FR2504745A1 - IGNITER FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

THE INVENTION RELATES TO AN IGNITER FOR REACTION ENGINES AND OTHER INTERNAL COMBUSTION ENGINES. THIS IGNITER CONTAINS A TUBULAR CERAMIC INSULATOR 17 WHICH CONTAINS A SIGNIFICANT PROPORTION OF SILICON NITRIDE AND WHICH IS PROVIDED INSIDE THE CAP 13 OF THE IGNITER 10, SO THAT DISRUPTIVE DISCHARGE OCCURS ALONG A SURFACE 24 OF THE INSULATOR 17, ADJACENT TO THE SPARKLER FORMED BETWEEN A CENTRAL ELECTRODE 14 AND A GROUND ELECTRODE CONSTITUTED BY A SURFACE 18 OF THE SOCKET 13. THE USE OF SILICON NITRIDE ELIMINATES THE BERYLLIUM OXIDE WHICH IS TOXIC. FIELD OF APPLICATION: REACTION ENGINES AND OTHER INTERNAL COMBUSTION ENGINES.

Description

The invention relates to an igniter of the type

  high energy, intended for an internal combustion engine.

  In use, for example in a jet engine, such an igniter is ignited by a capacitive discharge ignition device, either of the high voltage type or of the low voltage type. The disruptive discharge of the high voltage igniters usually occurs. along a surface of a dielectric ceramic located adjacent a spark gap formed between a center electrode and a ground electrode A "high" voltage should be applied, usually in the range of 10,000 to 30,000 volts, to ionize the spark gap formed between the electrodes to allow the discharge of the igniter.

  Lighters intended for lighting devices

  Low voltage mage, usually around 200

  at 5000 volts, have an electrically semi-

  adjacent a spark gap formed between a central electrode and a ground electrode It is

  appeared in an igniter with a semi-surface

  conductive so arranged, the voltage required for a disruptive discharge is reduced compared to that required for an igniter o this position is occupied

by an insulator.

  Whether the igniter is high voltage or low voltage, the spark appearing between the ground electrode and the central electrode accompanies a discharge of a

  capacitor previously charged The discharge of condensa-

  gives the spark a high energy, namely

up to about 20 joules.

  It has been suggested and used in the prior art

  various electrically semiconducting and insulating materials

  placed in close proximity to the spark gap

  For example, U.S. Patent No. 3,558,959 discloses low voltage and high voltage ignition devices.

  a low-voltage igniter using semi-

  conductors composed of mixtures of alumina and hot-pressed silicon carbide It is also suggested that it was possible to produce semiconductors

  suitable for low voltage applications

  a body made of a mixture of silicon carbide

  aluminum silicate, by drowning the body

  in silicon carbide particles, and in process

  In addition, United States Patent No. 3,968,057 discloses a process for the production of baking (see, for example, U.S. Patent Nos. 3,376,367 and 3,573,231). an alumina-bonded silicon carbide semiconductor for a high-energy, low-voltage ignition device, and US Patent No. 4,120,829, discloses an improved carbide semiconductor silicon, having a glass bonding phase, not

conductor of the electric current.

  U.S. Patent No. 3,052,814 discloses silicon nitride bonded silicon carbide semiconductor bodies for low voltage igniters. According to the latter patent, lighters

  having a semiconductor body of silicon carbide

  silicon nitride are better able to withstand the compressive forces, extreme temperatures, vibrations and erosion effects of sparks encountered during operation in a combustion chamber, than igniters using the materials of the PRIOR ART The use of semiconductor bodies formed of a nitrided mass of Si and Si C has been found to minimize the problems posed by excessive porosity, insufficient compressive strength, and low resistance to erosion. by the

  sparks, and variations in the ehi-

  appearing in the combustion chamber (with consequent variation in

  These problems are posed by semi-electric

  suggested igniter conductors in the prior art.

  British Patent No. 717,555 discloses a method for producing, from silicon metal, silicon nitride shaped bodies. The reaction-bonded silicon nitride bodies thus produced are described as being resistant to thermal shock, as having

  high mechanical strength and being very resistant

  In addition, the dielectric properties of silicon nitride bodies produced in accordance with the process described in the aforementioned US Pat. No. 717,555 are shown to be similar to those of silica. that it would be possible to use

  silicon nitride bodies in many applications.

  cations at high temperature, these applications include

  jet combustion chambers, ejector nozzles, combustion chambers and rocket ejector nozzles, and

body of spark plugs.

  Although it has been suggested to incorporate

  Many materials are used in igniters for use under very stringent conditions (see, for example, U.S. Patent Nos. 2,684,665, 2,786,158, 3,344,304 and 3,558,304. 959),

  it has not been suggested, so far, in the prior art

  to use silicon nitride, alone or mixed with other materials, on the surface of insulators adjacent to the igniter spark gap controlled by high-voltage, high-energy ignition circuits.

  igniters are subject to thermal stresses

  extreme electrical and electrical characteristics when used in jet engines and other

  internal combustion engines Insulators known

  now used in such igniters, are produced from materials such as alumina and beryllium oxide, both known for the production of ceramic bodies which are satisfactory electrical insulators when they are

  conveniently located near the end of all

  of a high-energy igniter. However, the iso-

  Alumina latters are subject to significant spark erosion and degradation by thermal shock, in service Although insulators made from beryllium oxide are much more durable and more resistant to thermal shock than those produced from of alumina, it is considered that beryllium oxide

  is toxic to humans and therefore less desirable

  table to use it extensively in manufacturing

igniters.

