Patent Publication Number: US-6220030-B1

Title: Stirling engine burner

Description:
TECHNICAL FIELD 
     This invention relates to a burner. The present invention is more particularly concerned with a burner for use in a heat exchange arrangement. It is particularly suitable for use with an external combustion engine where the engine is powered by a heat source and is not fuel dependent. 
     With an external combustion engine the heat developed from combustion of fuel in the burner is transferred through a heat exchanger to the working fluid of the engine. Such an external combustion engine can, for example, be one which operates on a Stirling Cycle. 
     BACKGROUND ART 
     A Stirling Cycle engine operates on a closed thermodynamic cycle in which one mass of gas is repeatedly expanded and compressed. Unlike an internal combustion engine, there are no valves, intake or exhaust ports, and no combustion in the cylinders. The engine therefore has very low noise output and can be dynamically balanced, thereby resulting in virtually no engine vibration. Little maintenance is required because the combustion products are kept away from the moving engine parts. A Stirling Cycle engine operates with externally heated cylinder heads. The burner of the present invention is thus particularly suited for providing the external heat source. 
     Desirably, a burner for a Stirling Cycle engine is able to burn different liquid and gaseous fuels. The burner should be quiet in operation otherwise the advantage of a quiet engine operation is lost. The burner desirably also has cool external surfaces and is sufficiently compact for mounting with the cylinder head of the engine. It goes without saying that the burner should also be efficient. 
     Examples of such burners can be seen in U.S. Pat. Nos. 4,352,269 (Dineen), 5,005,349 (Momose) and 5,590,526 (Cho). In Cho and Momose, either the inlet air or the exhaust air follows a passage that allows for heat exchange from the combustion chamber. Momose also permits some heat exchange between the exhaust gases and the inlet air, but only on one pass of the inlet air past the exhaust gas passageway. Dineen discloses a burner with an annular heat exchange means and an annular burner about the Stirling engine. The exhaust is centrally located at the top of the burner. 
     However these three burners have a limited amount of thermal connection between the inlet air and exhaust gases, reducing the efficiency of the heat exchange aspects of the burner. Also, with the burner disclosed in Dineen portions of the exterior of the burner will be hot as they are immediately adjacent the exhaust gas passageways of the burner. 
     A further difficulty of the disclosed burners is the complexity of manufacture or construction of the burner disclosed. 
     It is an object of the present invention to provide a burner for an external combustion engine which effectively addresses the question of efficient heat exchange with in the burner. It is a further object of the present invention to provide a burner which addresses the question of simplicity of manufacture. 
     A yet further object of the present invention is to provide a burner which meets or goes some way to achieving all or some of the aforementioned requirements or at least to provide the public with a useful choice. 
     Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only. 
     DISCLOSURE OF INVENTION 
     According to one aspect of the present invention there is provided a burner or an external combustion engine, said burner comprising: 
     an external housing; 
     a shroud within the external housing, said shroud in use defining at least in part a centrally located combustion chamber; 
     inlet air means from which inlet air is directed over an internal wall surface of the housing for cooling thereof; 
     guide means for directing inlet air to the combustion chamber, said guide means directing the inlet air such that, in the use of the burner, the inlet air effects a cooling of the shroud prior to the inlet air entering the combustion chamber; 
     fuel inlet means directing the fuel to the combustion chamber; 
     an igniter for igniting the fuel; and 
     gas exhaust means; characterized in that 
     said external housing, the shroud and the guide means are formed as a series of nested layers about the combustion chamber, said layers being arranged to maximized the heat exchange between any two adjacent layers. 
     In the preferred form of the invention there is provided heat exchange means whereby inlet air, after having applied a cooling effect to the housing, is heated before being directed to the shroud. Preferably, the heat exchange means has inlet means for receiving exhaust gases from the combustion chamber, and outlet means connected to the gas exhaust means. 
     In the preferred form of the invention the burner is adapted for mounting to the external combustion engine, which most preferably is an engine operating on a Stirling Cycle. 
     Preferably, the means for directing air flow to the combustion space includes heat exchange means with the exhaust gases, for heating said air flow. 
     Preferably, the combustion space is defined at least in part by the shroud over which air heated by said heat exchange means passes before entering said combustion space. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Further aspects of the present invention will become apparent from the following description, which is given by way of example only, and with reference to the accompanying drawings in which: 
     FIG. 1 is a section view of the preferred embodiment of the burner of the present invention; and 
     FIG. 2 is a plan view of the preferred embodiment of the burner of the present invention. 
