Background The present invention relates to a stove and more particularly to a liquid fuel priming system and burn control for a portable camping stove. Most current liquid fuel stoves require a priming process that involves pressurizing a fuel reservoir, opening a control valve to release a small volume of liquid fuel through a primary burn jet into a priming cup, and then completely closing the valve. Next, the user must ignite the fuel in the priming cup, which is positioned adjacent to a portion of the primary fuel delivery system. The resulting combustion flame heats the portion of the fuel delivery system, thereby causing vaporization of the fuel, which is necessary for proper use of the stove. If the user has delivered too much fuel into the priming cup, the priming flame can be larger than required for preheating the primary fuel delivery system. In addition to wasting fuel, a large flame also presents a safety hazard as does the ignited liquid fuel in the priming cup.

Once the priming fuel has burned, the user must reopen the control valve to permit pressurized and vaporized fuel through the jet for normal operation of the stove. If the priming flame prematurely extinguishes, the user must open the control valve and relight the stove to ignite the vaporized fuel. Conversely, if the user opens the valve before the fuel delivery system is completely preheated, a mixture of liquid and vaporized fuel may be ejected from the jet, causing a large flare up from the stove that presents its own set of hazards.

In addition to the described pressurized liquid fuel stoves there is a genre of proposed non-pressurized liquid fuel stoves referred to as capillary force vaporizer ("CFV") stoves. These proposed stoves rely upon capillary force to transport fuel from a storage vessel to a burning orifice, and are described in the following United States patents: 6,634,864, 6,347,936, 6,162,046, and 5,692,095, which are incorporated herein by reference. While avoiding some of the hazards associated with pressurized stoves, there is still the requirement to preheat or prime the stove for use. Heretofore, the same or similar methods to those described above were necessary with respect to the proposed CFV stoves.

Summary of the Invention The invention is directed to a burner arrangement, whether used as a priming system for liquid fuel stoves to facilitate preheating and subsequent igniting of the stove's main burner, or as a primary burner for a stove or other device wherein a combustion flame is desired. The invention applies equally to conventional liquid fuel stoves that require pressurization of fuel reservoirs and liquid fuel stoves that do not require pressurization of fuel reservoirs. The invention is also directed to a control arrangement for modulating the output of a CFV burner as well as establishing a heat conduit from a priming torch to the CFV.

Burner embodiments of the invention rely upon CFV technology and comprise a hollow cylinder of generic cross section having a closed first end and an open second end separated by a body portion wherein a portion of the cylinder distant from the second end defines a jet orifice that exposes the interior of the cylinder to the environment. The hollow cylinder further comprises a feed wick disposed therein and at least substantially occupying the space defined by the cylinder. In addition, certain embodiments of the invention incorporate a dosing means for metering fuel to the second end prior to ignition of the fuel. In select embodiments of this type, the dosing means comprises a pump arrangement for supplying fuel to at least to a portion of the feed wick adjacent the second orifice at least prior to ignition of the burner. Backflow prevention means are also provided to ensure that a vapor bias is present to generally direct vaporized fuel towards the second orifice. In one series of embodiments, the backflow means comprises a check valve while in another series of embodiments the backflow means comprises a constriction in the feed wick to create a micro-porous region.

Because heat is necessary to vaporize fuel residing in the feed wick, it is desirable to construct the hollow cylinder from a material having high thermal conductance such as found in many metals, and particularly copper, brass and some steels. Additionally, and in certain embodiments, an auxiliary heat transfer element can be integrated with or positioned in contact with the hollow cylinder, preferably at or proximate the first end, to facilitate heat transfer and/or increase thermal mass.

In preferred first embodiments, the burner is a priming torch and comprises, in addition to a cylinder, a feed wick and backflow prevention means, a dosing means in the form of a pump to provide the necessary amount of liquid fuel to the feed wick. The user must operate the pump, which then fills the feed wick with pressurized liquid fuel and preferably additional fuel to the point that excess fuel is expelled from the jet orifice. The backflow prevention means, which may be a check valve, temporarily retains the pressurized fluid at the fee wick. The user then ignites the excess fuel present on the outer surface of the cylinder, which heats the cylinder and forces vaporized fuel out of the jet orifice, which is then automatically ignited by the heating flame. Once the torch has vaporized the fuel contained in the priming torch or a pressure equilibrium is reached, it self-extinguishes. This small burst of energy is ideal for preheating a liquid fuel stove; the amount of energy supplied and the power delivered can be adjusted by changing size and geometry of key components in the system as will be described in greater detail below.