  The invention is based on the observation that it is possible to produce an improved high-energy type igniter by suitably assembling, in such an igniter, an insulator body composed of substantially pure silicon nitride or a base material. silicon nitride, and having a surface covered, at the moment of a discharge, by a spark formed between

  a center electrode and a ground electrode.

  It has been found that high-energy igniters, which comprise suitably formed bodies, containing a large proportion of silicon nitride and placed in their appropriate positions in their caps, have a longer life under service conditions encountered in such applications. that jet engines, where igniters are subjected to severe thermal, mechanical and electrical

  seems that the thermal, mechanical and electrical properties

  apparent effects of the insulator bodies composed of silicon nitride materials not only allow these materials to oppose greater resistance to spark erosion and thermal shock degradation than that of the insulators produced.

  in alumina # but also unexpectedly

  due to these bodies behaving almost as well as insulators composed of beryllium oxide, without raising the toxicity problems posed by the latter material Therefore, the invention relates to an improved igniter using silicon nitride, which can be produced without presenting the hazards to the personnel associated with the manufacture of igniters

containing beryllium oxide.

  The subject of the invention is therefore an improved high-energy igniter for jet engines and

  other internal combustion engines.

  Another object of the invention is an igniter comprising

  a ceramic insulator which contains a large proportion of silicon nitride, the insulator being housed annularly in the base of the igniter, near the ignition end, so that a disruptive discharge, produced between a center electrode and a ground electrode of the igniter, will appear along

the surface of the insulator.

  The invention will be described in more detail with reference to the accompanying drawing by way of non-limiting examples and in which: Figure 1 is a longitudinal section of the high voltage igniter according to the invention; FIG. 2 is a longitudinal section at

  enlarged, partially schematic scale of an isola-

  silicon nitride nozzle disposed in the base of the igniter shown in Fig. 1; and

  FIG. 3 is a longitudinal section through

  schematic of the ignition end of another embodiment of the high-voltage igniter

according to the invention.

  As shown in detail in FIG.

  high voltage igniter, high energy, indicated overall-

  10, has an ignition end 11 and a connecting end 12. The igniter 10 comprises a metal base 13, a central electrode 14 and insulators 15, 16 and 17 mounted in an annular space formed between the base 13 and The base 13 has an annular portion 18 facing inwardly located at the ignition end 11 of the igniter 10 and constituting a ground electrode. In use, the igniter 10 is mounted. removably so that the annular portion 18 enters the ignition chamber of an associated motor (not shown) and is set to

  mass of the engine by contacting the base 13 with the latter.

  The insulator 15, which is a body made of alumina, is fitted close to the connection end 12 of the igniter 10 in order to form a cylindrical cavity 19 in which a contact of an associated ignition device (no shown) can be electrically engaged with a portion of the central electrode 14 which enters the cavity 19 The insulator 16, which is a body made of alumina, has a central bore containing the central electrode 14, and it is protruding axially from the bottom of the cavity 19 to form a section

  tubular 20 terminating at a point

  the ignition end 11 of the igniter 10, at which point this insulator is disposed between the insulator

  17 and the central electrode 14, in an annular space 21.

  The insulator 17, which is a body made of

  substantially pure silicon nitride, is housed in the

  21 and it comprises a tubular section 22 located between a portion of the insulator 16 and the base 13, and it extends axially towards the end 12 of

  igniter connection 10 An extreme tip 23 of allu-

  mage, widened radially, is mounted on the central electrode 14 and is arranged in the annular space 21

  so that part of this mouthpiece is adjacent to V'iso-

  17 silicon nitride, at the end of all

  The silicon nitride insulator 17 has a portion that extends axially from its tubular portion 22 to the ignition end 11 of the igniter 10, this portion having a surface 24 adjacent to a

  spark gap formed between the end or the tip 23 of allu-

  mage of the central electrode 14 and the annular electrode

18 of the mass of the base 13.

  The insulator 17 made of silicon nitride is

  in vertical section and on an enlarged scale on the

figure 2.

  As shown in detail in FIG. 3,

  the ignition end of a high-voltage, high-energy igniter according to the invention is indicated generally at 25. The igniter 25 comprises a lower metal base

Z 304745

  26 connected to an upper metal base 27 by a

  silver solder indicated in 28, and it also includes

  a central electrode 29 which has a mouthpiece

  ignition and ring insulators 31 and 32.

  Only a tubular portion of the insulator 31 is shown. The bottom cap 26 has an annular portion 33 facing inwards and constituting a ground electrode. In use, the igniter 25 is removably attached so that the portion ring finger 33 gets into

  the ignition chamber of an associated engine (not shown

  The insulator 31, which is a body made of alumina, is housed in an annular space 33 formed between the upper base 27 and is grounded to the motor by contacting the upper base 27 with the latter.

  and the central electrode 29 and has a central bore

  tral in which are arranged a section of the electrode

  central 29 and a tubular section 34 of the insulator 32.

  A gas-permeable talc seal is annularly formed between the bottom cap 26 and the tubular section 34 of the insulator 32 and fills an area between an annular-outer flange 36 of the insulator 32 and an inner annular flange 37

bottom cap 26.

  The insulator 32, which is a substantially pure silicon nitride body, extends axially from its tubular portion 34 to a point located a short distance from the annular mass electrode 33 and occupies, at this location, an annular space 38 formed

  between the lower pellet 26 and the central electrode 29.

  The insulator 32 made of silicon nitride has a sur-

  face 39 which is adjacent to a portion of a radially thinned section 40 of the central electrode 29, while a surface 41 of the insulator 32 is adjacent to a spark gap formed between the ignition end 30 of the central electrode 29 and the annular electrode 33 of

  mass formed by the lower pellet 26.

  It should be noted that an insulator having, for example, the overall shape of one of the insulators 17 and 32 shown in FIGS. 1-3, can be realized

  in any suitable material, based on silicon nitride

  rather than substantially pure silicon nitride, and can be used in close proximity to the ignition end of an igniter according to the invention so that a disruptive discharge occurs along the

  of a surface of this igniter For example, such an iso-

  can be made from silicon oxynitrides

  aluminum-aluminum ("SIALON") or from compositions -10 of silicon nitride or "SIALON" and one or more additional components, added as sintering auxiliaries, for example Y 203, Ce 203, 203, Sc 203, Cr 203, Mg O, Zn O, Ni O, Ti O 2, Sn O 2 and Sr O 2 These sintering aids are particularly useful in sintering

  without pressure of a composition of the type "SIALON" Cepen-

  lant, an igniter according to the invention, comprises an insulator in which the proportion of silicon nitride is large, that is to say at least 50% by weight, and

  preferably at least 65% by weight.

  Only two embodiments of the invention

  have been described above with reference to the drawings.

  An igniter according to the invention may also be produced by means of a two-piece insulator having, for example, the overall shape of the insulator 17 shown in FIGS. 1 and 2 and consisting, for example, of a nitride of substantially pure silicon, hot pressed, or a "button" based on silicon nitride, bound to

  an alumina isolator Surface 24 must be

  killed from these silicon nitride materials; the button can have a thickness down to about 3.2 mm, its thickness preferably being

  less than 4.8 mm and, even more desirably

  The silicon nitride materials are unexpectedly found to exhibit good erosion resistance by high-energy sparks of the type occurring in the igniter 10. and in similar igniters such as

that shown in Figure 3.

  The aluminum nitride insulator of the igniter according to the invention, whether it is a complete insulator or a button glued to an insulator made of alumina, and in all cases, that it is composed essentially of silicon nitride, or silicon nitride mixed with other materials, can be produced by hot pressing, as indicated above, or

  by sintering processes without pressure or bonding

  However, silicon nitride insulators

  Hot-pressed cium are preferred because they generally exhibit greater erosion resistance than insulators obtained by non-pressure sintering or reaction-bonding processes. Therefore, hot pressed bodies are particularly suitable for igniters subjected to severe constraints in service

  as is the case, for example, in jet engines.

  However, when the geometry of an igniter requires machining of an insulator body after fabrication and firing, pressure-free sintering or bond-reaction is preferred because these processes impart to the body a

better machinability.

  It goes without saying that many modifications can be made to the igniter described and shown

  without departing from the scope of the invention.

Claims (6)

  1 igniter having an end (11) of allu-   mage and a connecting end (12), characterized in that it comprises a metal base (13) removably mountable in a combustion engine   internal and presenting, at the ignition end of the   a surface (18) which constitutes an annular electrode   mass guide, a ceramic insulator (16) housed in the metal base and having a central bore, a central electrode (14) housed in this bore of the ceramic insulator and having an ignition end <23) spaced from the annular mass electrode of the   base with which it forms a spark gap, and an isola-   an insulator (17) containing a large proportion of silicon nitride and housed within the base, said insulator (17) having a surface (24) adjacent to the spark gap   and traveled by a spark when a discharge occurs   between the ignition end of the central electrode and the ground electrode of the pellet.   2 Lighter according to claim 1, characterized   rised in that the silicon nitride insulator and   the ceramic insulator comprise tubular sections   (20, 22) disposed in an annular space (21) formed between the metal base and at least a portion of the central electrode.   3 lighter according to claim 2, characterized in that the insulator (17) of silicon nitride extends   axially from its tubular portion to the end of allu-   mage of the igniter, to the surface along which the disruptive discharge occurs.   4 Lighter according to any one of the claims   1 to 3, characterized in that the silicon nitride insulator consists of a hot pressed ceramic.   An igniter according to any one of the claims   1 to 3, characterized in that the silicon nitride insulator consists of a sintered ceramic without pressure. 1 1   An igniter according to any of the claims   cations 1 to 3, characterized in that the silicon nitride insulator consists of a bonded ceramic by reaction.