Patent Publication Number: US-2004048216-A1

Title: Gas burner

Description:
SUMMARY OF THE PRIOR ART  
       [0001] There are a number of apparatus known in the art for using gas heating as a means of cooking. An important part of such apparatus, is the gas burner which provides the outlet for the gaseous fuels, which are then combusted to generate heat. Thus a number of methods have been devised to improve the operating characteristics of such gas burners over time.  
       [0002] For example it is known in the art to pressurise the air supply to the burner. In U.S. Pat. No. 4,622,946 for instance, a gas burner is described with one fixed speed fan on the burner inlet and both the gas and air flow is controlled by a valve which supplies multiple burners. It is also known to use a fan to extract the exhaust gases from the burner, where the combustion takes place in an enclosed space such as described in U.S. Pat. No. 5,800,157 and also European Patent Application No. 801270. Also in European Patent Application No.887590 a gas burner is described with gas and air fed through orifices (of matched sizes) into a mixing chamber with a fan pressurising the flow which is supplied to the burner head.  
       [0003] It is also known in the art to vary the shape of the outlet ports to improve operation. For example in U.S. Pat. No. 5,649,822 and PCT Patent Application No. 98/15780 gas burners are disclosed with angled outlet ports. In U.S. Pat. No. 5,800,159 a gas burner is described including flared stability ports. It is also known to have a gas burner with flare in vertical plane of the outlet ports and substantial circumferential area in, for example, German Patent No. 4427953  
       [0004] However, while these prior art systems do provide improvements in certain areas of operation, they are not suited for use with a range of gas supplies, may be large or expensive to manufacture, and may not provide distributed flame contact with the heating vessel.  
       [0005] It is an object of the present invention to provide an improved gas burner which goes someway to overcoming the above mentioned disadvantages or which will at least give the public a useful choice.  
       SUMMARY OF THE INVENTION  
       [0006] Accordingly in a first aspect the present invention consists in a gas burner comprising  
       [0007] a burner housing including at least one internal cavity and at least three openings, all being in fluid communication with said internal cavity,  
       [0008] an outlet assembly including a number of outlet ports in fluid communication with said a first of said openings, and a burner cap attached to said outlet assembly,  
       [0009] adjustable gases supply means for providing an adjustable flow of gaseous fuels, in fluid communication with a second of said openings,  
       [0010] oxygen supply means for providing a flow of gases at least containing oxygen, in fluid communication with a third of said openings, and  
       [0011] pressurisation means associated with said third opening for pressurising said flow of gases at least containing oxygen,  
       [0012] wherein in use pressurisation means causing said flow of gases at least containing oxygen to flow through said internal cavity and mix with said adjustable flow of gaseous fuels, the combination thereof flowing through said first opening and then said number of outlet ports to be combusted, and said adjustable gases supply means being readily accessible and removable, through the removal of said outlet assembly.  
       [0013] Preferably said pressurisation means comprises a variable speed fan.  
       [0014] Preferably said outlet assembly includes a venturi through which said adjustable flow of gaseous fuels flows, thereby causing said flow of gases at least containing oxygen to mix with said flow of gaseous fuels.  
       [0015] Preferably said gas burner further comprises control means and means for supplying a variable relating to the gases flow rate of said flow of gaseous fuels to said control means, whereby said control means varies the energisation of said pressurisation means according to said variable.  
       [0016] Preferably said burner housing includes a spiral volute connecting said first opening to said second opening.  
       [0017] In a further aspect the present invention consists in a gas burner comprising,  
       [0018] a burner housing including at least one internal cavity and at least three openings, all being in fluid communication with said internal cavity,  
       [0019] an outlet assembly including a number of outlet ports in fluid communication with said a first of said openings, said number of outlet ports encompassing a substantial portion of the outer circumference of said outlet assembly around number of outlet ports,  
       [0020] adjustable gases supply means for providing an adjustable flow of gaseous fuels, in fluid communication with a second of said openings, and  
       [0021] oxygen supply means for providing a flow of gases at least containing oxygen, in fluid communication with a third of said openings,  
       [0022] wherein in use said flow of gases at least containing oxygen flows through said internal cavity and mixes with said adjustable flow of gaseous fuels, the combination thereof flowing through said first opening and the said number of outlet ports to be combusted.  
