US3726088A

US3726088A - On-demand variable flow closed loop gas generator system with a variable area injector

Info

Publication number: US3726088A
Application number: US00173510A
Authority: US
Inventors: W Kretschmer; P Heady
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1971-08-20
Filing date: 1971-08-20
Publication date: 1973-04-10
Anticipated expiration: 1990-04-10

Abstract

A closed loop monopropellant on-demand fuel feeding system for firing a reaction control device. The system includes a single bellows variable area injector having no valves other than an explosive disc in the propellant supply system separating the gas generator from the fuel storage tanks. The injector comprises a stationary pintle with swirl slots and a movable orifice plate attached to the bellows to vary the area of the swirl slots.

Description

nite States Patent Kretschmer et al.

[ 1 Apr. 10, 1973 [5 ON-DEMAND VARIABLE FLOW 3,234,731 2/1966 Dermody et al. ..60/39.74 A

CLOSED LOOP GAS GENERATOR s SYSTEM WITH A VARIABLE AREA agee 3,462,950 8/1969 Che a1 ..60/39.74A INJECTOR v a2 75 Inventors: Willi K. Kretschmer, Santa Cruz; Primary Examirwrcarlwn Cwyle Paul Heady, Jr Mount Herman, Assistant Examiner-Warren Olsen both of Calif Att0rneyR. S. Sciascia et al.

[73] Assignee: The United States of America as [57] ABSTRACT represented by the Secretary of the Navy A closed loop monopropellant on-demand fuel feeding system for firing a reaction control device The system Flledi g- 1971 includes a single bellows variable area injector having [211 App. No; 173 510 no valves other than an explosive disc in the propel- Y lant supply system separating the gas generator from the fuel storage tanks. The injector comprises a sta- [52] US. Cl. ..60/39.74 A, 60/39.82 E, 60/229, tionary pintle with swirl slots and a movable orifice 60/258 plate attached to the bellows to vary the area of the [51] Int. Cl ..F02k 9/02 swirl slots. [58] Field of Search ..60/39.74 A, 258, 60/229, 243, 200, 39.48, 39.82 E

[56] References Cited 10 Claims, 9 Drawing Figures UNITED STATES PATENTS 3,527,056 9/1970 Hofi'rnan ..60/258 'r r TP I I -i 59- 5 .1 A\ & a A lllllll nzlus\\: \\\\\\o\" v PATENTEDAPRI 01973 SHEET 2 OF 4 PATENTEDAPR] 0 I973 SHEET [1F 4 FIG 6B (IN-DEMAND VARIABLE FLOW CLOSED LOOP GAS GENERATOR SYSTEM WITH A VARIABLE AREA INJECTOR BACKGROUND OF THE INVENTION l. Field of the Invention The invention relates generally to an on-demand variable flow gas generator system and more particularly to a monopropellent on-demand closed loop fuel feeding system with a variable area injector for firing a reactor control system.

2. Description of the Prior Art The previous systems, to vary the flow, were based on using several injector valves which required a complicated control system. Moreover, the previous systems, to vary the flow, required additional injectors with the capability of switching the injectors on or off in order to maintain enough injector differential pressure (A P) for atomization.

SUMMARY OF THE INVENTION The present invention overcomes the aforementioned problems by reducing the number of valves and injectors while maintaining continuous flow through the injectors. Moreover, the unique system is simple, fully automatic, and can be used in any propulsion device with monopropellent or bipropellent systems. Briefly, the present invention includes a single bellows variable area injector having no valves other than an explosive disc in the propellent supply system separating the gas generator from the fuel storage tanks.

The variable area injector is of theswirl type where the propellant is brought into rotation in orifice plate by slots located in a stationary pintle. The variation in flow is obtained by using the orifice plate to cover and uncover a series of slots in the pintle and thereby change the effective entrance area to the swirl chamber to match the varying exit area of the cone and orifice. Movement of a slotted sleeve, which is joined to the bellows, is initiated by a pressure differential across the bellows and swirl chamber from the decrease or increase in chamber pressure.

