Patent Publication Number: US-6042368-A

Title: Appliance for burning a combustible gas, and method of burning such a gas

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a burning appliance for burning a combustible gas, in applications including stoves, heating appliances, lighting appliances, welding appliances, etc. 
     The term &#34;burning appliance, appliance for burning and appliance&#34; is intended to cover various appliances, which have the common characteristic of using the burning of a combustible gas to generate heat, but which can in other respects be differentiated in terms of their applications including stoves, heating appliances, lighting appliances, welding appliances, etc. 
     DESCRIPTION OF THE RELATED ART 
     The Assignee hereof manufactures and sells under the trade marks of MAX XTREME™, XPEDITION™ and XPERT™ a line of portable stoves for camping and hiking. The burners on such stoves are supplied with the combustible gas in the liquid phase from a fuel can under pressure. The liquid fuel changes phase to the gaseous phase within the stove and burns the in the gaseous phase. 
     Appliances of this kind in general comprise: 
     (i) a relatively massive metal body forming a heat sink, in which there is formed a passage for the flow of the combustible gas from an inlet to which it is fed under pressure, to an outlet from which it is discharged in the gaseous phase; 
     (ii) a member forming also a heat sink, namely a tap, for controlling the flow rate of the combustible gas, preferably in liquid phase, flowing down the aforementioned flow passage; this control member is separate from and connected to the metal body by a flexible pipe; 
     (iii) a member for mixing primary air in which a stream of the combustible gas in the gaseous phase, obtained at the outlet for discharging in the gaseous phase, in order to obtain a mixture that can be burned; and 
     (iv) a burner for burning the mixture to be burned, thermally connected with the metal body. 
     The expression &#34;relatively massive&#34; means that the mass of the metal body is greater than that strictly needed from which to hollow out the combustible gas flow passage. 
     The expression &#34;heat sink&#34; means the property whereby the metal body can store up heat, on account of its mass, especially by heat exchange with its surroundings. 
     The term &#34;in thermal connection with&#34; means any arrangement whereby the burner can exchange heat with the metal body, mainly by conduction and/or radiation; an arrangement of this kind may include mounting the burner directly to the metal body. 
     Although the aforementioned appliances are quite satisfactory, their performance at the time of lighting could be improved, at low temperatures, for example down to -5° C., and/or when using a combustible gas which contains a relatively significant fraction of light hydrocarbons, for example a 60/40% butane/propane mixture. Such conditions often lead to incomplete vaporization of the combustible gas, which can affect the performance of said appliances and result in flaring. 
     For this type of appliance it has been proposed, in accordance with document EP-A-0 703 409, that the vaporization can be improved by providing and arranging a vaporization loop, connected to the combustible gas flow passage and arranged on and outside the metal body, extending close to the burner and in a heat exchange relationship therewith. 
     An arrangement of this kind can substantially improve vaporization only during operation, but not when the appliance is being started or lit. 
     SUMMARY OF THE INVENTION 
     For an appliance supplied with combustible gas in the liquid phase, the present invention is an arrangement that makes it possible to improve the degree of vaporization of the combustible gas, particularly when starting or lighting the appliance. 
     In accordance with one aspect of the invention, to this end, the control member includes a pressure reducer, at least partially incorporated into the metal body and comprising a chamber into which the combustible gas is admitted in the liquid phase at high pressure, and a chamber from which said gas is discharged at low pressure, at least partially in the gaseous phase, these chambers being formed in the metal body, together with a valve situated for the most part within the metal body. 
     Using a suitable experimental procedure, and for a flow rate of combustible gas (60/40% a butane/propane mixture) of the order of 240 g/h, at -5° C., it was demonstrated in an appliance according to the present invention, and with all other aspects unchanged, the phenomenon of flaring, explained earlier, is avoided, or in any case limited to an acceptable level. 
     In accordance with another aspect of the invention, two unexpected advantages, which have been confirmed experimentally, are also provided. 
     Firstly, another phenomenon known as fogging, which arises out of the burning of a combustible gas, which is supplied in the liquid phase, is reduced. Under some circumstances, when the pressure of the combustible gas in the liquid phase increases substantially, the gas may be discharged from the burner in an atomized form, that is to say in the form of a suspension of droplets in a gaseous phase. This is the phenomenon known as fogging, which can significantly disrupt the operation of the burner. 
     In accordance with one aspect of the invention, the aforementioned phenomenon practically disappears or in any case is confined within acceptable limits. 
