US3558251A

US3558251A - High tension igniter plugs

Info

Publication number: US3558251A
Application number: US801546A
Authority: US
Inventors: Louis Jules Bauger; Roland Robert Charles Beyler; Adolphe Robert Lefebvre; Herve Alain Quillevere; Michel Bernard Schenher
Original assignee: SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1968-02-27
Filing date: 1969-02-24
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26
Also published as: FR1592091A

Abstract

AN IGNITER PLUG COMPRISING INNER AND OUTER ELECTRODES DEFINING THEREBETWEEN AN ANNULAR PASSAGE ENDING IN AN ANNULAR GAP FOR DEVELOPMENT OF IGNITION SPARKS. A GAS IS FED TO THE PASSAGE FOR EMERGENCE THROUGH THE GAP. A WHIRLING MOTION IS IMPARTED TO THE GAS IN THE PASSAGE TO GIVE THE SPARKS A LIKE WHIRLING MOVEMENT. ALTERNATIVELY OR ADDITIONALLY, THE OPERATIVE END PORTION OF THE INNER ELECTRODE FORMS ARE OUTWARDLY FLARING DEFLECTOR FOR THE FLOW OF GAS TO PROMOTE THE FORMATION OF AN IGNITION FLAME.

Description

Jan'. 26,1971'1 L. J. BAUGER ETAL 5 3,558,251

, H HIGH TENSION IGNITER PLUGS Filed Feb; 24, 1969 4 Sheets-Sheet 1 FIG. 7a

Jan. 26, 1971 J. BAUGER ETAL 3,558,251

- HIGH TENSION IGNITER PLUGS Filed Feb. 24, 1969 4 Sheets-Sheet 2 wal QJ MMQIUJ (Oil Jan) CEHWU 155251971 L, ,BAUG.L; ETAL 3,558,251

HIGH TENSION IGNITER PLUGS v Filed Feb. 24, 1959 r 4 sheet -shat 5 mwamw L. J. BAUGER ETAL 3,558,251

HIGH TENSION IGNITER PLUGS 4 Sheets-Sheet 4 Filed Feb. 24, 1969 O 1X1 il United States Patent 3,558,251 HIGH TENSION IGNITER PLUGS Louis Jules Bauger, Vanves, Roland Robert Charles Beyler, Levallois-Perret, Adolphe Robert Lefebvre, La Rochette, Herve Alain Quillevere, Issy-les-Moulineaux, and Michel Bernard Schenher, Paris, France, assignors to Societe Nationale dEtude et de Construction de Moteurs dAviation, Paris, France Filed Feb. 24, 1969, Ser. No. 801,546 Claims priority, application France, Feb. 27, 1968,

Int. Cl. l zs 3/00 US. Cl. 431-266 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a high tension igniter plug for igniting a fuel mixture, for example an air/fuel mixture in the combustion chamber of a jet engine.

{High tension igniter plugs produce sparks between determinate points on two electrodes. Conventionally, such igniter plugs have an inner or central electrode and an outer or earth electrode in the form 'of a cylindrical element connected to earth and surrounding the central electrode, said cylindrical electrode carrying at its operative extremity one or more tips directed towards the inner electrode, the spark arcs being struck between the inner electrode and the nearest point or points of said tip or tips.

It is an object of the invention to provide a high tension igniter plug of improved operating efiiciency, in particular a plug capable of providing faster ignition.

The high tension igniter plug according to one feature of the invention comprises an inner electrode, an outer electrode surrounding the inner electrode to define an annular passage therebetween, said electrodes having operative extremities relatively positioned for development of ignition sparks or arcs therebetween during use, and means for imparting a whirling or gyratory motion to a gas or gas/ vapour mixture which in use is fed to the annular passage for emergence through the annular gap between the operative extremities of the electrodes.

Thus, we have discovered that, if the aforementioned tips on the outer electrode are removed, and if a substantial flow of air or of some other gas is created between the inner electrode and the outer electrode, the arc struck between the operative extremities of the electrodes splits into several individual sparks distributed more or less uniformly around the annular gap between the electrode extremities. Moreover, the gas stream tends to project the ionised arcing zone downstream and thus increases the volume of the zone so that the sparks, whilst continuing to strike between the electrodes, are bowed in the downstream direction beyond the electrode extremities. Furthermore, when the air or other gas is made to gyrate or whirl in the annular gap between the electrode extremities, the sparks striking between the electrodes are likewise given a whirling or gyratory movement, so that they move through the environmental vapourised fuel mixture to be ignited, which mixture is invariably subject to local variations in richness.

