WO1999009355A1

WO1999009355A1 - Device and method for affecting an object by means of pressure waves

Info

Publication number: WO1999009355A1
Application number: PCT/SE1998/001473
Authority: WO
Inventors: Curt Larsson
Original assignee: Försvarets Forskningsanstalt
Priority date: 1997-08-14
Filing date: 1998-08-14
Publication date: 1999-02-25
Also published as: SE510054C2; SE9702940L; SE9702940D0

Abstract

Device and method for affecting an object by means of pressure waves, where the pressure waves are generated by fuel being introduced to and ignited in a cylindrical combustion chamber (2), which have a closed rear end (3) and an open front end (4). A rapidly rotating vortex ring (11) is created when a pressure wave (16), generated at an ignition, forces the gas enclosed in the combustion chamber (2) out through the opening (10) of a ring-shaped flange (9), which has an internal diameter that is smaller than the inside diameter of the combustion chamber and which is arranged at the front end (4) of the combustion chamber. The vortex ring (11) moves forwards in the longitudinal direction of the combustion chamber and causes an impact on an object which is hit by it.

Description

Device and method for affecting an object by means of pressure waves

The present invention relates to a device and a method for affecting an object by means of pressure waves produced by ignition of an explosive gas mixture in a combustion chamber. The device and the method can be used for affecting or incapacitating people without inflicting permanent injuries on them.

It is previously known that sound waves in the form of infrasound can be used for destroying buildings or other objects and killing or injuring people. Infrasound con- sists of sound waves with frequencies below 20 Hz and cannot be registered by the human ear. Infrasound of sufficient strength can, however, affect a human body, and at certain frequencies body parts such as belly, loins etc. can start resonating. This resonance can cause indisposition, dizziness and vomiting. In order to achieve these effects by means of infrasound, sound waves with high energy content is required. It has, however, turned out to be difficult to achieve functioning devices for generating and directing these infrasonic waves.

The patent document US 3 612 211 A shows a method of generating infrasound by means of interference. According to the method, sound waves are emitted from two directional sound sources, which sound waves have such a frequency and phase in relation to each other that infrasound is produced when they intersect. It is required very strong sound waves if the generated infrasound shall be able to affect an object in the desired manner, this method is therefore energy-intensive. Furthermore, it is difficult to direct the strong sound waves, which makes it difficult to determine beforehand were the interference effects will occur.

Another way of generating infrasound is previously known from US 4 349 898 A. This document shows an acoustic weapon system which is intended to have a destructive and lethal effect. The infrasound is produced by blowing air, for instance from a jet engine, through a system of rotating masks, whereupon sound pulses with predetermined frequencies and phases are produced. The sound pulses are thereafter focused on a target by means of a sonic lens. This weapon system takes up a lot of space and is complicated.

The object of the invention is to provide a simple device which is easy to handle and which with a low energy consumption can cause effects similar to infrasound at the object towards which the device is directed. Another object is to provide an acoustic weapon which can emit sound pulses of such a frequency and strength that it can be used for affecting or incapacitating people without inflicting permanent injuries on them.

The invention is based on a technique of generating strong sound waves through ignition of an explosive gas mixture in a cylindrical combustion chamber. This technique is previously known from the patent document US 4 642 611 A. Fuel is injected into the rear part of the combustion chamber where it is mixed with air, whereupon an explosive gas mixture is produced. The explosion that occurs when the gas mixture is ignited creates a strong sound wave which propagates out through the open front end of the combustion chamber. The new with the invention is that a ring-shaped flange, whose opening diameter is smaller than the inside diameter of the combustion chamber, is arranged at the exhaust port of the combustion chamber. When the pressure wave from an explosion forces the gas enclosed in the combustion chamber out through the flange opening, a rapidly rotating gas ring with a high energy content, a so called vortex ring, is created. The rapid rotation of the vortex ring makes it an "acoustic projectile", which well contained moves straight on through the air in the longitudinal direction of the combustion chamber at a speed of about 40-60 m/s. By repeated explosions at a frequency below 20 Hz a series of pressure pulses in the form of vortex rings is created, which when they hit an object give rise to effects corresponding to those caused by strong infrasound. The emitted vortex rings can be said to be a pseudo-infrasound, and can for instance be used for scattering blocking crowds of people and thereby create a clear way for transports. The invention can also be used in connection with removal of mines in order to trigger pressure sensitive mines.

