WO2004024653A2 - Multi-stage gas generator and gas generants - Google Patents

Abstract

A gas generator is described that may have two or more compartments, each with a separate initiator. One compartment may discharge before another. Each compartment may have the same propellant. The propellants may have different geometries in each compartment, producing different rates of gas evolution from each compartment. The gas generator may produce a rapid initial inflation, followed by a more gradual inflation rate in subsequent stages. One propellant used may include ammonium nitrate as an oxidizer, a fuel such as CL-20, and a binder such as polycaprolactone. A second propellant may include approximately 70-95% energetic nitramine fuel, 5-25% energetic polymer binder, and 0.1-5% flash suppressant, respectively, by weight. An inflation rate of an airbag may be controlled by connecting a gas generator to the airbag, causing each of the chambers to discharge at a different, predetermined time, and causing the effluent of each chamber to flow into the airbag.

Description

MULTI-STAGE GAS GENERATORAND GAS GENERANTS

BACKGROUND OF THEINVENTION

This invention relates to a dual or multi-stage gas generator that utilizes an improved gas generant formulation or formulations. Gas generators, also known as inflators, have numerous commercial and military applications. For example, they may be used to deploy airbags used in automobiles, to inflate floatation devices, and may be used in oxygen generating devices. For further example, gas generators may be used to inflate airbags used in deploying and aiming submunitions.

Gas generators operate by burning a propellant contained therein extremely rapidly, usually in the millisecond range. Until now, gas generators have typically burned the propellant in airbags in one stage, causing, providing less than optimal control over the deployment.

The propellants used in airbags have generally contained sodium azide, which, upon ignition, yielded particulates, including hot metallic oxides, and corrosive products, thus requiring expensive filtering systems to be certain these products do not damage the munitions or related equipment. Alternative propellants have produced high temperature effluent and/or gases including various oxides of nitrogen (NO_x), which also have required systems to protect the equipment. Such airbag systems have also required various protective coatings, in order to prevent damage to the bags caused by the harmful by-products of combustion.

To date, uniform and reliable gas generation for the systems indicated above, has been difficult to achieve, both mechanically with respect to gas generation rate or slope, as well as chemically with respect to control of the solid particulates and effluent resulting from propellant combustion. To date, at least one or more of the components, e.g., the oxidizers, of the gas generants have been metal-based, leading to the formation of hot metallic solids or particulates as byproducts of combustion. Major airbag manufacturers continue to use sodium azide (NaN₃) as the main fuel constituent in their gas generant formulation and metallic oxides, e.g., copper oxide, iron oxide, molybdenum trioxide, as major oxidizer constituents in their formulations. Upon combustion, these gas generant formulations generate very hot copper-based, iron-based, or molybdenum-based solid byproducts, as well as NO, NO , SO₂, CO, and CO₂. Such byproducts many times can escape controls. Some of these combustion byproducts are extremely toxic to humans and may be of great concern even if such gas generant byproducts are produced in only small quantities.

Some airbag systems have been based on propellants aside from sodium azide, see, for example, U.S. Patent No. 5,482,579, where cellulose acetate, perchlorate and a metal oxide were used. However, these systems still generate hot metal particles or toxic or hot gases that require a filtration system to prevent harm to the airbags.

Other variations in airbags have been explored. For example, some use a mechanical means to control airflow in airbags. See, for example, U.S. Patent No. 6,050,601. Mechanical means are, however, relatively slow compared to the extremely fast inflation required in airbags. Others have used systems that rely on stored gas for inflation. See, for example, U.S. Patent No. 6,089,597. Because of the difficulty in maintaining stored gas for long periods of time, these systems have not been widely used.

U.S. Patent No. 5,876,062 relies on using a resistance wire to ignite the propellant. Vibration of the airbag system can cause the ignition wire to break, leading to malfunction of the system. Furthermore, a filtration system is also required. U.S. Patent No. 6,199,906 relies on electronic logic to determine the extent to which the airbag is deployed. However, the system still generates noxious effluent and attempts to eliminate them through certain gas ports.

Furthermore, the system recognizes that there may be accidental ignition of some portions of the system when exposed to heat or fire.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a gas generator having two or more compartments, each with a separate initiator, with one compartment discharging before another, i.e., the compartments discharge sequentially.

An objective of the present invention is to provide a gas generator with reduced weight, size and fewer geometric constraints from the design perspective. It is also an objective to eliminate the need for a filter system. It is also an objective to provide a gas-generating inflator, which eliminates or at least reduces the size of the internal structural members of the pressure vessel, i.e., combustion chamber. It is a further objective to provide a less costly gas generator, both in terms of fewer parts and lower process manufacturing operations.

One embodiment may include a gas generator including at least two chambers. Each chamber may be capable of discharging gas at a different time and different volumetric rate and each chamber may contain an initiator and the same propellant that is in the other chamber(s).

The gas generator may include a propellant that is composed of on a weight basis approximately (a) 84-95% of an oxidizer, (b) 3.4-13.4% of a fuel, and (c) 1.5-2.6% of a binder. The products of combustion of the propellant may be non-toxic gases. The propellant fuel may be selected from CL-20, RDX, HMX, GAP, NGU, TATB, LLM-105, EDNA, and mixtures thereof. The binder may be selected from PCL, PIB, GAP, polyvinylpyrrolidone, and mixtures thereof. The oxidizer may be ammonium nitrate. The propellant may include on a weight basis approximately 70-95% energetic nitramine fuel, 5- 25% energetic polymer binder and 0.1-5% flash suppressant.

A second embodiment may include a process for controlling the rate of inflation of an airbag. A gas generator having at least two chambers that are each capable of discharging gas at a different rate may be connected to the airbag. Each of the chambers may be caused to discharge gas or effluent at a different, predetermined time. The process may include causing the effluent of each of said chambers to flow into the airbag.

The gas generator may be positioned in a vehicle and may be activated in response a vehicle collision. The airbag may be used for ejecting one or more submunitions from a weapon and the gas generator may be activated in response to a trigger signal. The trajectory of a submunition may be controlled by deployment of the airbag.

A third embodiment may include a process of using a multi-stage gas generator, having on a weight basis approximately 70-95% energetic nitramine fuel, 5-25% energetic polymer binder and 0.1-5% flash suppressant,for propelling small, medium and large caliber ammunition from a weapon system. The gas generator may be inserted into a barrel of a weapon system and ammunition may be inserted. The gas generator may be activated and gas expelled from the gas generator may be used to propel the ammunition. A fourth embodiment may include an eco-friendly gas generant propellant. The eco-friendly gas generant propellant may be composed of (a) 84-95% of an oxidizer on a weight basis, (b) 3.4-13.4% of a fuel on a weight basis, and (c) 1.5-2.6% of a binder, on a weight basis. The products of combustion of the propellant may be non-toxic gases.

The eco-friendly gas generant propellant fuel may be selected from CL-20, RDX, HMX, GAP, NGU, TATB, LLM-105, EDNA, and mixtures thereof. The eco-friendly gas generant propellant binder may be selected from PCL, PIB, GAP, polyvinylpyrrolidone, and mixtures thereof. The eco-friendly gas generant propellant oxidizer may be ammonium nitrate.

In certain embodiments, the same propellant may be used in each compartment or chamber. The propellants may have different geometries in each compartment, which results in different rates of gas evolution from each compartment. A gas generator of the present invention may be designed to reach maximum inflation or full deployment in the same amount of time as the current, single-stage gas generators. However, compared to previously known gas generators, the generator of the present invention may have a more rapid initial inflation, with a more progressive propellant geometry, followed by a more gradual inflation rate in the subsequent stages. The sequential inflation rates may improve safety to vehicle occupants and/or provide improved final velocity control for the ejection of munitions and submunitions.