In this connection, it should be mentioned that the electrodes are generally carried by ceramic components and it is known, for the purpose of cooling these ceramic components, to cause air to circulate along the igniter plug; the sparks are not affected by the airflow, the latter serving only for cooling purposes.

It will be apparent that the speed of the emergent gas or mixture should be maintained at a value below the value which would extinguish the sparks, which latter value depends upon the voltage and supply frequency, as those skilled in the art will appreciate.

Preferably, the operative extremities of the electrodes are relatively shaped in such a manner that the annular gap therebetween has a throttling effect on the gas or gaseous mixture passing therethrough during use.

The means for imparting a whirling or gyratory motion to the gas or gaseous mixture may conveniently.comprise a plurality of vanes located in the annular passage. Alternatively, the gas or gaseous mixture may be fed into the passage through an arrangement of helical grooves.

Means are preferably provided for heating the gas fed to the annular passage, in order to facilitate ignition, for example of a jet engine when cold.

If desired, the plug may include a longitudinal bore in the inner electrode for injection of fuel therethrough during use, and passage means for diverting a portion of said fuel for mixture with the gas fed to the annular passage.

In accordance With a further feature of the invention, a high tension igniter plug comprises an inner electrode, an outer electrode surrounding the inner electrode to de fine an annular passage, therebetween, said electrodes having operative extremities relatively positioned for development of ignition sparks or arcs therebetween during use, and throttle means for a gas or gas/vapour mixture which in use is fed to the annular passage for emergence through the annular gap between the operative extremities of the electrodes, said throttle means comprising an outwardly flaring generally conical deflector forming part of or carried by the operative extremity of the inner electrode. This deflector either may be used in combination with the means for imparting a whirling or gyratory motion to the gas or gaseous mixture or may be used independently of this latter means. The deflector creates, in the flow of gas or gaseous mixture emerging from the annular passage, a backwash zone which promotes the formation of an ignition flame in the environmental vapourised fuel mixture on contact with the sparks.

If the means for imparting a whirling or gyratory motion to the air is used in combination with the deflector, then the environmental vapourised fuel mixture is ignited by the rotating elongated sparks and an ignition flame develops in the backwash zone shielded by the deflector.

The invention may be carried into practice in various ways, but some practical embodiments of high tension igniter plug according thereto will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates the basic elements of an igniter plug in accordance with the invention, viewed in axial section;

FIGS. 1a, 1b and 1c are end views of said plug, illustrating the distribution of the sparks at various air speed values;

FIG. 1d is a schematic view similar to that of FIG. 1, showing a modification;

FIG. 2 illustrates a practical embodiment of igniter plug in accordance with the invention, considered in section on the line II-II of FIG. 3;

FIG. 3 is a sectional view on the line III-III of FIG. 2;

FIG. 4 is a sectional view of the line IVIV of FIG. 2;

FIG. 4a is a view similar to that of FIG. 4, showing a variant embodiment;

FIG. 5 is a view similar to that of FIG. 2, showing another embodiment;

FIG. 6 is a longitudinal half-section through part of a jet engine combustion chamber incorporating an igniter plug similar to that illustrated in FIG. 5; and

FIG. 7 is a view similiar to those of FIGS. 2 and 5, showing another embodiment.

The igniter plug schematically illustrated in FIG. 1 has an inner electrode constituted by a rod a carrying, at its operative end, a conical deflector b. The rod a is supported by a ceramic component d on the axis of an outer cylindrical electrode c. The electrodes are supplied in the conventional way from a high voltage supply and air is blown through the annular passage defined between the electrodes in the direction of the arrows f.

If air is not blown through the annular passage, or if the air flows in the direction of the arrow 1 at a negligible velocity, when a spark e will be struck in a straight line between the electrodes (FIG. 111) along the shortest possible path.

