Abstract:
A stove apparatus includes a frame having an interior opening. A burner is mounted within the opening. A liquid fuel container is mounted on the frame within the opening. A fuel conduit extends between the container and the burner. A heat shield extends about the burner and separates the burner from the fuel container. Preferably the apparatus has a manually operable device which simultaneously regulates a valve controlling a flow of fuel from the fuel container to the burner and a control device controlling the output of a compressor supplying compressed air to the burner. The compressor may have a suction port. The apparatus then includes a suction conduit connecting the suction port to the fuel container, whereby the compressor can selectively draw fuel into the container. The fuel container may have a vent body mounted thereon. The suction conduit is connected to the vent body. The body has a valve for preventing fuel from entering the conduit from the container. The valve may include a chamber with a valve seat at the top of the chamber. A check valve ball, buoyant in the fuel, is movably mounted in the chamber. If fuel is drawn into the chamber, the check valve ball floats to the top of the chamber and blocks the fuel from entering the suction conduit.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to liquid fuel stoves and, in particular, to portable liquid fuel stoves for military use. 
     Portable stoves are used for a variety of purposes such as military operations. They are used in range ovens, steam tables, tray ration heaters, field sanitation equipment and stock pot heating racks. These appliances perform such functions as roasting, grilling, broiling, frying, heating water and other liquids and baking. They are typically utilized in such field equipment as tents, other shelters, containerized mobile kitchens and mobile kitchen trailers. These appliances may also be used in an open field without the benefit of shelter. 
     Such stoves may operate under difficult field conditions and must be reliable in operation and perform to a high level in order to meet the demands of some users. 
     Some previous portable stoves have had serious problems and disadvantages. They sometimes take a long time to ignite, are not reliable and may perform inadequately if not operated according to strict procedures. Some are not capable of being re-fueled in an appliance, making it necessary to remove the stoves in order to fuel them. This is both labor intensive and inconvenient in the relatively tight quarters of field kitchens for example. Moreover, some are also labor intensive to operate and maintain. They utilize a pressurized fuel tank which contains an explosive fuel. This may present a potential hazard. 
     Currently there is a demand for a replacement for certain types of portable stoves. The replacement units preferably should be robust in terms of durability. Service and maintenance should be simple, as they often must be conducted by a technically untrained stove operator. Field service should not require specialized tools. Cleaning should be accomplished by simple procedures such as wiping the stoves down with a soapy wet cloth. Such stoves must be rugged enough to withstand transportation as unrestrained cargo in ground vehicles, often moving over rough terrain. 
     Also, such units should be capable of burning certain fuels, such as military JP-8 fuel, which some previous stoves are incapable of burning. Also, for some applications, a multifuel stove is desired which would be capable of burning such alternative fuels as JP-8; DFA, DF-1 and DF-2 (military diesel fuels), #1 and #2 diesel fuel, kerosene and JP-5. 
     Accordingly, it is an object of the invention to provide an improved stove adaptable for a wide variety of purposes including installation in existing appliances such as range ovens, steam tables, tray ration heaters, field sanitation equipment and stock pot heating racks. 
     It is also an object of the invention to provide an improved stove which is capable of performing such functions as roasting, grilling, broiling, frying, heating water and other liquids and baking. 
     It is also an object of the invention to provide an improved stove which is capable of being utilized in such field equipment as tents, other shelters, containerized mobile kitchens and mobile kitchen trailers. 
     Is a further object of the invention to provide an improved stove which is capable of burning JP-8 fuel. 
     It is a still further object of the invention to provide improved stove which is capable of burning a variety of liquid fuels such as JP-8, diesel fuels or kerosene. 
     It is still further object of the invention to provide an improved stove which is easy to ignite, reliable to operate and easy to maintain. 
     It is still further object of the invention to provide an improved stove which can be refueled in the appliance and which does not have a pressurized fuel tank. 
     SUMMARY OF THE INVENTION 
     In accordance with these objects, there is provided, according to the invention, a stove apparatus having a frame with an interior opening. There is a burner mounted within the opening. The apparatus includes an air compressor mounted on the frame. There is an air conduit which extends between the compressor and the burner. A liquid fuel container is mounted on the frame within the opening. A fuel conduit extends between the container and the burner. A heat shield extends about the burner and separates the burner from the fuel container. A fuel control valve controls a flow of fuel from the fuel container to the burner. There is a control device for controlling output of the compressor. 
