Abstract:
A burner with a flame detector is provided. An atomizing chamber has an aperture. A flame tube is in front of the atomizing chamber, adapted to direct combusting fuel introduced by the atomizing chamber along an interior of the flame tube. A photodiode circuit is located behind the atomizing chamber. A filter is adapted to filter out signals from the photodiode outside of a predetermined bandwidth. Light from combusting fuel in the flame tube reaches the photodiode through the aperture. The output of the filter indicates the presence or absence of the flame in the flame tube based on at least whether enough light received and converted by the photodiode has a flicker rate within the predetermined bandwidth.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The instant application claims priority to U.S. Provisional Application 62/274,879, entitled SYSTEM AND METHOD FOR DETECTING FLAME WITHIN A BURNER, filed on Jan. 5, 2016, the contents of which are expressly incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Various embodiments described herein relate generally to detection of operating characteristics of a burner, such as the presence of a flame. More specifically, various embodiments described herein relate to detecting the presence of a flame in the burner by detecting the presence of light flicker consistent with a flame for the particular burner. 
       BACKGROUND 
       [0003]    In a burner of solid, liquid or gaseous fuel it is of known importance to sense the presence of flame to monitor and verify burner operation. It is also important to verify correct combustion within the burner to control the emission of pollutant combustion products into the atmosphere. 
         [0004]    A prior art methodology for detecting the presence of flame from combustion in burners is to use a photo resistor, typically of cadmium sulphide, to act as a light detector that responds to the light generated by the flame. A drawback of this methodology is that a photo resistor cannot accurately distinguish between sources of light, and can therefore give a false positive based on external light sources or even the glow of material heated by the burner. To minimize false positives the photo resistor can be located in the burner at positions that tend not to receive external light, such as the barrel of the burner, but these locations are exposed to the heat of combustion and requires a design that can withstand such extreme heat. 
     
    
     
       DRAWINGS 
         [0005]    Various embodiments in accordance with the present disclosure will be described with reference to the drawings, in which: 
           [0006]      FIG. 1  shows an embodiment of the invention. 
           [0007]      FIG. 2  shows an embodiment of the invention inside of a burner. 
           [0008]      FIG. 3  is an exploded view of the embodiment of  FIG. 2 . 
           [0009]      FIG. 4  shows the atomizing chamber and flame tube of  FIG. 2 . 
           [0010]      FIG. 5  shows the support and photodiode of  FIG. 2 . 
           [0011]      FIG. 6  shows the microcomputer of  FIG. 2 . 
           [0012]      FIG. 7  shows the ignitor transformer of  FIG. 2 . 
           [0013]      FIG. 8  shows the compressor of  FIG. 2 . 
           [0014]      FIG. 9  shows the fuel metered pump of  FIG. 2 . 
           [0015]      FIG. 10  shows a hypothetical not to scale representation of the output of band pass filter  104  set for a frequency of 5-40 Hz. 
           [0016]      FIG. 11  shows another embodiment of the invention. 
           [0017]      FIG. 12  shows another embodiment of the invention. 
           [0018]      FIG. 13  shows another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In the following description, various embodiments will be illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. References to various embodiments in this disclosure are not necessarily to the same embodiment, and such references mean at least one. While specific implementations and other details are discussed, it is to be understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the scope and spirit of the claimed subject matter. 
         [0020]    Several definitions that apply throughout this disclosure will now be presented. The term “substantially” is defined to be essentially conforming to the particular dimension, shape, or other feature that the term modifies, such that the component need not be exact. For example, “substantially cylindrical” means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series and the like. The term “a” means “one or more” unless the context clearly indicates a single element. 
         [0021]    As used herein, the term “front”, “rear”, “left,” “right,” “top” and “bottom” or other terms of direction, orientation, and/or relative position are used for explanation and convenience to refer to certain features of this disclosure. However, these terms are not absolute, and should not be construed as limiting this disclosure. 
         [0022]    Shapes as described herein are not considered absolute. As is known in the burner art, surfaces often have waves, protrusions, holes, recess, etc. to provide rigidity, strength and functionality. All recitations of shape (e.g., cylindrical) herein are to be considered modified by “substantially” regardless of whether expressly stated in the disclosure or claims, and specifically accounts for variations in the art as noted above. 
         [0023]    It is an object of at least some embodiments of the invention to provide a flame detector that can detect optical flicker characteristics of the flame based on the type of fuel being burned. 
         [0024]    Flame tends to have an associated frequency, known as the flicker frequency. In general fire has a flicker frequency of 1-40 Hz, although the frequency tends to be different for particular type of fuel and/or burning environment. At least some embodiments of the invention specifically react to the presence of significant light at that frequency range to the exclusion of light at other frequencies. By way of non-limiting example, the AIRTRONIC atomizing burner sold by BABINGTON TECHNOLOGY burns diesel fuel at a flicker rate predominately within from 5 Hz to 40 Hz. 
