Ammunition and explosives – Igniting devices and systems
Patent
1994-05-24
2000-11-28
Jordan, Charles T.
Ammunition and explosives
Igniting devices and systems
F42B 310
Patent
active
06152039&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the initiation of propellants, especially for guns, rockets, gas generators and similar known applications.
2. Discussion of Prior Art
Present techniques for the initiation of propellants are not ideal in a number of respects. For example, large calibre guns may incorporate a charge of stick propellant, (ie. a collection of propellant sticks) which is initiated by a device known in the United Kingdom as a tube vent electric (TVE). In such a device a hot burning material is caused to deflagrate rapidly by the conversion of an electrical stimulus into hot particle output through holes in its body thereby initiating the surrounding propellant material. Internal ballistics and reproducibility of gun performance are affected. The TVE also occupies a significant fraction of the volume of the propellant charge. The initiatory material in the TVE is moisture-sensitive and is also sensitive to rough usage so that the propellant may or may not ignite in the manner predicted and even when it does ignite the burning process may be unpredictable.
Modern gun propellants may comprise compositions formulated to have low vulnerability to attack by bullets, fragments and the like. Such compositions are inherently more difficult to initiate and it may be difficult or impossible to initiate such compositions by conventional techniques.
In rocket motors the design of the propellant igniter presents problems. The igniter throws a rain of rapidly moving burning particles into the propellant charge. The energy of the igniter is often so high that the charge may be damaged, especially at low temperatures, and this can lead to unpredictable ballistics.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an apparatus for the initiation of a propellant comprising a combustion chamber, a charge of propellant in the chamber and means for igniting the propellant of the charge by microwave heating comprising a source of microwave radiation, a microwave transparent window in a wall of the said chamber and means for applying microwaves from the said source into the said chamber via the said window, the propellant charge, or one or more regions thereof, comprising or containing microwave sensitive material for absorbing microwave energy from said source whereby to heat and ignite the propellant, and wherein the said chamber is a resonant cavity for the microwaves.
The means for applying microwaves from the said source may be a conventional waveguide structure.
The propellant of the charge is preferably a solid propellant comprising a gun or rocket propellant, although it may also be a propellant for use in a gas generator, eg for use in a gas inflator or base drag reduction of a projectile.
The frequency of microwaves provided by the said source may conveniently be variable so that the frequency may be tuned to match the dimensions of the chamber.
The source may be any known source such as a klystron or a solid state oscillator such as a Gunn diode, avalanche diode or impatt diode.
The frequency of the microwaves coupled into the propellant charge is likely to be in the range 0.1 GHz to 100 GHz.
The required energy density of the microwaves coupled into the propellant charge depends on the microwave sensitive material to be energised. The energy density is likely to be at least 10.sup.8 watts per kg of material to be excited for a typical lossy dielectric used in conjunction with a typical, eg. double base, propellant material. The energy density may however be reduced if the microwave sensitive material is itself more easily ignitable than the propellant.
The propellant charge to be ignited may comprise material which itself is microwave sensitive. For example, propellants containing as major ingredients nitrocellulose and nitroglycerine have been found to show the required sensitivity.
Alternatively, or in addition, a microwave sensitive additive or dopant material may be added to the propellant composition for the purpose
REFERENCES:
patent: 3601054 (1971-08-01), Christianson
patent: 4446826 (1984-05-01), Kimura et al.
patent: 5088411 (1992-02-01), Kurokawa et al.
patent: 5146044 (1992-09-01), Kurokawa et al.
Microwave Resonant Absorption of Potential Exothermic Compounds, Final Report; Dr. F.J. Murray, General Dynamics Corp., Pomona, CA, Dec. 1989.
Electrothermal Thrusters Utilizing Electrodeless Discharges; Tahara et al, Osaka University; Extract from the 20th International Electric Propulsion Conference, p. 575-582, 1988.
Baker Francis Sidney
Lee Peter Raymond
Jordan Charles T.
Royal Ordnance Plc
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