US2942420A

US2942420A - Ignition mechanism

Info

Publication number: US2942420A
Application number: US692796A
Authority: US
Inventors: Albert G Clark
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1957-10-28
Filing date: 1957-10-28
Publication date: 1960-06-28
Anticipated expiration: 1977-06-28

Description

June 28, 1960 A, G, CLARK IGNITION MECHANISM Filed Oct. 28, 1957 df@ nTTORN-'y K R 3 0 Rm w w mfg/4 M 4 5 HR 6 mo E 4. m 1.... m A w w a. 7

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Unite States IGNITION MECHANTSM Filed Oct. 28, 1957, Ser. No. 692,796

4 Claims. (Cl. 60-39.82)

The present invention relates to an ignition mechanism and more particularly to an ignition mechanism for combustion devices capable of delivering a large thermal energy in the form of a high temperature plasma.

Presently, ignition means used for combustion chambers and afterburners, rocket motors, decomposition gas generators and other similar .types of `combustion devices are invariably spark plugs, glow plugs, pyrotechnic ignitors, and the like. In general, spark and glow plugs are limited to handling and delivering smaller amounts of energy and at lower temperature than is frequently needed to reliably ignite engines and afterburners at high temperature where dame-outs are encountered. Further, such devices as spark plugs are unable to ignite monopropellants of the more stable varieties because of the high resistance to ignition inherent in these materials.

In some present applications, a pyrotechnic ignitor using a powder charge is used but this particular method has the drawbacks of mechanical complication for a repetitive operation system due to reloading; also powder charges represent a logistic problem since they must be handled as ammunition. In addition, there are present applications which require greater amounts of ignition energy than can be provided even with fairly sizeable powder charges, and for these applications, an ultra high temperature ignition device or mechanism would be required to provide satisfactory ignition.

The present invention comprises an ignition mechanism utilizing a fluid stabilized arc as a source of an ultra high temperature plasma jet for igniting stable monofuels and air-fuel systems at high altitude to thereby promote ignition under normally diiiicult combustion circumstances. Specifically, the present invention provides an electric arc and plasma producing device operatively coupled to a combustion chamber so that the fluid stabilized arc is directed within the chamber `to sustain combustion therein. In this manner, a super heated plasma working fluid is used to produce ignition by virtue of transfer of heat from the working fluid to the combustion medium to be ignited.

In addition, the present invention provides an electrode feeding mechanism for maintaining a reasonably constant arc gap in the electric arc and plasma producing device by automatically providing means of feeding a predetermined amount of positive electrode material, consumed in each operation, through a suitable gearing and roller feed mechanism operated by solenoid means.

An object of the present invention is the provision of an ignition mechanism for combustion chambers and after burners, rocket motors, decomposition gas generators and other similar types of combustion devices, .utilizing a super heated plasma working uid to produce i-gnition by virtue of transfer of heat from the working fluid to a medium to be ignited.

Another object is to provide an ignitionmechanism utilizing an ultra high temperature plasma jet from 'a uid stabilized arc having large amounts of ignition energy for .igniting engines and afterburners at high altitudes.

latent A further object of the invention is the provision of an ignition system suitable for aircraft application and capable of delivering a high thermal energy in the form of a high temperature plasma, and having electrode feeding means for maintaining a substantially constant arc gap.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

Figure 1 is a sectional view of a preferred embodiment of the invention;

Figure 2 is a side View, partly in section, of the device of Figure 1, showing the striker wire at the start of the operation;

Figure 3 is a sectional view of the device taken on the line 3-3 of Figure 2 looking in the direction of the arrows, and showing the arc stabilizing uid inlet; yand Figure 4 is a sectional view of the device of Figure l. showing the striker wire feeding mechanism.

Referring now to the drawings, there is illustrated a pre-l ferred embodiment 10 provided with an electric arc and plasma generator 12 suitably secured to a combustion chamber 14, as hereinafter disclosed. The arc and plasma generator `12 is provided with a generally cylindrically shaped housing 16 of a suitable insulating material such as Lucite, or the like, having a spin chamber 17 and a feeder mechanism chamber 18 formed coaxial therewith by the utilization of a cover structure 20 securely mounted on the housing by securing means, such as a connecting ring 21, or the like. A positively energized rod electrode or anode 22 of graphite, or the like, is axially and adjustably supported within the housing 16, While a negatively energized generally ring-shaped electrode or cathode 24 coaxial to said anode is mounted within a suitable opening at one end of the spin chamber coinciding with the lower end wall of the housing 16.

