Ignition system and igniter with ruthenium ground electrode and platinum iridium alloy center electrode

Abstract

The present invention discloses an igniter for a gas turbine engine, the igniter having: a housing; the insulator is fixed in the shell; a center electrode secured within the insulator and electrically isolated from the housing by the insulator, the center electrode having an ignition tip formed of a platinum iridium (PtIr) alloy and having a diameter of at least 0.09 inch; and a ground electrode mounted on the housing and terminating at the ignition end of the igniter, the ground electrode spaced from the ignition tip by a gap, the ground electrode having at least one needle comprising ruthenium (Ru) or a ruthenium alloy. The igniter is advantageously used with an ignition system having a positive polarity pulsed output.

Description

Technical Field

[0001] The invention relates to an igniter with a noble metal electrode. Background Art

[0002] It is known to use precious metal electrodes in igniters to provide long service life for the igniter. This is advantageous for igniters used in aviation jet engines and more generally for gas turbine engines. Many alloys and combinations of platinum group metals have been proposed, and many are in commercial use. The long-lasting performance of these electrodes is due to inherent characteristics such as good operating voltage, low resistivity, high thermal conductivity and good oxidation resistance, which minimize electrode erosion. For some applications of these precious metal electrodes, such as in automotive spark plugs, the material properties allow the electrode diameter to be reduced relative to more traditional spark plugs, thereby allowing the use of less material (and therefore lower cost) while reducing the required spark voltage. Summary of the invention

[0003] According to one aspect of the present invention, there is provided an igniter for a gas turbine engine, comprising: a housing; an insulator fixed within the housing; a center electrode fixed within the insulator and electrically isolated from the housing by the insulator, the center electrode having an ignition tip formed of a platinum-iridium (PtIr) alloy and having a diameter of at least 0.09 inches; and a ground electrode mounted on the housing and terminating at an ignition end of the igniter, the ground electrode being spaced apart from the ignition tip by a gap, the ground electrode having at least one needle containing ruthenium (Ru) or a ruthenium alloy.

[0004] The igniter may include any of the following features alone or in any technically feasible combination:

[0005] -The firing tip has a diameter of 0.11 to 0.15 inches.

[0006] -PtIr alloys contain a mixture of platinum and iridium ranging from Pt70Ir30 to Pt99Ir1.

[0007] -PtIr alloys contain a mixture of platinum and iridium ranging from Pt80Ir20 to Pt95Ir5.

[0008] -PtIr alloys contain a mixture of platinum and iridium ranging from Pt85Ir15 to Pt95Ir5.

[0009] - The ground electrode comprises a plurality of needles, each needle having a diameter of 0.022 inches to 0.122 inches.

[0010] - Each needle contains at least 99.9% ruthenium.

[0011] - The firing tip has a diameter of 0.12 inches, the PtIr alloy comprises Pt90Ir10, the needle has a diameter of 0.072 inches, and the ruthenium comprises at least 99.9% ruthenium.

[0012] According to another aspect of the present invention, an ignition system is provided, comprising the igniter of the two preceding paragraphs. The ignition system may further comprise a positive polarity exciter and an ignition lead connected to the exciter at one end and to the igniter at the other end. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Preferred exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals denote like elements, and wherein:

[0014] Figure 1 A gas turbine ignition system constructed in accordance with an embodiment of the present invention including an exciter, an ignition lead, and an igniter is shown;

[0015] Figure 2 yes Figure 1 A partial cross-sectional view of an igniter;

[0016] Figure 3 yes Figure 2 an enlarged view of the working end of the igniter; and

[0017] Figure 4 is a graph comparing various igniters having different combinations of ground electrode and center electrode materials and diameters. DETAILED DESCRIPTION

[0018] Figure 1 A gas turbine ignition system 7 constructed in accordance with an embodiment of the present invention is shown including an exciter 8, an ignition lead 9, and an igniter 10. The ignition system 7 is a positive polarity ignition system having an exciter 8 including a unipolar positive polarity exciter that outputs only positive spark pulses for delivery to the igniter 10 via the ignition lead 9.