As soon as air is blown through the passage at an appreciable speed (FIG. lb), the spark e divides into several individual sparks e, provided that the respective end rims of the outer electrode c and deflector b form substantially coaxial circles, and the individual sparks e bow outwards in the downstream direction. If the speed of the air is increased, the sparks divide again and bow further out along paths of increased length. It will thus be seen, in FIG. lc, that when the speed of the air at the exit from the annular passage reaches a predetermined level, for example of from 4 to 5 metres per second, a large number of sparks e", distributed around the deflector b, are produced, forming a projecting annular bead of sparks (FIG. 1). When, moreover, the air is made to whirl in the annular passage, the sparks are individually caused to execute a rotational movement about the axis of the plug.

FIG. 1 also illustrates the advantages of the deflector in accordance with the invention. The flow of air passing between the electrodes creates, in the slipstream of the deflector b, a backwash zone g (FIG. 1) in which develops the flame produced when the sparks contact with the vapourised fuel mixture present at h. The use of the deflector also has the advantage, since it throttles the annular passage in the region of the sparking zone, of increasing the air speed at this point; this produces a further multiplication and extension of the sparks and creates the substantially stationary volume g where the flame can establish itself.

In FIG. 1d, the deflector b extends in the longitudinal direction outwardly beyond the outer electrode c so that the free edge b of the deflector is situated beyond the free edge c of the outer electrode in this longitudinal direction. The air deflected by the deflector exits through the annular gap 1' between the free edges b and c carrying with it the sparks, which thus extend and curve to occupy an annular volume e which projects radially outward substantially beyond the outer electrode. When the air in the annular passage is made to rotate, the sparks are likewise made to rotate and sweep through the whole of the volume e As this volume 6 is larger than the volume swept by the sparks in the arrangement of FIG. 1, the sparks ignite the environmental vapourised fuel mixture more rapidly. As in the arrangement of FIG. 1, the deflector b promotes the initial development of the flame by creating a static backwash zone behind it.

In FIG. 1d, the deflector b is not of straight conical form, as shown in FIG. 1, but presents a concave surface to the emergent air, thereby to guide the air radially outwards.

FIGS. 2 to 4 illustrate a practical embodiment of igniter plug having air-heating and fuel-injection facilities.

In this embodiment the annular passage between the electrodes passes a flow of air to which has been imparted a whirling or gyratory component. In the embodiment of FIG. 4a, the annular passage passes a purely axial flow of air.

The igniter plug incorporates a metal body which has a head 1 and a skirt portion 2. The head 1 is in the form of a cylindrical block carrying two bosses 3, 4, respectively adapted to receive components providing heater current supply and components providing high tension supply. The head is recessed at two different diameters 5 and 6. The skirt 2 is in the form of a hollow cylinder provided at one end with a flat flange 7 adapted to be fixed to the adjacent face of the head 1 using countersunk screws 1'. The flange 7 carries a boss 8 containing a fuel-injection passage 9, the purpose of which will be explained hereinafter. The flange is also provided with holes 2' for use in the assembly of the igniter plug in a jet engine combustion chamber as will be explained hereinafter with reference to FIG. 6.

The plug has an inner electrode 10 in the form of a rod provided externally with a conical shoulder 11 at one end and a threaded portion 12 at the other, and carries externally a sealing collar 13 and a boss 14. The boss 14 in fact comprises a plurality of inclined vanes 20 (FIG. 4) or axially directed vanes 20a (FIG. 4a). The electrode rod 10 contains a longitudinal bore 15 opening at the operative end of the electrode into a conical shoulder 11 through a threaded hole which receives a fuel atomiser 16. The remote end of the bore 15 communicates through radial holes in the electrode 17 with an annular peripheral throat 18. Other radial holes 19 in the electrode 10, also leading from the passage 15, open on to the electrode periphery in the region of the boss 14, between the blades 20 (FIG. 4) or 20a (FIG. 4a).