In preferred second embodiments, the burner is also a priming torch but lacks the dosing means and replaces the mechanical check valve with a micro-porous region formed in the feed wick. The micro-porous region regulates the volumetric flow of fuel there past, and maintains a pressure gradient between the liquid fuel and the vaporized fuel during operation of the torch. Upon exhaustion of the fuel between the micro-porous region and the jet orifice, the torch self-extinguishes. The micro-porous region is preferably created by imparting a radial constriction in the cylinder, thereby forming a crimp in the feed wick at that location.

Control arrangements of the invention comprise a plate that selectively occludes at least one jet orifice in a CFV burner. In multiple orifice CFV burners, the plate selectively occludes some or all of the orifices, preferably by rotation of the plate about the burner. Rotational embodiments of the plate include at least one aperture through which at least one orifice may be selectively exposed or occluded. Because of the proximity of the plate to the CFV burner, it preferably includes a heat conduit for conducting heat generated by an external source such as a priming torch to the CFV burner, thereby assisting in creating an environment for operation of the CFV burner.

These and other aspects of the invention will become more apparent upon inspection of the several Figures and accompanying detailed description of the several embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross section elevation view of a capillary force vaporizer stove including a pump-operated priming torch; Figure 2 is a detailed cross section view of the pump-operated priming torch used in conjunction with the stove of Figure 1 ; Figure 3 is an elevation view of the priming torch of Figure 2; Figure 4 is a cross section elevation view of a static priming torch for a combustion device; Figure 5 is a perspective view of a heat return prong; Figure 6 is a perspective view of a positioning ring; Figure 7 is a perspective view of a capillary force vaporizer (CFV) component; Figure 8 is a plan view looking down through a heat return prong and handle at the prong base, with CFV orifices in the full "on" position; Figure 9 is a plan view as in Figure 8 but wherein the orifices are partially occluded to the "half on" position; Figure 10 is a plan view as in Figure 8 but wherein the orifices are fully occluded to the "full off" position; Figure 11 is an elevation view of a high efficiency pot; Figure 12 is an elevation cross section elevation view of a high efficiency pot; Figure 13 is a plan view of a single finned ring component of a high efficiency pot; and Figure 14 is a detailed elevation view of two stacked finned rings.

DETAILED DESCRIPTION OF THE SEVERAL EMBODIMENTS Stove 10 comprises priming torch assembly 30 and CFV burner 70, as shown in Fig. 1. These two components are disposed in housing 12, which has upper surface 14, lower surface 16 and side surface 18, together defining fuel reservoir 20. To better understand the components and operation of priming torch assembly 30, operation of burner 70 will first be explained. Liquid fuel, such as purified gasoline (white gas), is drawn up by primary wick 64 from fuel reservoir 12 and fed into a capillary material 66, which has a high surface to fuel interface tension. This interface tension thus generates a capillary pressure. Heat is applied to the side of material 68 opposite of reservoir 12, causing the fuel therein to vaporize. As long as pressure on the heated or vaporizing side of material 68 does not exceed the capillary interface pressure, fuel will continue to flow through material 68 towards the heated side. A sealed chamber haying orifice 72 can be established on the vaporizing side to create a high velocity jet of vaporized fuel. The vaporized fuel jet mixes with air and is ignited when it enters a high temperature zone, such as a hot target burner 76 or a flame present at jet orifice 54. Further understanding of the operation of CFV burner 70 can be gained by reviewing US patent numbers 6,634,864, 6,347,936, 6,162,046, and 5,692,095, which were previously incorporated by reference. Turning then to Figs. 1-3, priming torch assembly 20 is shown in detail. While the illustrated embodiment shows an integrated priming torch comprising dosing means 40 and priming torch 22, equivalent functionality has been obtained through the use of separate components. In this integrated assembly, which is best shown in Figure 2, priming torch 22 comprises main body 24 and torch tube 30. Main body 24 includes upper end 26, which is adapted to receive lower end 34 of torch tube 30, and lower end 28, which includes recess 29 and partially defines pressure cavity 46.

