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.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This invention pertains to ignition and sensing systems and more particularly to flame ignition and flame detecting or sensing systems. Even more particularly, the invention pertains to such systems having a spark type ignition. 
         [0003]    2. Description of the Related Art 
         [0004]    A gas pilot burner is a device used to create a stable pilot flame by combustion of a low flow rate (relative to the main burner) gaseous fuel-air mixture. The pilot flame is used to light a larger main burner, or a difficult to light fuel. Gas pilot designs normally include an ignition system and a flame detection system. The two most common types of ignition systems used in gas pilot burners are high tension (HT) and high-energy ignition (HEI). Flame detection is typically by a flame ionization detection (FID) system. 
         [0005]    An HT flame ignition system typically utilizes a high voltage source and an HT spark plug or spark rod. The high voltage source provides high voltage, low current pulses. Often, such pulses will be 15 kV or greater and from about 10 to about 50 mA. HT systems create low amperage sparks that bridge an air gap created in a spark plug or between a spark rod and the grounded pilot frame. This spark is used to ignite the fuel-air mixture and, thus, generate the pilot flame. While this type of ignition can be low cost, it can be inconsistent when ignition conditions are not ideal. Moisture from steam or rain, contamination and heavy fuel can all generate ignition problems when using an HT system. 
         [0006]    An HEI system typically utilizes a capacitive discharge exciter to pass large current pulses to a spark rod. The large current pulses are often greater than 1 kA. The spark rod or igniter probe for an HEI system is generally constructed using a center electrode surrounded by an insulator and an outer conducting shell over the insulator such that, at the ignition end of the spark rod, a high-energy spark can pass between the center electrode and outer conducting shell. HEI systems have the ability to maintain powerful high energy sparks in adverse conditions such as cold temperatures, heavy fuels (heavy gases or oils), contamination of the igniter plug with coking or other debris and moisture presence due to steam purging or rain. 
         [0007]    For safety considerations, it is important that the ignition system ignites the fuel-air premix as soon as possible after the main fuel gas valve opens. It is also important that the flame ionization detection system registers the flame signal as soon as possible after the flame is established. Together, rapid ignition and flame detection help minimize the chance of explosion due to raw fuel being pumped into a burner. Typically, there is a burner management system (BMS) that controls the fuel and ignition systems while monitoring the flame ionization detection system. Often, the burner management system will give five seconds or less of fuel flow time before closing the fuel valve if flame is not proven. The window for ignition and detection is therefore very short. 
         [0008]    Most prior HT ignition systems have used a combined HT and flame detection system wherein ignition must occur and then an electromechanical switch de-energizes the exciter and energizes the flame detector. This means ignition and detection are sequenced into two distinct time periods, each occupying a portion of the maximum limited allowable fuel valve open time window. HT or HEI systems allowing for simultaneous ignition and flame detection have relied on using completely separate ignition and detection systems. It would be beneficial to have a powerful ignition system, such as an HEI system, and a flame detection system that can operate simultaneously through the entire window where the flame detection system is an integral part of the HEI systems; that is, without utilizing completely separate ignition and detection systems. 
       SUMMARY 
       [0009]    In accordance with one embodiment of the present invention, there is provided a pilot burner comprising a source of electrical energy, a spark rod and a housing. The spark rod has a first end, a second end and a flame rod connected thereto at the second end. The spark rod is connected to the source of electrical energy at the first end such that the electrical energy causes a spark at the second end. The housing has a fuel flow passage, which contains the second end of the spark rod. The position of the flame rod in the housing and the connection of the spark rod to the source of electrical energy is such that when no flame exists adjacent to the second end of the spark rod, no current flows between the flame rod and the housing and when a flame exists adjacent to the second end of the spark rod, current flows between the flame rod and the housing. The source of electrical energy and the pilot burner are capable of simultaneously generating the spark and providing the current. 
         [0010]    In another embodiment of the invention, there is provided an apparatus for ignition and flame detection comprising a first electrode, a second electrode and a third electrode. The first electrode and second electrode each have a first end and a second end. The first electrode and the second electrode are positioned and electrically insulated from each other such that a spark tip is formed by the second ends so that, when the first ends are connected to a source of electrical energy, a spark can pass between the second end of the first electrode and the second end of the second electrode. When fuel is adjacent to the second end of the second electrode, the spark ignites the fuel and produces a flame. The second electrode is configured and positioned relative to the third electrode such that, when the flame is present between said second electrode and said third electrode, electricity is conducted between the second end of the second electrode and the third electrode but, when no flame is present, electricity is not conducted between the second electrode and the third electrode. 