In certain embodiments, one propellant or gas generant used in a gas generator according to the present invention may include (1) ammonium nitrate as the oxidizer, which is non-toxic and non-corrosive, as opposed to existing airbag propellant formulations, (2) a fuel having a high energy density and high stability, such as CL-20, or other suitable fuels, the characteristics of which will be described below, and (3) a binder such as polycaprolactone (PCL), polyisobutylene (PIB), or glycidyl azide polymer (GAP). Fuels that may be used as alternatives to, or in combination with, CL-20 for the fuel of the present invention have comparable or greater values of the following physical characteristics: density, heat of formation, and heat of decomposition. Examples of such suitable fuels include, but are not limited to, tri-amino-trinitro-benzene (TATB) and 2,6-diamino-3,5-dinitropyrazine-l -oxide (LLM-105). In certain embodiments, a second propellant may include approximately 70-95% energetic nitramine fuel, 5-25% energetic polymer binder and 0.1-5% flash suppressant.

In certain embodiments, the generation of hot metal particles, e.g., cupric oxide (CuO), may be avoided and expensive filtering systems, as used in current airbag systems, may not be needed. The use of coated airbags may be avoided.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a two-stage gas generator. The parts of one embodiment are identified in FIG. 1A and typical dimensions are shown in FIG. IB. For a smaller design, the parts are shown in FIG. 1C and the dimensions in FIG. ID.

FIG. 2 shows the deployment of a two-stage gas generator compared to that of a single-stage gas generator.

FIG. 3 shows a typical single-stage gas generator of the prior art.

FIG. 4 shows an airbag deploying several submunitions S in a weapon system including gas generator 40 in a spine tube 41.

FIG. 5, including FIGS. 5A-C, shows an airbag deploying a parachute to decelerate a submunition and to control its speed and trajectory.

FIG. 6 shows propellant grain configurations: FIG. 6 A - neutral burning, FIG. 6B - progressive burning, FIG. 6C - uniform burning.

FIG. 7 shows a logarithmic plot of burning rate vs. pressure at various temperatures.

FIG. 8 shows a representative ignition train.

FIG. 9 shows various ignition systems in FIGS. 9 A-F.

FIG. 10 shows an electrically operated initiator. FIG. 11 shows ignition initiation for different configurations cut into the grain face of the propellants.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a new type of gas generator. This new type of gas generator may be used in various military and commercial applications, such as for example, in airbags used for deploying submunitions, aiming warheads, automobile airbag systems, flotation devices, producing oxygen in oxygen generating devices and other applications. These gas generators have at least two chambers, which condition allows the respective gas volumes to be produced under different conditions, i.e., the profile of pressure vs. time for the gas volume produced by each chamber can be different.

In this way, by designing multiple chambers differently, the gas generator can be adapted to the need of the particular application. For example, in order to improve control of the trajectory, a dual-chamber gas generator can be used, with one chamber being designed to provide an initial very quick, partial deployment of the airbag, when compared to previously known gas generators. The second chamber may be designed to provide a second, much slower expansion of the airbag, when compared to previously known gas generators.

In certain embodiment, a two-stage gas generator may be used in an automobile airbag system that is designed to activate upon rapid deceleration of the vehicle, such as that which occurs upon impact between an automobile and an object. An inertial switch may trigger the gas generator or inflator to deploy an airbag in the system.

In certain embodiments, the sequential release of gas from each chamber of the gas generator, and subsequent gradual inflation of the airbag, may provide, for example, improved control of the trajectory of a munition or submunition during its horizontal and transitional paths and during its downward free fall.

A dual stage, or two-stage, generator according to one embodiment of the present invention is shown in FIG. 1. A gas generator 10A is shown in FIG. 1 A. In this design two combustion chambers 1 exist within the housing enclosure 2, and are separated by a 3.00-mm thick wall 3. Each combustion chamber contains a propellant 4, with both propellants having the same formulations but different geometry. Propellant geometry is selected to produce the desired first-stage and second-stage performance.

Two igniters may be present, one for each combustion chamber. The two igniters may be designed to function with a 5-20 ms. difference between the progressive, or quicker or high R_Q, burning propellant and the neutral, or slower or low R_Q, burning propellant. The igniters may include an ignition enhancer 5, which surrounds the initiator 6 and is designed to boost the power of a propellant upon ignition. Rupture disks 7 allow the released gas to be funneled into the gas ports 8, where the gas is released. Certain embodiments, e.g., a miniature design such as that used in side airbags, may include a slag filter 9. The slag filter 9 may be used advantageously as a heat sink, and not necessarily as a particulate filter. The hot gases produced by the gas generator pass through the slag filter and lose heat to the slag filter by conductive heat transfer.

In exemplary embodiments, the slag filter may be coated with a sodium aluminosilicate powder, also known as zeolite, e.g., Zeolite CVB-100. This is the case when the gas generant includes CL-20, GAP, and KNO_3. In such embodiments, the zeolite coating acts to reduce the gas temperature, thereby reducing the likelihood of burn damage to equipment, as well as premature detonation of the explosive. The zeolite coating can also trap harmful gases such as NO_x and CO. In other words, the zeolites may act as molecular traps for larger-size diatomic and polyatomic gases. The percent of zeolites used in the slag filter may range from between 1 and 10%, more preferably from between 3 and 1%, and most preferably at 5%, by weight of the filter. Alternatively, suitable high-surface-area materials may be used to produce the same result.

A gas generator for a typical airbag can be quite small. The overall dimensions for one airbag can be approximately 85 mm x 44 mm. The dimensions of such a typical gas generator 10B are shown in FIG. IB.

For airbags requiring more output, e.g., for larger munitions, more propellant weight is needed and a larger gas generator may be used. The amount of propellant can be calculated and the size gas generator adjusted accordingly. Referring now to FIGS. 1C and ID, a smaller-size or miniature size dual-stage gas generator design is shown. Gas generators IOC and 10D, respectively, are principally the same as those shown in FIGS. 1 A and IB, but they are smaller in size, with less mass of the propellant. The partition between the two combustion chambers is aimed at eliminating unnecessary safety concerns, namely preventing propagation to the adjacent combustor port. If one propellant is deployed, the heat produced by the reaction may heat up the propellant in the adjacent chamber, and, upon deploying the second, a severe high pressure may cause the airbag to malfunction.

The gas generant in each chamber of the dual-chamber gas generator is generally the same, formulation-wise, with each gas generant having a different geometry. Essentially, the gas generants may have a cylindrical, hexagonal, or rosette (the most efficient) geometry, with 37, 19, 7, or 1, perforations, or none at all. Depending on the desired application, the second gas generant in the second chamber, as well as any subsequent gas generants in additional chambers, may be less progressive with fewer perforations, neutral, or regressive as compared to the first gas generant. In a preferred two-chamber airbag, the ratio of gas generation in the first chamber to that in the second chamber is greater than one. For example, for the gas produced by the first chamber, the change of pressure as a function of time may be two or more times greater than the change of pressure as a function of time for the gas produced from the second chamber.

The ability to vary both the time of ignition of each chamber along with varying the perforation geometry yields a high degree of control over the inflation characteristics of the airbag. That is, the change of pressure with time can be controlled very well. For example, see FIG. 2, where a two-chamber gas generator is used. At the initial part of the inflation, change of pressure vs. time is much steeper than the control, i.e., single stage gas generator, while the rate of change in the second stage is more gradual than the control. Using an airbag having the two-stage gas generator has a much-improved control of inflation rate vs. a one- stage gas generator.

