switched on for the 190 kiloohm voltage divider used in airplanes, with the connection point the two highest sensitivities in the visible spectral resistances to the control grid of a cold cathode area come into question. In the case of lean mixtures, tetrode 32 is connected. No free carbon particles are deposited on this tetrode 32, parallel to a storage capacitor of 250 micro- and the spectrum of the explosion flame is simply farad, and the ignition circuit of the explosive charges 33 35 is determined by the gases. This leads to a return in the suppressant reservoir is switched into the path of the total radiant energy in the ratio cathode circuit of the tube. Even the one with fat mixtures. In Fig. 8 this Ver value of the second voltage divider is chosen so that ratios of the approximate energy distribution (E) over that the tetrode 32 is normally non-conductive. the visible spectrum for excessively rich (curve A) and only after the triode 31 has become conductive 40 for lean mixtures (curve B) are shown. The all-voltage rise makes the tetrode 32 conductive and the mean direction of the curve is determined by the black lets the 250 microfarad capacitor itself be determined by the body radiation of the carbon particles, tetrode 32 discharging and thereby the explosive charges during the peaks at around 3000, 4000 and 33 ignite. 5000 Angstrom through the radiation of the combustion

In Fig. 6 is another circuit with a 45 gases are generated.

AC power source 41 shown without rectification. The diagram shown teaches that the flame

The photocell 40 is arranged in such a way that it is normally red in the case of rich mixtures that

A thyratron tube 42 becomes conductive, but via the red when the mixture becomes leaner

which detonates the explosive charges 43 lying in a row is comparatively weaker, whereby the increasing

be det. A disadvantage of the thyratron tubes is the 50 mm blue coloration of the flame with a decrease

Filament; however, they can be accompanied by a stronger current of the luminous intensity.

as cold cathode tubes of the appropriate size, while the sensitivity of photo reproduction

permit. times sufficient to access the reduced luminosity

In Fig. 7, the circuit of a photoelectric lean mixture can be addressed, can with an arrangement cell with the use of a hot cathode triode 55 the use of simple emission cells shown. The control grid of the triode 51 is identical to that of two photoelectric cells connected in parallel Anode of a photoelectric cell 50 connected, which may be useful, for example, in the current cathode receives a negative bias. In the event of defective circuits according to FIGS. 5 to 7, they are switched on, with Due to the effect of light on the photocell 50, one cell is red-sensitive, while the other is blue-grid practically free, so that the tube 51 is a high 60 sensitive. Using two or more Anode current lets through, which becomes an electromagnetic relay of photoelectric cells connected in parallel 52 excited. The relay 52 keeps one in the ignition circuit, of course, the sensitivity of the device via the lying contact 52 σ open. Increase most of the mixing range on cell 50. It Falling light results in a negative bias on the can also be more than one cell of the grid of the tube 51, whereby the anode current thereof 65 of the correct sensitivity can be used. It is is reduced that the relay 52 drops out and also possible, the radiation of the ignition spark Contact 52a in the ignition circuit of the explosive charges by adding certain substances in traces to the 52 is closed. Increase fuel in the tank considerably. Such

With this circuit, a very large amount of substances can be evaporated with the fuel and

achieve effective reinforcement. Regarding the receipt, 70 remain stored anyway. You are not allowed to either

harmful influence on the engine or the fuel system to have. Such a substance is, for example, iron pentacarbonyl.

The visible light influence of a light source is known to follow an inversely proportional quadratic equation, i. i.e., the light intensity decreases with the square of the distance. However, if the walls in the tank are colored white, it increases Radiation of the ignition spark reflected from the walls of the tank increases the sensitivity of the photoelectric Cells significantly, and the inverse quadratic equation becomes invalid. Shiny metal interior walls also give an improvement. It can also be used to reinforce the photoelectric Cells covered by light, light guides or optical amplifiers can be used.