       [0023] Preferably the total commutative width of said number of outlet ports is greater than 70% of the outer circumference of said outlet assembly around number of outlet ports.  
       [0024] Preferably the vertical height of said number of outlet ports is less than 2 mm.  
       [0025] Preferably the vertical height of said number of outlet ports is 1 mm.  
       [0026] Preferably each of said number of outlet ports are angled at a radial angle greater than 0 degrees.  
       [0027] Preferably each of said number of outlet ports are angled at a radial angle between 40 to 50 degrees.  
       [0028] Preferably each of said number of outlet ports are flared outwards.  
       [0029] Preferably each of said number of outlet ports are flared outwards at between 6 and 12 degrees.  
       [0030] To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.  
       [0031] The invention consists in the forgoing and also envisages constructions of which the following gives examples. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0032] One preferred form of the present invention will now be described with reference to the accompanying drawings in which;  
     [0033]FIG. 1 is a cross section of the gas burner according to the preferred embodiment of the present invention,  
     [0034]FIG. 2 is a cross section of the outlet assembly according to the preferred embodiment of the present invention,  
     [0035]FIG. 3 is a perspective view of the outlet assembly according to the preferred embodiment of the present invention,  
     [0036]FIG. 4 is a blown out perspective of the gas and air intake manifold according to the preferred embodiment of the present invention,  
     [0037]FIG. 5A is a plan views of the outlet assembly according to the preferred embodiment of the present invention,  
     [0038]FIG. 5B is an enlarged plan view of the outlet ports according to the preferred embodiment of the present invention,  
     [0039]FIG. 6 is a cross section of an outlet assembly according to an alternative embodiment of the present invention, and  
     [0040]FIG. 7 is a block diagram illustrating the control strategy for the variable speed fan. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0041] The present invention provides an improved gas burner which provides lower emissions, a greater operating range and improved performance over that of prior art gas burners. The present invention includes a variable speed fan to pressurise the air supply to be mixed with the gas for combustion. The present invention also includes innovative outlet ports which improve the quality and distribution of the output flame over a greater operating range as compared to the prior art devices.  
     [0042] Referring now to FIGS.  1  to  4  the gas burner  100  is comprised of a main body  102 , a variable speed fan  104 , an outlet assembly  106  and a burner cap  108 . The main body  102  also includes a top cover  103  which is attached on top of the main body during manufacture using bolts  97  which screw into prethreaded holes  115  in the main body  102 . This 2 part structure is to allow the fan  104  to be located in slots  105  and locked in place without the need for further bolts. The entire gas burner  100 , is attached to the top face plate  95  of a gas appliance by a helically threaded locking nut  107  which threads onto the outer thread  110  of the top cover  103  which forces the face plate  95  down onto the top cover  103 . The outlet assembly  106  is shown in more detail in FIGS. 2 and 3 which slides down in place atop the top cover  103 . Similarly the burner cap  108  is positioned atop the outlet assembly  106 .  
     [0043] The gas supply is connected to the main gas inlet  109  on the exterior of the main body  102 . This connects through to a gas inlet orifice  111  positioned at bottom of a central chamber  113  in the main body  102  directly below the outlet cylinder  114 . The gas jet fitting  112  screws into the gas inlet orifice  111 . It will be appreciated that the present invention is modular whereby different output ranges can be achieved by the replacement of outlet assembly  106  with one of a range of interchangeable assemblies. Such assemblies range in size according to maximum output, but have the same inner dimensions to be fitted interchangeably to the same main body  102 . Further modularity is achieved by the ability to replace the gas jet fitting  112  as required for different gas supplies eg: LPG versus natural gas. Similarly maintenance and cleaning are also simplified by this modularity, and simple construction.  
     [0044] In order for the gas to mix adequately with the air supply the present invention includes a venturi  116  is formed by the underside of the burner cap  108  and the upper face of the outlet assembly  106 . The venturi effect result from the convergence of the flow path at the top of the outlet cylinder  114 , followed by a horizontal, divergence  120 . This venturi effect draws in the air in with the gas flow.  
     [0045] The air supply pressurised by the fan  104 , follows a flow path best shown in FIG. 4. The air swirls horizontally through a spiral volute  122 , which terminates in the central cavity  113 . At this point as the gas is jetted up from the gas jet fitting  112  up into the venturi  116 , the combination of the venturi action, and the mixing action of the swirling pressurised air, causes the air and gases to mix thoroughly.  