Solid propellants are often divided into two classes, gas generator and rocket motor propellants. This division is based primarily on their energy content. Gas generator propellants generally contain ammonium nitrate as an oxidizing agent and have only a small amount or no metallic additives. Double-base compositions and those containing nitramines, e.g., RDX, HMX, EDNA, NGU, etc., ammonium perchlorate, etc., as the oxidizer may sometimes be included as a gas generator, as in the case of N-5, the gas generator of the U.S. Army's Wide Area Munition (WAM) reserve battery. Ammonium perchlorate is one of the popular oxidizers for rocket motor propellants; metals such as aluminum are often added to increase the energy content. As the energy content of the propellant increases so does the flame or combustion temperature. Flame temperatures of most gas generator propellants range from 1600° to 3000° F (870° to 1650° C), while rocket propellants generally have flame temperatures that range from 3000° to 6000° F (1650° to 3315° C).

In certain embodiments, solid propellants are used that have a flame temperature between 1600° and 3000° F (870° to 1650° C). The fuel used may be synthetic rubber, or a plastic selected on the basis of chemical structure, mechanical properties, and processability. Some of the materials commonly used are butadiene-acrylic acid, butadiene/methylvinylpyridine, cellulose acetate, nitrocellulose, polyisoprene, and polyvinylchloride. The oxidizing agent most commonly used in almost all gas generator propellants is ammonium nitrate. All composite propellants contain additives in one form or another to achieve the desired burning rate, temperature sensitivity, flame temperature, gas output, and physical properties.

Multibase solid propellants are also used as gas generants. As a matter of fact, this is the type of solid propellant formulation used in the WAM battery gas generator. These, as previously discussed, generally have a higher flame temperature, between 2300° and 3500° F (between 1260° and 1926° C), and have more solid particles in the exhaust. These homogeneous formulations are basically of unstable chemical compounds such as nitrocellulose and nitroglycerin, which are capable of combustion in the absence of all other materials, i.e., they are extremely easy-to-ignite propellants. The most common propellant of this type, sometime referred to as "double-base" propellant, is largely a colloid of nitroglycerin and nitrocellulose.

Mixing of double-base propellant ingredients may be carried out, for example as in the case of N-5 propellant, by charging raw ingredients to a mixer in a particular sequence to achieve desired properties of the finished propellant. Mixers in common usage are horizontal and vertical types, i.e., the axis of rotation of the mixing blades is either vertical or horizontal. The action of the blades may thoroughly disperse, mix and incorporate the various ingredients into one homogeneous blend. This mixing may be closely controlled as to rate, or speed of blade rotation, and time. Over-mixing or under-mixing can produce a propellant that does not meet ballistic or physical property requirements.

Solid propellant grains may be formed by extrusion, as in the case of N-5 propellant, by compression molding, or by casting. Since most propellants are limited by their chemistry to one or two of these methods and since some grain geometries are more suited to one processing method than the other, it is seldom possible to form a particular grain by all the available methods. Therefore, it is necessary to determine whether the specific formulation and shape desired are suited to the processing techniques available. Grains can be machined by equipment found in most well equipped machine shops.

The energy release rate of a solid propellant gas generator depends greatly on the grain configuration. The possible geometric configurations are virtually limitless. Most applications require a relatively constant energy for a time of 20 to greater than 100 seconds, or a short duration of 1 to 10 seconds at a relatively high-energy release rate. Typical propellant grain configurations are shown in FIG. 6.

The end-burning rate or cigarette-burning rate, for example as shown in FIG. 6A, is restricted on the diameter and one end, leaving the other end exposed and free to burn uniformly, i.e., undergo neutral burning, for the entire length. This configuration is used for the longer duration, low energy release rate. The configuration shown in FIG. 6B has restrictor, which is also shown as 114 in FIG. 11, or deterrent applied to all surface of the grain except the inner diameter. When this exposed propellant is ignited, it will burn outwardly, exposing more and more propellant as the flame front progresses. This configuration will produce a progressive energy release rate. The grain configuration shown in FIG. 6C has the inner and outer diameter unrestricted. With both the inner and outer diameter ignited, the energy release will be of uniform rate; however, the time of burning will be considerably shorter than with the end burner shown in FIG. 6A. Many other configurations and special geometries are used to obtain the desired energy release rate. Commonly used geometries may include 7 and 19 perforations, cylindrical granules, which are progressive, and multi-perforated rosette type configurations, which have high efficiency and energy release rate.

The energy release rate of a propellant grain may reference the start of the ignition cycle to the end [d (dp/dt)/dtj. This rate may also be referred to as the relative quickness (R_q) or vivacity. Relative quickness is controlled by propellant geometry, i.e., grain diameter, perforation diameter, web length and the number of perforations. Such propellants are referred to as quick propellants and generate pressures in a closed chamber in fractions of a millisecond. Quick propellants almost always require deterrents, or inert material, to slow their burning time to an acceptable safe rate. Such deterrents are applied to the surface of the propellant in one of many coating techniques.

Examples of deterrent coatings that may be used include, but are not limited to, polyester plasticizer (Paraplex) (Hercote), diethylene glycol dimethacrylate (DEGDMA) and dibutylphathalate (DBP). The first two deterrent coatings have proven very effective in reducing the rate of energy release upon ignition of propellant grains. DBP may be less- preferred, however, as it appears to migrate over extended periods of time, in particular at temperatures above 140° F (60° C).

When propellants are deterrent-coated, the coating normally impregnates the grain throughout, but remains on the surface in relatively higher concentration. This may result in a burning slow-down, i.e., a pressure reduction/control, in the initial stage of the ballistic cycle. In the case of DBP, the coating, due to its low molecular weight, migrates to the center of the grain until equilibrium is attained, when equal distribution of the coating is attained throughout the grain. As a result, upon ignition of the grain, the energy release rate is relatively higher than expected leading to LAT failures or higher sigma.

Propellant burning rate is the rate at which the combustion zone progresses into a mass of propellant, and may be referred to as the mass burning rate. Burning rate is a function of the particular propellant formulation, the chamber pressure, and the propellant temperature. Normally, burning rate, at a specific propellant temperature, may be expressed as:

r = aPⁿ or r = a (p/1000)ⁿ

If burning rate versus pressure is plotted on a logarithmic paper, the curve is a straight line, with the slope of the line as "n" and with "a" as the burning rate intercept at 1 psia or 1000 psia. Most solid propellants follow this straight-line function. However, with some propellants the pressure exponent (n) is not a constant, that is, it may vary at high or low pressures. For a few propellants, the pressure exponent remains a constant over a limited range of pressures. With the latter types of propellants, burning rate data may be derived from empirical data or burning rate plots. Propellant burning rate is also dependent on the ambient propellant temperature. The temperature sensitivity is usually not a constant. It varies with ambient temperature, decreasing at high and low temperatures, hence it is usually given for a specific temperature range; normally 160° to -65° F (71 to -53°C). Temperature sensitivity at constant pressure, σ_p, is given by:

σ_p (%/F) = { [ln(r₂/r ]/(T₂-T } X 100 P_c = constant in gas generator

Temperature sensitivity of pressure system with a constant burning area-to-nozzle area ratio is given as:

π_k (%/F) = { |Tn(P_c3 P_ci)]/(T₂-Tι)} X 100 K„ = constant in gas generator

On a logarithmic plot, this is represented by the intercepts of the burning rate-vs.-pressure lines at various temperatures with a 45° slope line, as shown in FIG. 7.

