Combined high energy igniter and flame detector

Abstract

An apparatus and method are provided for improved gas pilot burners, which are capable of simultaneous flame ignition and flame detection. More particularly, the invention provides for an apparatus and method capable of simultaneous high-energy ignition and flame ionization detection in a high-energy igniter that utilizes a spark rod located in a fuel channel.

Claims

1. An apparatus for high-energy ignition and flame detection comprising: a first electrode having a first end and a second end; a second electrode having a first end and second end wherein said first electrode and said second electrode are positioned and electrically insulated from each other such that a spark tip is formed by said second ends so that, when said first ends are connected to a source of electrical energy, a spark can pass between said second end of said first electrode and said second end of said second electrode and, when fuel is adjacent said spark tip, said spark ignites said fuel with said high-energy ignition to produce a flame; a third electrode wherein said second end of said second electrode is configured and positioned relative to said third electrode such that when said first ends are connected to said source of electrical energy and when said flame is present between said second electrode and said third electrode, electricity is conducted between said second end of said second electrode and said third electrode but when no flame is present electricity is not conducted between said second electrode and said third electrode; and a source of fuel fluidly connected to said housing; and wherein: said spark can pass between said second end of said first electrode and said second end of said second electrode, and simultaneously, said electricity can be detected when said electricity is conducted said third electrode is a housing defining a fuel flow passage and wherein said spark tip is located within said fuel flow passage said source of electrical energy has a first terminal at a first potential and a second terminal at a second potential wherein said second potential is less than said first potential and above ground potential; and said first end of said first electrode is electrically connected to said first terminal and said first end of said second electrode is electrically connected to said second terminal and wherein said housing is grounded.

2. The apparatus according to claim 1 wherein said source of electrical energy has a third terminal electrically connected to said second electrode and wherein said source of electrical energy provides a rectified current through said first terminal so as to generate said spark capable of high-energy ignition, and wherein said source of electrical energy provides an alternating current through said third terminal such that when said flame is present between said second electrode and said third electrode, electricity is conducted between said second end of said second electrode and said third electrode but when no flame is present electricity is not conducted between said second electrode and said third electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of one embodiment of the current invention.

(2) FIG. 2 is a perspective view of the apparatus of FIG. 1 with partial invisible walls.

(3) FIG. 3 is a perspective view with partial cutaway of a pilot burner tip in accordance with the embodiment illustrated in FIGS. 1 and 2.

(4) FIG. 4 is a perspective view with partial cutaway of a spark rod tip and flame rod in accordance with FIGS. 1 and 2.

(5) FIG. 5 is a perspective view with partial cutaway of a pilot burner tip in accordance with another embodiment of the invention.

(6) FIG. 6 is a perspective view with partial cutaway of a pilot burner tip in accordance with yet another embodiment of the invention.

(7) FIG. 7 is a graphical representation of a rectified current similar to the rectified current across the flame rod-wall gap that occurs when a flame is present.

(8) FIG. 8 is a graphical representation of an alternating current such as detected by the flame detection circuit when there is a short or fault in an HEI/FID system in accordance with the present invention.

DETAILED DESCRIPTION

(9) The description below and the figures illustrate a pilot burner or ignition system of the type used in a furnace having a main burner that supplies a fuel and air mixture to the furnace and a pilot burner adjacent to the main burner for igniting the fuel and air mixture. While the invention is described in the context of a pilot burner for such a furnace, it will be appreciated that the inventive ignition device is more broadly applicable as an ignition and flame detection system for fuels.

(10) Referring now to FIGS. 1 through 4, an ignition device or pilot burner 10 in accordance with one embodiment of the invention is illustrated. Pilot burner 10 has a housing 12. Housing 12 is comprised of a main pipe or tube portion 14, electronics enclosure 16 and fuel introduction pipe 18. Tube portion 14 has a wall 20 having a first end 22 and a second end 24 and a longitudinal fuel flow passage or fuel channel 26 defined by wall 20. First end 22 is connected to electronics enclosure 16 and the wall 20 defines an opening 28 at second end 24. At or near first end 22 will be a sealing device 30 which seals fuel channel 26 so that it is not in fluid flow communication with electronics enclosure 16 and, hence, so that fuel cannot enter electronics enclosure 16.