[0019] The ignition system 7 can be implemented in a variety of ways suitable for many different turbine engine applications, such as for commercial, business and military aircraft, helicopters, industrial gas engines and other turbine generators. The construction, operation and use of commercially available positive exciters and ignition leads for these different turbine engine applications are known and / or available to those skilled in the art and will not be described in detail herein.

[0020] like Figure 2 As shown, the igniter 10 has a conventional structure, except for its ground and center electrodes. As will be appreciated by those skilled in the art, the igniter 10 is of the type constructed for a gas turbine engine, such as for aviation applications in jet engines. See also Figure 3 The igniter 10 includes a housing 20, an insulator 30 and a center electrode (CE) 40 extending downward through the center of the housing 20 and the insulator 30 to a working or firing end 50, the working or firing end 50 including a firing tip (or needle) 46 and a ground electrode (GE) 60, the ground electrode (GE) 60 being separated from the firing tip by a gap.

[0021] The housing 20 includes an upper housing 22, a lower housing 24 and a bushing 26. The upper housing 22, the lower housing 24 and the bushing 26 are each made of a suitable metal or metal alloy (e.g., stainless steel). The materials of each component 22-26 can be the same or different. The upper and lower housings 22, 24 are physically and electrically connected by interference fit at the lower end of the upper housing 22 and the upper end of the lower housing 24 via mating shoulders at the overlapping area of ​​the two housings. Figure 2 Similarly, bushing 26 is physically and electrically connected to upper housing 22 by being crimped or otherwise fitted at its lower end within an upper portion of the upper housing.

[0022] The insulator 30 includes an upper insulator 32 and a lower insulator 34, each of which can be made of ceramic or other suitable non-conductive materials. As shown, the lower portion of the upper insulator 32 fits within the upper portion of the lower insulator 34 and has sufficient length to prevent any discharge between the center electrode 40 and the shell 20 across the mating surfaces of the insulators.

[0023] The center electrode 40 includes an upper end having an ignition cable contact 41 made of tungsten or other suitable conductive metal or alloy. The contact 41 is connected to an electrode cap 42 made of stainless steel or other suitable conductive metal or alloy. TM ) etc. is threaded, welded, crimped or otherwise connected to the electrode cap 42, and the upper end of the central electrode rod 44 is surrounded by a glass seal 45 below the cap 42. For more details, see Figure 3 At the lower end of the center electrode 40, a precious metal ignition tip 46 is welded, brazed or otherwise appropriately secured to the lower end of the center electrode rod 44 at a joint 47. Each of the above center electrode components 41-47 is electrically connected so that spark energy applied from the energizer 8 via the ignition cable 9 to the igniter 10 can pass through the center electrode 40 and generate a spark between the CE ignition tip 46 and the ground electrode 60.

[0024] Also like Figure 3 As shown, the ground electrode 60 includes a plurality of noble metal needles 62. Figure 3Two of them are shown. For the igniter 10, six such needles 62 are equally spaced about the circumference of the lower end of the lower shell 24 and extend radially inward to the radial center of the shell 24 (and the central axis of the center electrode 40), terminating near the edge of the opening in the lower insulator 34. Through this opening, a spark can jump between the CE firing tip 46 and one or more ground electrode needles 62 through a space 70 that leads to the external environment of the igniter to initiate combustion of the air / fuel mixture in an internal combustion engine (e.g., a gas turbine engine). Each needle 62 extends radially inward within a through hole in the lower shell 24 that aligns the needle at 90° relative to the central axis of the center electrode assembly. The needles 62 are brazed and then welded to the appropriate position of the lower shell 24 by an outwardly facing weld 63. It should be understood that other arrangements of the ground electrode 60 are possible, including ground electrode needles 62 at angles other than 90° relative to the central axis of the center electrode 40, angling the needles 62 so that they do not intersect the central axis, and using more or fewer needles 62.