The relationship between σ_p and π_k is:

π_k= σ_{p /}(l - n)

Because of the many different applications for gas generators, the requirements placed on the ignition system for specific units vary widely. Consequently, every phase of the gas generator operation, from the method of initiation to the effects of the exhaust gas products, should be thoroughly considered. For example, in the ignition secondary charge, rapid, reliable, reproducible ignition over the desired temperature is a goal for any solid propellant gas generator. Some of the ignition parameters most frequently specified by the user are the time required for ignition, i.e., the time interval between signal to start burning and achievement of steady burning of the grain, maximum ignition pressure, igniter combustion products, and the range of temperatures and pressures at which reliable ignition should take place. It may be desirable for ignition systems for solid propellant gas generators to produce rapid, reliable ignition of the propellant grain over a wide temperature range. These systems are often quite complex and are made up of a number of components as shown in FIG. 8, which shows an initiator 80, a secondary charge 81 , and an initial burning surface 82.

An ignition system that may be used for the present invention may include an electrically actuated initiator, a pyrotechnic or secondary charge, and the propellant grain, as will be described below. The initiator ignites the secondary charge, which ignites the propellant grain surface. The secondary charge should provide energy over an adequate time to complete ignition of the grain surface and pressurize the gas generator free volume. The word "booster" is frequently used in identifying the sustaining charge of an ignition system.

Energy output of the initiator is small when compared to the total energy required for grain ignition, as its function is only to ignite an easily ignitable pyrotechnic material in close proximity. Some designs require additional energy during the initial portion of firing to compensate for heat losses into the inert gas generator components; for this, the grain initial burning surface is contoured, through grooves, slots or holes, to provide additional burning surface. This contouring soon burns out leaving the desired burning surface.

In designing an ignition system to meet specified requirements, e.g., for use within embodiments of the present invention, certain parameters may be fixed, or they may be varied, e.g., within narrow limits. Fixed parameters relate to the initiating mechanism for the igniter, type and configuration of the propellant, chamber design, and nozzle or orifice size. Igniter performance, which may be varied to comply with the end-item requirements under the conditions imposed by other design features, may be affected by factors including the following:

Choice of primary initiator; Type of ignition train or secondary charge; Composition of the ignition materials;

Density and shape of the secondary ignition charge, e.g., compacted, loose, etc.; and Igniter hardware design, including electrical connections, e.g., pigtails, AN connector, etc. For reliable ignition, most gas generator propellants require steady input of energy; first to decompose the binder and oxidizer, and then to allow the combustion process to reach equilibrium condition. Igniters based on this principle are referred to as " sustainer" igniters. In summary, ignition system functions or steps can be summarized as follows:

Provide thermal energy a rate and quantity sufficient to ignite the propellant grain;

Pressurize generator free volume; and

Furnish gas and/or heat to supplement grain output until thermal equilibrium is attained.

Step 3 is a regressive requirement since thermal equilibrium is approached asymptotically. Proper ignition design should, therefore, include the following:

A fast-burning charge designed to rapidly pressurize the case and burn out on pressurization; and A sustainer that has an energy output that approximates a right triangle as a function of time.

It is desirable to obtain maximum energy output to pressurize the case and start the ignition process. The sustainer is initiated by the pressurization charge and regresses from a maximum initial output to zero at the point at which thermal equilibrium is attained. This ignition system model serves as the basis for design of ignition systems having "smooth" pressure-time characteristics: i.e., rapid pressurization to operating pressure, with no significant peaks, followed by neutral pressure-time curve throughout burning. Empirical equations have been developed to estimate the igniter energy requirement. Final tailoring of the igniter may be conducted through ballistic testing of the gas generator system.

The techniques used to provide the model ignition requirements vary widely. Some typical systems are depicted in FIG. 9. However, most ignition systems consist of the following components: initiator, 91; primer, 92; booster, 93; and sustainer, 94, where the booster and sustainer form the secondary charge. As shown in FIG. 9C and FIG. 9E, respectively, type "C" and type "E" ignition systems may be used in certain embodiments. Other ignition systems may also be used.

With reference to FIG. 10, initiation devices may be divided into two main categories, electrically operated or mechanically operated. Electrically operated initiators 100 (as shown in FIG. 10) are either hot wire- or exploding bridge-wire-initiated. Mechanically operated initiators are actuated by impact or shock. Electrically operated initiators may be used in preferred embodiments.

A hot wire initiator may have a resistance wire or element mounted between two electrodes 102, 103. This element may be coated with a low ignition temperature pyrotechnic bead. Electric current flowing through the bridge- wire 101 or element raises the temperature of the pyrotechnic to above its auto-ignition temperature, initiating the pyrotechnic and the remainder of the pyrotechnic train. The resistance of the wire and the ability of the initiator elements to conduct heat away from the pyrotechnic may determine the no-fire and all-fire characteristics of the initiator. High current initiators, e.g., 1 ampere/1 watt to 5 ampere/5 watt, have large heat sinks or heat dissipation ability.

Exploding bridge- wire initiators are similar to the hot wire type except that a high-energy electric pulse applied across the bridge- wire 101 causes it to vaporize, thereby converting electrical energy into thermal energy and igniting the adjacent pyrotechnic material. A gap is often used in the initiator circuitry to provide an open circuit to direct currents; but for a high - voltage pulse this gap is bridged and the resistance wire is exploded.

FIG. 11 shows the type of saddle that might be expected with various configurations. It shows that, by the proper use of either or both systems, the desired ignition pressure-time curve may be obtained. To provide a smooth transition between the ignition and propellant combustion equilibrium conditions, ignition sustainers are often used. One type of ignition sustainer may be a small pellet and/or a disc 111 of energetic propellant bonded to the surface of the grain 113. Grooves 112 cut in the grain face provide increased burning surface and aid in obtaining rapid ignition. The secondary charge, if properly designed, may prevent a "pressure saddle" or momentary lowering of the pressure because of heat losses to the surrounding metal components.

Selection of an initiator may depend on the means available for providing heat energy to the primary ignition material. An electrical current may be applied through a low-resistance, e.g., 0.02 to 5.0 ohms, bridge-wire, imbedded in a heat-sensitive pyrotechnic composition. A rule of thumb is that the lower the energy of the solid propellant, the greater the ignition system output required. Physical parameters that influence the design of the ignition charge system are free volume, grain configuration, and propellant burning surface. Rapid ignition is assisted greatly by pressurization, but caution should be taken to prevent pressure overshoot during the ignition phase. When determining the requirements for a gas generator system, careful consideration should be given to the ignition system before fixing any physical configuration.

Operation of one embodiment will now be described. Upon receipt of the signal to the initiator(s), the more progressive gas generant undergoes rapid ignition and generates sufficient pressure to inflate the airbag to 35-85% of its full capacity, preferably 45% to 85% of its capacity, and most preferably 65%-85% of its full capacity. The second gas generant, in the second chamber, is initiated at some given time t=45%-95% of t_pmax(f,rst gas generator). That is, the gas generant in the second chamber may be initiated when 45-95% of the gas has been generated from the first generator. Preferably, the gas generant in the second chamber may be initiated when 65%-95% of the gas has been generated from the first generator. In preferred embodiments of the present invention, the gas generant in the second chamber may be initiated when 90%-95% of the gas has been generated from the first generator.