An alternative embodiment involves a more complicated open loop system including a two-position fixed area injector which works on the principle that for each thrust step, which is initiated by operating gas valves, a propellent valve is required to match the flow demand to maintain a constant pressure and continuous flow. The subject matter of the aforementioned invention is disclosed in copending U.S. Pat. application Ser. No. 173,508 by W. K. Kretschmer and P. A. Heady, Jr.

STATEMENT OF THE OBJECTS OF THE INVENTION A primary object of the present invention is to provide a closed loop two-propellent system utilizing a variable area injector which maintains continuous flow.

Another object of the present invention is to provide a simple, fully automatic, closed loop propellent system which is capable of being used with any monopropellent or bipropellent liquid propellent device.

Another object of the present invention is to provide a system with variable fuel propellent flow to a gas generator at a closed loop system which will maintain a constant combustion chamber pressure at flow variations of about ten to one.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an assembly drawing of the on-demand gas generator system of the present invention;

FIG. 2 is a drawing of the gas generator of FIG. 1 wherein thruster valves are used in place of the warm gas valves of FIG. 1;

FIG. 3 is an illustration of the unique solid igniter used in the system shown in FIGS. 1 and 2;

FIG. 4 is an illustration of the unique warm gas valve used in the gas generator of FIG. 1;

FIG. 5 is a schematic drawing of the closed loop system of which the gas generators of FIGS. 1 and 2 are a part;

FIG. 6 is an illustration of the unique variable area single bellows injector used in the gas generators shown in FIGS.1, 2, and 5;

FIG. 6A is an illustration of the unique pintle cone and orifice plate of injector of FIG. 6;

FIG. 6B is an illustration of the swirl slots of the injector of FIG. 6; and

FIG. 6C is an illustration of sleeve dash'pot of the injector of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT There are two somewhat similar on-demand gas generators, namely, the closed loop system shown in FIG. 5 and the open loop system, not shown, but disclosed in the aforementioned copending application. Both systems have good response to change in flow demand for simulation of thrust pulses of different duration and energy at relatively constant chamber pressure (P,). FIG. 1 shows the general scheme of the on-demand gas generator used in the open and closed loop systems. The closed loop system shown in FIG. 5, which is the subject matter of the present invention, is simple and requires few components.

The variable area injector, illustrated in FIG. 6, combines a flow regulation valve and spring-loaded bellows into one integrated unit. Flow changes in the injector are initiated by chamber pressure I decrease or increase through changes in gas flow demand by chamber pressure P decrease or increase through changes in gas flow demand by switching gas valves on or off. The pressure drop across the injector for different flow rates varies within a relatively narrow band and the P pressure changes are equal to this A P variation. A more detailed description of the unique closed loop system of FIG. 5 and the injector of FIG. 6 are set forth below.

In contrast, the open loop system with a dual twoposition injector, described in the aforementioned copending application, works on the principle that for each thrust step, which is initiated by operating gas valves, a propellent valve is required to match the flow demand to maintain constant P pressure. The twoposition injectors of the open loop system reduce the number of valves required to three and maintain continuous flow through the injector at an injector A P of about 35 psi, or above, at the orifice for six thrust steps.

Referring to FIG. 1, the on-demand variable flow closed loop gas generator system 1 comprises gas generator 3, injector assembly 5,

hot gas valves

11, 13, 15 and 17 and

gas nozzles

25, 27, 29 and 31. The closed loop system also includes an igniter 2 which is illustrated in FIG. 2 and described in conjunction with FIG. 3. The volume of the gas generator is a function of the characteristic length of the chamber and the throat or nozzle area. The upper and middle section of chamber 69 contains aperature 49 opening onto orifice plate 9 and pintle 7 of injector assembly aperature 50 is provided to accept igniter 2, shown in FIGS. 2 and 3.