     In one embodiment, the apparatus has a movable front access panel and controls mounted on the access panel. 
     There may be a knob which simultaneously regulates the fuel control valve and speed of the compressor. 
     Preferably the compressor has a suction port. The apparatus then includes a suction conduit connecting the suction port to the fuel container and to a valve operatively connected to the suction conduit. The compressor can selectively draw fuel into the fuel container for refueling the stove. 
     The fuel container may have a vent body mounted thereon. The suction conduit is connected to the vent body. The vent body is mounted on top of the container and has a fuel tube extending to near the bottom of the container. There may be a float slidingly mounted on the tube and a first switch operatively connected to the compressor. The float has means for actuating a switch to stop operation of the compressor when fuel is near the top of the container. 
     In one preferred embodiment the body has means for preventing fuel from entering the suction conduit from the container. This includes a chamber having a top and a bottom. There is a check valve seat at the top of the chamber. A check valve ball, buoyant in the fuel, is movably mounted in the chamber. A conduit extends from near the bottom of the chamber to the container. If fuel is drawn into the chamber, the check valve ball floats to the top of the chamber and blocks the fuel from entering the suction conduit. For example, the valve seat may be conical in shape, tapering inwards towards the suction conduit. The chamber may have a frustum shaped portion adjacent the seat. The frustum shaped portion has walls tapering inwardly towards the valve seat which are less acutely sloped than the valve seat. 
     Stoves according to the invention offers significant advantages over the prior art. They utilize a non-pressurized fuel system which is inherently safer than a pressurized system. The stoves can be refueled in the appliances. They are also capable of burning JP-8 fuel or, alternatively, a variety of different fuels such as JP-8 fuels, military diesel fuels, kerosene or JP-5. 
     Stoves according to the invention also may include electronic ignition which facilitates starting of the appliance. They are easy to operate and reliable in operation. Warming up time is reduced from 30 minutes to 120 minutes in some prior art devices to approximately 2 minutes. The startup is smoke-free and they are capable of shutting off immediately without going through any elaborate shutdown procedure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is an isometric view of a stove according to an embodiment of the invention, the front panel thereof being shown in the open position; 
     FIG. 2 is a side elevation thereof; 
     FIG. 3 is a schematic diagram thereof; 
     FIG. 4 is a side view, partly broken away, showing the fuel regulator and fuel pickup tube thereof and a fragment of the fuel tank in ghost; 
     FIG. 5 is an isometric view thereof with the heat shield removed and the burner shown exterior to the frame; 
     FIG. 6 is an isometric view of the heat shield; 
     FIG. 7 is a front view thereof; 
     FIG. 8 is a sectional view of the control knob thereof; 
     FIG. 9 is a side view, partly in section, of the vent assembly for the fuel tank thereof; 
     FIG. 10 is an exploded view of the control panel thereof; 
     FIG. 11 is a front, isometric view of the control panel; 
     FIG. 12 is aside view, partly in section, of the compressor thereof; 
     FIG. 13 is a rear view thereof, partly in section and partly broken away; 
     FIG. 14 is an isometric, exploded view of the fueling assembly thereof; 
     FIG. 15 is a continuation of FIG. 14, showing the flame sensor, needle valve, solenoid for controlling the compressor and the knob of the control panel; 
     FIG. 16 is a front elevation of the battery pack thereof; and 
     FIG. 17 is a diagrammatic view of the fuel regulator thereof. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, and first to FIGS. 1 and 2, these show a stove  20  according to an embodiment of the invention. The stove has six sub assemblies, the first being frame assembly  22 , best shown in FIGS. 1,  5  and  6 , which includes frame  40  with an interior opening  41 , a fuel container  102  mounted on the frame within the opening, heat shield  103  and a reflector  105  mounted within cavity  107  in the heat shield. 
     The second sub assembly is burner assembly  24 , shown best in FIG.  5  and schematically in FIG.  3 . This includes an air aspiration, infrared burner of a type previously known and disclosed in U.S. Pat. No. 5,527,180. This burner utilizes a two-stage combustion process which recirculates combustion gases to achieve complete fuel vaporization. By recirculating the combustion products and re-burning the gases within the burner head  25 , the two-stage process burns virtually all of the hydrocarbons, approaching complete combustion. The benefits of a complete combustion are numerous, including maximum efficiency and heat transfer, no smoke and very low carbon monoxide emissions. When multiple stove units are used in an enclosed kitchen, near complete combustion is necessary to insure the health and safety of cooking staff. The infrared burner technology helps preserve clean breathable kitchen air. 