[0025] As will be appreciated by those skilled in the art, the igniter 10 receives high voltage pulses from the exciter 8 sufficient to generate a spark between the CE ignition tip 46 and one or more ground electrode needles 62. These pulses are transmitted to the igniter 10 via the ignition lead 8, which, according to its conventional construction, includes a center conductor and a metal coaxial braid, foil, or other shield separated from the center conductor by an insulator. In the illustrated embodiment, the exciter 8 is connected to the ignition lead 9, whose coaxial shield is electrically connected to the output ground terminal of the exciter and whose center conductor is connected to the spark output terminal of the exciter. The other end of the ignition lead 9 is mechanically and electrically connected to the igniter 10, so that its housing 20 and the ground electrode needle 62 are electrically connected to the coaxial shield, and the center electrode 40 and the CE ignition tip 46 are electrically connected to the center conductor of the ignition lead 9.

[0026] Since the exciter 8 is a positive polarity exciter, it outputs a high voltage positive polarity pulse (relative to the grounded coaxial shield) onto the center conductor of the ignition lead 9. Thus, the igniter 10 receives the high voltage positive polarity pulse and conducts it to its CE ignition tip 46, causing it to generate a positive polarity spark at the gap between the ignition tip 46 and one or more ground electrode needles 62.

[0027] Igniter 10 utilizes a combination of platinum group metals / alloys for both CE firing tip 46 and ground electrode needle 62, which, combined with the specific dimensions of firing tip 46, has been found through testing to exhibit surprisingly long service life. Figure 4, shows a graph including test results indicating the life characteristics of a number of different ignition tip metals and sizes. The life characteristics are illustrated by a plot of the center electrode depth into the insulator versus the total number of sparks before failure. The center electrode depth starts at approximately 0.18" (inch) and increases with the life of the igniter due to erosion of the igniter tip 46. The red area indicates excessive electrode erosion early in the life of the igniter, while the green area indicates the preferred operating combination of low erosion and high spark count. Testing was conducted with the igniter tips exposed to 75 psig and 1,500°F. Note that the lifetime spark count captured under these conditions (~2M to 3M sparks) is significantly less than the lifetime spark count when sparking at ambient pressure and temperature.

[0028] Figure 4 12 different center electrode and ground electrode material combinations are shown in Figure 1, several of which are labeled and three of which have data point labels for ease of viewing. Of the three, the triangular data point line represents an igniter with a center electrode tip of Pt90Ir10 (90% platinum by weight, 10% iridium by weight) and a ground electrode needle of Ru (99.9% or purer ruthenium), which showed greater than average electrode erosion (>0.300 electrode depth) but better than average spark life (2,000,000 sparks before failure). Switching materials between the center electrode and ground electrode, as indicated by the curve labeled with square data points, showed greater electrode wear (>0.430 electrode depth), but still a large improvement in total spark life (2.4M sparks). This test was conducted using a Pt90Ir10 alloy center electrode with a diameter of 0.100".

[0029] Further testing surprisingly showed that in the larger 0.120” diameter center electrode, the combination of Ru for the ground electrode pin and Pt90Ir10 alloy for the center electrode pin significantly improved life (3.7M sparks) while keeping electrode erosion to a minimum (0.270 electrode depth). This was achieved by Figure 4 The circular data point curve in FIG. 1 is shown. This unexpectedly favorable performance appears to be due not only to the combination of Ru for the ground electrode pin and Pt90Ir10 for the center electrode pin, but also to the use of a larger center electrode diameter (0.120"). Without wishing to be bound by any theory of operation or explanation, it is believed that the performance advantage occurs in part due to the unipolar positive spark voltage applied to the spark plug (where the ground electrode is grounded) and the reduction in erosion of the center electrode due to its acceptance of electrons across the spark gap and its increased size.

[0030] Therefore, the further combination of ground electrode Ru material, center electrode PtIr material and increased diameter, and use of the igniter in a positive polarity ignition system, allows for significantly extended service life of the igniter in a gas turbine or other internal combustion engine.