     In accordance with another aspect of the invention, a relatively stable or constant operation is achieved, when the flow rate of combustible gas is relatively low, and when the heat transferred from the burner to the metal body remains limited. 
     In accordance with yet another aspect of the invention, the pressure reducer comprises a valve of the upstream type, that is to say a shutter situated in the inlet chamber and returned toward a seat. 
     According to this arrangement, operation is improved for two reasons: 
     (i) any increase in pressure in the inlet results in a corresponding relative reduction in the reduced pressure in the discharge chamber, and this makes the appliance self regulating; and 
     (ii) any overpressure of the combustible gas in the liquid phase causes the valve of the pressure reducer to close, and therefore closes the pressure reducer; in particular, the pressure reducer is designed so that the overpressure at which it closes is fixed at a value, which is lower than the pressure that would cause deformation of the use-once or disposable container. 
     The solution according to the present invention also provides the following additional advantages: 
     (i) By working at a relatively low or reduced pressure, larger passage crosssections can be used, especially in the injector of the means for mixing in primary air, and this avoids or limits the phenomenon of blocking, and increases the life of the burning appliance. This advantage is very relevant to a burner, in which gas is supplied in the liquid phase, because the impurities conveyed in the liquid becomes deposited in the appliance as the combustible gas vaporizes. 
     (ii) The appliance is made more compact, and this allows a relatively short reaction time during movements of the pressure reducer, and in particular allows the burner to be extinguished in a relatively short period of time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is now described with reference to the appended drawings, in which: 
     FIG. 1 is a view in vertical section through a burning appliance according to an embodiment of the present invention; 
     FIG. 2 is a perspective view of the appliance depicted in FIG. 1; and 
     FIG. 3 is a detail of FIG. 1, illustrating a filter for filtering the combustible gas. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     In accordance with FIGS. 1 and 2, there is depicted, identified in general terms by the numerical reference 1, a stove, forming an appliance or device for burning a combustible gas, for example a liquefied petroleum gas, especially butane and/or propane. 
     In general terms, the appliance 1 comprises: 
     (i) a relatively massive metal body 2 both forming the framework of the appliance and serving as a heat sink, in the sense that this metal body is, on the one hand, a good conductor of heat and, on the other hand, on account of its mass allows heat to be accumulated or stored; 
     (ii) a member 6 for controlling the flow rate of the combustible gas, including a pressure reducer or regulator, partially incorporated into the metal body 2; 
     (iii) a member 26 for mixing primary air in with a stream of the combustible gas in the gaseous phase in order to obtain a mixture that can be burned; 
     (iv) a burner 7 for burning the mixture to be burned, in the gaseous form; and 
     (v) a means 24 of connecting the appliance 1 to a source of combustible gas in liquefied form and under pressure; in this case, but not depicted, this source includes a disposable container of the canister type comprising a valve, for drawing off liquid fuel. The valve is of an aerosol valve type, comprising a pedestal with a polygonal crosssection, for example a hexagonal crosssection, which will be discussed later; the connector means is covered in another text by the Assignee hereof (U.S. patent application Ser. No. 08/905,797, filed Aug. 12, 1997, incorporated herein by reference), and makes it possible to open the container, using its withdrawing valve, and to provide a sealed connection between the container and the appliance, and to fix the container to the appliance positively and reversibly. 
     In operation, the appliance 1 defined earlier has the particular feature of being fed with combustible gas in the liquid phase and at a relatively high pressure, and of burning this same combustible gas in the gaseous phase and at a relatively low or reduced pressure. 
     The various parts or components identified earlier will now be described. 
     The metal body 2 is designed, in general, to form a passage 3 down through which the combustible gas can flow, in the liquid and/or gaseous phase, from a liquid-phase feed inlet 4 to a gaseous phase discharge outlet 5. The metal body 2 has a protruding appendage 2a inside which there is formed a duct 4 forming the feed inlet for the combustible gas in liquid form and under pressure. A settling well 22, the crosssection of which is relatively larger than the mean crosssection of the flow passage 3, is formed in the metal body 2 and forms part of the passage 3. The upper end 22b of this well coincides with the outlet 5 for discharging the combustible gas in the gaseous phase at reduced pressure, as described below. 