Gas tube openings

51, 53, 55 and 57 are provided to accept

hot gas valves

11, 13, and 17, respectively. The aforementioned hot gas valves may be replaced by a standard thruster cluster if desired. The igniter 2 and injector 5 are threaded into

valve openings

49 and 50, respectively of cylindrical chamber 69. To protect the chamber walls and domes from overheating a silica phenolic insulation or other equivalent material may be used. More specifically, the generator may be lined with a spiral wound 0.2 inch thick silica phenolic liners. This insures gas flow over the liners in the direction of the spiral windings and prevents delamination. The generator shown in FIG. 1 can be provided with gas tube liners 23 to

line tube openings

51, 53, 55 and 57. impingement liners 25 may be used to line cylindrical chamber 69. Chamber liners 27 can be used to line chamber domes 65 and 67 to prevent overheating of the chamber domes. Nicrome screens 19 including screen supports 21 may be installed into gas generator 3 to filter contaminents and to prevent nozzle blockage. The screens are respectively mounted in the ends of

domes

65 and 67, adjacent to cylindrical chamber 69 and supported in the axial direction by the semi-tubular shaped screen supports 21. The screen supports 21 are preferably made of columbium or the equivalent.

Domes

65 and 67 each contain

ports

59 and 61 to function as a gas relief valve or safety valve. Safety disc assembly 41, with extension pipe 39, is attached to port 61 of dome 67. Safety disk 41 can be ruptured at 2,000 psig and acts as an upper limit gas pressure relief valve. Dome idle orifice 45 and extension pipe 37 are attached to port 59 of dome 65. The idle orifice takes the place of an idle gas relief valve. The idle orifice includes the idle flow nozzle 47 and a 750 psi burst disc 43. The burst disc 43 bursts at ignition and provides a bypass flow for exhaust gas at idle flow. Openings are also provided in the

extension pipes

37 and 39 for temperature probes TP.

Referring to FiG. 5, the closed loop system 111 comprises squib 113, fuel expulsion gas generator 115,

' pressurization line 117,

Otto Fuel tanks

119 and 121,-

burst disc 123, fuel feed line 125, gas generator igniter 131, Otto Fuel gas generator 129,

thruster valves

133 and 135 and variable flow injector 127. Each of the

clusters

133 and 135 contains four thruster valves, or four warm gas valves, as the case may be, at each end of the chamber of gas generator 129, as illustrated in FIG. 1. Flow changes in the injector are initiated by a chamber pressure P decrease or increase through changes in gas flow demand by switching gas valves on or off. The pressure drop across the injector for different flow rates varies within a relatively narrow band; a P pressure is equal to the differential pressure variation A P. An ancillary solenoid switch may also be used.

Referring to FIG. 2, the gas generator 3 comprises cylindrical chamber 69, two dome ends and 67 and

thruster cluster

71 and 73. The thruster valve clusters include thruster valves with thruster nozzles which attach directly to the domes, 65 and 67, as illustrated in FIG. 2. A sectional view of gas inlet 63 of injector 5 is also illustrated. The propellent injector 5 is located in the middle of cylindrical chamber 69. It should be noted that the warm gas valves shown in FIG. 1 and 6 are used to simulate the above-mentioned thruster cluster shown in FIG. 2. A description of the warm gas valves shown in FIG. 6 will follow.

The ignition of Otto Fuel can be accomplished by an electric preheater or with solid igniter. The latter device is more desirable because ignition must be instantaneous. In FIG. 3 is illustrated the solid igniter 2 used in the system shown in FIGS. 1 and 2. Solid igniter 2 comprises filter 79, foil discs 81 and 91, nozzle 83, burst disc 87 and stand pipe 89. Propellent grain is located in the inner upper body of igniter 2. Ball powder 85 circumferentially surrounds burst disc 87 and stand pipe 89. To obtain a rapid gas generator pressure rise from solid igniter 2, smokeless powder is used as a booster because it has a high burning rate and is a good gas producer. To maintain the pressure level, the non-perforated external burning cylindrical propellent grain 75 is simultaneously ignited with the powder 85 which continues to burn for about 0.4 seconds. The igniter 2 consists of two

chambers

2a and 2b which are internally separated by foil rupture disc 81. The front chamber 2a contains the igniter nozzle 83 with filter 79. Igniter assembly 2 is threaded into aperature 50 of gas generator 3 in the plane of injector 5 and tilted at an angle of 30 to the axis of the injector 5. The rear chamber 2b contains a burst disc 87 and a stand pipe 89 which prevents the loss of powder 85 into gas generator 3 before burning and during ignition.

The ignition may be completed by an igniter squib 77 or a similar device. The propellent grain 75 is preferably nonperforated, or holeless grain, to provide a longer burning time. It has been found by experimentation that by eliminating the hole in the grain, the grain burning time increased by 3 A times, or from 0.15 to 0.4 seconds, using 20 grams including about 0.5 grams of boron potassium nitrate (BKNO A normal charge of ball powder would be between 6 and 12 grams for good results. The rupture disc 87 is set to burst at about 750 psig with a peak pressure in the gas generator of about 770 psig at 0.4 second with a grain burnout at 0.4 second.

To simulate the on-demand condition in the Otto Fuel gas generator, a total of four warm gas valves are required. Referring to FIG. 4, each of the gas valves 1 1, 13, 15 and 17 comprises a water cooling manifold 93,

bellows 95, poppet head 97,

seat insert liners

99, 101,

103 and 105, and nozzle 107. Each valve has a sealed pneumatic valve bellows with an operational gas temperature of about 1,500 F at 1,500 psig pressure. The gas valves simulate the function of the aforementioned thruster cluster. However, the warm gas valves may be used as the thruster valves in certain types of vehicles using reaction control devices such as target drones. All gas passages are lined with columbium material and the valve seat and poppet units are also made of columbium material. A provision for water cooling is desirable in the operative system. Each valve is fitted with a nozzle 107 that is installed downstream of the gas valves. The warm gas valve opening sequence can be calculated and established in a standard manner. The activation may be by gas generator pressure or an ancillary solenoid valve. The discussion of the valves is informational only and not the subject matter of the present invention.

Referring to FIGS. 6, 6A, 6B and 6C, the unique variable area injector 139 is a swirl type and comprises stationary pintle 141, attaching nut 143, O ring seal 145, top plate 147, sleeve 149, dash pot 151, metal 0 ring 159, bellows flange 161, housing 163, bellows 165, orifice plate 167, swirl slots 183, and fuel flow paths 179. The propellant is brought into rotation in orifice plate 167 by means of tangential swirl slots 183 in the stationary pintle 141. At the exit of the injector 139 a conical sheet of fuel develops having fine atomized droplets. The variation of flow in the design is obtained by moving orifice plate 167 which uncovers a series of swirl slots 183 in pintle 141 and changes the effective exit area of swirl slots 183. Movement of the orifice plate 167, which is joined to bellows 165 is initiated by the pressure differential A P across the bellows 165, sleeve 149 and swirl chamber 185. The flange 150 of injector sleeve 149, shown in FIG. 6C, is a piston which is connected to dash pot seal 151. The flange 150 of sleeve 149, which is attached to orifice plate 167, is free to move vertically within the limits of flange limiting area 187. The pintle 141 includes a downward extending portion 181 and cone 141k which forms a swirl chamber 185. The downward extending portion 181 includes eight swirl slots 183. Each slot forms a 45 angle to a line tangent to the exterior section. The pintle point, or cone, 141b extends, when bellows 165 is in the expanded position, so that the attached orifice 167 and the pintle point Mlb form a line parallel to the base of the orifice 167 when in the closed position. The top of the pintle 141 has a hollow section 161a to allow the fuel to flow when burst disc 123, shown in FIG. 5, is fractured. The fuel flows through side ports 173 of pintle lel along a path through sleeve 149 ports 175 and between bellows 165 to the swirl slots 183. Sleeve 149 includes three small

pressure balancing holes

153, 155 and 157 located on sleeve flange 150, as shown in FIG. 6C. The sleeve 149 includes upper ports 175 which align with pintle ports 173 and lower ports 177 which align with swirl slots 183 and to form a continuous fuel flow path direct to swirl chamber 185. When bellows 165 is extended so that swirl slots 183 are open, the fuel flows through swirl slots 183 to swirl chamber 185 and into the orifice aperature 171 that opens onto gas generator 3. The inner vertical walls of the bellows 165 and the vertical walls of the sleeve 149 form the flow path for the fuel. The sleeve 149 is also ported at the top and bottom, thus forming a path for fuel flow, as mentioned above. The orifice plate 167 includes a bored orifice section 171 allowing fuel to exit into generator 3. The orifice plate further includes a circular slotted or recessed portion 169 to accept the downward extending portion 181 of the pintle 141 and to act as a closure means to control the amount of swirled fuel from the swirl slots 183 exiting into the gas generator 3. The total effective flow area is a function of the slots and orifice plate exit areas. The cone angle of the pintle is designed to bring the pintle diameter and the hole of the swirl plate into an even position, as described above. A small movement of the swirl plate, about 0.007 inch from this point, is enough to develop a cone spray of approximately 54 at the desired low flow of 0.09 lb/sec of Otto Fuel with an injector A P of 23 psi. Dash pot seal 151 is incorporated into the design to help eliminate excessive pressure oscillation during idle flow. The seals 151 may be made of Teflon or other similar material. The fixed pintle 141 is fastened to top plate 147 by nut 143. The injector housing 163 is attached to top plate 147 and is separated slightly by metal 0 ring 159. The pintle cone 141b and the downward extending section 181, when openly aligned with sleeve ports 177, form a flow path 179 to swirl chamber 185. The pintle 141 is fixed wherein the bellows 165 is operatively coupled to the orifice plate 167. The sleeve 149 is attached to orifice plate at recess section 169 so that when bellows 165 compresses or expands, the orifice plate 167 and sleeve 149 move correspondingly and in phase with bellows 165.

The overall system functions in the following manner with approximate timing sequences being determined by experimentation, as illustrated in Table I.

TABLE I Time (seconds): 0 Ignition of solid igniter squib 0.016 Power to solenoid of propellant value 0.16 Arrival and ignition of Otto Fuel in gas generator 0.180 Rupture of burst disc 0.40 Solid igniter burst Referring to FIG. 1, burst disc 123, located between fuel feed line and

Otto Fuel tanks

119 and 121, bursts at ignition. The idle orifice 45 takes the place of a gas relief valve for idle operation.

Referring to FIG. 6, the flange of sleeve 149 has three

holes

153, 155, and 157 drilled to allow for the exchange of Otto Fuel between the upper and lower side of the flange 150. The holes are each 0.0135 inches in diameter. The system then functions as a dash pot when coupled with a dash pot seal 151 to damp out excessive pressure oscillations during idle flow.

Holes

153, 155 and 157 allow the necessary pressure equalization. The system has stable operation with rapid flow changes up to 7.25/1 and the capability of handling flow variation of 13/1 with changes in the spring constant of the bellows and the injector valve stroke. Moreover, increases to 20/ l for idle periods are possible by adding a fixed flow pilot hole to the injector. The system requires no valves other than an explosively operated burster disc 123 in the propellant supply line 125 to separate the gas generator and the propellant tank during storage. The fuel system is selfregulating and responds almost instantaneously to changes in chamber pressure P from idle to demand flow. This type of unique injector can also be used with other monopropellants such as hydrazine and MHF as well as bipropellants. The gas generator may be constructed of titanium or other similar lightweight high temperature material that is well known in the art.

What is claimed is:

7 flow means, variable flow injector, igniter and a gas generator with a plurality of thruster means, said injector comprising in combination:

a. a fuel inlet operatively connected to said fuel flow means;

b. fuel discharge ports;

0. a stationary pintle device including said fuel inlet and said discharge port and a cone shaped point attached to a circular shaped downward extending portion, said downward extending portion including a means for swirling fuel and a plurality fuel discharge slots;

(1. a vertically extending partially enclosed sleeve with an upper flange portion and a lower flange portion having swirling fuel exit ports said sleeve circularly encompassing said stationary pintle;

e. a bellows portion circularly encompassing said sleeve, said circularly surrounding pintle wherein a space between said bellows and said sleeve forms a fuel flow path for said fuel;

f. an orifice plate operatively attached to said bellows and said sleeve so that when said'bellows compresses or expands said sleeve and said plate move in a vertical direction with respect to said bellows;

g. said plate having an orifice opening onto said gas generator; and

h. said sleeve having a recessed portion to accept said downward extending portion of said pintle wherein said recessed portion varies the discharge area of said slots.

2. The device in claim 1 wherein said igniter is operatively attached to an opening into said gas generator at a 30 angle from said injector to allow a convergence between ignited fuel and injector fuel at locus point in said generator.

3. The device recited in claim 1 wherein said igniter is divided into a first section and a second section wherein said first and second section are separated by a foil burst disc, said first section comprising a solid propellent grain and a squib to ignite said propellant and a filter attached to a nozzle, said nozzle discharging said ignited propellant at such a pressure to break said disc, thus allowing propellant to enter said second section, said second section comprising ball powder surrounding a further burst disc and a foil disc which separates said second section from the chamber of said gas generator, said ignited propellant subsequently igniting ball powder and breaking said discs, thus allowing said ignited propellant to enter said gas generator.

4. The device recited in claim 1 wherein said sleeve includes a pressure equalization means.

5. The device recited in claim 4 wherein said equalization means is a flange extending from the upper portion of said sleeve and said flange including three pressure equalization holes wherein said flange is located between a vertical limiting means whereby said vertical movement of said flange bellows and orifice plate are limited by said limiting means.

6. The device recited in claim 5 wherein said equalization means further includes a sealing means coupled to said flange wherein said flange having holes and said sealing means, when located in said limiting means functi nsas dash 7. e device re ited in iaim 1 wherein said swirl slots are tangentially intermittently located at 45 of the side walls of said downward extending portion of said pintle and in a stationary relationship with respect to said orifice.

8. The device recited in claim 7 wherein the propellant is brought into rotation into said orifice plate by means of said tangential slots of downward section of said stationary pintle in a swirl chamber formed by said orifice and said slots.

9. The device recited in claim 8 wherein said movable orifice includes a slotted portion to accept said downward extending portion with said tangential slots whereby said orifice plate in moving away from said pintle said tangential slots are uncovered thus varying the efiective area of said swirl chamber.

10. The device recited in claim 9 wherein said swirl chamber is joined to the bellows wherein said movement is initiated by a pressure differential across the bellows and swirl chamber wherein the resistance to movement by said bellows is further controlled by a pressure equalization means.

I I! III

Claims

1. An on-demand closed loop variable flow gas generator for a reaction control system including a fuel flow means, variable flow injector, igniter and a gas generator with a plurality of thruster means, said injector comprising in combination: a. a fuel inlet operatively connected to said fuel flow means; b. fuel discharge ports; c. a stationary pintle device including said fuel inlet and said discharge port and a cone shaped point attached to a circular shaped downward extending portion, said downward extending portion including a means for swirling fuel and a plurality fuel discharge slots; d. a vertically extending partially enclosed sleeve with an upper flange portion and a lower flange portion having swirling fuel exit ports said sleeve circularly encompassing said stationary pintle; e. a bellows portion circularly encompassing said sleeve, said circularly surrounding pintle wherein a space between said bellows and said sleeve forms a fuel flow path for said fuel; f. an orifice plate operatively attached to said bellows and said sleeve so that when said bellows compresses or expands said sleeve and said plate move in a vertical direction with respect to said bellows; g. said plate having an orifice opening onto said gas generator; and h. said sleeve having a recessed portion to accept said downward extending portion of said pintle wherein said recessed portion varies the discharge area of said slots.

2. The device in claim 1 wherein said igniter is operatively attached to an opening into said gas generator at a 30* angle from said injector to allow a convergence between ignited fuel and injector fuel at locus point in said generator.

6. The device recited in claim 5 wherein said equalization means further includes a sealing means coupled to said flange wherein said flange having holes and said sealing means, when located in said limiting means, functions as a dash pot.

7. The device recited in claim 1 wherein said swirl slots are tangentially intermittently located at 45* of the side walls of said downward extending portion of said pintle and in a stationary relationship with respect to said orifice.

9. The device recited in claim 8 wherein said movable orifice includes a slotted portion to accept said downward extending portion with said tangential slots whereby said orifice plate in moving away from said pintle said tangential slots are uncovered thus varying the effective area of said swirl chamber.