Abstract:
The invention relates generally to a fuel burner, and more particularly, but without limitation, to a high-efficiency gas burner with a gas pre-heat feature. Embodiments of the invention include a preheat tube that is coupled inline between a pressurized gas source and an orifice. The preheat tube may be formed into an elongated loop. An air/gas mixing tube extends inside the loop formed by the preheat tube from a proximal end near the orifice to a distal end away from the orifice. The distal end of the air/gas mixing tube is exposed to a portion of the preheat tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/211,161, filed on Mar. 28, 2009. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates generally to a fuel burner, and more particularly, but without limitation, to a high-efficiency gas burner with a gas pre-heat feature. 
         [0004]    2. Description of the Related Art 
         [0005]    Fuel burners, such as those used in conventional furnaces, convert fuel into a flame and/or heat. Conventional burners have many drawbacks, however. For instance, a conventional burner in a furnace or space heater may burn no more than 70-80% of the fuel. Such combustion inefficiencies waste valuable fuel. Incomplete combustion may also result in pollution by-products such as carbon monoxide (CO) that are damaging to the environment. Moreover, because CO concentrations in excess of 50-60 parts per million (ppm) may be harmful to humans, low-efficiency burners present a health risk when used in confined spaces. 
         [0006]    For at least the foregoing reasons, higher-efficiency burners are urgently needed. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention seeks to overcome one or more of the shortcomings described above. Embodiments of the invention include a preheat tube that is coupled inline between a pressurized gas source and an orifice. The preheat tube may be formed into an elongated loop. An air/gas mixing tube extends inside the loop formed by the preheat tube from a proximal end near the orifice to a distal end away from the orifice. The distal end of the air/gas mixing tube is exposed to a portion of the preheat tube. 
         [0008]    In operation, the pressurized gas source is activated, and the gas is ignited as it escapes the orifice. Upstream from the orifice, gas in a portion of the preheat tube is preheated by a flame extending through the distal end of the air/gas mixing tube. A consequence of gas preheating is highly-efficient combustion. 
         [0009]    The description is in this summary is intended to be exemplary only. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will be more fully understood from the detailed description below and the accompanying drawings, wherein: 
           [0011]      FIG. 1  is an elevation view of a gas burner, according to an embodiment of the invention; 
           [0012]      FIG. 2  is a plan view of the gas burner, according to an embodiment of the invention; and 
           [0013]      FIG. 3  is an elevation view detailing a portion of the gas burner, according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Embodiments of the invention will now be described more fully with reference to  FIGS. 1-3 , in which an embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, reference designators may be duplicated for the same or similar features. 
         [0015]    The fuel described herein is a gas, and could be propane (a/k/a liquid petroleum gas (LPG)). But the invention is not limited to propane burners; natural gas or other fuels may be used. 
         [0016]      FIG. 1  is an elevation view of a gas burner, according to an embodiment of the invention. As shown therein, a burner may include a coupling  1  (within view ‘A’), a preheat tube  2 , an orifice  3 , and an air/gas mixer  4 . The coupling  1  may be constructed of brass. In one respect, the coupling  1  is configured to couple a gas line (not shown) from a pressurized gas source (not shown) to an input end of the preheat tube  2 . The gas line (not shown) may be threaded into the coupling  1 . The input end of the preheat tube  2  may be silver-soldered to the coupling  1 . The preheat tube  2  may be, for instance, 30 inches length of ¼ inch diameter stainless steel tubing that is formed in an elongated loop configuration. 
         [0017]    The coupling  1  is also configured to couple an output end of the preheat tube  2  to the orifice  1 . The output end of the preheat tube  2  may be silver-soldered to the coupling  1 . The orifice  3  may be, for instance, a burner orifice or a pilot orifice. The orifice  3  may include threads on an input end of the orifice to interface with the coupling  1 . An output end of the orifice  3  includes a hole of a predetermined diameter to regulate the preheated gas output from the orifice  3 . 
         [0018]    The air/gas mixer  4  may be, for instance, a 12 inch long, 3 inch diameter, steel tube. The air/gas mixer  4  may be disposed inside the loop formed by the preheat tube  2 . A proximal end of the air/gas mixer  4  is relatively near the orifice  1 ; a distal end of the air/gas mixer  4  is relatively far from the orifice  1 . The distal end of the air/gas mixer  4  is exposed to a portion of the preheat tube  2 . 