(11) Fuel introduction pipe 18 is in fluid flow communication with a fuel source 19 and longitudinal fuel flow passage 26 of tube portion 14. Generally, a fuel-air mixture will be introduced into passage 26 through pipe 18 such that the fuel-air mixture will flow in a generally longitudinal direction towards second end 24 and out opening 28.

(12) Extending longitudinally along longitudinal passage 26 is a spark rod 31. Spark rod 31 has a first end 32 extending into electronics enclosure 16 and a second end 33 located near the second end of tube portion 14. Spark rod 31 is comprised of a center electrode 34, an insulating sleeve or tube 37 and an outer shell or electrode tube 40. Center electrode 34 has a first end 35 located within electronics enclosure 16 and a second end 36 located near, but spaced away from, second end 24 of tube portion 14 so that it is inside tube portion 14. Electrode tube 40 has a first end 41 located within electronics enclosure 16 and a second end 42 located near, but spaced away from, second end 24 of tube portion 14 so that it is inside tube portion 14. Insulating sleeve 37 has a first end 38 located within electronics enclosure 16 and a second end 39 located near second end 24 of tube portion 14 and, as shown, just short of the second ends of center electrode 34 and electrode tube 40 so as to form a well 54. Second ends of center electrode 34, insulating sleeve 37 and electrode tube 40 form spark tip 43 of spark rod 31 (as best seen in FIGS. 2 and 3). It should be understood that while spark rod 31 is illustrated as having a center electrode covered by a concentric insulating sleeve and a concentric electrode tube, it could have any other suitable design. Generally, spark rod 31 will have a first electrode and a second electrode that are electrically isolated from each other but with ends that are adapted to transmit a spark from one electrode to the other upon application of an electrical charge on the opposite ends of the electrodes.

(13) As illustrated, spark rod 31 extends through a second insulating sleeve 44 that isolates spark rod 31 from housing 12, which is connected to ground wire 29 so that housing 12 is at ground potential. Generally, spark rod 31 is held in place by second insulating sleeve 44. While spark rod 31 can be attached to second insulating sleeve 44, it is preferred that they be slidingly engaged so that spark rod 31 can be removed from second insulating sleeve 44 at either first end 32 or second end 33. Second insulating sleeve 44 is held in place by sealing device 30 and structural supports 46, which are connected to second insulating sleeve 44. Optionally, structural supports 46 can be made from insulating material and connected directly to spark rod 31 without use of second insulating sleeve 44; however, this can hamper removal of spark rod 31 from first end 32 and/or second end 33.

(14) Additionally, at second end 33 spark rod 31 has a flame rod 48 attached to electrode tube 40. Flame rod 48 is a conducting material that extends towards wall 20 of housing 12 but is not in contact with housing 12. Additionally, flame rod 48 is positioned such that when spark rod 31 has ignited the fuel-air mixture to produce a flame 50, flame rod 48 will be located within the flame.

(15) As illustrated, spark rod 31 is a high-energy igniter (HEI) probe. Accordingly, spark rod 31 should be suitable to pass large current pulses (often greater than 1 kA) from an energy source, further described below, to the spark tip and, thereby, generate a spark at the spark tip. The purpose of an HEI probe is to provide high ignition power. In applications with low temperatures, heavy fuels (heavy gases or oils), contamination of the igniter plug with coking or other debris, or moisture presence due to steam purging or rain, the main fuel may be difficult to light but an HEI system has the ability to maintain powerful high energy sparks in these adverse conditions.