         [0025]    Referring now to  FIG. 1 , an embodiment of the invention includes a burner with a photodiode circuit including one or more photodiodes (the photodiode circuit referred to herein generically as photodiode  102 ) that can detect the AC component (flicker) and DC component (absolute light level) of light from a flame  100 . 
         [0026]    Photodiode  102  may be reactive to all light. Photodiode  102  may also have a higher sensitivity to yellow light rather than orange or red light, as yellow is common to fire while red and orange are common to the glow from hot metal heated by the burner. Photodiode  102  may also have a higher sensitivity to blue light rather than other light (or in addition to other specific light such as yellow), as blue is common to fire for certain fuels such as natural gas. Photodiode  102  is mounted in the burner at a position to observe where the flame  100  would be found. 
         [0027]    The output of photodiode  102  is sent to a filter  104 , which may be a band pass filter. Filter  102  removes any DC component of the output of photodiode  102 . The frequency range of the filter  104  is also set to encompass the expected flicker rate of flame from the burner for the particular fuel, but preferably exclude frequencies of typical light sources (e.g., 50 Hz and higher for external light bulbs). By way of non-limiting example, the range could be set to about ±3 Hz around the expected flicker frequency (e.g., 11-17 Hz for a 14 Hz flicker rate), or around a greater range (e.g., 5-40 Hz for particular flicker rate), or to simply remove frequencies of typical light sources (e.g., 50 Hz and above). Significant output of filter  104  will thus indicate the presence of flame based on the presence of light having the expected color and flicker rate. In contrast, any output of filter  104  will be significantly lower in response to other sources of light, and such sources would tend to be a different color and/or flicker rate than passed by the embodiment. 
         [0028]    The output of filter  104  is sent to a control  106  (either directly or through intervening circuitry). The presence of a substantial signal for output of filter  104  indicates the presence of a flame, and controller  106  can respond accordingly. Similarly, the absence of a substantial signal (e.g., no signal, a noise signal, or other de minimus signal consistent with minimal reaction to light from other sources) indicates the absence of a flame. 
         [0029]    By way of non-limiting example,  FIG. 10  shows a hypothetical not to scale representation of the output of band pass filter  104  set for a frequency of 5-40 Hz. The output for filter  104  in the absence of flame is shown at  1002 ; there may be some signal present, although it can be considered consistent with background noise or other remote sources of light. The output of filter  104  in the presence of flame is shown at  1004 , which is significantly more active than  1002 . 
         [0030]    Controller  106  determines whether the output of filter  104  is consistent with the absence or presence of flame, such as by requiring a predetermined minimum value of the output of filter  104  to be considered the presence of flame. One methodology of determination is to take the average of the output of filter  104  over a period of time (e.g., a repeating 100 ms window); in the presence of flame, the average  1006  for signal  1004  could be on the order of 3 times the expected amplitude of the average  1008  of signal  1002  for the absence of flame. Another methodology is to take the average of the peaks of the signal within the window; in the presence of flame, the average  1010  for signal  1004  could be on the order of 10 times the amplitude of the expected average of  1012  of signal  1002  for the absence of flame. Memory associated with controller  106  may store a predetermined value by which the above averages are compared. The invention is not limited to the manner in which controller  106  interprets the output of filter  104  to determine the absence or presence of flame. 
         [0031]    Filter  104  may be hardware, software, or a combination thereof. Controller  106  similarly may be hardware, software, or a combination thereof. Filter  104  and controller  106  may be distinct components, integrated components, or overlapping components. By way of non-limiting example, filter  104  and controller  106  may both be software run on a processor of a common control, such as microcomputer  206  shown in  FIG. 2 . The invention is not limited to the implementation of the filter  104  and/or controller  106 . 
         [0032]    Referring now to  FIGS. 2 and 3 , and non-limiting example of a burner  200  that can utilize the photodiode  102  is shown. Burner  200  includes a flame tube  202 , a blower  204 , a microcomputer  206  (which may be controller  106  or a distinct component, work in combination with controller  106 , overlap in functionality with controller  106 , or include controller  106  along with other functionality), a fuel reservoir  208 , an igniter transformer  210 , a compressor  212 , and a fuel metered pump  214 . The various components are supported by a housing  216 . 
         [0033]    Referring now to  FIGS. 3 and 4 , the combustion chamber components of burner  200  are described in more detail. Flame tube  202  may include an outer barrel  402  and an inner barrel  404 . An atomizing chamber  408  is rearward of the flame tube  202 , and receives fuel from fuel reservoir  208  (pathway not shown). A mounting ring  412  is mounted on the rear of atomizing chamber  408 . A support  410  is mounted in rearward of ring  412 , and supports photodiode  102 . Atomizing head  408  includes an aperture  414  substantially at the center thereof, through which light from within flame tube  202  can reach photodiode  102 . A casing  406  (which is part of the blower  204 ) has a flange that engages with the rear of outer barrel  402 . Components are connected and mounted in manners known in the burner art and not further discussed herein. 
