WO2008129264A1

WO2008129264A1 - Alcohol fuel burner system

Info

Publication number: WO2008129264A1
Application number: PCT/GB2008/001367
Authority: WO
Inventors: Geoffrey Allen; Keith Hallam
Original assignee: H & E Knowles (Lye) Limited
Priority date: 2007-04-24
Filing date: 2008-04-17
Publication date: 2008-10-30
Also published as: GB0707858D0

Abstract

A wick (10), comprising a plurality of substantially inflexible members forming channels through which fuel may flow by capillary action, said wick constructed from a material able to withstand the temperatures resulting from fuels such as ethanol, and providing a predictable and consistent flow of fuel, with reduced wick soaking time.

Description

Alcohol Fuel Burner System

The present invention relates to a wick for use in a fuel burner, and is particularly concerned with fuel burners used to heat horticultural structures, for example greenhouses and cold-frames.

Greenhouses and cold frames operate by artificially increasing the temperature inside to allow an extended growing season for plants. The effectiveness of a greenhouse or cold frame may be augmented by installing a fuel burning heater.

Known heaters comprise a liquid fuel reservoir, often paraffin, and a wick which transports the fuel to a burner head at a given rate to provide a limited energy output.

Known wicks are constructed from flexible strands of fabric material, loosely woven into strips with one end in contact with the liquid fuel. The fuel soaks into the fabric until the wick is saturated. The upper end of the wick can then be lit and fuel will continue to be drawn up through the fabric as it is burnt off at the top.

A problem with this type of wick is it can take a long time (20 minutes) for the fuel to soak up the wick from base to tip.

Another problem is that fabric materials cannot generally withstand the temperatures produced by fuels such as ethanol. Ethanol is a preferred fuel in this application because:

• It combusts at a higher temperature, implying a lower fuel supply rate, and thus a smaller reservoir may be used for the same heat output, and flame life,

• it is derived from non-fossil fuel sources (it is a biofuel),

• it does not produce toxic carbon monoxide, unlike paraffin and

• it does not smell as strongly. Accordingly, it is an object of this invention to provide an improved wick for a fuel burner with improved flow characteristics and temperature resistance.

According to a first aspect of the invention there is provided a wick comprising a plurality of substantially inflexible members arranged such that channels formed between the peripheries of said members permit flow of fluid along said channels by capillary action.

By "channels" we mean any conduit of regular or varied cross section, possibly branching and / or converging, which permits fluid flow from one location to another.

According to a second aspect of the invention there is provided a wick comprising a substantially inflexible elongate member, defining an inner channel which permits the flow of fluid therealong by capillary action.

The construction of the wick from inflexible material allows materials with a high softening temperature (and hence high melting point) and low coefficient of thermal expansion to be considered. The inflexibility of the wick also allows design to a specific and invariant fuel flow rate, providing a predictable and consistent heat output ideal for creating the controlled environment required in horticultural applications. By using a capillary action along a substantially inflexible member, fuel passes from the reservoir end of the wick to the burner end much more quickly than with the fabric material wicks.

According to an embodiment of the invention, there is a plurality of said hollow members arranged such that channels formed by their peripheries permit the flow of fluid therethrough by capillary action.

Preferably, the members are constructed from a material with a higher melting point temperature than the temperature of burning ethanol. Preferably, the members are constructed from a material with a thermal expansion coefficient low enough so as not to impair the shape, and consequently function of said channels.

By using a material with a high softening temperature, and/or low thermal expansion coefficient the effects of the temperature of burning fuel on the performance of the device are minimal. Both melting and significant dimensional change are avoided with could potentially alter the flow characteristics of the device in use. Ideally, a material combining both of these characteristics, such as a borosilicate should be used. ,

According to a further embodiment of the invention, the members are parallel, and preferably straight. This provides the minimum distance from fluid reservoir to flame, and consequently permits the use of channels for capillary action to operate.

Preferably, the members are surrounded by a sheath, with fluid entry and exit points exposed, and may project from said sheath. The sheath acts to hold the wick together and form a protective casing for the possibly fragile members. Ideally the wick also comprises a location feature which abuts a feature of the fuel burner assembly of known type in order to locate the wick relative to a fuel reservoir and intended flame location. This feature could be an annular lip, and may provide sealing means in order to separate the flame region from the fuel reservoir.

According to a further embodiment of the invention, said members are elongate and circular in cross-section, and arranged in a hexagonal pattern so that channels are formed by the peripheries of three adjacent members. Preferably, the diameter of the members should be between 0.4, and 4mm, and ideally lmm, in order to provide a reasonable amount of capillary rise for a wick of 17- 170mm in length. If the wick is hollow, then ideally the diameter of the inner channel should be approximately 0.75mm.

Ideally, the wick should be sufficiently short with respect to the size of the channels to allow fluid passage by capillary action alone. According to a further aspect of the invention, there is provided a method for manufacturing a wick, comprising the steps of:

• providing a plurality of substantially inflexible members, either of solid cross- section or with channels therethrough.

• arranging said members so that at least part of their peripheries are in contact with one or more adjacent members.

• heating the members to a temperature at which the adjacent members fuse.

This method of manufacture, is advantageous in that it does not require adhesives, or mechanical joining means, and the entire assembly can be constructed simultaneously, and in a short space of time.

Preferably, a sheath constructed from the same material as the members is placed around them prior to heating and surrounds and adheres to them during the heating stage. Ideally, the members and sheath are constructed from a borosilicate, and heated to a temperature in the region of 675 - 68O⁰C for up to 6 hours.

A wick will now be described in detail by way of example and with reference to the accompanying drawings, in which:

Fig.l is a perspective view of a first wick in accordance with the present invention;

Fig.2 is a sectional view of the wick in Fig.l in situ in a fuel burner;

Fig.3 is a detailed end-view of the wick members and channels of Fig. 1 in the direction denoted by HI in Fig.2; Fig. 4 is a perspective view of some wick members of a second wick in accordance with the present invention; and

Fig.5 is a perspective view of a third wick in accordance with the present invention.

A wick 10 is designed to fit into a heater 11.

The wick 10 comprises a core 12 and a sheath 14 surrounding the core.

The core 12 comprises a plurality of elongate, substantially inflexible members 16, preferably manufactured from a borosilicate. The members 16 are circular in cross- section, and arranged in contact in adjacent rows. The rows are offset in a direction parallel to their orientation by a distance C equal to half the member diameter, d/2. Consequently closed channels 18 are formed by the perimeters at three adjacent members 16 which run the length of the core 12.

The sheath 14 is a hexagonal tube having open ends 22, 24. The sheath 14 is preferably manufactured from the same material as the core 12. The sheath 14 envelops the sides of the core 12, and comprises an upper annular flange 26. The inner periphery 30 of the sheath 14 is in contact with the outer layers of members 16 forming peripheral channels 20.

The heater 11 is of known type, and comprises a wick mounting member 28 and a fuel reservoir 32 with base 34. The wick mounting member 28 comprises a piece of sheet material with an aperture 29 to receive the wick 10.

The wick 10 is positioned such that the annular flange 26 rests on the wick mounting member 28, and the wick 10 projects through aperture 29, such that the lower end 22 of the core 12 is submerged in the fuel reservoir 32, and sits just above the base 34 of the heater 11. The positioning of the lower end 22 of the wick core 12 in the fuel reservoir 32 causes the fuel to be drawn up the channels 18, 20 by capillary action to the upper end

24 of the core 12. At this point, the fuel may be ignited, and the depletion of said fuel at end 24 causes more fuel to be supplied from the reservoir 32 providing a flame until the fuel reservoir 32 is depleted.

The inflexibility of the wick 10 provides a known dimension at channels 18, 20 which provides a predictable and consistent flow of fuel. Construction of the wick from borosilicate means that the wick can withstand the fuel combustion effectively indefinitely as the wick material will not burn off with use. Also, the heat generated by the flame will not affect the dimensions of the channels and consequently flow characteristics, as borosilicate has a low coefficient of thermal expansion and a high softening temperature relative to the temperatures encountered by the wick in burning of ethanol-based fuel.

In the example described herein, the wick length is 58mm, and circular members have diameter, d=lmm. Preferably the wick is 50-100mm long and 10-30mm in diameter.

The wick 10 is manufactured by packing the members 16 into a bundle inside the sheath 14. This assembly is then heated to a temperature proximate the softening temperature of the borosilicate which fuses the members 16 to each other and to the sheath 14. The wick is typically heated to around 675 to 680 degrees for about 5 hours to achieve the desired level of fusion.

Any material protruding from the end of the wick can then be machined or ground off if not desired.

Referring to figure 4, alternative members 116 are arranged substantially similarly to those in wick 10. Channels 118 are formed between the members 116 as per channels 18. The members 116 differ from the members 16 in that they define inner channels 150 running along their length. The inner channels 150 are dimensioned to draw fluid along their length in the same manner as the channels 118. As such, the flow rate through a wick utilising such members 116 can be increased.