The inner electrode 10 is carried by an insulating ceramic component 21 of cylindrical external form, which is located in the recess 5 of the metal head 1 and abuts the base of said recess. The end portion of the electrode 10, i.e. the end portion remote from its operative end, is located in a central bore 22 of said component 21 and a nut 23, screwed on the thread 12, locks the collar 13 against the component 21. The latter component contains a radial passage 24 which, in the assembled position, opens at one end into the annular throat 18 and at the other into the base of a threaded hole 25 in the metal head 1, in order to communicate with the passage 9 through a small pipe 26 passing through a seal 27 clamped in position by a ring 28 which is screwed into the threaded hole 25. The component 21 contains a cavity 29 of which the peripheral wall 30 contains a hole 31 for the high tension input, and a cavity 32 of the same diameter as the recess 6 in the metal head 1. A ceramic plug 33, containing a recess 34 for the nut 23, fits into the cavity 32 and the recess 6, flush with the face of the metal head 1, being secured in position by a cover 35 which is in turn fixed in position by screws 36.

The igniter plug has an outer electrode 37 in the form of a hollow cylindrical element externally carrying, near to one of its ends, a projection 38 which abuts against an internal circular shoulder 39 formed at the end of the skirt 2 of the plug body. The other end of the electrode 37 is force-fitted over an insulating ceramic carrier 40. The latter contains a cylindrical bore 41 in which engages the boss 14, i.e. the

blades

20 or 20a, carried by the inner electrode. The ceramic carrier 40 is also formed with an external annular projection 42 interrupted by wide grooves 43, which projection fits inside the recess 5 of the metal head 1 and abuts the peripheral wall 30 of the cavity 29 in the ceramic component 21. An electrical resistor 44, wound around the carrier 40 between the grooved collar 42 and the electrode 37, is connected with the heating current conductors 45 which pass through the projection 42 and the boss 3 of the metal head 1, terminating in a conventional electrical adaptor 46 screwed into said boss.

with the internal electrode 10 and its earth terminal is in contact with the metal head 1. The high tension source, which has not been shown, should be capable of producing sparks which are sufiiciently strong and of suitable frequency to ignite a vapourised fuel mixture. The high tension current source, as well as the adaptor 47, can be of conventional kind.

The ceramic component 21 is maintained in contact with the base of the recess and with the plug 33 by the grooved projection 42 of the ceramic carrier 40 which is fixed to the electrode 37, the shoulder 39 of the skirt 2 bearing against the projection 38 of said electrode when the flange 7 is clamped against the head 1 by the screws 1'. The various components of the igniter plug are thus firmly held in position, the outer electrode being in electrical contact with the earth terminal of the electrical adaptor 47 through the intermediaries of the skirt 2 and the head 1, and the inner electrode 10 being maintained in electrical contact with the terminal 48. The

ceramic components

21 and 40 provide electrical insulation between the igniter plug and the resistor 44. Moreover, the ceramic component 40 co-operates with the straight or inclined vanes of the boss 14 in order to centre the inner electrode 10.

The igniter plug is supplied with compressed air through an orifice 49 in the skirt 2. The air thus enters the annular space 50 defined between the skirt 2 and the electrode 37, in which space it is heated by the resistor 44 when current is supplied to the latter, and passes from said space 50 into the cavity 29 through the grooves 43 in the projection 42 of the carrier 40. The heated air then passes from said cavity 29 into the bore 41 of the carrier 40, between the vanes 20 (FIG. 4) which impart a whirling or gyratory motion as it passes along the annular passage between the inner electrode 10 and the outer electrode 37 and thence around the deflector 11. In the modification of FIG. 4a, the vanes 20a serve to guide the air in the axial direction only.

The deflector 11, located at the operative end of the plug, creates a static zone which promotes ignition.

A supply of the fuel takes place through the passage 9. In the embodiment illustrated, this is open at both ends so as to be capable of being supplied at either end, this by closing off one end and connecting the other end to a pressurised fuel source after fitting a filter. The pressurised fuel flows through the passage 9 into the passage 15, thence through the pipe 26, the passage 24, the throat 18 and the holes 17 into the bore in the inner electrode. A portion of the fuel is injected through the holes 19 and slightly enriches the air at the level of the

vanes

20 or 20 formed by the boss 14, the fuel enriching the air more completely downstream of the deflector 11, where it is atomised by the atomiser 16.