         [0034]    In operation, igniter transformer  210  ignites atomized fuel sprayed by atomizing chamber  408  to generate a flame plume in flame tube  202  toward the distal end of flame tube  202 , and may depend on operating conditions extend beyond the distal end of flame tube  202 . Light from the flame passes through aperture  414  onto photodiode  102 . Light within the flicker rate passed by the filter  104 . Filter  104  will thus output a signal consistent with the presence of flame, and controller  106  can respond accordingly. To the extent that color sensitivity is also provided (e.g., yellow and/or blue), then sources of light from a different color at the noted flicker rate would be disregarded as non-indicative of the presence of flame. 
         [0035]    After the flame is extinguished, the photodiode  102  will cease to output corresponding signal from the flame&#39;s light. There may be other sources of light (i.e., ambient light, heated metal in the flame tube  202 ) that photodiode  102  reacts to, but would not produce a meaningful and/or sufficient output from filter  104  due to the absence of the corresponding color (if burner  200  is color sensitive) and/or the lack of flicker rate at the frequency of filter  104  (which may be part of microcomputer  206  or a distinct component, work in combination with microcomputer  206  or overlap in functionality with microcomputer  206 ). The absence of meaningful/sufficient output from filter  104  is interpreted by controller  106  as the absence of flame in the flame tube  202 . 
         [0036]      FIG. 5  shows a variety of views of support  410  and photodiode  102 . Photodiode  102  is mounted on a circuit board  502 , which in turn is mounted on support  410 . Circuit board  502  is connected via appropriate wires (not shown) to microcomputer  206 . Circuit board  502  may support other circuits as desirable. 
         [0037]      FIGS. 6-9  show various views of the structure of microcomputer  206 , igniter transformer  210 , compressor  212 , and fuel metered pump  214 , respectively. 
         [0038]    The above embodiment provides several advantages of the light detector of the prior art. Since the components can be selected to specifically detect and respond to sources of light consistent with the flame produced by the fuel type and architecture, it is not significantly responsive to other forms of light. This allows the photodiode  102  to be placed rear of the atomizing chamber  408 , which is not exposed to the heat of the emerging flame and thus does not require a heat tolerant design. A light detector of the prior art could not be placed at this location due to its reactiveness to other forms of light, which required it to be mounted in a heat exposed position and required a heat tolerant design. 
         [0039]    Burner  200  as shown herein is simply exemplary, and other burners (particularly atomizing burners of BABINGTON TECHNOLOGY) may also be used. The invention is not limited to the burner environment. 
         [0040]    Referring now to  FIG. 11 , another embodiment of the invention is shown. As noted above, different fuels may emit light at different frequency ranges, and may peak at different ranges. Control  106  can identify the type of fuel if the predominance of light received at a particular frequency range corresponds to that fuel. In this embodiment, the burner includes several filters  104   a - 104   n , where n is at least two (2) (referred to generically as  104   x ). Each filter  104   x  may pass a different range of light. By way of non-limiting example, filter  104   a  may be set to pass 5-40 Hz for flame detection as above, filter  104   a  may be set to pass 11-17 Hz (14 Hz±3) for a particular fuel, and filter  104   c  may be set to pass 23-30 Hz (27 Hz±3) for a different type of fuel. A filter  104   x  could be set to only pass the DC component of the light from photodiode  102 , which may be useful for certain calculations (e.g., how much flame is present). Any number of filters may be provided, for overlapping or distinct ranges, for the purpose of detection of flame and/or detection of a particular type of fuel. 
         [0041]    As discussed above, burner  200  may optionally be color sensitive, such as by photodiode  102  being a specific wavelength diode with a higher sensitivity to yellow light rather than orange or red light. However, the invention is not so limited, and other forms of color sensitivity may be provided. By way of non-limiting example, photodiode  102  may be, or at least partially contain, a color sensing circuit that can detect different colors of incoming light, for which filter  104  and/or controller  106  would process the yellow light to the exclusion of other colors of light. A mechanical, optical and/or electrical filter  1202  could be placed in front of photodiode  102  to only pass color light such as in  FIG. 12 . A separate color sensing circuit  1302  could also be provided separate from or partially overlap with photodiode  102 , such as in  FIG. 13 , and mounted rearward of atomizing chamber of  408  (e.g., mounted on support  410 ). The invention is not limited to the particular manner in which the color of the flame is determined. 
         [0042]    The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims.