Monitoring turbomachine spark plug wear by visually detecting differential wear

Abstract

The invention relates to a spark plug (6) for a turbomachine combustion chamber. The spark plug (6) comprises a first region (60) and a second region (62) adjacent to the first region (60) and having electrical properties different from those of the first region (60). The second region (62) is designed to be visible when the spark plug (6) is located in the combustion chamber to visually detect wear of the spark plug (6) due to differential wear of the first region (60) relative to the second region (62). (See Figure 4a for abbreviations.)

Description

Description Title of the invention: Wear monitoring of a tur- spark plug bomachine by visually detecting differential wear technical field

[0001] = The invention relates to the general technical field of aircraft turbomachinery such as turbojets and turboprops. It relates to a spark plug ignition for a turbomachine combustion chamber. Previous technique

[0002] The combustion chambers of turbomachinery of known structure comprise a spark plug to ignite a pool of air and fuel mixture injected into the combustion chamber.

[0003] — In a spark plug comprising a semiconductor material, the production sparks between a central electrode and a peripheral electrode through the Semiconductor material causes erosion of the semiconductor material. Erosion of this semiconductor material and oxidation of the electrodes can lead to the replacement of the spark plug.

[0004] To estimate the wear of a spark plug, it is known to evaluate the voltage of the knocking sound at which a spark occurs through the spark plug, since the The spark plug's breakdown voltage tends to increase with wear. spark plug. It is relatively difficult to monitor spark plug wear. since the spark plug must be removed from the combustion chamber. Furthermore, the spark plug is often replaced after being removed from the combustion chamber combustion. Description of the invention

[0005] The invention aims to solve at least partially the problems encountered in the solutions from prior art.

[0006] In this regard, the invention relates to a spark plug for a combustion chamber Turbomachine combustion. The spark plug includes a first electrode and a second electrode.

[0007] — According to the invention, the spark plug comprises a first region and a second region adjacent to the first region and which has properties electrical systems different from those of the first region. The second region is designed to be visible, especially when the spark plug is located in the chamber combustion, to visually detect wear on the spark plug differential of the first region with respect to the second region.

[0008] = Thanks to the second region, it is possible to monitor the wear of the spark plug Reliable ignition during visual inspection of the spark plug in the turbomachine combustion chamber, while minimizing the complexity of the turbomachine control system, as well as the turbomachine's mass and size. Visual inspection can be performed without removing the spark plug from the combustion chamber, for example, using endoscopic control. This simplifies spark plug monitoring and reduces both the duration and cost of combustion chamber maintenance. Thanks to the spark plug according to the invention, it is possible to reliably replace the spark plug before a combustion chamber ignition failure occurs due to spark plug wear. Monitoring spark plug wear allows, in particular, for longer intervals between combustion chamber maintenance operations. Furthermore, the method of monitoring spark plug wear can do without an electronic spark plug control system, which limits the complexity of a turbomachine control system, the mass and size of the turbomachine. The invention may optionally include one or more of the following features, combined or not. According to a particular design feature, the spark plug includes a semiconductor material which is located between the first electrode and the second electrode. According to a particular embodiment, the spark plug is annular around a longitudinal axis of the spark plug, the second electrode being located around the first electrode, the second region being angularly adjacent to the first region. Preferably, the first electrode is a central electrode and the second electrode is a ground electrode. According to a particular design feature, the second region extends angularly between 1 / 8 and 3 / 4 of the spark plug around the longitudinal axis of the spark plug. According to a particular design feature, the second region extends along the longitudinal axis over a length between 1 mm and 15 mm of the spark plug length along the longitudinal axis. According to one embodiment, the spark plug includes a longitudinal spark end at which the spark plug is configured to produce a spark. The spark plug includes a longitudinal power end which is opposite the spark end and which is configured to connect the spark plug to a power source. The second region is closer to the longitudinal spark end than to the longitudinal feed end. According to one embodiment, the spark plug includes an intermediate region between the first and second electrodes. The first and second regions each extend from the first electrode to the second electrode through the intermediate region. According to a particular embodiment, the first electrode of the second region, the second electrode of the second region and / or the intermediate region of the second region comprise a first portion and a second portion, the first portion having electrical properties different from those of the second portion. Preferably, the first portion has a shape complementary to that of the second portion. According to a particular embodiment, the first region has a first electrical conductivity, and the second region has a second electrical conductivity that differs from the first. The first portion has a third electrical conductivity that is substantially homogeneous, and the second portion has a fourth electrical conductivity that is substantially homogeneous and different from the third. Preferably, the second electrical conductivity is strictly less than the first electrical conductivity. Preferably, the third electrical conductivity is strictly less than the fourth electrical conductivity. According to a particular feature of the design, the second region includes a recess in relation to the first region. According to a particular feature of the design, the second region includes an addition of material compared to the first region. According to a particular embodiment, the second region comprises a second material having electrical properties different from those of a first material of the first region. According to a particular feature of the design, the second region includes a visual indicator to visually identify the second region in relation to the first region. Preferably, the visual indicator includes a different color than that of the first region. Preferably, the visual indicator includes a geometric shape different from that of the first region. Preferably, the visual indicator includes a visual marking. The invention also relates to a combustion chamber for a turbomachine, comprising a spark plug as defined above. The invention also relates to a turbomachine comprising the chamber of combustion as defined above. The turbomachine is in particular an aircraft turbomachine such as a turbojet, a turboshaft engine or a turboprop. The invention also relates to a method for monitoring the wear of a spark plug as defined above in a turbomachine combustion chamber. The monitoring procedure includes a visual inspection of the spark plug in the combustion chamber to detect spark plug wear by differential wear of the first region compared to the second region. According to one embodiment, the monitoring method includes spark plug wear detection during visual inspection of the spark plug, when wear is detected in a spark plug wear indicator area by sparking between the first electrode and the second electrode through the second region of the spark plug. According to one particular embodiment, the monitoring method includes the replacement of the spark plug in the combustion chamber when wear is detected in the wear indicator area of ​​the spark plug by sparking between the first electrode and the second electrode through the second region of the spark plug. Brief description of the drawings The present invention will be better understood upon reading the description of exemplary embodiments, given purely for illustrative purposes and in no way limiting, with reference to the attached drawings in which: [fig.1] is a partial schematic representation in a longitudinal half-section of a turbomachine combustion chamber comprising a spark plug according to the invention: [fig.2] is a partial schematic representation in longitudinal section of a spark plug of known structure when it produces sparks; [fig.3] is a partial schematic representation in longitudinal section of a spark plug of known structure when it is worn; [fig.4a] is a partial schematic representation in longitudinal section of a spark plug according to a first