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Referring to FIG. 1, a burner  10  for a Stirling cycle engine E is there shown. The burner  10  is primarily formed from sheet steel. As will become apparent from the following description, many of the components can be fabricated by the known technique of metal spinning. 
     Referring to both the FIGS. 1 and 2, the burner  10  includes an outermost or external housing  11 . The external housing  11  can be generally described as being a shell which is substantially of an inverted dish shape. In the drawings and in the description following, the ‘base’ of the inverted dish is uppermost, so that the sides of the external housing  11  slope upwardly and inwardly. 
     However, it will be appreciated by those skilled in the art that the burner  10  can be at any orientation; the description of the ‘base’ of the shell of the housing  11  as being uppermost being used here only as an example and for ease of description of the elements of the burner  10 . 
     A central opening  12  is formed in the external housing  11  which has a cover plate  13  with a central orifice through which a connector end of an igniter  15  is located. A grommet or seal element  15   a  can be provided to form a seal between the opening  12  and igniter  15 . The igniter  15  may be of any conventional type, for example the igniter  15  may be a glow plug or a spark igniter, as is desired. 
     Opening into the housing  11  is a duct  16  which is connectable to a blower (not shown) for the introduction of air. According to a preferred form of the invention the air is preheated slightly by, for example, the crank case (not shown) of the engine E to which the burner  10  is fitted, in the preferred embodiment. 
     A skirt or extension  17  projects downwardly from the terminal lower end  18  of the housing  11 . The skirt  17  may be of any shape, but is preferably cylindrical in cross-section. 
     Located inwardly from the inside wall surface of the housing  11  and extending down from the uppermost part of the housing  11 , in which opening  12  is formed, is a partition wall  19 . As with the housing  11 , this wall  19  is formed by a shell and is substantially an inverted dish in shape. As with the housing  11 , the partition wall  19  is provided with an extension formed by a skirt  20  which terminates above the terminal edge of skirt  17 . The skirt  20  may also be of any shape, but is preferably cylindrical in cross-section. 
     The external housing  11  and associated skirt  17  are shown in FIG. 1 as being two separate parts. However it will be appreciated by those skilled in the art that these two parts may be formed integrally. Likewise, the partition wall  19  and skirt  20  are shown in FIG. 1 as two parts, but may be formed integrally, as is desired. 
     The burner  10  has an inner shroud or shell  21  which as shown mounts on the hot end of the engine E. It will be appreciated by those skilled in the art that the hot end of engine E is only represented diagrammatically to illustrate the mounting and relationship of the burner  10  on the engine E. In addition to providing the means of mounting the burner  10  to the engine E, the inner shell  21  defines with the top end of the engine E a combustion zone within the combustion chamber C. 
     Thus, the combustion chamber C is formed and bounded by the inner shell  21 , with a central opening  22  through which hot air and fuel flow, a seal  99 , and by the top of the engine E with heat exchangers  36 , each heat exchanger  36  having attendant cooling fins  35 . 
     The centrally disposed opening  22  is formed in the shell  21 . Extending upwardly, and substantially concentric with opening  22 , is a tubular member  23 . The upper end of the tubular member  23  provides, or is associated with, a mounting flange  24 . The tubular member  23  incorporates perforations (not shown) along the length thereof and about the circumference. Thus the tubular member  23  permits the air to flow across the upper surface of the shell  21 , to the central opening  22 . The perforations may be circular holes, slots, louvers, or a combination of these, as is desired. Alternatively, if desired, the tubular member  23  may be of a mesh material. 
     A second tubular member  25   a  depends downwardly from the mounting flange  24  and is substantially concentric with tubular member  23 . This second tubular member  25   a  terminates above the portion of the inner shell  21 . 
     The mounting flange  24  provides a means of mounting, via mechanical fasteners (not shown) of known type, an igniter assembly G with a fuel line injector  34 . The assembly G and injector  34  fit into the central opening  12  of the external housing  11 . The assembly G also includes a flange by which the assembly G is secured to the mounting flange  24 . 
     Sandwiched between the flange of the igniter assembly G and the mounting flange  24  is the upper end of a second inverted shell  27 . The second inverted shell  27  is also dish shaped. As can be seen in FIG. 1 of the drawings, this second shell  27  extends downwardly towards the first inner shell  21  but terminates short thereof. Preferably, the gauge thickness of inner shells ( 21 ,  27 ) is greater than that of the other components of the burner  10 . 