Referring to figure 5, a wick 200 is shown comprising a core 212 and a sheath 214 which surrounds the core. The wick 200 is supported via an annular flange 226 on a wick mounting member 228 as per wick 10. A Viton gasket 227 is shown disposed between the flange 226 and the mounting member 226 in order to reliably seal the unit and prevent unnecessary evaporation of fuel.

The core 212 comprises a plurality of packed irregularly-shaped soda glass particles 260. The particles 260 are packed in a random order and fused to each other and the sheath 214 utilising the same manufacturing method as described above for the wick 10.

Due to the irregular nature of the particles 260, small channels are formed between them which in turn form channels which run the length of the wick. As such, capillary action of the fuel through these channels transports it to the head of the wick.

It should be noted that a particle size of less than 422 microns (i.e. of a size that passes through a 40-mesh sieve) and preferably between 250 and 420 microns (between a 40- and 60-mesh sieve) works well.

Many variations of the above embodiments fall within the scope of the present invention. For example, the material used for the wick need not be borosilicate or soda glass, but may be of any material that is capable of sustaining both the channels and the flame under working temperatures. For example, copper or steel, or simply plain glass could be used.

The particles in wick 200 need not be irregularly-shaped, but may be spheres or other shapes that form channels when packed.

Claims

1. A wick comprising a plurality of substantially inflexible members arranged such that channels formed between the peripheries of said members permit flow of fluid along said channels by capillary action.

2. A wick comprising a substantially inflexible elongate member, defining an inner channel which permits the flow of fluid therealong by capillary action.

3. A wick according to claim 2, in which a plurality of said members are arranged such that channels formed by the peripheries of said members permit the flow of fluid therethrough by capillary action.

4. A wick according to claim 1 in which said members are elongate.

5. A wick according to any preceding claim in which said members are parallel.

6. A wick according to any preceding claim in which said members are straight.

7. A wick according to any preceding claim in which said members are circular in cross-section.

8. A wick according to claim 7 in which the members are arranged such that the centres of the cross-sections of three adjacent members lie on the apices of a triangle and a channel is formed by the peripheries of the three adjacent members.

9. A wick according to claim 7 or 8 in which the diameter of the members is between 0.4mm and 4mm.

10. A wick according to claim 9 in which the diameter of the members is lmm.

11. A wick according to claims 2 or 3 or any of claims 5 to 10 when dependent on claim 2 or 3 in which the diameter of the inner channel is approximately 0.75mm.

12. A wick according to claim 1 in which the members are particles.

13. A wick according to claim 12 in which the members are substantially spherical.

14. A wick according to claim 12 or 13 in which the particles are smaller than 422 microns.

15. A wick according to claim 14 in which the particles are sized between 250 and 420 microns.

16. A wick according to any preceding claim in which said members are surrounded by a sheath, leaving fluid entry and exit points open.

17. A wick according to claim 16 in which said members extend beyond a first end of the sheath.

18. A wick according to claim 17 in which said members extend beyond a second end of the sheath, opposite the first end.

19. A wick according to any of claims 16 to 18 in which said sheath comprises a location feature which abuts a feature of a fuel burner assembly of known type in order to locate the wick with respect to the fuel source and intended flame location.

20. A wick according to claim 19 in which the location feature is an annular Hp.

21. A wick according to claim 19 or 20 in which the location feature comprises flexible sealing means between it and said fuel burner assembly.

22. A wick according to any preceding claim in which the wick length is sufficiently low in order to allow the passage of the fluid through the wick by virtue of capillary action alone.

23. A wick according to any preceding claim in which the wick length is in the range of 17- 170mm.

24. A wick according to any preceding claim in which said members are constructed from a material with a higher softening temperature than the temperature of burning ethanol.

25. A wick according to any preceding claim in which said members are constructed from a material with a higher melting temperature than the temperature of burning ethanol.

26. A wick according to any preceding claim in which said members are constructed from a material with a thermal expansion coefficient low enough so as not to impare the shape, and consequently function of said channels when operating at the temperature of burning ethanol.

27. A wick according to claim any preceding claim whereby said members are constructed from a borosilicate.

28. A method for manufacturing a wick, comprising the steps of:

• providing a plurality of substantially inflexible members,

• arranging said members so that at least part of their peripheries are in contact with one or more adjacent members,

• heating the members to a fusion temperature at which the adjacent members fuse.

29. A method for manufacturing a wick according to claim 28 in which a sheath being constructed from the same material as said members is placed in contact, surrounding said members and adheres to them during said heating process.

30. A method for manufacturing a wick according to claim 28 or 29 in which the material is borosilicate and the fusion temperature is in the region of 675-680⁰C.

31. A method for manufacturing a wick according to any of claims 28 to 30 comprising the step of cutting any excess material projecting from the sheath.