[0031] For the embodiment shown and described above, the igniter 10 includes a CE firing tip 46 having a diameter of 0.12" and formed of Pt90Ir10, while the ground electrode has a diameter of 0.072" and is formed of Ru. Although these materials and center electrode diameters are Figure 4 The specific circular data point curve results shown are critical, but other embodiments of the igniter may use a PtIr alloy as the center electrode, ranging from Pt70Ir30 to Pt99Ir1, more preferably in the range of Pt80Ir20 to Pt95Ir5, and even more preferably in the range of Pt85Ir15 to Pt95Ir5 closer to the tested Pt90Ir10. Similarly, in some embodiments, the Ru ground electrode may be made of a suitable ruthenium alloy, rather than pure ruthenium or nearly pure ruthenium. In addition, the center electrode needle may have a diameter other than the tested 0.12" diameter, and in some embodiments may be greater than or equal to 0.11" up to a maximum that is technically or commercially feasible, or may be within the range of the tested 0.12" diameter, such as in the range of 0.09" to 0.15". Although this range covers Figure 4 The square data point curve in FIG. 1 is shown, but it should be understood that an igniter having these characteristics can still achieve good spark life and is therefore commercially acceptable. In addition, the ground electrode needle 62 has a diameter of 0.072", but in other embodiments it can be in the range of 0.022" to 0.122".

[0032] It should be understood that the foregoing description is one or more embodiments of the present invention. The present invention is not limited to the specific embodiments disclosed herein, but is limited only by the appended claims. In addition, the statements contained in the foregoing description relate to the disclosed embodiments and should not be interpreted as limitations on the scope of the invention or on the definitions of terms used in the claims, unless the terms or phrases are clearly defined above. Various other embodiments and various changes and modifications to the disclosed embodiments will become apparent to those skilled in the art. For example, the igniter 10 can have different housings, insulators, and ignition end structures, which use the above-mentioned Ru-based ground electrode and PtIr-based center electrode for different applications, such as gas turbine generators, automotive spark plugs, etc. In addition, the alloys provided herein may include trace elements, or in some embodiments, relatively small amounts of other elements.

[0033] As used in this specification and claims, the terms "eg," "for example," "for instance," "such as," and "like," and the verbs "comprise," "have," "include," and their other verb forms, when used in conjunction with a list of one or more components or other items, are to be interpreted as open-ended, meaning that the list should not be viewed as excluding other additional components or items. Other terms are to be interpreted using their broadest reasonable meaning unless they are used in a context that requires a different interpretation. In addition, the term "and / or" is to be interpreted as an inclusive or. Thus, for example, the phrase "A, B, and / or C" would be interpreted to cover the following: "A"; "B"; "C"; "A and B"; "A and C"; "B and C"; and "A, B, and C."

Claims

1. An igniter for a gas turbine engine, comprising: case; an insulator fixed in the housing; a center electrode secured within the insulator and electrically isolated from the housing by the insulator, the center electrode having a firing tip formed of a platinum-iridium (PtIr) alloy and having a diameter of at least 0.09 inches; as well as A ground electrode mounted on the housing and terminating at the firing end of the igniter, the ground electrode being spaced apart from the firing tip by a gap, the ground electrode having at least one needle containing ruthenium (Ru) or a ruthenium alloy.

2. The igniter according to claim 1, wherein: The firing tip has a diameter of 0.11 to 0.15 inches.

3. An igniter according to any one of the preceding claims, wherein: The PtIr alloy comprises a mixture of platinum and iridium in the range of Pt70Ir30 to Pt99Ir1.

4. An igniter according to any one of the preceding claims, wherein: The PtIr alloy comprises a mixture of platinum and iridium in the range of Pt80Ir20 to Pt95Ir5.

5. An igniter according to any one of the preceding claims, wherein: The PtIr alloy comprises a mixture of platinum and iridium in the range of Pt85Ir15 to Pt95Ir5.

6. An igniter according to any preceding claim, wherein: The ground electrode includes a plurality of needles, each needle having a diameter of 0.022 inches to 0.122 inches.

7. An igniter according to any preceding claim, wherein: Each of the needles comprises at least 99.9% ruthenium.

8. An igniter according to any one of the preceding claims, wherein: The firing tip has a diameter of 0.12 inches, the PtIr alloy comprises Pt90Ir10, the needle has a diameter of 0.072 inches, and the ruthenium comprises at least 99.9% ruthenium.

9. An ignition system comprising the igniter according to any one of the preceding claims.

10. The ignition system of claim 9 further comprising a positive polarity exciter and an ignition lead connected at one end to the exciter and at another end to the igniter.

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