     The connector means 24, in the illustrated embodiment, by way of example, includes a collet 28 including a tapped internal thread 28b, and mounted so that it cannot rotate on the metal body 2, and including pawls 28a distributed and spread out about its axis. The pawls 28a have, on the one hand, a nose 28c designed to be snap-fastened pushed inside a collar provided in a corresponding way on the disposable container, and more precisely on the valve, and on the other hand an oblique contact surface 28d, designed to cooperate with a corresponding oblique contact surface 27c of a cam 27 described below. The cam 27 is mounted so that it can rotate freely inside the collet 28, including a chamber 27a having a polygonal cross-section, for example a hexagonal crosssection, in which the appendage 2a described earlier is contained and including the liquid-phase feed duct 4. This cam 27 has an external screw thread 27b in mesh with the tapped internal thread 28b of the collet 28. 
     In relation to the structure of the container described earlier, and in particular the polygonal crosssection of the pedestal of its valve, the operation of the connector means 24 can be deduced from the earlier description, starting from the position depicted in FIG. 1. The container is attached to the appliance 1, on the one hand by snap-fastening the pawls 28a under the annular collar of the valve, and on the other hand by inserting the pedestal of the latter in the chamber 27a. As soon as this attachment has taken place, and in particular due to the seal 30, the valve of the container is opened, and a sealed connection is made between the open container and the appliance. Using the canister, it is possible to screw the moving cam 27 with respect to the stationary collet 28, move the cam and the collet closer together in terms of translation, and bring the oblique contact surfaces 27c and 28d into contact. From this moment on, the pawls 28c are pushed out positively under the annular collar of the valve of the disposable container and the latter becomes locked in a leaktight manner to the appliance 1. The foregoing steps are completely reversible. 
     The regulator or pressure reducer 6 or control member is characterized by the fact that it is integrated or incorporated at least in part into the metal body 2 of the appliance. The pressure reducer 6 is preferably, but not exclusively, a pressure reducer with a valve 10 of the upstream type, that is to say a pressure reducer in which the valve or shutter 11 is situated in the inlet chamber for the combustible gas at high pressure, being returned toward the seat 12. 
     In accordance with the embodiment shown in FIG. 1, the control member 6 comprises: 
     (i) a body 31 inserted in the metal body 2, determining the aforementioned seat 12; 
     (ii) a chamber 8 into which the combustible gas is admitted in the liquid phase at high pressure, determined both in the body 31, and therefore in the metal body 2; 
     (iii) a chamber 9 from which the combustible gas is discharged at low pressure, at least partially in the gaseous phase, formed in the metal body 2; 
     (iv) the valve 10 of the upstream type, which combines the shutter 11 with its seal, and the seat 12 against which said shutter is returned by a spring 32; 
     (v) a diaphragm 20, closing the discharge chamber, the circular edge of which is clamped between the metal body 2 and an outer bonnet 21 mounted on said body; 
     (vi) a cap 33, integral with or fixed to the diaphragm 20, resting against the end of the shutter 11 at the opposite end to the seat 12; 
     (vii) a spring 18, resting at one end against the cover 33, outside the discharge chamber 9, and at the other end against a slide 17, mounted freely and axially inside the bonnet 21; and 
     (viii) an operating member 15, situated outside the metal body 2 and comprising at least two marked positions, one in which the valve 10 is open and in which the pressure of the combustible gas leaving the discharge chamber is controlled, and the other a closed position in which the valve 10 is locked in the closed position; this operating member 15 combines, first of all the bonnet 21 described earlier, mounted on the metal body 2; secondly, the slide 17 mounted so that it can move freely in terms of translation within the bonnet 21, resting against the means or spring 18 for returning the diaphragm 20; thirdly a means or spring 19 for returning the slide 17, away from the diaphragm 20 of the pressure reducer, resting at one end against the bonnet 21 and at the other end against the slide 17; and fourthly a means for actuating the slide 17 in terms of translation, composed of a knob 16, mounted so that it can rotate freely coaxially on the bonnet 21 and comprising two symmetric ramps 16a in rotation with respect to the axis 13 and in contact respectively with two opposed studs 17a of the slide 17. 
     Various positions of adjustment may be formed on the symmetric ramps 16a between the two marked, open and closed, positions of the operating member 15. 
     As clearly shown in FIG. 1, the inlet chamber 8 of the illustrated embodiment is immediately adjacent to the liquid phase inlet 4, and this has the advantage of limiting the amount of combustible gas that remains in the appliance and is vented to atmosphere when a disposable container is disconnected from said appliance as described earlier. Furthermore, this chamber 8 is preferably immediately adjacent to the axis 14 of the burner, which places it, at least partially, in the region for heat transfer from the burner 7. 