     The third sub assembly is the controller and associated wire harness assembly  26  shown in FIG.  10  and schematically in FIG.  3 . 
     The fourth sub assembly is compressor assembly  28  shown best in FIGS. 12 and 13. Compressor  68  provides compressed air for nozzle  69  of the burner assembly  24 , as shown in FIG.  3 . As discussed below, the compressor also serves to draw fuel into the fuel container. 
     The fifth sub assembly is fuel delivery block assembly  30 , shown in FIG.  14 . The sixth sub assembly is fuel level/vent assembly  32  shown best in FIG.  9 . 
     Referring to these sub assemblies in more detail, and first to sub assembly  22 , frame  40 , shown best in FIG. 5, is constructed chiefly of aluminum tubing welded together about opening  41 . In this embodiment there are three horizontal tiers of tubing, namely tiers  45 ,  47 , and  49 . There is also a plurality of vertical members such as member  51 . Thus the frame is a perimeter frame in this example which extends about the central opening  41 . 
     Fuel container  102 , somewhat wedge-shaped in this example, is mounted on the frame within the opening. Manual filler cap  64  and fuel regulator  130  are mounted on one side of the container. Vent valve  62  is mounted on top  63  of the container. Heat shield  103 , together with reflector  105 , are mounted on top  109  of the frame by a plurality of bolts  111  in this example. The heat shield and reflector are of stainless-steel in this example. 
     Referring to FIG. 5, burner assembly  24  includes burner  42  with burner head  25 . When assembled, as seen in FIG. 1, the burner head  25  projects through opening  27  in the heat shield and is located within cavity  29  formed therein. It may be seen that the heat shield extends about the burner and separates the burner from fuel container  102 . 
     The burner is supplied with fuel by air aspiration type nozzle  69  as shown in FIG.  3 . The purpose of the nozzle is to transform liquid fuel into a finely atomized spray with increased surface area to promote mixing of the air and fuel and facilitate evaporation. Nozzle  69  is a twin fluid air-assist type nozzle, also known as a siphon type air atomizing nozzle. Introducing high velocity air into the slow-moving fuel causes the fuel to be disintegrated by the mechanical energy from the air. Additionally, the compressed air flows through the nozzle, creating a low-pressure area inside the nozzle cavity. This low-pressure is used to siphon the fuel from the container  102  through the fuel regulator and needle valve described below and the nozzle into the combustion chamber of the burner. 
     Compressor  68  supplies pressurized air to the nozzle through air conduit  71 . The nozzle siphons fuel from fuel container  102  through siphoning fuel line  103 . 1  and provides an atomized fuel spray  105  which is ignited within the burner. As mentioned above, this type of burner is known and is disclosed in U.S. Pat. No. 5,527,180. The burner utilizes a two-stage combustion process where the combustion products are re-circulated and re-burned, eliminating virtually all hydrocarbons and approaching complete combustion. 
     Compressor assembly  28 , including compressor  68 , is shown in FIGS. 1,  12  and  13 . The compressor is a single piston diaphragm compressor in this example, although other types of compressors or air pumps could be substituted in alternative embodiments. The compressor includes an electric motor  75  with an eccentric device  77  mounted on shaft  79  thereof. Rod  81  connects the eccentric device to intake disk  83  and compression disk  85  which are connected on opposite sides of diaphragm  87  by screw  89 . Rotation of the motor causes reciprocation of the rod and deflection of the diaphragm. There is also an integral accumulator  23  built in to head  25 . 1  and cylinder  27 .  1 . 
     There is an inlet reed valve  300  and an outlet reed valve  302 . The diaphragm goes down on intake and draws air through reed valve  300 . The diaphragm goes up on output and the compressed air is forced pass reed valve  302 . The accumulator volume dampens pulses resulting from this operation. 
     There is an air pressure adjustment screw  70  to adjust the air pressure. The screw bypasses high-pressure air from the high-pressure side to the low-pressure side. The compressor has an outlet  29 . 1  for pressurized air connected to conduit  71  and a suction outlet  33  connected to conduit  35 . 