Torch tube 30 has lower end 34, which as previously described fits in a recess or bore formed in upper end 26 of main body 24, and has upper end or head 32. Unlike lower end 34, upper end 32 is substantially closed to the environment. The only exposure upper end 32 has with the environment is through proximately located jet orifice 33, which is formed in body portion 36 of torch tube 30. While the illustrated location of orifice 33 is preferred, those persons skilled in the art will appreciate that any location at or proximate to upper end 32 will establish a functional torch. Feed wick 38 is disposed in torch tube 30 and substantially occupies all internal space thereof. The lower distal end of feed wick 38 is exposed to pressure cavity 46 to enable effective reception of fuel exposed thereto. Feed wick 38 is preferably derived from a high porosity material suitable for capillary transport of liquids such as fiberglass or cellulose. Heat transfer coil 50 substantially surrounds the upper portion of torch tube 30, and operates to more evenly distribute heat generated initial heating and from jet orifice 33 during operation of the torch assembly to facilitate movement of fuel from reservoir 12 via capillary force transport.

Dosing means 40 comprises open-ended resilient priming cup 48, which extends from end cap 42, defines volume 49 to provide fuel to torch tube 30 in a manner that will be described in detail below. Dosing means 40 further comprises end cap 42 and check valve 44, which together with recess 29 of main body 24 define pressure cavity 46. For servicing purposes, end cap 42 is preferably removably attached to lower end 28 of main body 24, such as by threaded coupling or friction (snap) fit. Also as described below, the volume of volume 49 is selected to provide only enough fuel to enable sufficient preheating and ignition of CFV assembly 62.

Still referring to Figs. 1-3, the operation of priming torch assembly 20 will now be described. To initiate operation thereof, a user need only depress upper end 32 of torch tube 30 to cause sufficient fuel dosing of feed wick 38, and expose jet orifice 33 to an ignition source. The dosing, i.e., transfer of fuel, occurs as follows: depression of upper end 32 of torch tube 30 causes main body 24 and end cap 42 to extend further into reservoir 20 until the lower portion of priming cup 48 contacts bottom surface ,14 of reservoir 12. Once in contact, a defined volume of fuel is held within volume 49. Upon further depression of upper end 32, resilient priming cup 48 undergoes volume reducing compression (similar to a bulb pump), which causes pressurized fuel to move through check valve 44 into pressure cavity 46 and torch tube 30. Upon release of torch tube 30 by the user, torch tube 30 is biased to its starting position by compression spring 52; backflow from pressure cavity 46 into volume 49 upon rebound of torch tube 30 is prevented by check valve 44. . Upon decoupling of priming cup 48 from bottom surface 14, additional fuel from reservoir 12 is permitted to enter into volume 49 for subsequent use.

Preferably the volume of volume 49 has been chosen so that one depression of torch tube 30 transfers a sufficient quantity of fuel to fill pressure cavity 46 and to eject a small amount of excess fuel out of jet orifice 33. Excess fuel preferably migrates down the upper portion of torch tube 30 and wets the exterior torch tube wall as well as heat transfer coil 50. The user then ignites upper end 32 with an open flame where after a priming flame sweeps over upper end 32, heating the upper portion of torch tube 30 and heat transfer coil 50. Shortly there after, fuel present in the upper portion of feed wick 38 at the interface with the interior wall of torch tube 30 begins to vaporize while liquid fuel is retained in the interior and lower portions of feed wick 38. If the stove were accidentally tipped at this point, liquid fuel would not spill out onto the user or any supporting surfaces. As a consequence of this vaporization and increased pressure, priming torch assembly 20 ejects vaporized fuel from jet orifice 33 and sends out a directed blue flame that hits and adheres to heat return prong 82, as best depicted in Fig. 1. Unlike priming operations of the prior art that rely upon yellow flames, blue flames are indicative of combustions efficiencies exceeding 90%. Moreover, because the flame is controlled as opposed to random, a target structure such as heat return prong 82 is more efficiently heated, further increasing the overall efficiency and safety of the present priming apparatus. The directed blue flame thus provides the user with a clean and fast method for warming heat return prong 82 and indirectly CFV assembly 62 with minimal use of fuel and maximum safety. In this fashion, an optimal amount of fuel is safely used to preheat CFV assembly 62 prior to its ignition. Indeed, once enough heat is applied, fuel from the fuel reservoir 12 moves through CFV assembly 62, and is vaporized fuel is ejected through one or more burner orifices 72 (see Fig. 7). The vaporized fuel then impinges upon diffusion disk 76 while some residual flame exists at jet orifice 33, thereby igniting the main flame of the stove before the last of the priming fuel is used. Adjustments to the parameters of priming torch assembly 22 (e.g., stroke and/or bore of torch tube 30, volume of pressure cavity 46, or volume of volume 49) can be used to change the amount of fuel delivered to the feed wick 38 and upper end 32. Changing the dimensions of upper end 32, or the diameter of torch tube 30 or jet orifice 33, makes it possible to adjust the energy discharge rate, duration, and total energy output of the assembly. Thus, a number of variables can be modified to suit the particular priming needs associated with a wide variety of CFV burners.