In the following, the invention will be further described by way of example with reference to the accompanying drawings, in which

fig. 1 shows in a side view a first embodiment of a device according to the invention, fig. 2 shows a cut A-A according to figure 1 , fig. 3 shows a cut B-B according to figure 1 fig. 4a-e show how a vortex ring is created with a device according to the invention and fig. 5 shows in a cross-sectional view a second embodiment of a device according to the invention. The device 1 shown in figure 1 comprises a cylindrical combustion chamber 2 which has a closed rear end 3 and an open front end 4. At the rear part of the combustion chamber 2 an electric igniter 5 is arranged, which is connected with a current source via a line 6a,6b. The igniter 5 comprises two electrodes 13a, 13b, see figure 3, which from different directions extends into the combustion chamber 2. The electrodes 13a, 13b are arranged in such a way that a gap 15 is formed between their ends in the centre of the combustion chamber 2. A device 7 for controlled injection of fuel is likewise arranged at the rear part of the combustion chamber 2. The rear part of the combustion chamber 2 can also be provided with a device for introduction of compressed air in order to facilitate the creation of an explosive fuel- air mixture in the combustion chamber.

In the shown embodiment, the rear part of the combustion chamber 2 is provided with two nozzles 14a, 14b, see figure 3. Through one of the nozzles 14a, fuel is supplied from a fuel source via a fuel line 8a. The fuel can for instance be propane gas. Through the other of the nozzles 14b, compressed air is supplied from a source of compressed air via a compressed air tube 8b. The introduction of fuel and compressed air can for instance be regulated by means of an electrically controlled solenoid, arranged in connection with the respective nozzle 14a, 14b.

At the front end 4 of the combustion chamber a flange 9 is mounted. The flange 9 is ring-shaped and has an internal diameter which is smaller than the inside diameter of the combustion chamber. Consequently, the flange 9 forms a contracted combustion chamber 2 opening 10.

When the device 1 is activated, fuel and compressed air is injected via the nozzles 14a,14b into the combustion chamber 2, where it is mixed and creates an explosive gas mixture. Thereafter, the igniter 5 is charged with electric current from a current source, whereupon an electric spark occurs in the gap 15 between the two elec- trodes 13a, 13b of the igniter. The spark ignites the gas mixture, whereupon an explosion occurs. The pressure wave 16 from the explosion forces the non-burnt gas residues in the combustion chamber 2 forwards towards the open end 4 of the combustion chamber. When the gas enclosed in the combustion chamber 2 at high velocity is forced by the pressure wave 16 out through the flange opening 10, a whirling ring 11, a so called vortex ring, is created at the outside of the opening. This vortex ring 11 constitutes a fast spinning energy packet, which at high velocity moves straight on in the longitudinal direction of the combustion chamber, as shown with the arrow 12 in figure 1. Figure 4a-e illustrates the process during the creation of a vortex ring. In figure 4a, the pressure wave 16 from an explosion has just reached the walls of the combustion chamber. Figure 4b-c show how the pressure wave 16 propagates and forces the gas enclosed in the combustion chamber 2 forwards and out through the flange opening 10. Figure 4d shows how a vortex ring 11 is created at the outside of the opening, and figure 4e shows how the pressure in the combustion chamber 2 decreases and thereafter returns to normal pressure at the same time as the vortex ring 11 under continued rotation moves forwards through the air.

By repeated injection and ignition of fuel, new vortex rings 11 are created, which one after the another in a tight beam move forwards through the air in the longitudinal direction of the combustion chamber. When the vortex rings 11 hit an object they cause pressure impacts on it. If an object is hit by vortex rings 11 which are periodically generated at a frequency below 20 Hz, the object will be affected in the same way as though it were exposed to a strong infrasound field. It has turned out that a frequency of 6-7 impacts per second (6-7 Hz) is suitable for causing dizziness and indisposition among the people which are hit by the vortex rings.

The combustion chamber 2 is suitably formed with an inside diameter of about 20 cm and an internal length of about 50 cm. The optimum diameter of the flange opening 10 depends on the diameter of the combustion chamber and the pressure and the length of the explosion. It has turned out that a flange opening 10 of a diameter which is about half as large as the inside diameter of the combustion cham- ber can be suitable. The higher the pressure of the explosion, the larger flange opening 10 is required to make possible the creation of a vortex ring 11.

