Ignition system and igniter having a ruthenium ground electrode and a platinum-iridium alloy center electrode

Abstract

An igniter for a gas turbine engine includes a shell, an insulator secured within the shell, a center electrode secured within the insulator and electrically insulated from the shell by the insulator, the center electrode being formed from a platinum-iridium (PtIr) alloy and having a firing tip having a diameter of at least 0.09 inches, and a ground electrode attached to the shell and terminating at a firing end of the igniter spaced from the firing tip, the ground electrode having at least one pin comprising ruthenium (Ru) or a ruthenium alloy. The igniter is advantageously used with an ignition system having a positive polarity pulse output.

Description

[Technical Field]

[0001] The present invention relates to an igniter having a noble metal electrode. Background technology The use of noble metal electrodes in igniters is known to provide the igniters with a long service life. This is advantageous for igniters used in aircraft jet engines and, more commonly, gas turbine engines. Numerous alloys and platinum group metal combinations have been proposed, and many are in commercial use. The long-lasting performance of these electrodes is attributed to their inherent characteristics, such as good operating voltage, low electrical resistivity, high thermal conductivity, and good oxidation resistance, which minimizes electrode erosion. In some applications of these noble metal electrodes, such as automotive spark plugs, the material properties allow for smaller electrode diameters compared to more traditional plugs, thereby allowing for the use of less material (and therefore lower costs) while reducing the required spark voltage.

[0002] overview In accordance with one aspect of the present invention, there is provided an igniter for a gas turbine engine comprising: a shell; an insulator secured within the shell; a center electrode secured within the insulator and electrically insulated from the shell by the insulator, the center electrode being formed from a platinum-iridium (PtIr) alloy and having a firing tip having a diameter of at least 0.09 inches; and a ground electrode attached to the shell and terminating at a firing end of the igniter spaced from the firing tip, the ground electrode having at least one pin comprising ruthenium (Ru) or a ruthenium alloy.

[0003] The igniter may include any of the following features, alone or in any technically feasible combination:

[0004] -Ignition tip diameter is 0.11 to 0.15 inches. The PtIr alloy comprises a mixture of platinum and iridium in the range of Pt70Ir30 to Pt99Ir1.

[0005] The PtIr alloy comprises a mixture of platinum and iridium in the range of Pt80Ir20 to Pt95Ir5.

[0006] The PtIr alloy comprises a mixture of platinum and iridium in the range of Pt85Ir15 to Pt95Ir5.

[0007] The ground electrode comprises a plurality of pins, each having a diameter in the range of 0.022 inches to 0.122 inches.

[0008] Each of the pins contains at least 99.9% ruthenium. The firing tip has a diameter of 0.12 inches, the PtIr alloy comprises Pt90Ir10, the pin has a diameter of 0.072 inches, and the ruthenium comprises at least 99.9% ruthenium.

[0009] According to another aspect of the invention, there is provided an ignition system comprising the igniter of the previous two paragraphs. The ignition system may further comprise a positive polarity exciter and an ignition lead connected at one end to the exciter and at the other end to the igniter.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS Preferred exemplary embodiments of the present invention will now be described in conjunction with the accompanying drawings, in which like numerals refer to like elements, and in which: FIG. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 illustrates a gas turbine ignition system including an exciter, ignition leads, and an igniter configured in accordance with one embodiment of the present invention. [Figure 2] FIG. 2 is a partial cutaway view of the igniter of FIG. 1. [Figure 3] FIG. 3 is an enlarged view of the working end of the igniter of FIG. 2. [Figure 4] 1 is a chart comparing various igniters having different combinations of ground electrode (ground electrode) and center electrode (center electrode) materials and diameters. DETAILED DESCRIPTION OF THE INVENTION

[0012] Detailed Description 1 illustrates a gas turbine ignition system 7 including an exciter 8, an ignition lead 9, and an igniter 10 configured in accordance with one embodiment of the present invention. The ignition system 7 is a positive polarity ignition system having the exciter 8 comprising a unipolar positive polarity exciter that outputs only positive spark pulses that are sent to the igniter 10 via the ignition lead 9.

[0013] Ignition system 7 can be implemented in a variety of ways suitable for any of a number of different turbine engine applications, such as those used in commercial, industrial, and military aircraft, helicopters, industrial gas engines, and other turbine-generators. The construction, operation, and use of commercially available positive polarity 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.

[0014] As shown in Figure 2, igniter 10 has conventional construction with the exception of its ground and center electrodes. As will be appreciated by those skilled in the art, igniter 10 is of a type configured for gas turbine engines, such as those used in aviation applications in jet engines. Referring also to Figure 3, igniter 10 includes a shell 20, an insulator 30, and a center electrode (CE) 40 extending downwardly through the center of shell 20 and insulator 30 to a working or firing end 50 that includes a firing tip (or pin) 46 and a ground electrode (GE) 60 spaced apart from the firing tip.