The gas generant in the second chamber provides the remaining inflation of the airbag to achieve an overall internal gas pressure equal to the pressure rated for that airbag for that specific subsystem. That is, when the gas has been completely generated from both chambers of the novel system, the final gas pressure in the airbag is equal to that from the current, one- stage, gas generators. The rate of gas generation in the proposed art is controlled by means of providing propellants that generate different rate of gas release. By providing different rates of gas release, the pressure versus time curve would have two slopes for the two-stage system. One slope, e.g., one corresponding to the first gas generant in the first chamber, could have a very steep slope [(dp)ι/)dt)ι], while the second slope for the second gas generant could have a less steep slope [(dp)₂/(dt)₂. The effective time to maximum volume, which corresponds to the full deployment of the airbag, would still be the same, but would be controlled in a manner that would prevent a powerful shock to the airbag.

In the commercial industry or commercial applications, this performance is advantageous because it may prevent severe accidental mishaps and possible fatalities, which may occur when an airbag deploys in a vehicle moving at speeds over 100 mph (165 km per hour) or deploys into children, light-weight passengers, or passengers who are smoking pipes. In military applications, this performance is advantageous, as it provides improved control over the trajectory and prevents mishaps resulting from radical changes in trajectory that result from currently used airbag systems.

Embodiments of the present invention may have gas generator systems with even more than two chambers to allow even better control of the pressure vs. time curve, thus enabling the designer to match nearly any pressure vs. time profile.

Considerations in designing an inflator or gas generator for a passive airbag restraint system include the toxicity and noxiousness of the gas that fills the airbag. The inflator for an airbag may exhaust or filter gas and other materials, which might damage parts of the airbag. If the gas-generating composition is highly toxic or unstable, special handling may be required during the manufacturing process and may create disposal problems at the end of the useful life of the device, if any part of the munition and/or submunition(s) system survives.

For example, raw sodium azide, used as the gas-generating composition in most gas generators (for airbag applications), has a relatively high toxicity, which creates handling problems during the manufacturing process. Furthermore, if military personnel or civilians are exposed to remaining portions of the device, toxicity or environmental pollution concerns may need to be considered.

Currently used airbags are typically coated to prevent damage to the bags. Packaging restrictions add a further design consideration in the development of passive airbag inflators. For example, weight and size are primary factors in determining the suitability of vehicle inflator designs.

In embodiments of the novel gas generator disclosed herein, the need for complex, expensive filter systems (to remove hot, solid byproducts) is eliminated. (Filters are required in the current, one-stage gas generators. See part 11 in FIG. 3.) Elimination of the complex, expensive filter system means at least a 4% reduction in the cost of the gas generator.

Several propellants that are described herein and that may be used in new gas generators according to the present invention are believed to be novel. One comprises an oxidizer, a fuel, and a binder that is used to hold the components together. An embodiment of a propellant, described herein, has outstanding performance, is more environmentally acceptable than currently used propellants, and does not require the filtration systems currently needed in gas generators.

The oxidizer is preferably ammonium nitrate, which may constitute approximately 89.5 ± 5.5 % of the propellant. The oxidizer should be phase-stabilized to prevent melting and recrystallization to different particle size. An example of a suitable phase stabilizer is potassium nitrate (KNO₃), which may be present at a concentration of 0.5% to 7% and which may also prevent flash generation; the preferable concentration of the potassium nitrate is 0.5%) to 1%. This nitrogen-rich oxidizer, when stabilized is insensitive to impact, shock and electrostatic discharge, which makes it safe to handle, to manufacture, and to package. The phase-stabilized ammonium nitrate prevents phase transition of the oxidizer during thermal cycling.

The fuel may constitute approximately 8.4 ± 5.0 % of the propellant. Suitable fuels include nearly all nitramines, including CL-20 (C₁₀H₂ N₁₂O₁ ) (Thiokol Corporation), RDX (C₃H₆N₆O₆), HMX (C₄H₈N₈O₈), GAP(C₃H₅N₃O)„ (glycidyl azide polymer, or polycyclidyle azide) (3M Corporation, Minnesota), EDNA (ethylene dinitramine), TATB, LLM-105 and mixtures thereof. The preferred fuel is CL-20.

The binder may constitute approximately 2.1 ± 0.5% of the propellant and acts (1) as a binder to hold components together and (2) to prevent fracture of crystals, which would result in gas generating too fast. Suitable binders include polycaprolactone (PCL), polyisobutylene (PIB), polyvinylpyrrolidone and mixtures thereof.

GAP can be used as a combined fuel and binder. However, its combustion byproducts are toxic and increased amounts of ammonium nitrate are needed to overcome this negative. These higher concentrations of ammonium nitrate make the formulation difficult to process and to ignite.

In another embodiment, a gas generant may include the following: approximately 70-95% of CL-20 energetic nitramine fuel; 5-25% of energetic polyglacidyl azide (e.g., glacidyl azide polymer or GAP) or energetic polymer binder, e.g., polyisobutylene (Vistanex polymer) or PIB; and 0.1-5.0% of a flash suppressant such as potassium nitrate. The gas generant may be used in a two-stage gas generator and may be particularly useful for propulsion systems of small, medium and large caliber ammunition.

Other ingredients may optionally be added to the formulation. These may include (1) materials to control stability, such as for example ethyl centralite, Akardite I, Akardite II, diphenyl amine, or 2-nitrodiphenyl amine, which may be used at about 0.1-1.0%; (2) materials to control ballistic spikes and high initial pressure rise, a coating material, such as for example ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, allyl methacrylate or Hercote polyester, which may be used at about 0.1 -3.0%; and (3) materials to increase gravimetric density and dissipate static, such as for example graphite, which may be used at about 0.05-1.0%.

The propellant formulation may be processed either as a wet or dry mixture and pressed into tablets, disks or other shapes or extruded into granules. Commonly used blending techniques, such as those discussed in M.E. Fayed & L. Otten, Handbook of Powder Science and Technology (1984), Emil R. Riegel, Chemical Process Machinery (2^nd Ed. 1960, and Wolfgang Pietsch, Size Enlargement by Agglomeration Ch. 4 (1991), can be used.

The propellant used in the different chambers may generally have the same chemical composition, but they often differ in geometry, which impacts the rate of burning of the propellant in each chamber. For example, a propellant with more perforations has more surface exposure, which results in faster burning.

The density of the propellant is also an important indicator of its suitability. The preferred density should be approximately 92% or greater than the theoretical density. If the density is too low, not as much propellant can be fit into the chambers. Second, if the density is low, the propellant has a greater likelihood that it will fracture, leading to a different geometry of propellant, which will, as discussed above, have an effect on the burn rate.

The combustion of the propellant is safe, with the flame temperature of the gaseous products of reaction being less than 120° F (48° C). The products of combustion are generally limited to non-hazardous gases, namely water vapor, nitrogen, and carbon dioxide (CO ). These products are not hazardous to the environment. In addition, they are not corrosive, which means that uncoated airbags can be used in the system.

The amount of propellant in the novel gas generator is much less than is needed in currently used generators. Typically 70-100 gm of propellant is used in the prior art, while 5-8 gm is needed for the novel generator used for deploying submunitions.

To evaluate the performance of the gas generator, it is possible to use a ballistic tank test. The tank should have a capacity at least as large as the airbag for which the gas generator is used. Any commonly used ballistic test procedures can be used to evaluate the performance of the gas generator.

A variety of design considerations may be taken into account in developing an airbag system. First, the inflator should be capable of producing and/or releasing a sufficient quantity of gas to the airbag within the time limitation required of the air bag systems. Given the time limitation involved in military airbag systems, the airbag should deploy in roughly about 5- 100 milliseconds, depending upon the size of the airbag. Inflators should generally be capable of filling an air bag in these time frames with 15 to 200 liters, depending on the intended application.