When the igniter plug is supplied with high tension current through the adaptor 47, sparking develops in the annular gap between the edge of the deflector 11 and the outer electrode 37. The sparks are distributed around this annular gap and bow outwardly therefrom, in the manner previously described with reference to FIG. 1. In the modification of FIG. 4a, the sparks are stationary in position, but in the embodiment of FIG. 4 the sparks have a rotary movement around the annular gap, sweepskirt portion penetrating inside the flame tube of the combustion chamber. Consequently, assuming that the frequency of the supply current is sufficiently high, an annular bead of sparks is produced which considerably increases the available ignition volume, as mentioned above. The flame develops downstream of the deflector 11, fed by the atomiser 16, and then propagates itself through the flame tube, which is supplied with air and fuel in a conventional manner.

The heating of the air is not essential to the ignition function of the plug and it is within the scope of the invention to omit the resistor 44. Further, the injection of fuel for ignition, through the plug itself, can be omitted if desired. Thus, we have observed, in the course of trials using the plug, that an entirely separate combustion chamber injector for injecting fuel into contact with the operative end of the igniter plug may, in some circumstances, suflice on its own for the supply of fuel. However, it is necessary for efliciency that the sparks should not develop too far from the point of injection of the fuel and that the arcing volume should be relatively shielded from the airflows invariably present in the combustion chamber due to the supply of primary and secondary air.

FIGS. 5 and 7 respectively illustrate, by way of example, an igniter plug similar to that of FIGS. 2 and 4 or 4a but without any fuel-injection facility, and an igniter plug without any fuel-injection or air-heating facility. These igniter plugs operate in a similar manner to that of FIGS. 2. to 4 or that of FIG. 4a. Those elements which perform the same functions as corresponding elements in these earlier figures are given the same references, but with the addition of indices a and b in FIGS. 5 and 7 respectively.

In FIG. 5, the inner electrode 10a and its ceramic carrier 21a are simplified due to omission of the fuelinjection facility. The full line 52 schematically indicates the boundary of the backwash zone created in the wake of the deflector 11, and the broken-line 53 indicates the annular bead formed by the sparks. The elements of the embodiment of FIG. 7 are even simpler in design due to omission of the air-heating facility as well as the fuelinjection facility.

FIG. 6 shows the assembly of an igniter plug generally similar to that of FIG. 5 in a jet engine combustion chamber. The combustion chamber is of a well known type and, for this reason, is not described in detail. It is of an annular form and comprises an annular casing 54, an annular flame tube 55 having two

walls

55a and 55b welded at their forward zones to a burner ring 550 containing orifices (not shown) adapted for the introduction of primary air, the latter being schematically indicated in the drawing by the arrows 58. The burners 56 are welded in position around the peripheries of these orifices. FIG. 6 is a longitudinal half-section on the axis (not shown) of the annular combustion chamber, said axis being situated beyond the drawing, the half-section being taken between two neighbouring burners 56.

Each burner 56 comprises an operational fuel-injector (not shown) located on its axis 57. The reference 56' indicates the fixing of the burner ring 55c to the arms of the intake casing (not shown) of the combustion chamber. Secondary air, indicated schematically by the arrows 59, circulates -between the casing 54 and the flame tube 55.

Igniter plugs are located in predetermined positions between consecutive burners and slightly downstream of the burners. These predetermined positions, conveniently distributed in order to promote the propagation of the flame from one burner to the next, normally number two between consecutive burners, but a larger number of igniter plugs can be used if required. Each igniter plug 60 has a heating resistor but no fuel-injection facility. However, the embodiment of the igniter plug shown at 60 is constructionally slightly different from that of FIG. and in particular the high voltage supply adaptor (invisible) is directed perpendicularly to the heater current adaptor 47c secured in the boss 3c and connected to the heater resistor 44c. The other elements of the igniter plug 60, which perform the same function as corresponding elements in the embodiment of FIG. 5, are designated by the same references but carry the index c.

The igniter plug 60 is secured in a boss 61 in the casing 54 by means of screws 62 engaging in the holes 3'0 in the flange 7c, the skirt being located in

holes

63, 64 formed opposite one another in the casing 54 and the external wall 55a of the flame tube, respectively. The skirt 2c reaches slightly inside the flame tube and the orifice 490, located between the flame tube and the casing 54, is directed upstream in order to be supplied directly with secondary air 59.