         [0011]    In a further embodiment, there is provided an ignition device comprising a source of rectified current, a flame detection circuit, a fuel source, a housing, an electrode, an insulating sleeve, an electrode tube and a controller. The source of rectified current has a high potential terminal and a low potential terminal. The housing has an electronics enclosure and a tube portion forming a longitudinal passage that is in fluid flow communication with the fuel source such that fuel from the fuel source flows through the longitudinal passage. The electronics enclosure and the longitudinal passage are sealed such that the fuel cannot pass between them. The housing is electrically grounded and the electronics enclosure contains the source of rectified current and flame detection circuit. The electrode has a first end and a second end. The first end is in the electronics enclosure and is connected to the high potential terminal. The electrode extends into the longitudinal passage. The insulating sleeve extends over at least a portion of the electrode. The electrode tube has a first end and a second end, wherein the first end is in the electronics enclosure and connected to the low potential terminal. The electrode tube extends into the longitudinal passage and is positioned around the insulating sleeve such that the electrode and the electrode tube are positioned so that a spark can pass between the second end of the electrode and the second end of the electrode tube to ignite the fuel and, thusly, produce a flame. The first end of the electrode tube is connected to the flame detection circuit. The flame detection circuit provides a current to the electrode tube. The second end of the electrode tube is configured such that, when the flame is established, current is conducted between the second end of the electrode tube and the housing but, when no flame is present, current is not conducted between the electrode tube and the housing. The controller is connected to the electrode tube, the fuel source and the source of electrified current. The controller detects the flow of current between the second end of the electrode tube and the housing and stops the flow of rectified current to the first terminal if current flow occurs. 
         [0012]    In yet another embodiment, there is provided a process for simultaneous ignition and flame detection in a high energy igniter of the type that has a fuel channel having a grounded wall and a spark rod located therein with the spark rod being a type that has a center electrode and an electrode tube where the center electrode and electrode tube form a spark tip. The process comprises:
       (a) providing a current to the electrode tube such that when a flame is present adjacent to the spark tip, a current will flow from the electrode tube to the grounded wall;   (b) providing a first potential to the center electrode;   (c) providing a second potential to the electrode tube wherein the first potential and second potential cause the spark tip to spark;   (d) introducing a fuel and air mixture into the channel such that the spark can ignite the fuel and air mixture;   (e) detecting whether the current flows from the electrode tube to the wall; and   (f) shutting down the first potential when the current is detected.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic diagram of one embodiment of the current invention. 
           [0020]      FIG. 2  is a perspective view of the apparatus of  FIG. 1  with partial invisible walls. 
           [0021]      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 . 
           [0022]      FIG. 4  is a perspective view with partial cutaway of a spark rod tip and flame rod in accordance with  FIGS. 1 and 2 . 
           [0023]      FIG. 5  is a perspective view with partial cutaway of a pilot burner tip in accordance with another embodiment of the invention. 
           [0024]      FIG. 6  is a perspective view with partial cutaway of a pilot burner tip in accordance with yet another embodiment of the invention. 
           [0025]      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. 
           [0026]      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 
       [0027]    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. 
         [0028]    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 . 
         [0029]    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 . 
         [0030]    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. 
         [0031]    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 . 
         [0032]    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. 
         [0033]    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. 
         [0034]    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. 
         [0035]    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 . 
         [0036]    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. 
         [0037]    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 . 
         [0038]    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&#39;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 . 
         [0039]    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 . 
         [0040]    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. 
         [0041]    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 . 
         [0042]    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. 
         [0043]    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. 
         [0044]      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. 
         [0045]    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 . 
         [0046]    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 . 
         [0047]    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 . 
         [0048]    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 . 
         [0049]    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 μA). 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. 
         [0050]    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 . 
         [0051]    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. 
         [0052]    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.       
 
         [0059]    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. 
         [0060]    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. 
         [0061]    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.