In its operation, the gas generator receives a signal from an exterior or interior source, and then sends this signal to each initiator. The timing of the inflation of the airbag can be triggered by either a trigger signal transmitted to the gas generator, a sensor, such as an infrared (IR) sensor in the submunition that detects targets that match a defined set of IR requirements, a detector such as a direction sensor determining the point in the trajectory, a timer, data programmed into a computer incorporated in the weapon, or other techniques. The initiators function sequentially, with a delay, which may be on the order of millisecond(s), between the ignition or activation of each initiator.

The following examples are intended to further illustrate, not limit, the invention disclosed herein.

Example 1 : A two-stage gas generator A two-stage gas generator is shown in FIG. 1. FIG. 1A shows the parts of the generator, while FIG. IB shows representative dimensions. The total weight of propellant in this system is approximately 5 to 10 gm. A smaller design is shown in Fig. 1C, with corresponding, representative dimension being shown in Fig. ID. Embodiments shown in FIG. 1 may be used, for example, in airbag systems for deploying submunitions or in airbag restraint systems in automobiles.

Example 2: Performance data

The performance of an embodiment of one propellant according to the present invention comprising 87% CL-20, 12% polyglycidyl azide and 1% potassium nitrate (Table 1A), compared to a previously used propellant (Tables lB),is shown as evaluated by a thermochemical simulation program written in FORTRAN. The program shows the theoretical, thermochemical performance of the gas generant. The output shown lists, among other things, the expected theoretical density, the reaction temperature inside the chamber, the ratio of specific heats (shown as gamma), and the energy or impetus. It also lists the expected byproducts of combustion in moles, wt%, mole%, and volume%. The output values shown are based on 100 grams of propellant.

Example 3: Submunition deployment A munition system is assembled by surrounding a rocket with submunitions. An airbag may be inserted between the rocket and the submunitions. The system also includes a gas generator having at least two chambers. When the system is in the vicinity of the intended target(s), the gas generator becomes operational and inflates the airbag, thus deploying the submunitions. By having two or more chambers, the gas generator can inflate the airbag in a more predictable fashion than the one-chamber gas generator. This means that the submunitions will be deployed closer to the intended target.

Example 4: Using an airbag to control the trajectory of a submunition. Once the submunition of Example 3 is beginning its downward trajectory, an airbag connected to a parachute P on the submunition is inflated in order to deploy the parachute P. See FIG. 5A. This gas generator 50A has two or more chambers, and there is better control over the deployment of the parachute and, therefore, the trajectory of the submunition vs. earlier systems containing only one chamber in the gas generator. The parachute reduces the speed of the submunition and also balances it during its horizontal, transitional path and its downward freefall.

An alternative to the parachute is the use of the airbag itself to provide buoyancy to the submunition. See FIG. 5B. The airbag is attached to the submunition and, when inflated, acts like a balloon-type object. This airbag is inflated by the gas from the gas generator 5 OB and, rather than providing drag, which is provided by the parachute, the airbag provides buoyancy, which also impacts the trajectory of the submunition. See FIG. 5B, where the parachute P is replaced with an airbag A, shown as a balloon-like object, which is inflated by the gas generator 5 OB.

Example 5: Use of gas generator for propelling ammunition

A gas generator can be used to propel ammunition. Instead of gunpowder being used in ammunition casing, a gas generator can be used. The gas generator can be enclosed in a separate component, e.g., plastic or ceramic, placed in the muzzle before the ammunition. Alternatively, the gas generator can be loaded into the barrel 59 of the weapon, with no need for a casing, as shown in FIG. 5C, with gas generator 50C and projectile 58.

The amount of gas generant needed to propel munitions can be calculated using well-known formulas, which relate the amount of gas generant to the pressure generated and to the velocity of the munition. For example:

55-65 kpsi (379-448 Mpa) needed to propel any medium caliper round at a muzzle velocity equal to or 15% faster than current specifications.

55-65 kpsi (379-448 Mpa) is needed to propel a M919 medium caliper round at a muzzle velocity of 2000 m/s. The M919 cartridge is a 25mm, armor piercing, fin stabilized, discarding sabot, with tracer.

65-75 kpsi (448-517 Mpa) needed to propel any large caliper round at a muzzle velocity equal to or 30% faster than current specifications.

Example 6: Ignition system

Because of the need to ignite at a specific time the propellant in each chamber of the gas generator, it is critical that the ignition in one chamber does not accidentally ignite the propellant in another chamber. Furthermore, it is important that the chambers ignite at a specific time, since the gas generation rate from each chamber controls the inflation rate of the airbag.

For example, the first chamber of a typical two-chamber gas generator might generate 8-20% of the total amount of gas needed to inflate the airbag within, e.g., 10 milliseconds. The preferred fraction of the gas from the first chamber is 10-15%), and the most preferred amount is 15% of the total amount of gas needed.

The ignition system for the second chamber should ignite approximately at the end of the gas generation from the first chamber, and the rate of inflation from that chamber should control the final activity for which the airbag is used. For example, a rate combined burn time for both the first and second stage of, preferably, between 60 and 90 milliseconds is needed to eject the submunitions from a munition or to deploy a parachute to control the trajectory of a submunition.

Those familiar with this technology area will recognize that there are other variations of the invention that are consistent with the invention disclosed herein. While certain dimensions have been provided regarding exemplary embodiments, such embodiments or dimensions do not limit the scope of the present invention. The present invention may include any embodiments of any size that encompass the aspects described herein or equivalents thereto.

The following tables are included:

TABLE 1A

THERMOCHEMICAL CODE CALCULATION

NON-IDEAL EQUATION OF STATE HEP-100 PROPULSIONS-EXPLOSIVES

POLYGLYCIDYL AZIDE 12.000 POTASSIUM NITRATE 1.000 CL-20 87.000

DATE SETUP 5

OHFP= 21349.29 THEO DENSITY^ 1.9101 GM/CC .069008 LBM/LN**3 E= 0 (Table 1A, Continued)

EFP= 23119.04 OXYGEN BALANCE^ -14.14 TO CO2, 11.02 TO CO OMOX=

1.6337 C 1.5723 H.62178 X.0098905 N 2.7755 02.5767

S .1000E-6

OPOINT ON HUGONIOT - - SHOCK NELOCITY= 2362.98 M SEC,

PARTICLE N= 1088.8

P= 100000. PSI P= 6804.60 ATM T=4833.3 ΝG=3.45327 NT= 3.45327 S=196.755

CPG= 35.316 CPT= 35.316 FIXED CP GAMMA= 1.241 DHDT= 68.4529 GAMMA=

1.18404

WT PCT COND= .00000 MW GAS=28.959 H= 68673 CON= .00000 NSP=2.01273

SONIC NEO=1251.54 RHO= 49683756 PO=1.9990 NO=3.73251 IMPETUS=464268

E= 35505.381 DEDT=54.0953

0PRODUCT MW MOLES WT. PCT. MOLE PCT. VOLUME PCT

CH20 30.02649 5.73721E-05 0017 .0017 .0017

CH3 15.03506 5.15695E-07 .0000 .0000 .0000

CH4 16.04303 5.18412E-08 .0000 .0000 .0000

CΝ 26.01785 4.77911E-05 .0012 .0014 .0014

CO 28.01055 1.07953E+00 30.2381 31.2610 31.2610

COS 60.07455 1.46572E-09 .0000 .0000 .0000

CO2 44.00995 4.90906E-01 21.6047 14.2157 14.2157

CS 44.07515 4.69393E-11 .0000 .0000 .0000

CS2 76.13915 9.86104E-19 .0000 .0000 .0000

C2H2 26.03824 4.86256E-08 0000 .0000 .0000

C2H4 28.05418 4.45480E-11 .0000 .0000 .0000

H 1.00797 2.61555E-02 .0264 .7574 .7574

HCΝ 27.02582 2.58048E-04 .0070 .0075 .0075

HCO 29.01852 1.34084E-03 .0389 .0388 .0388

HΝO 31.01407 5.49614E-04 0170 .0159 .0159

HΝO2 47.01347 1.02943E-04 0048 .0030 .0030 (Table 1A, Continued)