     In this embodiment the fuel delivery nozzle  69  comprises part of fuel delivery block assembly  30  shown in FIG.  14 . It is connected to the burner to maintain concentricity so that the fuel spray remains in the center of the burner to minimize impingement on the burner. The nozzle is mounted on one side of block  61  thereof. There is a fuel needle valve  88  which meters fuel to the nozzle to control the rate of flow of fuel. 
     A feedback potentiometer  76 , shown in FIG. 15, controls the output of compressor  68  and thereby air pressure to the nozzle  69 . As the stove operates, fuel is siphoned from the fuel container through the fuel lines, the shut off solenoid  92 , shown in FIGS. 3 and 14, and the needle valve  88  to the nozzle  69 . The needle valve controls pressure drop across the metering orifice. This in turn controls the fuel flow to the nozzle. When control knob  72  is adjusted, two fuel flow parameters are altered simultaneously. These two fuel control parameters are arranged so that a linear fuel rate is maintained. This is accomplished by rotation of knob  72  which simultaneously controls the fuel supply to the burner via the needle valve and the compressor output via the feedback potentiometer. 
     As seen in the sectional view of FIG. 8, the knob  72  has a pair of projections  80  and  81  on inner face  83 . These are spaced apart and slidingly engage slots  84  and  86  in potentiometer  76 , shown in FIG.  15 . At the same time, the knob engages cap  87  of needle valve  88 . The needle valve has a male threaded stem  89  which engages corresponding female threads in block  61 . Therefore rotation of the knob rotates the valve stem, causing axial movement of the valve stem to control the flow of fuel to the nozzle. At the same time, the knob rotates the potentiometer to control the speed of the compressor such that the amount of air supplied to the nozzle is correct for the amount of fuel. The projections allow the knob to continue engagement with the potentiometer, while allowing axial movement of the valve stem by means of an axially compliant coupling. 
     A flame sensor  100  is also mounted on the block  61  shown in FIG.  15 . The flame sensor views the flame in the burner through an aperture  101  in the block  61  shown in FIG.  14 . The flame sensor is located immediately beside the nozzle  69 , optimizing the viewing angle. The view of the sensor is parallel to the axis of nozzle  69 . 
     The flame sensor measures the flare intensity and converts it to a DC voltage signal rather than steady state light. The sensor is designed to respond to changing light intensity rather than respond to steady-state light intensity. All flames have a characteristic changing light intensity or flicker frequency. The sensor is tuned to respond to a specific flame flicker frequency and ignore other sources of light intensities such as sunlight or fluorescent light. The sensor measures the flame intensity in the infrared spectrum. A threshold value for the DC signal is established. Over this threshold flame is present, below it no flame is present. 
     An ignitor  90 , also mounted on block  61 , ignites the air fuel mixture expelled from the nozzle. The ignitor is attached to the block  61  so its position relative to the nozzle and fuel spray is maintained. This is critical to ensure reliable flame ignition and longer ignitor life. 
     A fuel on/off solenoid valve  92  controls the flow of fuel to the nozzle through conduit  103 . 1  shown in FIG.  3 . Three-way, two position solenoid valve  94  selects between air filter  98  and the vent assembly  32  described below. This allows the suction outlet  33  of the compressor shown in FIG. 12 to select between two operating modes. The first, with the valve in the normal position, is where air is drawn through air filter  98  for normal operation of the compressor to supply compressed air to the nozzle. The second mode, with the valve in the energized position, is to draw air from the fuel container  102  during the refueling operation described below. 
     The sixth sub assembly, namely fuel level/air vent assembly  32 , shown in FIG. 9, includes a vent body  62  mounted on top of the fuel container  102 . The suction conduit  35  from the compressor, shown in FIG. 12, is connected to fitting  110  shown in FIG. 9 which is equipped with a check valve  124 . There is a solenoid valve  125  in the vent body which opens or closes the suction conduit. The valve opens to keep the fuel at atmospheric pressure when the stove is operational. During refueling, this valve is closed. It is also normally closed when the stove is non-operational. A suction conduit  122  extends between the solenoid valve and chamber  127  equipped with a fuel - resistant buoyant float  120 . The chamber communicates with the inside of the container through opening  129 . During refueling operations, suction is applied to the fitting  110  by the compressor, drawing air from the container and drawing fuel into the container through fuel line  131  shown in FIG.  2 . There is a quick connect fitting  133  on the fuel line adjacent front  135  of the stove. A hose from a fuel supply is coupled to this fitting during the refueling operation. 