         [0019]    For clarity, features that support the air/gas mixer  4  have been omitted from  FIG. 1 . In one embodiment, the air/gas mixer  4  could be secured to the coupling  1  using an L-shaped bracket (not shown). Alternatively, or in combination, the air/gas mixer  4  could be secured by welding portions of an outer surface of the air/gas mixer  4  to portions of the preheat tube  2 . 
         [0020]    Variations to the embodiment illustrated in  FIG. 1  and described above are possible. For instance, the coupling  1  may be divided into two components: a first component to couple the gas line (not shown) from the pressurized gas source (not shown) to the input end of the preheat tube  2 ; and a second component to couple the output end of the preheat tube  2  to the orifice  3 . In addition, burner components could be constructed using different materials and different dimensions than what is described above, according to design choice. Alternative joining techniques may also be used between components of the gas burner. 
         [0021]      FIG. 2  is a plan view of a gas burner, according to an embodiment of the invention. As shown therein, portions of the preheat tube  2  may be routed proximate to an exterior wall of the air/gas mixer  4 . A middle portion of the preheat tube  2  may be routed across an open distal end of the air/gas mixer  4 . 
         [0022]    Variations to the embodiment illustrated in  FIG. 2  are possible. For instance, the middle portion of the preheat tube  2  that is routed near the distal end of the air/gas mixer  4  need not pass straight across and through a linear axis of the air/gas mixer  4 . 
         [0023]      FIG. 3  is an elevation view detailing a portion of a gas burner, according to an embodiment of the invention. A first portion  1   a  of the coupling  1  couples the gas line (not shown) from the pressurized gas source (not shown) to the input end of the preheat tube  2 . A second portion  1   b  of the coupling  1  couples the output end of the preheat tube  2  to the orifice  3 . 
         [0024]    Variations to the embodiment illustrated in  FIG. 3  are possible. For instance, as described above, the first portion  1   a  of the coupling  1  could be separated from the second portion  1   b  of the coupling  1 . The shape of the orifice  3  may vary from what is illustrated in  FIG. 3 . 
         [0025]    To operate the burner, a user activates a pressurized gas source (for instance by opening a valve) and applies a spark proximate to a top side of the orifice  3 . The spark ignites a flame that extends through the air/gas mixer  4  and near the middle portion of the preheat tube  2 . One or both of the activation and sparking operations could also be performed by automated means. 
         [0026]    Cold (e.g., room temperature) pressurized gas is received via the first portion  1   b  of the coupling  1  at the input end of the preheat tube  2 . The gas pressure may be, for instance, 3-5 pounds per square inch (psi). The gas is preheated to approximately 600° F. by the flame while the gas is in the middle portion of the preheat tube  2  (near the distal end of the air/gas mixer  4 ). Accordingly, preheated gas is received by the orifice  3  from the preheat tube  2  via the second portion  1   b  of the coupling  1 . As the gas escapes the orifice  3 , it is burned at approximately 1025° F. The combustion flame is substantially contained by the air/gas mixer  4 , except that the flame may extend beyond the distal end of the air/gas mixer  4 . 
         [0027]    The referenced preheat and burn temperatures are exemplary for a particular propane burner. The preheat temperature and combustion temperature could vary for burners having different physical dimensions and/or for burners fueled by gases other than propane. 
         [0028]    Empirical results for a gas burner constructed substantially as illustrated in  FIGS. 1-3  indicate that the burner operates at 99.93% combustion efficiency when burning propane. This represents a 20-30% fuel savings compared to conventional burners. The propane burns so completely that the resulting flame is virtually invisible. This is because the principle by-products are water (H 2 O) vapor and carbon dioxide (CO 2 ). In fact, tests reveal that only 0.09% of the propane was converted into Carbon Monoxide (CO) pollution. Calculations for a 8′×12′×8′ room with one window, one door, and typical leakage (0.5 air exchanges per hour) predict CO levels of only 10 ppm (well below recognized safety thresholds). 
         [0029]    High-efficiency burners that are consistent with the invention disclosed and claimed herein may be especially suited to industrial and agricultural applications that burn large volumes of propane or natural gas. Other applications are also possible. 
         [0030]    It will be apparent to those skilled in the art that modifications and variations can be made without deviating from the spirit or scope of the invention. For example, alternative features described herein could be combined in ways not explicitly illustrated or disclosed. Thus, it is intended that the present invention cover any such modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.