(16) As described above, the HEI igniter probe is generally constructed using a center electrode 34, an insulation system (typically comprising insulation sleeve or tube 37) and outer shell or electrode tube 40. Outer electrode tube 40 is generally about 0.25 to 0.75 inches in diameter. In the past electrode tube 40 has been grounded and not isolated from the pilot frame or housing 12; however, it is an advantage of the current invention that electrode tube 40 not be grounded and be isolated from the housing and, hence, from ground, as is further described herein.

(17) Additionally, a semiconductor material 52 (see FIG. 4) can be applied to the insulation tube at the end of the tip to form a conductive path between the center electrode 34 and the electrode tube 40. This semiconductor is normally a pellet type piece placed at the end of the insulation tip or a film applied to the insulator itself This semiconductor assists the HEI probe with spark initiation by allowing a low level of current to pass in the semiconductor when the energy source applies an ignition pulse to the center electrode 34. This low level current flowing though the semiconductor creates a small ionized air zone above the path of current in the well 54 of spark rod 31. This small ionized air path is a low impedance pathway for current flow. Once the pathway is established, the electrical energy is able to flow unresisted except for circuit impedance, thereby creating a very high current and energy spark at well 54.

(18) Turning now to electronics enclosure 16, it has at least partially located therein a source of electrical energy, which includes a power supply 56, exciter 58 and flame detection circuit 60. Power supply 56 (as shown located outside of electronics enclosure 16) provides electrical power to both exciter 58 and flame detection circuit 60. A controller 62, sometimes referred to as a burner management system (BMS), is operationally connected to the source of electrical energy.

(19) Exciter 58 can be any high-energy exciter known in the art and suitable to provide a rapid electrical pulse to spark rod 31 and, thus, cause a spark at spark tip 43. Accordingly, exciter 58 will typically be a capacitive discharge device. In an exemplary exciter, exciter 58 has a transforming element 64, diode 66 and capacitor 68. Terminals 70 and 72 are in electrical connection with capacitor 68. Additionally, terminal 70 is connected to center electrode 34 at first end 35 and terminal 72 is connected to electrode tube 40 at first end 41. Terminal 72 is also connected to terminal 74 of flame detection circuit 60.

(20) Electrical input to exciter 58 can by controlled by switch 76, which is operationally connected to controller 62 (connections not shown). Accordingly, when controller 62 activates switch 76, transforming element 64 steps up the incoming voltage and diode 66 rectifies it such that capacitor 68 is charged by the step up transformer. When a predetermined threshold voltage is reached, switch 78 is closed by the exciter's controller (not shown). This causes the spark gap, between center electrode 34 and electrode tube 40 at spark tip 43, to connect to the potential deference stored on the capacitor 68 and create an arc. Thus, energy in capacitor 68 flows through terminal 70 (in this case the high potential terminal) through center electrode 34, across well 54 (spark gap), though electrode tube 40 and terminal 72 (in this case the low potential terminal) and back to the capacitor 68. This large capacitive current results in a powerful spark across well 54.

(21) Accordingly, for the illustrated exciter, it can be said that terminal 70 has a high potential and terminal 72 has a low potential with low potential terminal 72 having an electrical potential below the potential of high potential terminal 70 but above ground potential. This is achieved through galvanic isolation in the transforming element 64 and by electrical connection to terminal 74 of flame detection circuit 60.

(22) While the embodiment illustrated in FIGS. 1 and 2 utilizes an exciter than generates a rectified current, it should be understood that the invention is not limited to such an exciter. For example, alternatively, the exciter cannot utilize diode 66 so that the exciter comprises a ringing tank circuit. In such an embodiment, the exciter emits a high amperage alternating pulse and terminals 70 and 72 would alternate between being the high potential terminal and the low potential terminal; however, each would be above ground potential. Other forms of exciters useful in the present invention will be apparent to those skilled in the art based on the disclosure herein.

(23) As previously mentioned, flame detection circuit 60 is supplied power by power supply 56 through terminals 80 and 82. Flame detection circuit 60 is connected to ground wire 84 and is connected to low potential terminal 72 and electrode tube 40 through terminal 74. As mentioned above, terminal 70, electrode 34, terminal 72 and electrode tube 40 are all isolated from ground. Tube portion 14, however, is grounded. Accordingly, when flame detection circuit 60 is activated, there is potential across the gap 51 between flame rod 48 and tube portion 14. As explained below, only when a flame is present and extends between flame rod 48 and tube portion 14, will there be a conductive pathway between flame rod 48 and tube portion 14. However this pathway only conducts current from flame rod 48 to tube portion 14; hence, if the current applied is an alternating current, only a rectified current is passed, similar to that illustrated in FIG. 7.

(24) Flame detection circuit 60 provides a signal 86 to controller 62. Controller 62 is operationally connected to switch 76, flame detection circuit 60 and the fuel source 19 such that, based upon signals 86 received from flame detection circuit 60, controller 62 can start or stop either the exciter 58 or the fuel-air mixture flowing into pipe 18 or both, as further explained below.

(25) The tip of pilot burner 10 can be better seen with reference to FIGS. 3 and 4. At pilot burner tip 11, tube portion 14 comprises wall 20 and hood 21. Hood 21 can have air holes 88 located near the second end 33 of spark rod 31 to provide additional air to the flame once the fuel has been ignited. Spark rod 31 is seated inside second insulating sleeve 44. The insulating sleeve 44 is held in position concentrically or off center to tube portion 14 by sealing device 30 and structural support 46. Second end 36 of center electrode 34 and second end 42 of electrode tube 40 extend slightly beyond second end 39 of insulating sleeve 37 so as to form well 54; thus, the second ends form spark tip 43. Additionally, a semiconductor 52 can be deposited on the second end of insulating sleeve 37 to aid in spark conception. Flame rod 48 is welded or otherwise conductively affixed to the exposed end 89 of electrode tube 40. The flame rod 48 is bent in an elongated Z configuration in order to place it near hood 21 of wall 20 but not in contact with and a suitable distance from wall 20 so that there is no electrical conduction between flame rod 48 and wall 20 unless a flame is present. Although illustrated in an elongated Z configuration, other configurations, such as a scythe or curved shape configuration may be used. The flame rod can be constructed of any suitable conductive material so long as it is isolated from housing 12 and is positioned to be in the flame, after ignition has occurred, such that rectified current flow can occur, as further explained below.

(26) FIGS. 5 and 6 illustrate other embodiments using different flame rod configurations. In FIGS. 5 and 6 like components to those in FIGS. 1-4 have received like designations. Referring now to FIG. 5, flame rod 90 is formed by a portion of electrode tube 40, which extends out from the exposed end 89 of electrode tube 40 and from second end 33 of spark rod 31. Flame rod 90 has a cross section that is a partial circle, generally a half circle or C-shaped cross section such that at least a portion of the second end 33 is exposed to the fuel-air mixture passing through longitudinal passage 26 so that the spark occurring at second end 33 can ignite the fuel-air mixture. Flame rod 90 is designed to fit within the outer diameter of electrode tube 40 and, hence, within the inner diameter of second insulating sleeve 44. In other words, flame rod 90 does not extend radially outward from the electrode tube farther than the outer radius of the electrode tube. Accordingly, flame rod 90 allows spark rod 31 to slide through second insulating sleeve 44 so that it can be replaced from the first end 22 of tube portion 14; thus, improving the ease of replacement of spark rod 31. Because flame rod 90 extends longitudinally downstream from spark rod 31 and not radially outward, it can be advantageous for the spark rod to be located off-center of the tube portion 14 so that flame rod 90 is near to wall 20 and better able to establish electrical flow when flame is established.

(27) Referring now to FIG. 6, flame rod 92 has a first ring portion 94 that slides over and makes conductive contact with the exposed end 89 of electrode tube 40. Flame rod 92 has a second ring portion 96 and struts 98 extending between first ring portion 94 and second ring portion 96 to create apertures 100. Apertures 100 expose the second end 33 of spark rod 31 to the fuel-air mixture passing through longitudinal passage 26 such that the spark occurring at second end 33 can ignite the fuel-air mixture. Extending from second ring portion 96 are flame rod fingers 102. Fingers 102 can extend radially outwardly from second ring portion 96 or at an angle so that they extend radially and longitudinally outwardly from second ring portion 96. The tips 104 of fingers 102 should be located near but isolated from wall 20 so that they are not in contact with hood 21 of wall 20 and are a suitable distance so that there is no electrical conduction between flame rod 92 and wall 20, unless a flame is present. The tips 104 should be positioned to be in the flame, after ignition has occurred, such that rectified current flow can occur, as further explained below. First ring portion 94 can be fixedly attached to the exposed end 89 of electrode tube 40 or can be slidingly engaged onto the exposed end 89. If slidingly engaged onto the exposed end 89 then flame rod 92 can be removed to allow spark rod 31 to slide through second insulating sleeve 44 so that it can be replaced from the first end 22 of tube portion 14; thus improving the ease of replacement of spark rod 31.

(28) In operation, fuel and air are introduced into longitudinal passage 26. The fuel and air may be introduced from a fuel-air mixture source 19 into fuel introduction pipe 18 or may each be introduced from separate sources into fuel introduction pipe 18. Fuel introduction pipe 18 is in fluid flow communication with longitudinal passage 26 and the fuel and air in pipe 18 is under positive pressure so that fuel and air within pipe 18 flows into longitudinal passage 26. Within longitudinal passage 26, the fuel and air flows in a generally longitudinal direction through passage 26 around spark rod 31 and around and through structural supports 46. Structural supports 46 can be perforated and can be shaped into swirling or diffusion elements to induce premixing of fuel and air within longitudinal passage 26 and prior to reaching the second end 33 of spark rod 31. Whether mixed within longitudinal passage 26 or mixed prior to introduction to fuel introduction pipe 18, the air and fuel should be adequately mixed upon reaching the second end 33 of spark rod 31 to produce a flame upon exposure to a spark from spark tip 43.

(29) Prior to spark initiation, flame detection circuit 60 is powered up. Terminal 74 of flame detection circuit 60 is connected to potential terminal 72 of exciter 58 and electrode tube 40, thus supplying a small current potential to both. While this current can be direct current or alternating current, the operation will be described with respect to alternating current, except where indicated. Spark is initiated by closing switch 76; thus providing power to exciter 58. Center electrode 34 is connected to terminal 70 of exciter 58 and, as previously indicated, electrode tube 40 is connected to the terminal 72 of exciter 58 and flame detection circuit 60. Accordingly, in the embodiment of FIG. 1, since terminal 70, terminal 72, center electrode 34 and electrode tube 40 are isolated from ground, they are maintained at a higher potential than ground; however, when switch 78 is closed, there is a high potential difference between terminal 70 and terminal 72, This high potential difference is what creates the spark at spark tip 43.

(30) When the exciter 58 provides a sufficiently large potential difference, an electrical pulse will jump between electrode 34 to electrode tube 40 at the spark tip 43 of spark rod 31; preferably, the current will follow the ionized path created by the semiconductor 52. This electrical pulse will be in the form of a spark and can ignite the fuel-air mixture around second end 33 of spark rod 31.

(31) A flame produces free ions in the vicinity of the flame envelope that form an electrically conductive pathway. By placing two electrodes in the flame and applying a voltage between them, a small current will result (less than 10 A). If one of the electrodes is much larger than the other, current will flow more easily from the small electrode to the large electrode than vice-versa. By applying an AC voltage between the electrodes, a current rectifying property will result and a current will flow across the gap between the two electrodes similar to the rectified current illustrated in FIG. 7. Detection of this rectification can be used to prove the presence of a flame.

(32) In the invention, tube portion 14 is electrically grounded and serves as a third electrode. Flame rod 48 is designed to be much smaller than tube portion 14 and, when no flame is present, is electrically isolated from tube portion 14 of the housing 12, and hence from ground. Accordingly, if no flame is present, then no current will flow from flame rod 48 to tube portion 14. If the spark generated at second end 33 of spark rod 31 creates a flame, flame rod 48 is positioned to be in the flame. In other words, the flame rod 48 is positioned so that the flame 50 will bridge the gap 51 so that spark rod 31 is no longer electrically isolated from tube portion 14 and a rectified current (similar to that illustrated in FIG. 7) is established that flows from flame rod 48 to tube portion 14.

(33) Detection circuit 60 sends a signal to controller 62 based on the establishment of a current between flame rod 48 and tube portion 14. When a rectified current is established, detection circuit 60 sends a signal to controller 62. In response to the signal, controller 62 opens switch 76 to shutdown exciter 58 and, hence, stop spark rod 31 from generating sparks. If controller 62 does not receive the signal that a rectified current is established within a predetermined period of time (the timeout period), then controller 62 will shutdown exciter 58 and stop fuel introduction into pipe 18. Additionally, in the case of a short or ground failure, an alternating current can be established between flame rod 48 and tube portion 14, similar to the current illustrated in FIG. 8. If detection circuit 60 detects an alternating current flow between flame rod 48 and tube portion 14, it sends a signal to controller 62 and controller 62 will shutdown exciter 58 and stop fuel introduction into pipe 18. While a direct current can be used for flame detection, it will not allow the detecting of a short or ground failure in the manner of an alternating current.

(34) In one embodiment, an inventive integrated high energy ignition (HEI) and flame ionization detection (FID) device operates as follows: (a) The integrated HEI/FID device is powered up, which turns on the flame detection circuit 60. (b) The controller 62 begins polling the flame signal 86 from the flame detection circuit for proof of flame. If signal 86 indicates that an alternating current is flowing, then controller 62 aborts steps (e) to (f). (c) The controller powers the HEI exciter 58 by closing switch 76. The HEI exciter begins sparking the spark rod 31. (d) The controller opens the main fuel valve and continues to monitor the flame signal 86. (e) The controller shuts off the flow of fuel to pipe 18 if flame is not detected before the timeout period is up. The sequence can repeat from step (b) for a predetermined number of attempts. Repetition can be subject to a predetermined wait period between attempts. (f) If flame is proven within the time out period, the controller shuts down the HET exciter 58 and continues to monitor the flame signal.

(35) For safety considerations, it is important that the ignition system ignite the fuel-air mixture as soon as possible after introduction of fuel into pipe 18 has commenced. Accordingly, the timeout period is typically set very short, often five (5) seconds or less. Accordingly, it is important that the flame detection system registers positive flame signal as soon as possible after flame is established. As will be realized from the above description, the current invention has the advantage of being capable of simultaneous rapid ignition and flame detection utilizing an integrated ignition and flame detection system. The term simultaneous refers generally to flame detection during the period that the exciter is energized and the spark rod is sparking. In a system with sequential flame detection, the ignition attempt (sparking of the spark rod) is made, then the exciter is de-energized, and then the flame detector is energized to detect flame. If no flame is detected, the flame detector is de-energized and the exciter re-energized to initiate another spark. In a system with simultaneous flame detection, there is no de-energizing of the exciter for the spark rod before flame detection.

(36) Together, this simultaneous rapid ignition and flame detection help minimize the chance of explosion due to raw fuel being pumped into a burner. Prior art systems have not been able to achieve simultaneous ignition and flame detection in an integrated system. They instead relied on either sequenced ignition and flame detection or completely separate ignition and detection systems.

(37) Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.