[0015] Shell 20 includes an upper shell 22, a lower shell 24, and a bushing 26, each made from a suitable metal or metal alloy, such as stainless steel, which may be the same or different for each of components 22-26. Upper shell 22 and lower shell 24 are physically and electrically connected by an interference fit at the lower end of upper shell 22 and the upper end of lower shell 24 via mating shoulders at the overlapping regions of the two shells, as shown in FIG. 2 and as known in the art. Similarly, bushing 26 is physically and electrically connected to upper shell 22 by being crimped or otherwise fitted to its lower end within the top of the upper shell.

[0016] Insulator 30 includes upper and lower insulators 32, 34, each of which may be made of ceramic or other suitable non-conductive material. The lower portion of upper insulator 32 fits into the upper portion of lower insulator 34, as shown, and is of sufficient length to prevent discharge between center electrode 40 and shell 20 across the mating surfaces of the insulators.

[0017] The center electrode 40 includes an upper end having an ignition cable contact 41 made of tungsten or other suitable conductive metal or alloy. This contact 41 is connected to an electrode cap 42 made of stainless steel or other suitable conductive metal or alloy. A center electrode rod 44, made of ASTM F15 (Kovar™) or similar, is threaded, welded, crimped, or otherwise connected to the electrode cap 42 and is surrounded at its upper end by a glass seal 45 below the cap 42. Referring more particularly to FIG. 3 , at the lower end of the center electrode 40, a noble metal firing tip 46 is welded, brazed, or otherwise suitably secured to the lower end of the center electrode rod 44 at joint 47. Each of the aforementioned center electrode components 41-47 are electrically connected so that spark energy applied from the exciter 8 via the ignition cable 9 to the igniter 10 can travel through the center electrode 40 and ignite between the CE firing tip 46 and the ground electrode 60.

[0018] As also shown in FIG. 3 , the ground electrode 60 comprises a plurality of noble metal pins 62, two of which are shown. In the igniter 10, six such pins 62 are equally spaced around the lower end of the lower shell 24, extend radially inward toward the radial center of the shell 24 (and the central axis of the center electrode 40), and terminate near the edge of an opening in the lower insulator 34. Through this opening, a spark can fly between the CE firing tip 46 and one or more ground electrode pins 62 through a space 70 open to the igniter's external environment to initiate combustion of an air / fuel mixture in an internal combustion engine, such as a gas turbine engine. Each of the pins 62 extends radially inward within a through-hole in the lower shell 24, aligning the pin 90 degrees relative to the central axis of the center electrode assembly. The pins 62 are brazed and then welded in place to the lower shell 24 by an externally facing weld 63. It will be appreciated that other arrangements of the ground electrode 60 are possible, including angling the ground electrode pin 62 at an angle other than 90 degrees relative to the central axis of the center electrode 40, angling the pin 62 so that it does not intersect the central axis, and using more or fewer pins.

[0019] As will be appreciated by those skilled in the art, the igniter 10 receives high-voltage pulses from the exciter 8 sufficient to ignite between the CE firing tip 46 and one or more of the ground electrode pins 62. These pulses are transmitted to the igniter 10 via an ignition lead 8, which, according to its conventional construction, includes a center conductor and a metallic coaxial braid, foil, or other shield separated from the center conductor by an insulator. In the illustrated embodiment, the exciter 8 is connected to an ignition lead 9, whose coaxial shield is electrically connected to the exciter's output ground terminal and whose center conductor is connected to the exciter's spark output terminal. The other end of the ignition lead 9 is mechanically and electrically connected to the igniter 10 such that its shell 20, and therefore the ground electrode pin 62, is electrically connected to the coaxial shield, while the center electrode 40, and therefore the CE firing tip 46, is electrically connected to the center conductor of the ignition lead 9.

[0020] Because exciter 8 is a positive polarity exciter, it outputs a high voltage positive polarity pulse (with respect to the grounded coaxial shield) to the center conductor of ignition lead 9. As a result, igniter 10 receives and conducts the high voltage positive polarity pulse to its CE firing tip 46, generating a positive polarity spark across the gap between firing tip 46 and one or more of the ground electrode pins 62.

[0021] The igniter 10, using a platinum group metal / alloy combination for the CE firing tip 46 and ground electrode pin 62, along with the specific dimensions of the firing tip 46, has been found to exhibit surprisingly long service life through testing. Referring now to FIG. 4, a graph containing test results illustrating the life characteristics of several different firing tip metals and dimensions is shown. This life characteristic is demonstrated by a plot of the center electrode depth into the insulator versus the total number of sparks before failure. The center electrode depth begins at approximately 0.18 inches and increases with erosion of the firing tip 46 over the life of the igniter. The red zone indicates undesirable amounts of electrode erosion early in the igniter's life, while the green zone indicates a favorable operating combination of less erosion and more sparks. Tests were conducted with the igniter tip exposed to 75 psig and 1,500°F. Note that the number of lifetime sparks captured under these conditions (2M-3M sparks) is significantly lower than when sparking occurs at ambient pressure and temperature.