To make possible the creation of a vortex ring 11 , it is furthermore important that the pressure wave 16 from the explosion in the combustion chamber 2 is stable, i.e. that it has a sharp front and a sharp end. In order to get as good a stability as possible of the pressure wave 16, the explosive gas mixture should be well collected in an area around the gap 15 of the igniter before the ignition. In order to facilitate this, the combustion chamber 2 can be provided with a semi-spherical wall 17 at its rear end 3. This wall 17 can be displaceably arranged inside the combustion chamber, as shown in figure 5. The adjustment of the position of the wall is done by means of a threaded rod 18, which is rotatably mounted in the wall 17 and which extends through a tapped hole 19 at a rear end wall 20 of the combustion chamber 2. In order to contribute further in keeping the explosive gas mixture collected in the area around of the gap 15 of the igniter, a flange 21 can be placed inside the combustion chamber 2 in front of the igniter 5. In order not to cause turbulence in the pressure wave, this flange 21 should be formed with an inclined leading edge 22. The flange 21 can, like the semi-spherical wall 17, be displaceably arranged inside the combustion chamber 2. The adjustment of the position of this rear flange 21 is done by means of two threaded rods 23a,23b, which are rotatably mounted in the flange 21 and which extend through tapped holes 24a,24b at the flange 9 arranged at the front end 4 of the combustion chamber.

By adjustment of the position of the wall and the rear flange, it is possible to vary the volume of the space within which the gas mixture is kept collected before the ignition, in order thereby to achieve optimum conditions adapted to the fuel being used.

With the embodiments described above, a device is obtained which can emit vortex rings with an effective range of about 20 m. Since the device is relatively small, it can easily be mounted for instance on a vehicle and be used against people who try to stop the vehicle from getting through.

Claims

Claims:

1. Device for affecting an object by means of pressure waves, comprising a cylindrical combustion chamber (2), with a closed rear end (3) and an open front end (4), and a device (7) for controlled injection of fuel and an igniter (5) arranged at the rear part of the combustion chamber (2), characterized in that a ring-shaped flange (9) is arranged at the front end (4) of the combustion chamber, which flange (9) has an internal diameter which is smaller than the inside diameter of the combustion chamber and which is adapted such that a vortex ring (11) is created when a pressure wave (16), generated when the igniter (5) ignites fuel injected into the combustion chamber (2), forces the gas enclosed in the combustion chamber (2) out through the opening (10) of the flange.

2. Device according to claim 1, characterized in that the igniter (5) comprises two electrodes (13a, 13b), which extend into the combustion chamber (2) and which are arranged such that there is a gap (15) between the two ends of the electrodes, which gap (15) is centrally situated in the combustion chamber (2).

3. Device according to claim 1or2, characterized in that a device (14b) for introduction of air is arranged at the rear part of the combustion chamber

(2).

4. Device according to claim 3, characterized in that the device for introduction of air comprises one or several nozzles (14b), which are connected to a source of compressed air, and an electrically controlled valve arranged in connection with the respective nozzle (14b) for regulating the introduction of air.

5. Device according to one of claim 1-4, characterized in that the device (7) for injection of fuel comprises one or several nozzles (14a), which are connected to a fuel source, and an electrically controlled valve arranged in connection with the respective nozzle (14a) for regulating the injection of fuel.

6. Device according to one of claim 1-5, characterized in that a second flange (21) is arranged inside the combustion chamber (2), between the igniter (5) and the flange (9) arranged at the front end (4) of the combustion chamber, which second flange (21) is intended to keep the explosive gas mixture, that is created when fuel is injected into the combustion chamber and is mixed with air, collected in an area around the igniter (5).

7. Device according to one of claim 1-6, characterized in that the combustion chamber (2) is provided with a semi-spherical wall (17) at its rear end

(3).

8. Method for affecting an object by means of pressure waves, where the pressure waves are generated by fuel being introduced to and ignited in a cylindrical combustion chamber (2), which has a closed rear end (3) and open front end (4), characterized in that a rapidly rotating vortex ring (11) is created when a pressure wave (16), generated at an ignition, forces the gas enclosed in the combustion chamber (2) out through the opening (10) of a ring-shaped flange (9), which has an internal diameter that is smaller than the inside diameter of the combustion chamber and which is arranged at the front end (4) of the combustion chamber, which vortex ring (11) moves forwards in the longitudinal direction of the combus- tion chamber and causes an impact on an object which is hit by it.

9. Method according to claim 8, characterized in that the introduction and injection of fuel is periodically repeated a number of times at a frequency below 20 Hz so that a series of vortex rings (11) is created, which when they hit an object give rise to effects corresponding to those caused by strong infrasound.

10. Method according to claim 8 or 9, characterized in that the ignition of the fuel is achieved by means of an electric spark occurring in a gap (15) situated in the centre of the combustion chamber, between the ends of two electrodes (13a, 13b) which extend into the combustion chamber (2), when the electrodes are charged with an electric current.