HO2 33.00677 1.19781E-03 .0395 .0347 .0347

H2 2.01594 4.84599E-02 .0977 1.4033 1.4033

H2O 18.01534 1.99950E-01 3.6022 5.7902 5.7902

H2S 34.07994 1.21951E-09 .0000 .0000 .0000

K 39.10200 1.47607E-03 .0577 .0427 .0427

KCN 65.11985 2.53874E-05 .0017 .0007 .0007

KH 40.10997 1.95433E-04 .0078 .0057 .0057

KO 55.10140 9.95250E-04 .0548 .0288 .0288

KOH 56.10937 7.19459E-03 .4037 .2083 .2083

K2 78.20400 1.71521E-06 .0001 .0000 .0000

K2O2H2 112.21874 1.77041E-07 .0000 .0000 .0000

N 14.00670 5.70115E-04 .0080 .0165 .0165

NCO 42.01725 1.04003E-04 .0044 .0030 .0030

NH 15.01467 2.45661E-04 .0037 .0071 .0071

NH2 16.02264 1.70369E-04 .0027 .0049 .0049

NH3 17.03061 8.51301E-05 .0014 .0025 .0025

NO 30.00610 1.08944E-01 3.2690 3.1548 3.1548

NO2 46.00550 4.53166E-04 .0208 .0131 .0131

N2 28.01340 1.33158E+00 37.3021 38.5599 38.5599

N2O 44.01280 3.57999E-04 .0158 .0104 .0104

O 15.99940 2.53593E-02 .4057 .7344 .7344

O H 17.00737 8.69124E-02 1.4782 2.5168 2.5168

O2 31.99880 3.99547E-02 1.2785 1.1570 1.1570

O2NH 47.01347 9.51024E-05 .0045 .0028 .0028

S 32.06400 3.70221E-09 .0000 .0000 .0000

SH 33.07197 4.65480E-09 .0000 .0000 .0000

SN 46.07070 8.97632E-10 .0000 .0000 .0000

SO 48.06340 3.61416E-08 .0000 .0000 .0000

SO2 64.06280 5.17637E-08 .0000 .0000 .0000

SO3 80.06220 1.07851E-10 .0000 .0000 .0000

S2 80.12740 1.89955E-16 .0000 .0000 .0000

C(C) 12.01115 O.OOOOOE+00 .0000 .0000 (Table 1A, Continued)

K(L) 39.10200 O.OOOOOE+00 .0000 .0000

KOH(C2) 56.10937 0.00000E+00 .0000 .0000

KOH(L) 56.10937 0.00000E+00 .0000 .0000

KO2(C) 71.10080 O.OOOOOE+00 .0000 .0000

K2CO3(C) 138.21335 0.00000E+00 .0000 .0000

K2CO3(L) 138.21335 O.OOOOOE+00 .0000 .0000

K2O(C) 94.20340 O.OOOOOE+00 .0000 .0000

K2SO4(Cl) 174.26560 O.OOOOOE+00 .0000 .0000

K2SO4(C2) 174.26560 O.OOOOOE+00 .0000 .0000

K2S04(L) 174.26560 0.00000E+00 .0000 .0000

TABLE IB

OPRESSURE IS LESS THAN EXPLOSION PRESSURE - SHOCK VELOCITY NOT

DEFINED

OPOLNT ON HUGONIOT - - SHOCK VELOCITY = .00 M/SEC, PARTICLE V = .0 P=14.6960 PSI P=1.00000 ATM T= 3014.1 NG=3.52045 NT=3.52045 S=242.971

CPG=34.420 CPT=34.420 FIXED CP GAMMA*=1.255 DHDT=137.180

GAMMA=1.12634

WT PCT COND= .00000 MW GAS=28.405 H=10812 CO V= .00000 VSP=8706.95

SONIC VEL=996.843 , RHO=.00011485 PO=1.9990 VO=3.73251 IMPETUS=295154

E=-10273.488 DEDT=117.968

0PRODUCT MW MOLES WT. PCT. MOLE PCT. VOLUME PCT

CH20 30.02649 9.73010E-09 .0000 .0000 .0000

CH3 15.03506 1.29801E-12 .0000 .0000 .0000

CH4 16.04303 4.42698E-14 .0000 .0000 .0000

CN 26.01785 7.88188E-09 .0000 .0000 .0000

CO 28.01055 1.09242E+00 30.5993 31.0308 31.0308

COS 60.07455 1.27987E-11 .0000 .0000 .0000 (Table IB, Continued)

CO2 44.00995 4.79843E-01 21.1179 13.6302 13.6302

CS 44.07515 5.71998E-14 .0000 .0000 .0000

CS2 76.13915 7.89886E-23 .0000 .0000 .0000

C2H2 26.03824 2.82446E-15 .0000 .0000 .0000

C2H4 28.05418 6.63577E-21 .0000 .0000 .0000

H 1.00797 7.26263E-02 .0732 2.0630 2.0630

HCN 27.02582 4.70143E-08 .0000 .0000 .0000

HCO 29.01852 1.71113E-06 .0000 .0000 .0000

HNO 31.01407 2.41025E-06 .0001 .0001 .0001

HNO2 47.01347 9.20798E-08 .0000 .0000 .0000

HO2 33.00677 3.16439E-05 .0010 .0009 .0009

H2 2.01594 5.57205E-02 .1123 1.5828 1.5828

H2O 18.01534 1.78301E-01 3.2121 5.0647 5.0647

H2S 34.07994 1.53108E-11 .0000 .0000 .0000

K 39.10200 8.57419E-03 .3353 .2436 .2436

KCN 65.11985 2.86715E-09 .0000 .0000 .0000

KH 40.10997 9.22469E-06 .0004 .0003 .0003

KO 55.10140 1.41564E-04 .0078 .0040 .0040

KOH 56.10937 1.16550E-03 .0654 .0331 .0331

K2 78.20400 2.10895E-08 .0000 .0000 .0000

K2O2H2 112.21874 9.54520E-12 .0000 .0000 .0000

N 14.00670 3.31682E-05 .0005 .0009 .0009

NCO 42.01725 1.66628E-08 .0000 .0000 .0000

NH 15.01467 9.14180E-07 .0000 .0000 .0000

NH2 16.02264 1.41625E-07 .0000 .0000 .0000

NH3 17.03061 3.11613E-08 .0000 .0000 .0000

NO 30.00610 4.12393E-02 1.2374 1.1714 1.1714

NO2 46.00550 6.91077E-06 .0003 .0002 .0002

N2 28.01340 1.36712E+00 38.2977 38.8337 38.8337

N2O 44.01280 1.47549E-06 .0001 .0000 .0000

O 15.99940 6.28401E-02 1.0054 1.7850 1.7850

OH 17.00737 7.99003E-02 1.3589 2.2696 2.2696 (Table IB, Continued)