Photo voltage or blocking cells are not suitable for use in aircraft because the if necessary, relatively high temperatures acting on the cell decreases the sensitivity. In addition, as a result of the necessary low load resistance when reinforcing the Photocell output current difficulties. The advantage of these cells is that they excite themselves and are not dependent on an external power source. A typical output current in 1000 ohms is about 4 microamps, which allows for direct switching of a high-speed relay, for example a polarized one "Carpenter" relay is enough. However, the current is not sufficient to reliably switch a relay, if this is subjected to vibrations, so that it is desirable, means for amplifying the output current to accomplish. A magnetic amplifier is more suitable than a hot cathode tube amplifier; but it causes pulse delays of a few milliseconds, depending on the frequency of the input alternating current and the necessary reinforcement. However, in those cases where such pulse delays are permissible and the maximum temperature is still below the limit at which the sensitivity If the cell deteriorates excessively, the use of barrier cells is probably appropriate.

Even if many of the above conditions affect the conditions in explosions in Aircraft fuel tanks apply, sub-thickening agents can of course also be used for other tasks, where there is a possibility of explosions, for example where there is a risk of dust or powder explosions, can be used in a similar manner. The choice of photoelectric cell is under consideration the various prevailing operating conditions, such as the highest ambient temperature and distribution of a nascent explosion in that explosive atmosphere resulting light effect on the spectrum. Likewise, the choice of suppressant, the concentration required and the required depend Rate of distribution depends on the conditions associated with the task at hand.

Claims (12)

PATENT CLAIMS: 1. Device for suppressing explosions with fragile containers, each containing a suppressant and an explosive charge, which are arranged in the potentially explosive zone and whose explosive charge is detonated by means of photoelectric cells, which It respond to the glow of a fire, thereby characterized that in order to utilize the time interval between the ignition spark and the noticeable Pressure rise every photoelectric cell by means of an electrical amplifier so sensitive is designed that the light intensity of the ignition spark of a developing explosion sufficient to ignite the explosive charges in the fragile containers and the suppressant means before a noticeable increase in pressure in the potentially explosive area Zone is distributed. 2. Device according to claim 1, characterized in that the electrical amplifier each photoelectric cell is a photo-emission cell. 3. Device according to claim 1, characterized in that the electrical amplifier each photoelectric cell is a photo multiplier. 4. Device according to claim 3, characterized in that the sensitivity of the photo multiplier is greater than 1 microampere per lux. 5. Device according to claim 3 or 4, wherein the necessary for the multiplier dynodes high voltages through the high voltage connections with the inside of the housing of the photo multiplier connected transformer are removed, characterized in that the transformer and the high-voltage connections are embedded in a block of plastic insulating material. 6. Device according to one of claims 3, 4 or 5, characterized in that the multiplier dynodes of the photo multiplier can be fed directly with alternating current. 7. Device according to one of claims 1 to 6, characterized in that the electrical Amplifier a cold cathode tube, a potentiometer attached to a control electrode of the tube such bias gives that the tube is normally non-conductive and one between the poles an electrical power source and connected in series with the tube and the ignition circuit Contains storage capacitor, with the output side of the photocell between the anode and the The control electrode of the tube is connected, which means that the tube is then conductive when the photocell exposed to the light mentioned and the capacitor thereupon via the ignition circuit is discharged so that the explosive charge is detonated. 8. Device according to one of claims 1 to 7, characterized by several connected in parallel photoelectric cells, each responding to different spectral ranges. 9. Device according to claim 1, characterized in that each photoelectric cell as Photo voltage cell is formed, the output side to an electromagnetic high-speed switching relay are connected. 10. Device according to one of claims 1 installed in an aircraft fuel tank to 9, characterized by two photoelectric cells, one of which is in an upper corner of the tank and the other built into the diagonally opposite lower corner of the tank is. 11. Device according to claim 10, characterized in that the inner walls of the tank are white are colored. 009 677/39 12. Device according to one of claims 1 to 11, characterized in that as a suppressant a substance, e.g. B. a flammable liquid hydrocarbon is used, the the explosion by oversaturating the explosive Mixture suppressed and has a boiling point of about 26 ° C at normal pressure. References considered: British Patent No. 582 312. 1 sheet of drawings 009 677/39 11.60