     Further, the feed duct 4 is preferably aligned along an axis 13 with an axis of the pressure reducer 6, and more precisely with an axis of the valve 11. The axis 13 is itself preferably orthogonal or perpendicular to the axis 14 of the well 22 described earlier, which also corresponds to that of the outlet 5, through which the combustible gas is discharged in the gaseous form, of the injector 36, and of the burner 7 described below. 
     As shown more specifically in FIG. 3, a filter 40 can be placed in the well 22 immediately upstream of the member 26 for letting in primary air, in the direction in which the combustible gas flows. This filter is more particularly pushfitted into a hole formed in the injector 36, facing the well 22. The filter 40 and the well 22 are arranged one with respect to the other in such a way as to form a peripheral gap 41 between the wall of the well and a lateral part 40a of the filter, so that the filter 40 is arranged like a suction strainer. As a preference, the filter consists of a cylinder or plug of a sintered and therefore porous material (especially a metal). By varying the height of the filter 40 from the injector 36, the size of the lateral area 40a of the filter and therefore the time that the filter takes to block can be altered, all other things being equal. The upstream face 41b of the filter 40 is situated some distance from the lower end 22a of the well 22, as close as possible to the injector 36. 
     The member 26 for mixing in primary air combines, on the one hand, the injector 36 situated at the outlet 22b of the well 22, and on the other hand, openings 37a made in the tube 37 of the burner 7. The jet of combustible gas emitted by the injector 36 therefore entrains through the orifices 37a the primary air needed for combustion. 
     The burner 7 comprises two pressed parts 38 and 39 crimped together, forming a gap between them in which the mixture to be burned can circulate, the part 39 having perforations 39a. 
     A vaporization loop 23 outside the metal body 2 is preferably connected to the flow passage 3 for the combustible gas, in the direction in which this gas flows, between an intermediate inlet 25a consisting of an orifice made in the metal body 2, communicating with the discharge chamber 9, and an intermediate outlet 25b entering the well 22 some distance from its lower end 22a and approximately tangent to the circumference or cylindrical interior surface of the well 22. 
     These arrangements make it possible for heavy impurities liable to be deposited upon vaporization of the combustible gas, particularly by the swirling effect of the stream of gas in the well 22 to be held in the bottom of the well 22, which lies on the axis 14 of the burner. 
     The vaporization loop 23 is preferably designed to be removable from the metal body 2, and in particular from the inlet 25a and outlet 25b, which allows the loop to be adapted to suit the various configurations or arrangements of the burner 7, depending on the application or intended use of the appliance, without having to change the rest of said appliance. 
     This vaporization loop 23 plays a part in conducting the residual heat emitted by the burner 7 away to the metal body 2. 
     Because of what has been described earlier, and in operation, from being drawn off in the liquid phase and at high pressure from a disposable container, it will be appreciated by those skilled in the art that the flow of combustible gas in the illustrated embodiment is as follows: 
     (i) Entry in the liquid phase and at high pressure into the inlet chamber 8, possibly after filtration; the high pressure is, for example, 1 to 9 bar; 
     (ii) Controlled pressure reduction in the liquid phase across the valve 10, and passage of the combustible gas at low pressure into the discharge chamber 9, at least partially in the gaseous phase; 
     (iii) Entry and circulation of the combustible gas into and in the vaporization loop 23 and return of the combustible gas, entirely in the gaseous phase, to the well 22; 
     (iv) Passage of the combustible gas in the gaseous phase and at low pressure through the upper end 22b of the well 22, which communicates with the member 26 for mixing in primary air, namely the injector 36 from which a stream of the combustible gas is obtained; 
     (v) The mixture to be burned is obtained by mixing the stream of combustible gas with primary air and said mixture is burned in the burner 7. 
     All the aforementioned provisions make it possible to provide a significant improvement, as described earlier, to the operation of a burner, which burns in the gaseous phase, but is supplied with combustible gas in the liquid phase. 
     While the present invention has been described with respect to what is presently considered to be the preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements, some of which are discussed above, included within the spirit and scope of the appended claims. Therefore, the scope of the following claims is intended to be accorded the broadest reasonable interpretation so as to encompass all such modifications and equivalent structures and functions.