To enhance the safety of stove 10, normally closed O-ring seal 58 provides a positive seal between the environment and fuel reservoir 20; compression spring 52 ensures O-ring seal 58 is seated against upper surface 18 when primary torch assembly 20 is not depressed.

In embodiments utilizing a pressurized fuel reservoir, the pressure pump used to pressurize the reservoir can have two settings or two valves: one to release fuel to a priming system according to the invention and one to release fuel to the main burner. This alternate embodiment reduces the complexity of the system because a plunger pump (a means for providing pressurized fuel to the priming torch) would no longer be required. However, an alternate fuel line and dose control system may be required to deliver the fuel to the priming torch.

In the previously described embodiment, a combination of pressurized fluid delivery to feed wick 38 at lower end 34 of torch tube 30 and localized heating of upper end 32 of torch tube 30 created a capillary transport pressure bias towards jet orifice 33. As long as the pressure bias remained favorable towards jet orifice 33, vaporized fuel would continue to be ejected from orifice 33 and new liquid fuel would be delivered to replace that lost to vaporization. When the bias was no longer present, such as when fluid pressure in pressure cavity 46 dropped below a threshold level, the flame at jet orifice 33 would self-extinguish for lack of fuel. In the embodiment of Fig. 4, a priming torch is shown that has no moving parts, and requires no pressurized fuel to establish and maintain a capillary transport pressure bias. Priming torch 22' comprises torch tube 30' and feed wick 38', which extends from below lower end 34' to jet orifice 33'. In this respect, priming torch 22' is configured the same as previously described priming torch 22. Unlike priming torch 22, however, body 36' has been radially crimped to compresses strands 39' together, thereby creating a micro-porous region. This micro-porous region allows fuel to slowly wick there through, but prevents the rapid transport of liquids or vapors. Thus, the micro-porous region keeps pressurized vapor from being forced back through the crimped portion of strands 39'. In operation, a user would simply heat upper end 32' such as with a match or lighter, and vaporization of liquid fuel in upper end 32" would force vaporized fuel through jet orifice 33'. The fuel would ignite when exposed to an ignition source, which may also be the heat source, and the orifice would direct a jet flame. The degree of radial constriction and material selected for feed wick 38' determines the rate that liquid fuel could wick from lower end 34" to upper end 32', and can be selected to provide sufficient heat to prime and possibly ignite CFV burner 60, at which time it would self-extinguish.

As described above, a purpose of priming torch assembly 20 or priming torch 22' is to provide sufficient heat to CFV burner 60 so that CFV assembly 62 will generate vaporized fuel. Once ignited, CFV assembly 62 must retain sufficient heat to maintain the production of vaporized fuel (because vaporization of a liquid is endothermic, additional heat must be introduced into the process to maintain an appropriately high temperature for further vaporization). Therefore, another component of the invention provides heat feedback to CFV burner 70. Heat feedback system 78 comprises jet throttle plate 80 and heat return prongs 82, which are shown in Fig. 5, as well as indexing ring 84 (see Fig. 6). Jet throttle plate 80 defines two through-holes, circular hole 81a and elliptical hole 81 b. These holes are intended to selectively obstruct or expose orifices 72 of CFV head 70 (shown in Fig. 7), as will be described below. CFV head 70 has two tabs 74 that protrude radially outwardly there from and engage slots 86 of indexing ring 84 when CFV assembly 62 is fed there into. Flats 88 on indexing ring 84 mate with complementary flats in the stove housing (not shown) to prevent ring 84 and CFV assembly 62 from rotating during rotation of jet throttle plate 80.

Indexing ring 84 is preferably made from stainless steel because of its low thermal conductivity, since it is desirable not to transfer heat to the stove housing and fuel reservoir. Holes 85 may be added to further reduce heat conduction through this part. Heat return prongs 82 are preferably made from a high thermal conductivity material such as copper, the purpose being to act as a heat conduit between a source of heat such as priming torch assembly 20 or diffusion disk 76 and CFV assembly 62. The prong is preferably thick enough to provide sufficient heat to CFV head 70 to cause continuous fuel vaporization thereat.