     [0046] In the preferred embodiment of the present invention the variable speed fan is controlled as shown in FIG. 7. A controller  200 , either a microprocessor or any analogue equivalent, receives a signal from a rotary encoder  202  on the gas inlet valve  204  feeding the gas burner. It will be appreciated other sensors such as polentiometer or micro switches on a corn could equally be used. Based on a stored formula or lookup tables  205 , the controller adjusts the energisation  206  of the fan  208  depending on the setting of the gas valve. Alternatively the fan speed could be controlled based on actual flow rate of the gas as measured by a flow rate sensor. A further alternative would be closed loop control using direct feedback from the flame. The flame could be measured using CO 2 , O 2 , colour of light emitted etc and matched against optimum levels to decide whether a higher or lower flow of air is required.  
     [0047] After the venturi  116 , the gases/air mixture flows through the outlet ports  124 , formed by grooves  126  in the outer periphery of the upper face of the outlet assembly  106  and the underside of the burner cap  108 . Once the gas/air mixture flows through the ports  124  out into the atmosphere it combusts forming the characteristic ring flame around the circumference  128  of the burner head.  
     [0048] The grooves  126 , shown in more detail in FIGS. 5A and 5B have a number of distinguishing features. The grooves  126  are characterised in that they occupy greater than 70% of the circumference  128  of the burner head. Each quarter of the outlet assembly  106 , has a groove  142  at an angle of 40°  146  at one end and a groove  140  at an angle of 50°  144  at the other end. All the grooves in between are at angles increasing evenly from 40° and 50°. The grooves  126  are all angled at a range of angles to ensure that none of the flames significantly impinge on the trivet  129  as this will result in carbon monoxide production. In traditional burners a groove is missed where the trivet is. In the preferred embodiment of the present invention the trivet  129  is positioned in the wide space  131  between the quarterly transition between groove angling. In FIG. 5A the trivet  129  is shown at an angle of 45° between a groove  142  at 40° and a groove  140  at 50°. This configuration allows more even heating and since the ports are still close together they can light each other. Just inside the grooves  126 , is an annular channel  147 . This acts as a pressure buffer zone, which stabilises the gas flow from any variations in the supply pressure before being combusted.  
     [0049] The grooves  126  themselves are also carefully designed in shape. The inlet cross section  132  is of the same height as the outlet cross section  134  which are both approximately 1 mm, but the outlet port cross section  134  area is approximately 1.6 times that of the inlet cross section  132 . The flaring from inlet to outlet is 11 degrees, but can range from approximately 6 to 12 degrees. This gives a ratio of 3.5 to 4.5 of the groove length to the inlet width. The inlet cross section  132  is effectively a semi-circle whereas the outlet cross section  134  has rounded portions  136 ,  137  at either end connected by a flat portion  138  in the centre. Both the rounding and flaring are designed to give good flame shape for a wide range of burner output levels.  
     [0050] In an alternative embodiment of the present invention the outlet assembly  152 , is shown in FIG. 6 with a vertical venturi. Similarly to the preceding embodiment, the venturi include a narrowed section  150 , followed by a slowly diverging section  160 . Again this arrangement causes the flow of gas through the venturi to draw in air which mixes with the gas before combustion. In all other aspects this embodiment operates as for the preferred embodiment.  
     [0051] It will be appreciated by the foregoing the present invention presents a number of advantages over the prior art.  
     [0052] Gain in operating range of burner. Typical gas burners may have a turndown ration as low as 3:1 and while the best gas burners may achieve say 6:1 whereas electric elements are typically are better than 10:1. The present invention provides a burner with which ratios of better than 20:1 maybe achieved. The upper limit is increased by the use of the variable speed fan. Also the shaping of ports helps reduce gas velocity which helps flame to remain attached to the burner and not blow out at higher rates while the small cross sectional area allows the burner to be turned down low without burning back;  
     [0053] Reduced emissions and better efficiency from improved combustion;  
     [0054] Ability to change the jet of the burner from above without having to disassemble the product;  
     [0055] Ease of assembly/construction;  
     [0056] Increased efficiency due to increased flame contact with the cooking vessel.  
     [0057] The Burner is smaller than traditional burners for a given output, giving a significant increase in efficiency due to more flame in contact with a given size pot. Also reduces the “cold spot” in the middle of the burner.