In the combustion chamber of FIG. 6, the annular head of sparks must be carefully localised. The high speed of the primary air 58 separating the igniter plug from the zone in which the fuel in injected by the fuel injectors (not shown) at the centre of the burners 56 necessitates substantially instantaneous relaying of ignition. This is ensured by ignition injectors 65 each located upstream of an igniter plug 60 and comprising an atomiser 66 which atomises ignition fuel in the downstream direction, and an atomiser 67 which atomises ignition fuel for counterfiow. In traversing the zone in which the primary air is enriched and which is shielded by the arms of the burners, the flame developing at the igniter plug is rapidly transmitted to the zone of mixing at the injector 65.

It will be apparent that various modifications of the above-described embodiments are possible within the scope of the invention, as defined by the appended claims. For example, in the embodiments using inclined vanes 20 to impart a whirling or gyratory motion to the air in the annular passage, the deflector located at the extremity of the inner electrode 10 may be modified or even dispensed with, in part dependent on the high tension supply system used. Obviously, the dimensioning of the igniter plugs described may be modified. The high tension spark-generating current may be produced using a low frequency high supply voltage or a high frequency high supply voltage.

Although the above described assembly of an igniter plug is'concerned with a jet engine combustion chamber, the igniter plugs of the invention can be used for many other applications, for instance for the ignition of a jet engine afterburner.

We claim:

1. A high tension igniter plug, comprising:

a plug body,

an inner electrode insulatingly mounted on the plug body,

an outer electrode,

an insulating component mounting the outer electrode on the plug body to surround the inner electrode and to define an annular passage therebetween, the said electrodes having operative extremities relatively positioned for development of spark arcs therebetween, sleeve mounted on the plug body to surround the outer electrode and its supporting component in spaced relationship thereto, said sleeve having an aperture for gas supply, passage means in the plug components for feeding gas from the space between the said sleeve and the said outer electrode to the annular passage between the electrodes,

and an electrical heating element for heating said gas mounted in the space between the said sleeve and said outer electrode on the insulating component supporting said outer electrode.

2. A high tension igniter plug, comprising:

a plug body,

an inner electrode insulatingly mounted on the plug body,

an outer electrode mounted on the plug body to surround the inner electrode and to define an annular passage therebetween, the said electrodes having operative extremities relatively positioned for development of spark arcs therebetween,

a high tension connector mounted in the plug body and having respective electrical connections to the two electrodes,

passage means through the plug components to supply gas to the annular passage for emergence through the annular gap between the operative extremities of the electrodes,

passage means in the inner electrode for fuel injection,

branch passage means for diverting a part of said fuel into the air flow in the said annular passage,

and means in the passage for imparting a directional movement to the gas/fuel mixture thus produced.

3. A high tension igniter plug according to claim 2, in

which the said means for imparting a directional movement to the gas/fuel mixture comprises a plurality of shielded conical backwash zone on the remote side of the deflector.

5. A high tension igniter plug, comprising:

a plug body,

an inner electrode insulatingly mounted on the plug body,

and an outwardly flaring generally conical deflector forming the operative extremity of the inner electrode, at least a part of said deflector extending in the longitudinal direction beyond the operative extremity of said outer electrode.

6. A high tension igniter plug according to claim 5, in which the deflector presents a concavely curved surface to the gas which emerges during use from the annular passage.

7. A high tension igniter plug, comprising:

a plug body,

an inner electrode insulatingly mounted on the plug body and ending with a generally circular continuous operative extremity,

an outer electrode mounted on the plug body to surround the inner electrode and to define an annular passage therebetween, said outer electrode ending with a generally circular continuous operative extremity adjacent the operative extremity of said inner electrode to define therewith a continuous annular spark gap positioned endwise of said annular passage and forming a throat constriction thereof,

a passage means through the plug components to supply gas to the annular passage for emergence through the annular spark gap between the operative extremities of the electrodes,

and means for imparting a whirling motion about the plug axis to the gas flowing through and out of the annular passage.

References Cited UNITED STATES PATENTS 2,865,441 12/1958 Coupe 431-266X EDWARD G. FAVORS, Primary Examiner US. Cl. X.R.