Handle 90 is shown in plan view in Fig. 8, attached to heat return prong 82 via holes in the prong and protrusions in the handle. Handle 90 is used to rotate jet throttle plate 80 via heat return prong 82, which in turn causes orifices 72 to be occluded or exposed as best shown in Fig. 8 (both orifices 72 exposed), Fig. 9 (one orifice 72 exposed and one occluded) and Fig. 10 (both orifices 72 occluded). Handle 90 extends well out in a radial direction to a point (not shown) where it is not too hot to the touch. It rides on top of a heat sink ring, which is fastened to the top of fuel reservoir 12. The heat sink ring has two stops and a dent that the handle will touch against to signal the user of the full on, half on and off positions.

Jet throttle plate 80 has an additional feature identified as micro throttle 92. It was found with the particular orifices used that if the combined area was less than 0.00023 in2 then the fuel air mix is too lean and if the combined orifice area was more than 0.00029 in2 the mix was too rich when orifice 72 to diffusion disk 76 distance is 0.950 to 1.050 inches as shown in the illustrated embodiment. Because optimal burning characteristics were sought for a full burn condition (both orifices 72 exposed), incorporation of micro throttle 92 provided the means for adjusting the air to fuel mixture when only one orifice was used. Micro throttle 92 hinders air mixing with vaporized fuel when orifice 72 is exposed to create a stable but efficient flame. The illustrated embodiment can be adjusted to bum from a high intensity (roughly 5,500 BTU/hr with gasoline) with two orifices exposed, to one throttled jet (3,000 BTU/hr), to an off position. Furthermore, given the relative ease in replacing CFV assembly 62 as previously described, stove 10 can be made to burn multiple fuels with efficiency by changing CFVs incorporating different sizes of orifices 72. For example, the stove in Fig. 1 can quickly be altered to burn "white gas" and gasoline with one CFV assembly or to burn JP8 kerosene and US military logistics fuel ("Jet A") with another CFV assembly.

In addition to the use of orifice occlusion as a means for modulating the output of CFV burner 60, further means include modifying the amount of heat energy returned to CFV assembly 62. By modifying the amount of returned heat energy, the vapor pressure differential in CFV assembly 62 will also be modified. Thus, by changing the exposure of heat return prongs 82 to heat generated by CFV assembly 62, more or less vapor pressure will form at orifices 72. Such change can be accomplished by selectively disassociating portions of any heat feed back arrangement (such as heat return prongs 82) from either an emitted flame(s) or from CFV assembly 62.

Now turning to Figs. 11 and 12, high efficiency cooking pot 100 is shown. Cooking pot 100 has the ability to reduce that amount of fuel consumed when cooking and to reduce the amount of time needed to heat food or water by efficiently extracting neai τrom oι-v Durner 70. Cooking pot 100 includes container portion 102, which may be made from a variety of materials but in the present embodiment is made from stainless steel for its ability to withstand brazing, and its durability and longevity in use. Pot 100 also incorporates corrugated and staggered horizontally oriented copper fins 110 at the bottom of pot 100. These fins transfer heat from converting combustion gasses through the fins and up through the bottom of the pot. Protection for the preferably thin fins 110 is shown as annular housing 120 at the bottom of the pot. The outside of the pot has temperature stable insulation layer 104 such as foamed silicone. The insulation reduces heat losses from the pot while allowing the user to lift or otherwise handle the pot with bare hands during cooking and to use it effectively bare handed as a bowl while dinning.

Fins 110 can be formed from a thin flat ring of a highly conductive sheet of material such as copper, as shown in Fig. 13. Many fins are formed in concentric circles in a repeating pattern. During stove operation, the stove flame progresses radially out from the center, of the now finned, ring 112 and across the fins. Each circle of fins is rotationally spaced roughly one half pitch from the fins that are in the adjoining radial positions. As the flame passes over finned ring 112. gas boundary layers are broken to induce turbulence and provide increased convective heat transfer to the fins. Multiple finned rings are stacked and brazed together using a high temperature solder to form a high surface area, unitary structure. In the present example, four finned rings are vertically stacked to maximize heat transfer. Given the number of finned rings used, thin finned rings are preferred in order to minimize the mass of the assembly. A detailed view of two rings in a stacked configuration is shown in Fig. 14. Ideally the finned rings are be rotated or "clocked" with respect to each other so that channel sizes are relatively uniform. The structure is preferably brazed or otherwise bonded to the bottom of the pot 100 allowing a substantial portion of the heat contained in the flame to be transported to the pot bottom via thermal conduction. To minimize contact resistances and obtain improved heat transfer it is preferable that the solder fully wet the touching surfaces of the finned rings and to the pot bottom.