US3041835A - Ignition aid - Google Patents

Description

July 3, 196.2- c. B. HENDERSON ETAL 3,041,835

IGNITION AID 2 Sheets-Sheet 1 Filed Feb. 5, 1959 AGENT ga rifflvnrfldw July 3, 1962 c. B. HENDERSON ETAL 3,041,835

IGNITION AID 2 Sheehs--Sheei'I 2 Filed Feb. 5, 1959 INVENTOS ZM/'ks /Zemdezwl @I ae M ,5l/fiala BY f5 m W AGENT nited 3,641,835 Patented July 3, 1962 ration, f

This invention relates to a method and device for shaping and igniting the leading face of a column or mass of plastic monopropellant extruding into the combustion chamber of a gas generating apparatus, such as a rocket motor or gas turbine.

The term monopropellant refers to a composition which is substantially self-sufficient with regard to its oxidant requirements as distinguished from bipropellants where the fuel is maintained separately from the oxidizer source until admixture at the point of combustion.

There have recently been developed for use in gas generating apparatus, such as rocket motors, gas turbines and the like, a number of plastic monopropellants, which are particularly adapted for extrusion as cohesive, shape-retaining, continuously advancing masses or columns into a combustion chamber, where they are burned to generate high energy gases for developing thrust or power or for providing heat or gas pressure. The compositions have thixotropic properties and are suliciently iluid above a certain finite stress to be fed at ambient temperatures through shaping apertures into a combustion chamber. The leading face of the shape-retaining column presents a burning surface of predeterminable area, which can be varied and controlled by varying the rate of extrusion. These plastic monopropellants combine many of the advantages and eliminate many of the disadvantages of previously known liquid or solid propellants used to power similar devices.

Such plastic monopropellants are normally stored in a fuel tank from which they are extruded through an apertnred plate or other suitable extrusion member into a combnstion chamber. The primary purpose of the extrusion member is to divide the propellant into a plurality of separate masses or columns, thereby to increase the total burning area of monopropellant available in a combustion chamber, of preferably minimum length.

When burning equilibrium is reached at a given rate of extrusion, which should be higher than the linear burning rate of the monopropellant, the extruding column of monopropellant burns on all surfaces exposed in the combustion chamber and these surfaces converge in the clownstream direction forming a downstream edge or apex, depending on the shape of the extrusion orice. The angle of convergence at equilibrium is determined only by the ratio of the linear rate of extrusion to the linear burning rate of the particular monopropellant, regardless of the size of the extrusion aperture. The higher the value of this ratio, the more acute is the downstream angle of convergence resulting in a longer column of burning propellant having a proportionally larger burning surface area. The mass rate of burning is proportional to the burning surface area and to the linear burning rate. Consequently, the linear rate of extrusion is, at equilibrium, the deterrninative factor for the mass rate of burning.

Prior to ignition, the plastic monopropellant is ordinarily extruded from the fuel tank into the extrusion member sufficiently completely to ll the extrusion passages or orifices and to protrude into the combustion chamber for a short distance beyond the downstream end of the orifice, the length of protrudnig column being predetermined by such factors as the linear burning rate of the particular monopropellant composition, the desired equilibrium burning surface area, the linear rate of extrusion during burning, the desired start-up pressure-time characteristics, and the change in mass rate of gas-generation and, thereby pressure, as the initially ignited burning surface approaches the equilibrium burning surface.

The protruding portion of the monopropellant mass or column, prior to ignition, will have a cross-sectional geometry similar to that of the extrusion orifice, which functions, in eifect, asl a shaping orifice, and a plane-surfaced leading face. The plane-surfaced protruding column can be ignited by conventional methods, such as :a hot wire igniter, a squib, or the like. Ignition generally occurs iirst on the leading plane surface followed by ignition of the sides of the monopropellant column exposed in the combustion chamber. In some cases ignition of the sides may not occur until combustion chamber temperature and pressure have reached a relatively high value. There is also the possibility, in some instances, that the llame will not propagate down the sides before the length of the column, which, while burning on its plane surface at the linear lburning rate of the monopropellant, is being extruded at a higher rate, becomes so excessive as to result in slumping, fragmentation, or even protrusion out through the gas venting nozzle. After burning propagates down the sides, the surfaces converge in the downstream direction, as aforedescribed, eventually producing the equilibrium burning surface. In many applications, it is desirable, for smooth performance, to achieve the equilibrium mass rate of gas generation and combustion chamber pressure as quickly as possibly, so that the marked hiatus between ignition of the plane-surfaced monopropellant column and formation of the equilibrium burning surface is disadvantageous. To some extent, this can be counterbalanced by careful presetting of the initial degree of protrusion of the monopropellant into the cornbustion chamber prior to ignition and very closely regulated initial extrusion rate. However, this requires exceedingly ne and critical prescheduling and manipulation. There is the likelihood that equilibrium combustion chamber pressures will be reached too slowly or may 1go through a transient overshoot. In some cases, one or the other of these conditions may be desirable, but here again, the fine manipulation required to obtain the exactly desired programming is exceedingly diicult to achieve when the initial ignition surface of the plastic monopropellant is plane.

The object of this invention is to provide as an igniter for the plastic monopropellant, a wafer of solid propellant so positioned relative to the column of plastic monopropellant preliminarily extruded into the combustion chamber prior to ignition, that the wafer functions both to ignite the plastic propellant and to bring it very rapidly to burning surface equilibrium.

Other objects and advantages of the invention will be made obvious by the following detailed description taken in connection Iwith the accompanying drawings in which like reference characters refer to like parts throughout and wherein:

FIGURE 1 is a diagrammatic section view of the rear portion of a rocket engine in which the present invention nds application.

FIGURE 2 is a cross-sectional view taken along lines 2-2 of FIGURE 1 showing the igniter wafer with a portion cut away to show the extrusion plate.

FIGURE 3 is a fragmentary view showing equilibrium burning after ignition of the solid and plastic propellants shown in FIGURE l.

FIGURE 4 is a plan view of a different embodiment of the invention.

FIGURE 5 is an isometric view of still another embodiment.

FIGURE 6 is a fragmentary longitudinal section along lines 6--6 of FIGURE 5, showing the plastic mono- 3 propellant extruded downstream of the wafer orifice prior to ignition.

FIGURE 7 is a plan view of a modified form of the invention, showing single-orificed annular wafers.

FIGURE 8 is a plan view of a modification showing sealing closure of the downstream ends of the solid propellant Wafer orifices.

FIGURE 9 is a longitudinal section along lines 9 9 of FIGURE 8.

Broadly speaking, the invention comprises a wafer of readily ignitible solid propellant mounted on the downstream face of the extrusion member or plate, namely the face exposed to the combustion chamber, the wafer being provided with an orifice positioned in registry with the extrusion member orifice through which the plastic monopropelliant is yfed from the fuel chamber. The wafer orifice is, like the extrusion member orifice, axially oriented in the `downstream direction of plastic monopropellant fiow. Its cross-sectional area is at least as large as that of the extrusion member orifice and is preferably the same, although it can be somewhat larger. The interior walls of the igniter wafer orifice should be parallel to the direction of propellant flow and, thereby, to the lateral walls of the extruded column of plastic propellant prior to ignition. The cross-sectional geometry of the wafer orifice is preferably substantially the same as that of the extrusion member orifice. Small differences in geometry and cross-sectional area can be tolerated so long as there is no overlapping of the wafer over the extrusion member orifice to produce an obstruction to fiow.

The wafer orifice can be open to the combustion charnber at its downstream end or can be sealed by means of a transverse closure wall made of the solid propellant. Alternatively, a thin sheet of an inert (namely non-selfoxidant) solid material, such fas cellophane, can be laid over the wafer orifices. Such an inert protective covering is preferably not bonded to the solid propellant surface to 4avoid its having `an inhibiting effect. It should also be very thin so that it will decompose or be torn away upon ignition of the conventional igniter employed to ignite the solid propellant wafer.

The igniter wafer can be of a cross-sectional area sufficient to overlie substantially the entire downstream face of the extrusion plate, with wafer orifices in registry with each of the extrusion orifices; or sufiicient to overlie just a portion of the plate, with wafer orifices in registry only with those extrusion orifices present in that portion of the extrusion plate; or suliicient only to provi-de a registering wafer orifice for a single extrusion plate orifice. In some cases, it may be ladequate to provide only some of the plastic monopropellant columns extruding through the extrusion orifice with the circumscribing solid propellant. The igniter wafer, 4because of its position on the face of the extrusion plate at a level adjacent to the bases of the plastic propellant columns, is most suitably located to provide hot combustion gases which circulate down between the uncircumscribed columns to ignite them laterally. The very rapid initiation of equilibrium burning of the warfer-circumscribed plastic propellant columns hastens the build-up of temperature, pressure, and hot circulating combustion gases, which also promote ignition. Single-orificed igniter wafers can be employed to fcircumscribe one or several of the plurality of extrusion orifices in an extrusion plate.

For most efficient action, all surfaces of the solid propellant wafers are inhibited against burning except the downstream face. In the preferred embodiment, therefore, the lateral surfaces of the wafer, including the walls of the wafer orifice, `and its upstream base are inhibited. Inhibition can be accomplished in any conventional fashion, as by the application of a `coating of an inert polymer, such as polyvinyl chloride or cellulose acetate, free from oxidizer.

The igniter wafers can be attached to the face of the extrusion plate in any convenient manner, as by bonding with a suitable adhesive which also functions as a surface inhibitor.

in practice, prior to ignition, the plastic monopropellant is extrudml from the fuel chamber through the extrusion member into the wafer orifice to or beyond the downstream end of the wafer orifice, After ignition by ya conventional igniter, such as a hot wire or squib, the solid propellant wafer functions to ignite the plastic propellant because the hot combustion products produced immediately adjacent to the plastic propellant are above its ignition temperature. The leading plane surface of the plastic propellant column ignites practically simultaneously with ignition of the solid propellant.

To obtain the desired lateral ignition and downstream convergence of the burning lateral surfaces of the leading end of the plastic monopropellant column essential to formation of the equilibrium burning surface, at least some lateral surface, upstream from the initial planesurfaced leading face of the plastic propellant column, must be exposed to ignition by the circumscribing solid propellant, which is burning in a linear direction upstream from its original uninhibited burning surface. Any degree of such exposure Aaccompanied by lateral ignition facilitates generation of the equilibrium burning surface. This can be achieved by selection of a solid propellant material having a suitable linear burning rate relative to that of the plastic monopropellant, by preliminary adjustment of the relative downstream levels of the igniter wafer and the plastic propellant column, or by a cornbination of both of these factors.

`Where the solid propellant has a higher linear burning rate than the plastic propellant, it is obvious that after ignition, it will retreat upstream at a lfaster rate than the plastic propellant. if the plastic propellant is initially extruded to a level flush with the downstream end of the wafer orifice, Within which it is contained, after ignition of the downstream faces, the burning surface of the solid propellant wafer retreats upstream more rapidly than that of the plastic propellant column, thereby exposing to ignition lateral surface of the latter and inducing convergence. The higher the ratio of solid propellant linear burning rate to the plastic propellant linear burning rate, the more rapidly is the equilibrium burning surface configuration achieved.

The parameters, in terms of relative burning rates of the two propellants, wafer thickness and extrusion orifice diameter can readily be calculated `by those skilled in the art. To obtain a desired cone-shaped equilibrium burning surface, for example, the relationship of the burning rates, wafer thickness and orifice diameter can be determined as follows:

T0=time at ignition of the plastic propellant Tc=time at formation of the perfect cone, namely formation of the equilibrium cone angle t=thickness of solid propellant wafer d=idiameter of extrusion orifice rs=burning rate of solid propellant rp=burning rate of plastic propellant therefore Since, starting with initially flush propellant levels, the burning rate of the solid must be higher than that of the plastic to provide for lateral exposure of the latter, wafer thickness must be larger than extrusion orifice diameter in at least the same ratio `as the solid to plastic burning rates, and can be calculated for formation of the equilibrium cone from the foregoing mathematically expressed relationship.

The above embodiment, namely initially fiush propellant levels accompanied by a ratio of solid to plastic propellant burning rate greater than 1, produces most rapidly a substantially perfectly shaped equilibrium burnning surface. Very satisfactory results in terms of initiation of convergence and rapid effectuation of the equilibrium burning surface can, however, be achieved by extrusion of the plastic propellant prior to ignition for a predetermined distance beyond the downstream level of the wafer. This expedient pre-exposes lateral plastic propellant surface to ignition by the hot combustion products of the ignited solid propellant wafer. Under these circumstances, the linear burning rate of the solid propellant can be the same as that of the plastic propellant, or higher or lower within calculable limits. Here again, the required degree of plastic propellant protrusion and the thickness of the wafer for optimum performance can be calculated from the known burning rate and extrusion orifice diameter parameters.

Although certain predetermined ratios of the aforedescribed parameters provide optimum performance in terms of rapidity of equilibrium burning establishment, it is repeated that any degree of lateral ignition and downstream convergence of the leading end of the plastic monopropellant column ensures and hastens burning equilibrium. This is a practical advantage since it makes possible the use, within fairly broad limits, of the same available igniter wafer, suitably designed with an orifice or a plurality of orifices which can be placed in registry with an extrusion plate orifice or orifices, with different plastic monopropellants or with the same plastic monopropellant at a different prescheduled rate of extrusion and, therefore, different equilibrium burning surface.

In addition tofunctioning as an ignition and shaping aid, the solid propellant wafer generates hot combustion gases which speed build-up to the desired equilibrium combustion chamber pressure. A desired pressure-time curve can be prescheduled by varying the initial uninhibited burning surface area of the solid propellant and thereby, the mass rate of gas generation with a given propellant. Total burning surface area can, for example, be maximized by extending the wafer over the entire downstream surface of the extrusion plate, with, of course, properly mating orifices. A reduction in burning surface area can be achieved by reducing the cross-sectional area of the wafer relative to that of the extrusion plate or by employing a plurality of single-orificed wafers applied to selected extrusion plate orifices. The linear burning rate of the solid propellant at initial and increasing pressures is also a factor in determining the rate of pressure build-up and this, in turn, may be a factor in determining the particular practical ratio of the solid propellant linear burning rate relative to that of the plastic monopropellant.

Onsetrof extrusion of the ignited plastic monopropellant column into the combustion chamber should be delayed until at least a substantial degree of downstream convergence. has taken place, the optimum time being at the closest approach to equilibrium burning surface achievable under the given conditions prior to complete consumption of the solid propellant.

The plastic monopropellants, though cohesive and shape-retentive, will flow under stress, so that there may be some undesirable leakage into the combustion chamber .after a long period of storage at attitudes promoting ow under the stress of the propellants own weight or under stresses incident to handling or transportation. Some of the plastic monopropellant compositions tend to be hygroscopic, namely to absorb atmospheric moisture which may adversely affect their viscosity and burning properties. A protective closure or seal can be provided at the downstream end of the wafer orifice in the form of a layer of the solid propellant or of a non-selfoxidant material, such as a solid polymer, as aforedescribed. Where a solid propellant closure is used, it can be made integral with the igniter wafer. After ignition, the relatively thin closure layer burns down to the leading plane surface of the plastic propellant column, and ignites it.

Turning now to the drawings and, in particular to FIGURE l, there is shown a diagrammatic longitudinal view of the rear portion of a rocket engine of the type which, by way of example, is adapted to use the ignition device of the present invention. The rocket engine consists of `a fuel tank 1 which is of generally cylindrical shape and which contains a plastic monopropellant 2. Slidably mounted in the forward end of the fuel tank is an extrusion piston 3 which extrudes the monopropellant 2 through an extrusion member 4 into a combustion chamber 5. Nozzle 6 is in open communication with the combustion chamber to receive the gases generated therein and to discharge them to produce thrust. The piston 3 is actuated by pressurized gas, such as nitrogen, admitted into the forward portion 7 of fuel tank 1 from a storage tank of the pressurized gas not shown. The pressure of gas applied -to piston 3 and hence the rate of plastic monopropellant extrusion can be controlled and varied by valve means also not shown. A conventional igniter 8 is provided in the combustion chamber to ignite the wafer of solid propellant 9.

Extrusion plate 4 is provided with axial orifice passages lfl and l1 of circular cross section. A wafer of solid propellant 9 overlies the entire downstream face of extrusion plate 4 and is provided with circular orifices 10a and lla in registry with extrusion plate orifices 10 and il. The solid propellant igniter wafer 9 is adhesively bonded to the extrusion plate and is provided with an inhibitor coating 12 on all exposed surfaces, including the walls of the wafer orifices, except for its downstream initial burning surface 13. The plastic monopropellant 2, prior to ignition, is extruded downstream to the point where its plane leading surface 14 is flush with the downstream surface 13 of the solid propellant Wafer.

In this embodiment, it is essential that the burning rate of the solid wafer exceed that of the plastic propellent. For perfect equilibrium cone formation, the thickness of the wafer should exceed the diameter of each of the orifices in at least the same ratio as rs/rp. By satisfying this requirement for the larger orifices 10, a wafer of the same web thickness automatically satisfies this requirement for the smaller orifices. The wafer thickness can, of course, be reduced in the area of the smaller orifices to provide the same relationship of wafer thickness to orifice diameter as in the case of the larger orifices, but this is not essential.

FIGURE 3 shows the equiangled cones 15 and 16 formed at equilibrium burning a short time after ignition of solid propellant wafer and the leading end of the plastic monopropellant column. The solid propellant wafer has been largely, but not completely consumed. Extrusion of the burning, shaped plastic propellant columns into the combustion chamber can most effectively commence at the point shown.

FIGURE 4 shows the downstream face of an extrusion plate 4 having an extrusion orifice geometry similar to that of FIGURE 2. The igniter wafer 17, however, differs in covering only the central portion of the face of the extrusion plate and having wafer orifices 11a in registry only with the central seven extrusion plate oriices.

Extrusion plate orifice geometry can be varied in a multitude of ways determined by such factors as the desired ratio, for a given application, of total extrusion orifice cross-sectional area to extrusion plate cross-sectional area.

It is essential only that the solid propellant wafer be designed with mating orices. One of many available variations in extrusion orifice geometry is illustrated in FIGURE 5 by the hexagonal orifices 20 in extrusion plate 7 2l. The igniter wafer 22 of solid propellant is provided with mating orifices 23 and inhibited surfaces 24. FIG- URE 6 illustrates protrusion of columns of plastic propellant prior to ignition so that the leading plane surface extends beyond the downstream face of wafer 22, thereby exposing a portion of the upstream lateral sides 26.

FIGURE 7 shows single-oriliced solid propellant annular wafers 40 and 41 circumscribing selected individual extrusion orifices 42 and 43 in extrusion plate 44. This configuration has the advantage of reducing the amount of solid propellant burning surface area where such is desirable. The individual annular wafers are each inhibited on all sides except for the downstream face.

FIGURES 8 and 9 illustrate protective closure of the downstream ends of Wafer orifices :and 31 in solid propellant wafer 32 having inhibited surfaces 33, the wafer being bonded to extrusion plate 34 with its orifices in registry with lextrusion plate yorifices 35 and 36. The wafer is made of suicient thickness to provide a thin layer 37 of the solid propellant as a sealing closure across the ends of the wafer orifices.

The solid propellant compositions employed in making the igniter wafers can be `any suitable one known in the art which is readily ignited. It can, for example, be one of the conventional double-base propellants, eg. nitrocellulose gelatinized with nitroglycerine, or ya composite type propellant comprising a solid inert fuel, e.g., an inert solid polymer, such as polyvinyl chloride or cellulose acetate, preferably plasticized with a non-volatile plasticizer to reduce brittleness, containing dispersed therein a solid oxidizer, such as ammonium perchlorate or nitrate. Many such solid propellants having the different burning properties required for different applications are available for selection by those skilled in the art.

The monopropellant employed in the devices of this invention is preferably a plastic mass which is sufficiently cohesive to ret-ain a shaped form and which is extrudable under pressure at ambient temperatures. Many different plastic monopropellant compositions tailored to different performance requirements can be made having these desired physical characteristics. The monopropellant compositions generally preferably comprise a stab-le dispersion of `a finely-divided, insoluble solid oxidizer in a continuous matrix of an oxidizable liquid fuel.

The liquid fuel can be any oxidizable liquid, preferably an organic liquid containing carbon `and hydrogen. Suitable liquid fuels include hydrocarbons, such as triethyl benzene, dodecane, liquid polyisobutylene, yand the like; compounds containing oxygen linked toa carbon atom, as, for example, esters, like dimethyl maleate, diethyl phthalate, dibutyl oxalate, `and the like; alcohols, such as benzyl alcohol, triethylene glycol and the like; ethers such as methyl a-naphthyl ether `and the like; and many others.

The solid oxidizer can be any suitable, active oxidizing agent which yields :an oxidizing element such as oxygen, chlorine or fluorine readily for combustion of the fuel and which is insoluble in the liquid fuel vehicle. Such oxidizers include inorganic oxidizing salts such Ias ammonium, sodium and potassium perchlorate or nitrate and metal peroxides such as barium peroxide.

The `amount of solid oxidizer incorporated varies, of course, with the particular kind and concentration of fuel components in the formulation, the particular oxidizer, and the specific requirements for la given use, in terms, for example, of required heat release and rate of gas generation, and can readily be computed by those skilled in the art. Since the liquid vehicle can, in many instances, be loaded with as high as 80 to 90% of finely-divided solids, stoichiometric oxidizer levels with respect to the fuel components can generally be achieved when desired, as for example, in rocket applications Where maximum heat release and specific impulse are of prime importance. In some applications, stoichiometric oxidation levels may not be necessary or even desirable, as, for example, in gas turbines where relatively low combustion chamber temperatures are preferred, and the amount of oxidizer can be correspondingly reduced. Sufficient oxidizer must, of course, be incorporated to maintain active, gas-generating combustion.

Finely-divided solid metal powders such as aluminum or magnesium, may be incorporated in the monopropellant composition :as an additional fuel component along with the liquid fuel. Such metal powders possess the advantages both of increasing the fuel density and improving the specific impulse of the monopropellant because of their high heats of combustion.

The physical properties of the plastic monopropellant in terms of shape-retentive cohesiveness, tensile strength and thixotropy, can be improved by addition of a gelling agent, such as a polymer, e.g. polyvinyl chloride, polyvinyl acetate, cellulose acetate, ethyl cellulose, or metal salts of higher fatty acids, such as the sodium or magnesium stearates or palmitates. Ihe desired physical properties can also be obtained Without a gelling yagent by using a liquid vehicle of substantial intrinsic viscosity, such as liquid organic polymers, e.g. liquid polyisobutylene, liquid siloxanes, liquid polyesters, and `the like.

Many different plastic monopropellant compositions may also be used. It is, therefore, to be understood that this invention is not limited to use with any particular plastic monopropellant composition, but is directed fto the shaping and ignition of any extruded plastic monopropellant.

Although this invention has been described with reference to illustra-tive embodiments thereof, it will be apparent to those skilled in `the art that the principles of this invention can be embodied in other forms but Within the scope of the claims.

We claim:

1. In a gas ygenerating apparatus wherein `a plastic monopropellant is extruded from a fuel chamber through an orifice in an apertured member into a combustion chamber in the form of a shape-retentive, continuously extruding column, the leading face of which is burned in said combustion chamber to generate gases, lthe improvement comprising an igniter wafer of `solid propellant mounted on the downstream surface of the apertured member and provided with an orifice positioned in registry with said orifice in said apertured member.

2. In a gas generating apparatus wherein a plastic monopropellant is extruded from a fuel chamber through an orifice in an yapertured member into a combustion chamber in the form of a shape-retentive, continuously extruding column, the leading face of which is burned in said combustion chamber `to generate gases, the irnprovement comprising an igniter wafer of solid propellant mounted on the downstream surface of ythe apertured member `and provided with an orifice positioned in registry With said orifice in said apertured member, the wafer orifice having Walls parallel to the direction of ow of the palstic monopropellant, said wafer being inhibited against burning on all surfaces except its downstream surface.

3. In a gas generating apparatus wherein a plastic monopropellant is extruded lfrom a fuel chamber through a plurality of orifices in an apertured member into a combustion chamber in the form of shape-retentive, continuously extruding columns, the leading faces of which are burned in said combustion chamber to generate gases, the improvement comprising, an igniter wafer of solid propellant mounted to overlie at least a portion of the downstream surface of the apertured member and provided with orifices positioned in registry with all of the orifices in said portion of the apertured member.

4. In a gas generating apparatus wherein a plastic monopropellant is extruded from a fuel chamber through a plurality of orifices in an apertured member into a combustion chamber in the form of shape-retentive, continuously extruding columns, the leading faces of which are burned in said combustion chamber to generate gases, the improvement comprising, an igniter wafer of solid propellant mounted to overiie at least a portion of the downstream surface of the apertured member and provided with orifices positioned in registry with all of the extrusion member orifices in said portion of the apertured member, the wafer orifices having walls parallel to the direction of flow of the plastic monopropellant, said Wafer being inhibited against burning on all surfaces eX- cept its downstream surface.

5. ln a gas generating apparatus wherein a plastic monopropellant is extruded from a fuel chamber through an orifice in an apertured member into a combustion chamber in the form of a shape-retentive, continuously extruding column, the leading face of which is burned in said combustion chamber to generate gases, the in provement comprising an igniter wafer of solid propellant mounted on the downstream surface of the apertured member and provided with an orifice positioned in registry with said orifice in said apertured member, the wafer orifice having walls parallel to the direction of flow of the plastic monopropellant, and a transverse closure overlying its downstream end, said wafer being inhibited against burning on all surfaces except its downstream surface.

6. In a gas generating apparatus wherein a plastic monopropellant is extruded from a fuel chamber through a plurality of orifices in an apertured member into a combustion chamber in the form of shape-retentive, continuously extruding columns, the leading faces of which are burned in said combustion chamber to generate gases, the improvement comprising, an igniter wafer of solid propellant mounted to overlie at least a portion of the downstream surface of the apertured member and provided with orifices positioned in registry with all of the extrusion member orifices in said portion of the apertured member, the wafer orifices having walls parallel to the direction of flow of the plastic monopropellant, and transverse closures overlying their downstream ends, said wafer being inhibited against burning on all surfaces eX- cept its downstream surface.

7. An igniter wafer made of solid propellant for use in a gas generating apparatus wherein a plastic monopropellant is extruded through an orifice in an apertured member into a combustion chamber in the form of a shape-retentive, extruding column, the leading face of which is burned in said combustion chamber to generate gases, said igniter wafer being adapted for mounting on the downstream surface of the apertured member and having an orifice designed tobe positioned in registry with said orifice in said apertured member.

8. An igniter wafer made of solid propellant for use in a gas generating apparatus wherein a plastic monopropellant is extruded through an orifice in an apertured member into a combustion chamber in the form of a shape-retentive, extruding column, the leading face of which is burned in said combustion chamber to generate gases, said igniter wafer being adapted for mounting on the downstream surface of the apertured member and having an orifice designed to be positioned in registry with said orifice in said apertured member, said wafer orifice having walls parallel to the direction of flow of the plastic monopropellant and surface-inhibited against burning.

9. An igniter wafer made of solid propellant for use in a gas generating apparatus wherein a plastic monopropellant is extruded through an orifice in an apertured member into a combustion chamber in the form of a shape-retentive, extruding column, the leading face of which is burned in said combustion chamber to generate gases, said igniter wafer being adapted for mounting on the downstream surface of the apertured member and having an orifice designed to be positioned in registry with said orifice in said apertured member, said wafer orifice having walls parallel to the direction of flow of the plastic monopropellant and surface-inhibited against burning, and a transverse closure overlying its downstream end.

l0. An igniter wafer made of solid propellant for use in a gas generating apparatus wherein a plastic monopropellant is extruded through -a plurality of orices in an apertured member into a combustion chamber in the form of shape-retentive, extruding columns, the leading faces of which are burned in said combustion chamber to generate gases, said igniter wafer being adapted for mounting on the downstream surface of the apertured member and having orifices designed to be positioned in registry with the extrusion orifices in that portion of the apertured member over which said Wafer is mounted.

11. An igniter wafer made of solid propellant for use in a gas generating apparatus wherein a plastic monopropellant is extruded through a plurality of orifices in an aperttued member into a combustion chamber in the form of shape-retentive, eXtruding columns, the leading faces of which are burned in said combustion chamber to generate gases, said igniter wafer being adapted for mounting on the downstream surface of the apertured member and having orifices designed to be positioned in registry with the extrusion orifices in that portion of the apertured member over which said wafer is` mounted, Said wafer orifices having walls parallel to the direction of flow of the plastic monopropellant and surface-inhibited against burning.

12. An igniter wafer made of solid propellant for use in a gas generating apparatus wherein a plastic monopropellant is extruded through a plurality of orifices in an apertured member into a combustion chamber in the form of shape-retentive, extruding columns, the leading faces of which are burned in said combustion chamber to generate gases, said igniter wafer being adapted for mounting on the downstream surface of the apertured member and having orifices designed to be positioned in registry with the extrusion orifices in that portion of the apertured member over which said wafer is mounted, said wafer orifices having walls parallel to the direction of flow of the plastic monopropellant and surfaceinhibited against burning, and transverse closures overlying their downstream ends.

References Cited in the le of this patent UNITED STATES PATENTS 515,500 Nobel Feb. 27, 1894 1,506,323 ONeill Aug. 26, 1924 FOREIGN PATENTS 582,621 Great Britain Nov. 22, 1946

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