embodiment of the invention; [fig.4b] is a schematic representation viewed from its longitudinal sparking end of a spark plug according to the first embodiment of the invention; [fig.5a] is a partial schematic representation in longitudinal section of a spark plug according to a second embodiment of the invention; [fig.5b] is a schematic representation viewed from its longitudinal spark end of a spark plug according to the second embodiment of the invention: [fig.6a] is a partial schematic representation in longitudinal section of a spark plug according to a third embodiment of the invention; [fig.6b] is a schematic representation viewed from its longitudinal spark end of a spark plug according to the third embodiment of the invention: [fig.7a] is a partial schematic representation in longitudinal section of a spark plug according to a fourth embodiment of the invention; [fig.7b] is a schematic representation viewed from its longitudinal spark end of a spark plug according to the fourth embodiment of the invention: [fig.8a] is a partial schematic representation in longitudinal section of a spark plug according to a fifth embodiment of the invention; [fig.8b] is a schematic representation viewed from its longitudinal spark end of a spark plug according to the fifth embodiment of the invention: [fig.9a] is a partial schematic representation in longitudinal section of a spark plug according to a sixth embodiment of the invention; [fig.9b] is a schematic representation viewed from its longitudinal sparking end of a spark plug according to the sixth embodiment of the invention; [fig.10] illustrates the implementation of a method for monitoring the wear of a spark plug according to the invention. Description of the implementation methods Identical, similar or equivalent parts of the different figures carry the same numerical references in order to facilitate the transition from one figure to another. Figure ! schematically represents a combustion chamber 2 of an aircraft turbomachine. The combustion chamber 2 is annular around a longitudinal axis XX of the turbomachine. It comprises an outer casing wall 22 and an inner casing wall 23, a fairing 24, an outer wall 25 and an inner wall 26 which are joined by a chamber bottom 28. It also includes at least one spark plug 6, fuel injectors 4, injection systems 3, and a diffuser 20. The combustion chamber, for example, includes at least two spark plugs 6, which are generally of structures identical to each other. The outer casing wall 22 delimits the combustion chamber 2 radially outwards with respect to the longitudinal axis XX of the turbomachine. The inner casing wall 23 delimits the combustion chamber 2 radially inwards with respect to the longitudinal axis XX of the turbomachine. The outer casing wall 22, together with the outer wall 25, defines a first airflow passage 11. Similarly, the inner casing wall 23, together with the inner chamber wall 26, defines a second airflow passage 12. The outer wall 25 and the inner wall 26 are walls of revolution which are coaxial around the longitudinal axis of turbomachine XX, being symmetrical with respect to a longitudinal axis X1-X1 of the injection system 3 which is shown in Figure 1. They each include primary ports 27 for the introduction of a primary airflow and dilution ports 29 for the introduction of a dilution airflow into the combustion chamber 2. The fairing 24 extends upstream from the outer wall 25 and the inner wall 26, positioned upstream of the chamber bottom 28. It has central openings for housing the injection systems 3 and their corresponding injectors 4. The chamber bottom 28 has mounting openings for the injection systems 3, into which the fuel injectors 4 are inserted. The diffuser 20 is configured to supply the combustion chamber 2, including the injection systems 3, the primary ports 27 and the dilution ports 29, with hot air under pressure. The injection systems 3 are mounted on the bottom of chamber 28, spaced from each other in a circumferential direction. Each injection system 3 comprises, from upstream to downstream, a sliding passage 34, a screw 32, a venturi 35, and a mixing bowl 31. The sliding passage 34, the screw 32, and the mixing bowl 31 together form air supply means 30 to produce a layer of air-fuel mixture with the fuel injected by the corresponding injector 4. Each injection system 3 is connected to one of the fuel injectors 4, which is mounted in the sliding sleeve 34 at the injector nozzle. The fuel injectors 4 are each configured to inject fuel into the combustion chamber 2, where it mixes with air to produce a layer of air-fuel mixture in the combustion chamber 2. Each spark plug 6 is mounted through the outer wall 25 of the combustion chamber. It extends transversely to this wall, with its longitudinal axis ZZ being substantially orthogonal to the longitudinal axis X1-X1 of the injection system 3 of the injector 4, which is located near this spark plug 6. It serves to ignite the air and fuel mixture in combustion chamber 2. Throughout this discussion, a longitudinal direction is a direction that is substantially parallel to the longitudinal axis ZZ of the spark plug 6. A radial direction is a direction that is substantially orthogonal to the longitudinal axis ZZ of the spark plug 6 and intersects this axis. A circumferential direction is a direction around the longitudinal axis ZZ of the spark plug. With joint reference to Figures 1 to 9b, the spark plug 6 is annular about a longitudinal axis ZZ of the spark plug. It extends longitudinally between a longitudinal spark end 6a and a longitudinal supply end 6b which is opposite the longitudinal spark end 6a. The spark plug 6 is configured to produce a spark 13 at the longitudinal spark end 6a. It is configured to be connected to a power source at the longitudinal power end 6b, in particular an electrical pulse generator (not shown). The spark plug 6 comprises a first electrode 7, a second electrode 8, and an intermediate region located between the first electrode 7 and the second electrode 8. The first electrode 7 is a central electrode electrically connected to the power supply by a central conductor (not shown). The second electrode 8 is a peripheral electrode surrounding the first electrode 7 and radially outwards around the spark plug 6. The second electrode 8 serves as a ground electrode for the spark plug 6. In the various embodiments shown, the intermediate region comprises a semiconductor material 9. This semiconductor material 9 promotes a low breakdown voltage compared to an intermediate region containing a vacuum. It can be produced by sintering. The spark plug 6 is, in particular, a high-energy, low-voltage type spark plug capable of delivering at least one spark 13 with an energy between 0.1 and 3 Joules when supplied with a voltage of approximately 2 to 3 kV. Figure 3 shows a worn spark plug 6 that needs replacing. This spark plug 6 has a wear area 61 located between the center electrode 7 and the ground electrode 8. The wear area 61 is a void created by erosion of the semiconductor material 9 during the production of sparks 13 by discharge through the semiconductor material 9. It is relatively difficult to monitor the wear of a spark plug 6 of known structure, since it is necessary to remove the spark plug 6 from the combustion chamber 2 and the spark plug 6 is then often replaced. With reference to each of the embodiments shown in Figures 4a to 9b, the spark plug 6 according to the invention includes a visual wear indicator to detect vi- only the wear of the spark plug 6. More specifically, each of the spark plugs 6 comprises a first region 60 and a second region 62 which is adjacent to the first region 60 and which has different electrical properties from those of the first region 60. The second region 62 is visible when the spark plug 6 is installed in the combustion chamber 2, which allows an operator to visually spot wear of the spark plug 6 due to differential wear of the first region 60 compared to the second region 62. In the embodiments shown, the first region 60 has a first electrical conductivity and the second region 62 has a second electrical conductivity that is strictly lower than the first electrical conductivity. The first region 60 forms a preferred sparking zone compared to the second region 62 due to its lower electrical resistance. In particular, the semiconductor material 9 located in the first region 60 tends to erode more rapidly than that located in the second region 62. The semiconductor material 9 of the second region 62 then forms a wear indicator zone of the spark plug 6. In the embodiments shown, the second region 62 extends axially over a length that is less than the axial length of the first region 60 along the direction of the longitudinal axis ZZ of the spark plug 6. In particular, the second region 62 extends longitudinally over a length 12 between 1 mm and 15 mm of the length of the first region 60 along the longitudinal axis ZZ. The second region 62 extends along the direction of the longitudinal axis ZZ over a length 12 between 1 mm and 15 mm of the length L of the spark plug 6 along the longitudinal axis ZZ. The second region 62 is closer to the longitudinal spark end 6a than to the longitudinal supply end 6b. The first region 60 and the second region 62 extend radially each from the first electrode 7 to the second electrode 8 through the intermediate region which comprises the semiconductor material 9. The second region 62 is angularly adjacent to the first region 60. The second region 62 extends angularly over an angular distance Ac that is between 1 / 8 and 3 / 4 of the spark plug 6 around the longitudinal axis ZZ of the spark plug. The first region 60 extends angularly over the remainder of the spark plug 6 relative to the second region 62. In general, the second region 62 includes a first portion 72 which has electrical properties, including electrical conductivity, which are different from those of a second portion 74 of the second region 62 and / or from those of a corresponding adjacent portion of the first region 60. In each of the embodiments of Figures 4a to 8b, the first electrode 7 of the second region 62, the second electrode 8 of the second region 62, or the intermediate region of the second region 62 comprise a first portion 72 and a second portion 74 which has electrical properties different from those of the first portion 72. The first portion 72 has a shape complementary to that of the second portion 74. In particular, the second portion 74 has electrical properties similar to those of a corresponding portion of the first region 60. The first portion 72 has a third electrical conductivity that is substantially homogeneous, and the second portion has a fourth electrical conductivity that is substantially homogeneous and different from that of the third electrical conductivity. In particular, the fourth electrical conductivity is strictly lower than the third electrical conductivity. The first portion 72 includes, for example, a visual indicator to visually identify the first portion 72 in relation to the second portion 74, a different color from that of the second portion 74, a different geometric shape from that of the second portion 74 and / or a visual marking such as an impression. With reference more specifically to the first embodiment shown in Figures 4a and 4b, the second region 62 includes a recess 64 relative to the first region 60. The recess 64 is formed in the ground electrode 8 and constitutes a first portion 72 of the ground electrode 8. This first portion 72 is empty. The ground electrode 8 also includes a second portion 74 which has homogeneous electrical conductivity between the first region 60 and the second region 62 of the ground electrode 8. With more specific reference to the second embodiment shown in Figures 5a and 5b, the second region 62 includes a recess 64 relative to the first region 60. The recess 64 is formed in the central electrode 7 and constitutes a first portion 72 of the central electrode 7. This first portion 72 is empty. The central electrode 7 also includes a second portion 74 which has homogeneous electrical conductivity between the first region 60 and the second region 62 of the central electrode 7. With more specific reference to the third embodiment shown in Figures 6a and 6b, the second region 62 comprises a recess 64 relative to the first region 60. The recess 64 is formed in the semiconductor material 9 and constitutes a first portion 72 of the semiconductor material 9. This first portion 72 consists of a void. The semiconductor material 9 also comprises a second portion 74 which has homogeneous electrical conductivity between the first region 60 and the second region 62 of the semiconductor material 9. With more specific reference to the fourth embodiment which is represented In figures 7a and 7b, the second region 62 comprises a second material 66 in relation to the first region 60. The ground electrode 8 comprises the second material 66 and it forms a first portion 72 of the ground electrode 8. The ground electrode 8 also comprises a second portion 74 which is made of a first material which is homogeneous between the first region 60 and the second region 62 of the ground electrode 8. With more specific reference to the fifth embodiment shown in Figures 8a and 8b, the second region 62 comprises a second material 68 in relation to the first region 60. The central electrode 7 comprises the second material 68 and it forms a first portion 72 of the central electrode 7. The central electrode 7 also comprises a second portion 74 which is made of a first material which is homogeneous between the first region 60 and the second region 62 of the central electrode 7. With more specific reference to the sixth embodiment shown in Figures 9a and 9b, the second region 62 comprises a second material 69 in relation to the first region 60. The semiconductor material 9 comprises the second material 69 and forms a first portion 72 of the semiconductor material 9. The semiconductor material 9 lacks a second portion 74. The semiconductor material 9 of the second region 62 is formed from that of the first portion 72. Figure 10 represents a method for monitoring the wear of a spark plug 6 according to the invention when it is located in a combustion chamber 2 of a turbomachine such as that shown in Figure 1. The monitoring procedure 100 includes a visual inspection 101 to detect wear of the spark plug 6 by differential wear of the first region 60 compared to the second region 62. The monitoring method 100 includes checking 103 the wear of the spark plug 6 during the visual inspection of the spark plug 6 in a spark plug wear indicator area 6 which is formed by the semiconductor material 9 in the second region 62. The monitoring method 100 includes the replacement 107 of the spark plug 6 in the combustion chamber 2, when wear has been visually detected in the wear indicator area by electrical discharge between the first electrode 7 and the second electrode 8 through the semiconductor material 9. In the absence of wear detected in the wear indicator area, the monitoring process 100 ends at a step 105 of detecting the absence of wear of the spark plug 6 by leaving the spark plug 6 in place in the combustion chamber 2 and without replacing the spark plug 6. Thanks to the second region 62 of a spark plug 6 according to the invention, it is possible to reliably monitor spark plug wear 6 during a visual inspection of spark plug 6 in turbomachine combustion chamber 2, while limiting the complexity of a turbomachine control system, the mass and size of the turbomachine. Visual inspection of spark plug 6 can be carried out without removing spark plug 6 from combustion chamber 2, for example by means of endoscopic control, which facilitates the implementation of monitoring of spark plug 6 and limits both the duration of a maintenance operation of combustion chamber 2 and the cost of this maintenance operation. It is possible to reliably replace the spark plug 6 before a failure to ignite the combustion chamber 2 caused by wear of the spark plug 6. Monitoring the wear of the spark plug 6 allows, in particular, for longer intervals between maintenance operations of the combustion chamber 2. Furthermore, the method of monitoring the wear of the spark plug 6 can do without an electronic control system for the spark plug 6, which limits the complexity of a turbomachine control system, the mass and size of the turbomachine. Of course, various modifications can be made by a person skilled in the art to the invention just described without going out of scope of the disclosure of the invention. Alternatively, the spark plug 6 has a different structure from those of the embodiments shown. For example, it may not be annular around its longitudinal axis ZZ. Alternatively, the spark plug 6 is a high-energy, high-voltage type spark plug configured to produce a spark 13 when subjected to a voltage of approximately 15 to 20 kV. The intermediate region of the spark plug 6 may not include semiconductor material 9 but a vacuum. Alternatively, the first electrode 7, the second electrode 8, and / or the semiconductor material 9 have non-homogeneous electrical conductivity, for example, exhibiting a gradient along the longitudinal axis ZZ of the spark plug or a radial gradient. The electrical conductivity of the first portion 72 and / or that of the second portion 74 is non-homogeneous. Alternatively, the second electrical conductivity is strictly greater than the first electrical conductivity. The second region 62 forms a preferred sparking zone compared to the first region 60. The semiconductor material 9 of the first region 60 tends to form the wear indicator zone of the spark plug 6. Alternatively, the first portion 72 extends through the first electrode 7 and the intermediate region, the intermediate region and the second electrode 8, or from the first electrode 7 to the second electrode 8. Alternatively, the second portion 74 is made of the same material as the first portion 72. In this case, the first portion 72 may include an addition of material compared to the second portion 74. In particular, it may have a boss compared to the second portion 74. It may have a greater thickness than the second portion 74 in the radial direction. Alternatively, monitoring procedure 100 includes replacing spark plug 6 after a specified number of flights of the turbomachine including spark plug 6 and / or after a specified number of ignition cycles of the combustion chamber 2 of the turbomachine, following step 105 of detecting the absence of wear of spark plug 6. The 100 spark plug wear monitoring procedure can be implemented following the reporting of information relating to probable spark plug wear by a monitoring device (not shown) of a spark-generating system which includes the spark plug. This monitoring device determines, for example, the spark plug breakdown voltage, and signals information relating to probable spark plug wear when the breakdown voltage exceeds a threshold value. Alternatively, the monitoring device can determine the shape of an electrical wave passing through the spark plug when a spark is produced to signal information about spark plug wear. Such a monitoring device provides information relating to the wear condition of the spark plug which is obtained independently of the visual inspection of the spark plug according to the invention.

Claims

Demands

1. Ignition spark plug (6) for a combustion chamber (2) of tur- bomachine, comprising a first electrode (7) and a second electrode (8), characterized in that the spark plug (6) comprises a first region (60) and a second region (62) adjacent to the first region (60) and which has electrical properties different from those of the first region (60), the second region (62) being visible to identify visually, wear of the spark plug (6) by differential wear rent of the first region (60) compared to the second region (62).

2. Spark plug (6) according to the preceding claim, in which the spark plug (6) comprises a semiconductor material (9) which is located between the first electrode (7) and the second electrode (8).

3. Spark plug (6) according to any one of the preceding claims previous, in which the spark plug (6) is annular around of a longitudinal axis (ZZ) of the spark plug, the second electrode (8) being located around the first electrode (7), the second region (62) being angularly adjacent to the first region (60), the first electrode (7) being preferably a central electrode, the second electrode (8) being preferably a ground electrode.

4. Spark plug (6) according to the preceding claim, in which the second region (62) extends angularly between 1 / 8 and 3 / 4 of the spark plug (6) around the longitudinal axis (ZZ) of the spark plug ignition, and / or in which the second region (62) extends along the direction of the axis longitudinal (ZZ) over a length between 1 mm and 15 mm the length of the spark plug (6) along the longitudinal axis (ZZ).

5. Spark plug (6) according to any one of the preceding claims- preceding, in which the spark plug (6) comprises: a longitudinal spark end (6a) to which the spark plug The ignition system (6) is configured to produce a spark, and a longitudinal feed end (6b) which is opposite to the longitudinal sparking end (6a) and which is configured for Connect the spark plug (6) to a power source, the second region (62) being closer to the longitudinal end sparking (6a) than the longitudinal supply end (6b).

6. Spark plug (6) according to any one of the preceding claims- previous, in which the spark plug (6) comprising a region intermediate (9) between the first electrode (7) and the second electrode {8), the first region (60) and the second region (62) extending from the first electrode (7) to the second electrode (8) through the intermediate region (9), the first electrode (7) of the second region (62), the second electrode (8) of the second region (62) and / or the intermediate region (9) of the second region (62) comprising a first portion (72) and a second portion (74), the first portion (72) having properties electrical different from those of the second section (74), the first portion (72) having very preferably a complete form- commentary on that of the second portion (74).

7. Spark plug (6) according to the preceding claim, in which the first region (60) has a first electrical conductivity and the second region (62) has a second electrical conductivity which is different from that of the first electrical conductivity, in particular strictly lower than that of the first electrical conductivity, the first portion (72) having a third electrical conductivity which is substantially homogeneous and the second portion having a fourth electrical conductivity which is substantially homogeneous and which is different from that of the third electrical conductivity, in particular strictly greater than the third electrical conductivity.

8. Spark plug (6) according to any one of the preceding claims- preceding, in which the second region (62) includes a recess (64) in relation to the first region (60) and / or an addition of material by report to the first region (60), and / or in which the second region (62) comprises a second material (66, 68, 69) having electrical properties different from those of a first material of the first region (60) adjacent to the second material.

9. Spark plug (6) according to any one of the preceding claims preceding, in which the second region (62) includes an indicator visual aid to visually locate the second region (62) in relation to the first region (60), notably a different color from that of the first region (60), a geometric shape different from that of the first region (60) and / or a marking.

10. Method for monitoring the wear of a spark plug (6) according to any one of the preceding claims in a chamber of combustion (2) of turbomachine, including a visual inspection of the spark plug (6) in the combustion chamber (2) to detect spark plug wear (6) by differential wear of the first region (60) relative to the second region (62).

11. | Monitoring method according to the preceding claim, comprising spark plug wear detection (6) during inspection visual inspection of the spark plug (6) and preferably replacement of the spark plug (6) in the combustion chamber (2), when a Wear is detected in a wear indicator area of ​​the spark plug ignition (6) by sparking between the first electrode (7) and the second electrode (8) through the second region (62) of the spark plug ignition (6).