     Located between partition wall  19  and second inner shell  27  is an exhaust chamber  28  formed by yet further substantially dish shaped exhaust elements ( 29 ,  30 ). The upper ends of the exhaust elements ( 29 ,  30 ) are joined together but not joined to the partition wall  19  nor the outer housing  11 . The lowermost end of the exhaust element  29  is fastened to the lower end of the first inner shell  21 . The corresponding lowermost end of the other second exhaust element  30  extends downwardly and is substantially parallel to the skirt  20 . This lowermost end of the second exhaust element  30  extends below the end of the skirt  20 , and bends towards the skirt  17  and is fastened thereto at the end of the skirt  17  and the lowermost end of the second exhaust element  30 . 
     Coupled to the second exhaust element  30  is an exhaust duct  31  which extends through two openings ( 32 ,  33 ) formed in the partition wall  19  and the outer housing  11  respectively. The exhaust duct  31  can include fins (not shown), to increase the heat transfer area of the duct  31 . 
     The elements generally called ‘shells’ ( 11 ,  19 ,  30 ,  29 ,  27 ,  21 ), which make up the various main components of the burner  10 , are not rigidly inter-connected. This lack of rigid inter-connection reduces thermal stress within the material of the shells ( 11 ,  19 ,  30 ,  29 ,  27 ,  21 ), and in the burner  10  generally, as it allows for the thermal expansion of the shell metal. Minimal welding of the shells ( 11 ,  19 ,  30 ,  29 ,  27 ,  21 ) is thus required and that which is needed is very easy. 
     The above described burner  10  works as follows: fuel from the injector  34  progresses under capillary action along a mesh  25  mounted on the inner wall of second tubular member  25   a.  The tubular member  25   a  is heated by the incoming heated air flow over the outer surface of the tubular member  25   a.  This enables vaporized fuel to pass to the combustion zone of the combustion chamber C. 
     As indicated by dashed flow lines, cold air from the blower enters the external housing  11  via the duct  16  and passes over the inner surface of the external housing  11 . This achieves a cooling effect so that the outer surface of the housing  11  remains cool. 
     The air then passes along a flow guide formed by the spaced apart inner partition wall  19  and the second exhaust element  30  of the exhaust chamber  28 . The air flows around the end of the exhaust chamber  28  to flow along a further flow guide formed by the second inner shell  27  and the first exhaust element  29  of the exhaust chamber  28 . This flow of air over the exhaust chamber  28  thus provides for heat recovery with the result that the cool inlet air is further heated. Also, the exhaust gases are further cooled. 
     The heated inlet air then passes over the upper surface of the inner shell  21  to reduce the temperature of the inner shell  21 . The air is heated further and the shell  21  is cooled by this air flow. This ensures that the inner shell  21  does not become over-heated. 
     The heated air then flows into a space, which functions as a swirl generator space, through the perforations in the tubular member  23 . A rotating flow of air is created in the swirl generator space (between the tubular member  23 , the second tubular member  25   a  and the central opening  22 ). The turbulent air then flows down through the central opening  22  into the combustion chamber C. The turbulence initiated in the swirl generator space increases in rotational velocity as the air passes through the central opening  22 . This creates a strong vortex mixing zone in the top part of the combustion chamber C and causes good combustion to occur in the combustion zone of the combustion chamber C. 
     The flow of hot, combusted gases from the combustion zone of the combustion chamber C, as shown by the dotted line in FIG. 1, passes over the fins  35  of each of the hot end heat exchangers  36  of the engine E. The combusted gases then pass into an annular duct  37  and out through an exhaust port  38  into the exhaust chamber  28 . The exhaust gases then exit through the exhaust duct  31 . The exhaust gases can be recovered for further use. Such further use could, for example include use in a water heater or space heating arrangement. This is particularly useful when the engine E forms part of a domestic co-generation system. Other uses for the exhaust gases will be apparent to those skilled in the art. 
     Initial fuel vaporization and ignition is achieved from the igniter G in known manner. Once combustion has been initiated in the combustion chamber C, a continuous flame in the combustion zone of the combustion chamber C forms the heat source. Thus, the combustion process is optimised and the emission of pollutants minimised. 
     The burner  10  can burn a fuel selected from the group: diesel, liquid petroleum gas, natural gas, and other liquid and gaseous fuels. The burner  10  can do so with minimal or no change to the burner  10  itself. The burner  10 , according to the present invention, provides a number of advantages which results in the burner  10  being particularly suited for use with a Stirling Cycle engine.