A large source of electrical power is applied across

electrodes

22 and 24 to produce an electric arc 26 therebetween in the spin chamber. To prevent arc 26 from spreading and to contine it within a small enough volume to greatly increase its current density and temperature over that normally obtainable, a suitable iluid7 such as air, water, nitrogen, or the like, is introduced into the spin chamber 17 at high velocity through a tangentially arranged inlet nozzle 28 so as to whirl or circulate at high speed concentrically about the arc 26. A rotating column of uid is thus formed about the arc confining it within a considerably smaller cross sectional area than it would normally occupy and, in this manner, greatly increases the current density of the arc which raises the temperature of the arc.

Observation and theory indicates that in addition to.

confining arc 26 and greatly increasing its temperature, portions of the fluid circulating Vabout the arc become part of the arc, are heated by it, and are directed through aperture 25 in the ring electrode 24 as an arc plasma 28. It is believed, that when water is employed as the Huid, the portions thereof in close proximity to the arc 26 are heated and vaporized, and the vapor thereupon enters the arc stream and is propelled through the center aperture in electrode 24 through the action of vapor pressure and extreme temperature. After entering the arc stream, this vapor apparently becomes superheated steam, then decomposes into molecules of hydrogen and water and finally ionizes into charged ions.

Additionally, since plasma 28 contains ionized carbon, it appears that carbon particles eroded from

electrodes

22 and 24 `are also carried into the plasma stream. Hence, plasma 28 contains water vapor, oxygen, hydrogen, carbon, electrons, and charged ions when propelled through the aperture 25 into the combustion chamber 14, where the superheated plasma working fluid is used to produce ignition by virtue of transfer of heat from the plasma 28 to the medium 32 to be ignited.

The housing 16 is preferably cylindrically formed with the cover 20 suitably shaped to be removably connected thereto by the ring 21. If deemed necessary as a means of facilitating visual inspection of the working area, the housing may be formed from a transparent material, such as Lucite, or the like. A plurality of fastening means, such as bolts 30, or the like, are peripherially spaced about a ange 34 integral with the housing y16, to rigidly attach the generating device 12 to a wall structure 36 of the combustion chamber 14. A transverse deflector plate 38 with a cente-r aperture 39 is provided in the housing 16 to confine the column of circulating fluid Silabout the arc 26. Fluid escaping between the electrode 22 and the aperture 39 passes into a drain charnber 40 provided within the housing 16 and formed there in by the transverse detlector plate 38 and a Sealing structure 42. The sealing structure is provided with a plurality of leaf type fluid seals 44 which enables the rod electrode 22 to be progressively rotated and posi-- tioned as may be desired through the sealing structure and the aperture 39. A fluid drain 46 provided with suitable drain conduit, not shown, is formed in the housing 16 to drain the uid within the chamber 40.

The seal assembly 42 is secured to a separation plate 48 securely fixed between the housing 16 and the cover 20, and provided with an electrical insulating member i) which supports the leaf seals 44 within the seal assembly. In this manner, the structural arrangement prevents an inadvertent grounding of the electrode 22 with the negatively energized portion of the housing 1.6 and cover 2t). However, if the housing and the cover are made of insulating material, such as Lucite, or the like, the insulating material 50 may be replaced by a suitable supporting member for the leaf seals 44. Now, with this provided structural arrangement, the axially adjustable electrode 22 may be predeterminedly positioned with respect to the electrode 24, as it becomes eroded by the arc 26, by an automatic feeding mechanism 52.

The feeder mechanism 52 comprises a ratcheting sole noid 54 suitably coupled to a conventional source of power, not shown, and provided with a shaft 56 having a driving sheave S3 operatively secured thereon. A bevel gear 60 is mounted on the end of shaft 56 for operative engagement with a second bevel gear 62, located at right angles therewith and mounted on a shaft 63 rotatably mounted on the interior wall of the cover 20. A thi-rd bevel gear 64 is provided on a shaft 66 which is suitably mounted for rotation on the interior of the cover 20, so that the bevel gears form a gear train, having a predetermined gear ratio, from the solenoid shaft 56 to a striker wire spool shaft 66. A striker wire spool 68 is suitably mounted for mutual rotation with the shaft 66, and provided with a satisfactory amount of striker wire 70. The striker wire 70 is fed through an axial aperture in the electrode 22 so that the wire protrudes a predetermined length from the end of the electrode into the spin chamber 17.

A second sheave or roller '72 is mounted on a shaft 74 having shaft ends journalled in the interior structure of the cover and in parallel relationship with the shaft 56. In this manner, the electrode 22 is in .frictional engagement with the friction sheaves or

rollers

58 and 72 and predeterminedly actuated longitudinally within the housing 16. Hence, the striker wire 70 and the electrode 212 are differentially actuated, and the relative longitudinal movement of the wire and electrode is deter-mined by the ratio of the bevel gears. yConsequently, the feeder mechanism 52 automatically compensates for the portions of the electrode 22 `and the striker wire eroded in the operation of the preferred embodiment ltl.

As disclosed, fluid is continuously pumped into the spin chamber -17 under relatively high pressure to replace the fluid being absorbed into the are 26 and converted to plasma 28. The continuous ow of fluid also serves to cool electrodes 22 `and. 24, as Well as the housing f16 and thereby enable the arc and plasma generator 112 to handle considerably larger amounts of electrical power and, correspondingly, generate extremely high temperature electrical arcs.

Briefly, the preferred embodiment 10 comprises a pair of

electrodes

22 and 24, wherein one of the electrodes, cathode 24, is positioned in the end wall of the cylindrical spin chamber 17 coinciding with the wall of the combustion chamber 14, so that the electrode nozzle 25 opens on an axis at right angle to the wall 36 of the combustion chamber 14 on which the arc and plasma generator 12 is mounted. It should be understood, of course, that the mounting of the generator 12 with respect to the combustion chamber 14 is a matter of expediency with each intended installation. Further, the housing 16 is equipped with tangential duid inlet 28 with which the stabilizing fluid is introduced into the spin chamber 17. The rod anode 22 is adjustable along the longitudinal axis of the housing :through an automatic feeder mechanism 52.

Fluid from the spin chamber 17 escapes into the drain chamber 40 provided with the outlet 46 through which approximately over of the stabilizing fluid returns to the drain, not shown, and subsequently to a suitable storage accumulator, also not shown since of conventional design and application. To maintain a predeten mined and reasonable constant arc gap between the elec trodes as the anode electrode 22 is consumed in the arc, a small amount, approximately of an inch to 1A of an inch per ignition shot, is fed by the solenoid operated mechanism 52 through the coaction of the bevel gear train and the frictional roller means.

In the operation of the preferred embodiment 10, the plasma jet 28 with a temperature of approximately between l8,000 to 25,00()D F. will be generated for as long as desired, and up to several seconds if deemed necessary. The operation of the preferred embodiment is initiated by the closing of a suitable switch, not shown, which will energize the solenoid 54 which may operate, if de- Y sired, off a 24 volt power supply. The solenoid will feed through the gearing and sheave arrangement the striker Wire to strike an arc between the cathode electrode 24 and the anode electrode 22 as the gap therebetween is reduced by relative movement toward each other. Simultaneously the stabilizing fluid will be pumped, through a conventional pump mechanism, not shown, or otherwise displaced from the storage container, not shown, into the spin lchamber 17 to produce a rotating vortex to confine or compress the arc 26, forcing most of the current to ow in the center, and provide the Working fluid which boils, ionizes, disassociates and streams through the electrode nozzle 24 to form the plasma jet 28.

To control the duration of the plasma jet 2S, a preset timer or time relay, not shown, may be provided to stop the action after the necessary time for ignition has been established. l-f desired, this may be accomplished in a variety of ways; for example, further withdrawal of the electrode 2?. by reversing the direction of the solenoid 54 will increase the gap and the resultant voltage drop would reduce the current flow; or the action may be stopped, of course, by cutting off the power. Another method of stopping the action of the generator 12 is to cut-oh` the liow of stabilizing fluid which will make the arc 26 unstable and cause it to extinguish by itself. This last method is probably the best and simplest since 1t eliminates the necessity of having an additional device, such as a contacter, to handle the power fed to the electrodes 22 and l24v. i

in this manner, the present invention provides a small component ignition unit suitable for aircraft application which can deliver large thermal energy in the form of a high temperature plasma to mix with a combustible mixture that normally could not be ignited by conventional means. For example, tests have indicated that in one unit with overall housing dimensions of one and one half (l1/2) inches in diameter by two and one-half (2l/2) inches in length can deliver approximately ten (l0) kw. in the form of heated working fluid at a temperature of approximately 20,000 F. Further, the preferred embodiment is capable of repeated operation without replacement or" cartridges or other inert parts as in the case of Such a presently used technique as pyrotechnic ignitors.

The present invention is simple, safe and reliable and does not require strategic materials, or materials representing logistic supply problems such as slow burning powder propellants, and the like. The ignition of some chemical propellants and metallic propellants is presently limited by the unavailability of an adequate high temperature source to produce the temperature in the particles needed for their sustained combustion or decomposition. The present invention can produce temperatures approximately twice as high as any existing electrical or chemical combustion means and consequently will open new horizons to the combustion field.

It should be understood, of course, that the foregoing ydisclosure relates to only a preferred embodiment of the invention and that .it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set^forth in the appended claims.

What is claimed is:

1. An ignition system for a combustible mixture comprising a iluid stabilized arc generator having a pair of coaxial electrodes for forming an ultra high temperature plasma jet; a combustion chamber operatively coupled to said generator and containing the combustible mixture exposed to the plasma jet so that heat is transferred to produce ignition, electrode feeding mechanism operatively coupled to one of said pair of electrodes for maintaining a reasonable constant arc gap therebetween and actuating means operatively coupled to said feeding mechanism for feeding a predetermined amount of electrode material to replace that amount consumed in operation.

2. An ignition mechanism comprising an electrical arc and plasma generator having a spin chamber and a feeder mechanism integral therewith, an energized anode axially and adjustably supported within said feeder mechanism chamber and said spin chamber, an energized ring-shaped cathode mounted at one end of said spin chamber and axially opposed to said anode, a power source applied across said anode and cathode to produce an electric arc therebetween in said spin chamber, rotating fluid means formed about the electric arc to confine it within a small cross-sectional area and thereby increase its current density and temperature, a combustion chamber connected to said generator, so that the arc is propelled through said ringshaped cathode as a plasma jet to produce ignition due to transfer of heat from the jet to the combustible mixture, and means for predeterminedly positioning said anode with respect to said ringashaped cathode as it becomes corroded by the electric arc, said anode having an axial aperture, a striker wire axially adjustable within said aperture relative to said anode to protrude a predetermined length from the end thereof into said spin chamber to strilre the electric arc between said anode and said cathode.

3. An ignition mechanism for a combustible mixture, comprising means for delivering large thermal energy as a high temperature plasma at approximately 25,000 F., a combustion chamber operatively associated with said means to receive the plasma to sustain combustion therein.

4. in combination, a fluid stabilized arc plasma generator having a spin chamber, a ring electrode having a central aperture mounted in one end of the spin chamber, a rod electrode mounted to protrude into the other end of the spin chamber, said rod electrode and ring electrode being axially opposed to one another, means for connecting a source of electric power between the rod electrode and the ring electrode to produce an electric arc between them, means for injecting a lluid under pressure into the spin chamber to cause the iluid injected into the chamber to rotate concentrically about an are between the rod electrode and the ring electrode, whereby plasma produced by such an arc ilows through the aperture in the ring electrode; a combustion chamber adapted to have a combustible composition located within said combustion chamber; and means for mounting the arc plasma generator on the combustion chamber so that plasma produced by the generator can enter into the combustion chamber to ignite said combustible composition.

References Cited in the file of this patent UNITED STATES PATENTS 1,587,806 Thompson June 8, 1926 2,293,079 Ranke Aug. 18, 1942 2,587,331 Jordan Feb. 26, 1952 2,635,423 Oakes Apr. 21, 1953 2,662,104 Southern Dec. 8, 1953 2,768,279 Rava Oct. 23, 1956 2,784,553 De Corso Mar. ll, 1957 2,806,124 Gage Sept. 10, 1957 OTHER REFERENCES Scientilic American, August 1957, vol. 197, No. 2, pp. -88.