02 31.99880 8.04668E-02 2.5748 2.2857 2.2857

O2NH 47.01347 8.23853E-08 .0000 .0000 .0000

S 32.06400 2.63825E-09 .0000 .0000 .0000

SH 33.07197 4.00777E-10 .0000 .0000 .0000

SN 46.07070 1.08137E-11 .0000 .0000 .0000

SO 48.06340 2.92633E-08 .0000 .0000 .0000

SO2 64.06280 6.76497E-08 .0000 .0000 .0000

SO3 80.06220 9.04600E-12 .0000 .0000 .0000

S2 64.12800 2.86853E-17 .0000 .0000 .0000

S20 80.12740 3.09761E-18 .0000 .0000 .0000

C(C) 12.01115 0.00000E+00 .0000 .0000

K(L) 39.10200 0.00000E+00 .0000 .0000

KOH(C2) 56.10937 O.OOOOOE+00 .0000 .0000

KOH (L) 56.10937 O.OOOOOE+00 .0000 .0000

KO2(C) 71.10080 O.OOOOOE+00 .0000 .0000

K2CO3(C) 138.21335 O.OOOOOE+00 .0000 .0000

K2CO3(L) 138.21335 O.OOOOOE+00 .0000 .0000

K2O(C) 94.20340 O.OOOOOE+00 .0000 .0000

K2SO4(Cl) 174.26560 O.OOOOOE+00 .0000 .0000

K2SO4(C2) 174.26560 O.OOOOOE+00 .0000 .0000

K2S04(L) 174.26560 0.00000E+00 .0000 .0000

Claims

CLAIMSWhat is claimed is:

1. A gas generator comprising at least two chambers, each said chamber being capable of discharging gas therefrom at a different time and different volumetric rate, each said chamber containing the same propellant and an initiator.

2. The gas generator of Claim 1, wherein said propellant comprises on a weight basis approximately (a) 84-95% of an oxidizer, (b) 3.4-13.4% of a fuel, and (c) 1.5-2.6% of a binder, wherein the products of combustion of said propellant are non-toxic gases.

3. The gas generator of Claim 2, wherein said fuel is selected from the group consisting of CL-20, RDX, HMX, GAP, NGU, TATB, LLM-105, EDNA, and mixtures thereof.

4. The gas generator of Claim 2, wherein said binder is selected from the group consisting of PCL, PIB, GAP, polyvinylpyrrolidone, and mixtures thereof.

5. The gas generator of Claim 2, wherein said oxidizer is ammonium nitrate.

6. The gas generator of Claim 2, wherein said oxidizer is ammonium nitrate, said fuel is CL- 20, and said binder is polycaprolactone.

7. The gas generator of Claim 6, wherein said ammonium nitrate comprises approximately 89.5%), said CL-20 comprises approximately 8.4%, and said polycaprolactone constitutes approximately 2.1 % of said propellant.

8. The gas generator of Claim 1, wherein the geometry of said propellant is different from chamber to chamber.

9. The gas generator of Claim 1 , wherein said propellant comprises on a weight basis approximately 70-95% energetic nitramine fuel, 5-25%) energetic polymer binder and 0.1-5% flash suppressant.

10. The gas generator of Claim 9, wherein said nitramine fuel is CL-20.

30

11. The gas generator of Claim 9, wherein said polymer binder is GAP or PIB.

12. The gas generator of Claim 9, wherein said flash suppressant is potassium nitrate.

13. The gas generator of Claim 9, further comprising one or more ingredients selected from the group consisting of ingredients to control stability, coatings to control ballistic spikes and high initial pressure rise, and ingredients to increase gravimetric density and dissipate static.

14. The gas generator of Claim 9, having two chambers, wherein the change of pressure as a function of time from the first of said chambers is at least two times greater than the change of pressure as a function of time from the second of said chambers.

15. The gas generator of Claim 9, wherein said propellant is made by a process comprising: (a) preparing a mixture of the components of said propellant in wet or dry form,

(b) forming said mixture into tablets, disks or granules,

(c) if wet, allowing said tablets, disks or tablets to dry, and

(d) perforating said tablets, disks or tablets to achieve the desired geometry.

16. The gas generator of Claim 9, wherein said propellant has density greater than or equal to approximately 92% of theoretical density.

17. The gas generator of Claim 13, wherein said ingredients to control stability are selected from the group consisting of Ethyl centralite, Akardite I, Akardite II, Diphenyl Amine, and 2- Nitrodiphenyl Amine.

18. The gas generator of Claim 13, wherein said ingredients to control ballistic spikes and high initial pressure rise are selected from the group consisting of Ethylene Glycol Dimethacrylate, Diethylene Glycol Dimethacrylate, Allyl Methacrylate and Hercote Polyester.

19. The gas generator of Claim 13, wherein said ingredient to increase gravimetric density and dissipate static is graphite.

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20. The gas generator of Claim 1, further comprising an airbag operable to receive gas discharged from each of said chambers.

21. The gas generator of Claim 20, wherein said airbag is an uncoated airbag.

22. The gas generator of Claim 20, further comprising an inertial switch operable to produce a signal to trigger each of said chambers.

23. The gas generator of Claim 22, wherein said inertial switch is a microelectromechanical system (MEMS) accelerometer.

24. The gas generator of Claim 1 , further comprising a third chamber.

25. The gas generator of Claim 1 , wherein the products of combustion of said propellant comprise water, nitrogen, and carbon dioxide.

26. A process for controlling the rate of inflation of an airbag comprising:

(a) connecting a gas generator according to Claim 1 to said airbag;

(b) causing each of said chambers to discharge at a different, predetermined time; and (c) causing the effluent of each of said chambers to flow into said airbag.

27. The process of Claim 26, further comprising activating said gas generator in response to a vehicle collision, wherein said gas generator and airbag are positioned in a vehicle.

28. The process of Claim 26, further comprising activating said gas generator in response to a trigger signal and ejecting one or more submunitions from a weapon, wherein said gas generator and airbag are connected to said weapon.

29. The process of Claim 28, further comprising the step of firing said weapon.

30. The process of Claim 26, further comprising controlling the trajectory of a submunition.

31. The process of Claim 30, wherein controlling the trajectory of a submunition comprises:

(a) activating said gas generator; and

32 (b) using the gas from said gas generator to deploy a parachute on a submunition, wherein said deployment controls the trajectory of said submunition.

32. A process of using the gas generator of Claim 9 for propelling small, medium and large caliber ammunition from a weapon system, said process comprising:

(a) inserting said gas generator into a barrel of said weapon system;

(b) inserting said ammunition;

(c) activating said gas generator, and

(d) using gas expelled from said gas generator to propel said ammunition.

32. An eco-friendly gas generant propellant comprising:

(a) 84-95% of an oxidizer, on a weight basis:

(b) 3.4-13.4% of a fuel, on a weight basis; and

(c) 1.5-2.6% of a binder, on a weight basis; wherein, the products of combustion of said propellant are non-toxic gases.

33. The eco-friendly gas generant propellant of Claim 32, wherein said fuel is selected from the group consisting of CL-20, RDX, HMX, GAP, NGU, TATB, LLM-105, EDNA, and mixtures thereof.

34. The eco-friendly gas generant propellant of Claim 32, wherein said binder is selected from the group consisting of PCL, PIB, GAP, polyvinylpyrrolidone, and mixtures thereof.

35. The eco-friendly gas generant propellant of Claim 32, wherein said oxidizer is ammonium nitrate.

36. The eco-friendly gas generant propellant of Claim 32, wherein said oxidizer is ammonium nitrate, said fuel is CL-20, and said binder is polycaprolactone.

37. The eco-friendly gas generant propellant of Claim 36, wherein said ammonium nitrate comprises approximately 89.5%, said CL-20 comprises approximately 8.4%, and said polycaprolactone comprises approximately 2.1% of said propellant.

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