     There is a vertical tube  48 , shown in FIG. 9, brass in this example, which extends downwardly from vent body  62  to a position near the bottom of fuel container  102 . A pair of floats  170  and  171  are slidingly mounted on the tube. An annular stop  174  keeps float  170  near the top of the rod, while stop  176  limits its upward movement. Likewise float  171  has upper and lower stops  180  and  182 . Each of the floats has a magnet  184 . There is an internal reed switch  186  inside tube  48  adjacent each of the floats (only one shown). The switch adjacent float  171  is activated when the float reaches the lower position as illustrated. This provides a signal to the processor that the fuel container is near empty. The switch adjacent float  170  is positioned so it is activated when the float reaches the upper position against stop  176 . This signals the processor that the fuel tank is full and stops the compressor. 
     If float  170  fails to signal the processor and stop the compressor, then spherical float  120  rises in chamber  127  as fuel fills the chamber. The float acts as a check valve ball and rises against check valve seat  190  at the top of chamber. It may be observed that the check valve seat is conical in shape, tapering inwardly towards suction conduit  122 . This shape allows the ball to seal the conduit, but inhibits the ball from sticking in that position. The conduit has a frustum shaped portion  192  adjacent to the seat. This portion has walls tapering inwardly towards the valve seat, but they are less acutely sloped than the valve seat. This causes a Venturi effect which draws the ball  120  upwardly towards the valve seat, helping it seat in position to prevent fuel from entering the suction conduit and the compressor. 
     There is a regulator  130 , shown in FIGS. 1,  4  and  17 , which compensates for the changing lift height as the fuel is consumed so that the nozzle suction pressure remains constant. This maintains a constant fuel flow as the fuel level in the fuel container changes. Fuel has mass. Therefore, if the fuel level is high it needs less suction to lift. More suction is needed as the fuel is consumed. The regulator compensates for this. 
     Referring to FIG. 17, the regulator  130  in this embodiment is adapted from a chainsaw regulator. It includes a diaphragm  200  and a needle valve  202  having a rubber tip  204 . There is a lever  206  mounted on a fulcrum  208  which engages the needle valve and the diaphragm. There is a coil spring  210  which biases the lever towards the diaphragm. Normally the spring counters atmospheric pressure. The needle valve is pushed down and seals inlet  212 . A vacuum however deflects the diaphragm. The atmosphere pushes downwardly and opens the inlet. The diaphragm has a sintered bronze filter  216  which keeps dirt out of the diaphragm. 
     The regulator opens and allows fuel to flow only when a vacuum is present in the fuel line. Air under pressure is supplied to the nozzle. The Venturi effect creates a vacuum for suction to the nozzle. When the compressor stops, the vacuum is lost and the regulator stops the flow of fuel. 
     There is a fuel filter  132  attached to inlet  133  of the regulator as seen in FIG.  4 . The filter insures that the fuel passing into the fuel system is clean and prevents clogging of the fuel nozzle. 
     The fuel regulator is mounted on a boss  135  on the side of the fuel container  102 . It is sealed by means of an O-ring  137 . Screws  139  attach the regulator to the fuel container. The regulator is mounted low on the fuel container to maximize its effectiveness in compensating for changing fuel level. 
     Controller assembly  26 , best seen in FIG. 10, is mounted on the back of door  50  which is hingedly mounted to the frame adjacent its bottom, allowing the door to pivot open as seen in FIG.  1 . There is a latch  51 , shown in FIG. 11, which normally keeps the door closed. 
     Controller  52  is a microprocessor built into the back of circuit board  53 . 
     The front of the door serves as a control panel as shown in FIG. 11 including keypad  54  and indicator lights  58 . Thus the door provides two functions, front access to the interior of the stove and as controller packaging. The controller controls all electrical and process functions of the stove. It is microprocessor based. The micro-processor controls and modulates the input voltage and outlet as constant voltage to the components using PWM control. Each of the output circuits utilizes MOSFET style transistors with internal thermal protection to control the required devices. 
     LED panel  58  indicates to the operator flame hours and also error messages from internal diagnostics. 
     It will be understood by someone skilled in the art that many of the details described above are by way of example only and are not intended to limit the scope of the invention which is to be interpreted with reference to the following claims.