[0022] Twelve different center and ground electrode material combinations are shown in Figure 4, some labeled and three including data point markers for easy review. Of these three, the triangular data point line representing an igniter with a Pt90Ir10 (90% platinum, 10% iridium by weight) center electrode tip and Ru (>99.9% pure ruthenium) ground electrode pin shows above-average electrode erosion (>0.300 electrode depth) but also above-average spark life (2,000,000 sparks before failure). Swapping the center and ground electrode materials results in even greater electrode wear (>0.430 electrode depth) and even improved overall spark life (2.4M sparks), as shown by the curve with square data points. This test was conducted using a 0.100" diameter Pt90Ir10 alloy center electrode.

[0023] Further testing surprisingly revealed that a larger 0.120" diameter center electrode, combined with a Ru ground electrode pin and a Pt90Ir10 alloy center electrode pin, resulted in a significant improvement in life (3.7M sparks) while minimizing electrode erosion (0.270 electrode depth). This is illustrated by the circular data point curve in Figure 4. This unexpectedly advantageous performance is likely due to the use of a larger (0.120") center electrode diameter, as well as the Ru ground electrode pin and Pt90Ir10 center electrode pin combination. While not wishing to be limited by any theory or explanation of operation, the performance advantage is believed to be due in part to the unipolar positive spark voltage applied to the plug (with the ground electrode grounded) and the reduced center electrode erosion due to electron acceptance across the spark gap and its increased size.

[0024] Therefore, by further combining Ru material for the ground electrode with PtIr material for the center electrode, increasing the diameter, and using the igniter in a positive polarity ignition system, it is possible to significantly extend the service life of igniters in gas turbines and other internal combustion engines.

[0025] In 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, and the ground electrode has a diameter of 0.072" and is formed of Ru. While these materials and the diameter of the center electrode are important to the results of the particular circular data point curve shown in FIG. 4, other embodiments of the igniter can be fabricated using a PtIr alloy for the center electrode in the range of Pt70Ir30 to Pt99Ir1, more preferably in the range of Pt80Ir20 to Pt95Ir5, and even more preferably in the range of Pt85Ir15 to Pt95Ir5, which is closer to the tested Pt90Ir10. Similarly, in some embodiments, the Ru ground electrode can be made of a suitable ruthenium alloy rather than pure or nearly pure ruthenium. Also, the center electrode pin may have a diameter other than the tested 0.12", and in some embodiments may be 0.11" or greater up to the maximum technically or commercially feasible, or may be within a tested diameter range of about 0.12", for example, in the range of 0.09" to 0.15". While this range covers the square data point curve of FIG. 4, it will be understood that an igniter having these characteristics will still be capable of achieving good spark life and therefore commercially acceptable. Also, the diameter of the ground electrode pin 62 is 0.072", but in other embodiments may be in the range of 0.022" to 0.122".

[0026] It should be understood that the foregoing description is of one or more embodiments of the present invention. The present invention is not limited to the specific embodiments disclosed herein, but rather is defined solely by the following claims. Furthermore, statements contained in the foregoing description should not be construed as limitations on the scope of the invention or the definition of terms used in the claims, unless the term or phrase is expressly defined above in connection with the disclosed embodiments. Various other embodiments and various modifications and alterations to the disclosed embodiments will be apparent to those skilled in the art. For example, the igniter 10 may have different shell, insulator, and firing end configurations using the Ru-based ground electrode and PtIr-based center electrode described above for different applications, such as gas turbine generators and automotive spark plugs. Additionally, the alloys provided herein may contain trace elements, or in some embodiments, relatively small amounts of other elements.

[0027] As used in this specification and claims, the terms "e.g.,," "for example," "for instance," "such as," and "like," as well as the verbs "comprising," "having," "including," and other verb forms thereof, when used in combination with a list of one or more components or other items, should each be construed as open-ended, meaning that the list should not be considered to exclude other additional components or items. Other terms should be construed using their broadest reasonable meaning unless used in a context requiring a different interpretation. Furthermore, the term "and / or" should be construed as an inclusive OR. Thus, for example, "A, B, and / or C" should be construed to cover all of the following: "A," "B," "C," "A and B," "A and C," "B and C," and "A, B, and C."

Claims

1. 1. An igniter for a gas turbine engine, comprising: A shell and an insulator fixed within the shell; a center electrode secured within and electrically insulated from the shell by the insulator, the center electrode being formed from a platinum-iridium (PtIr) alloy and having a firing tip having a diameter of at least 0.09 inches; a ground electrode attached to the shell and terminating at a firing end of the igniter spaced from the firing tip, the ground electrode having at least one pin comprising ruthenium (Ru) or a ruthenium alloy; An igniter comprising:

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

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

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

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

6. 10. The igniter of any preceding claim, wherein the ground electrode comprises a plurality of pins each having a diameter in the range of 0.022 inches to 0.122 inches.

7. 10. An igniter according to any preceding claim, wherein each of said pins comprises at least 99.9% ruthenium.

8. 10. The igniter of any preceding claim, wherein the firing tip diameter is 0.12 inches, the PtIr alloy comprises Pt90Ir10, the pin diameter is 0.072 inches, and the ruthenium comprises at least 99.9% ruthenium.

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

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

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