GB2125160A - Air supply for stoves - Google Patents

Abstract

A cooking and/or heating stove, particularly for use in underdeveloped countries, comprises a cylindrical core 1 having a cone-shaped upper portion 2 and a grating 9 dividing the core 1 into an upper combustion chamber 10 and a combustion air chamber 11. Air is drawn into the combustion chamber 11 either by natural draft through apertures 5 in a bottom plate 6, or by forced draught from an air pump 25 operated by a handle 36. A valve operated by a lever 15 controls the flow of air into the chamber 11 and enables air to be taken either naturally or from the pump, or both. <IMAGE>

Description

SPECIFICATION Cooking and/or heating stove This invention relates to a cooking and/or heating stove. The stove of the invention is primarily, although not exclusively, intended for use in underdeveloped countries and, as such, will be capable of burning a wide variety of fuels.

For milleniums primitive stoves made of clay, mud or metal have been used and it is quite evident that despite some improvement in insulation little development has been made in efficiency or their ability to exploit to the full the use of expendible material as fuel.

Many examples of these stoves were displayed at a recent United Nations Conference and Exhibition on "New and Renewable Sources of Energy" held in Nairobi. All worked on the same, slow-burning, principle and were obviously at the mercy of the elements. Dry timber was an essential basic fuel and improvements in performance were claimed where charcoal or composite briquettes were used. These materials are costly to those on little, or no income at all.

Even the more improved versions required constant fanning by hand or the assistance of kerosene if there was no appreciable wind and if damp material was used the resulting smoke would be unacceptable.

The present invention seeks to provide a cooking and/or heating stove which is able to burn a wide variety of fuels and in a wide variety of wind conditions.

According to the invention there is provided a cooking and/or heating stove comprising a generally cylindrical container whose axis is approximately vertical in use, a grating positioned in said container so as to define an upper combustion chamber, open at the top, and a lower air chamber into which air for combustion is drawn, a hand-operated air pump and valve means for allowing combustion air to be drawn into said air chamber either from the exterior by natural convection, or from said air pump.

In an embodiment of the invention the valve means is operable between two positions: (i) a first position in which the inlet to the air chamber for natural draught is blocked while the inlet for pumped air is open; and (ii) a second position in which the inlet to the air chamber for natural draught is open while the inlet for pumped air is blocked.

Preferably the valve allows a variety of intermediate positions, between the above two extreme positions, in which the two inlets are partially opened, in order to cater for a variety of different conditions.

In an embodiment of the invention the inlets to the air chamber are such as to allow natural draught to enter (when the valve means allows) through one or more apertures in the bottom of the cylindrical container. Pumped air is passed to an annular gallery surrounding the container in the area of the air chamber, and a plurality of apertures are provided between the gallery and the air chamber, such apertures being regularly spaced about the circumference of the container in order to provide an even distribution of pumped air into the air chamber.

In order that the invention may be better understood an embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a cross sectional side view of one embodiment of a cooking stove according to the invention; Figure 2 is an underside view of the cooking stove of Figure 1; Figures 3A and B are plan and side views respectively of the grating used in the cooking stove of Figure 1; and Figure 4 is a plan view of the rotor forming part of the valve means used in the cooking stove of Figure 1.

Referring to the drawings, the stove comprises a cylindrical core 1 for example of mild steel which has a cone-shaped upper portion 2. Mounted on the top of the core 1 is a top plate 3 having a raised circumferential edge 4 and an aperture 35.

The lower end of the core 1 is closed by a bottom plate 6 having four approximately sector-shaped apertures 5 for a purpose explained hereafter. An outer casing 7 of rectangular shape surrounds the core 1 and has integral legs 8 to support the core 1 in an upright position during use.

A grating 9, shown in detail in Figure 3 is mounted across the inside of the core 1 and defines an upper combustion chamber 10 and a lower air chamber 11 into which latter air for combustion is drawn. Material to be burnt is placed on top of the grating. The grating is supported on an upstanding boss 12 to which it is attached by a bolt 13. The boss forms part of a cross shaped rotor 14, shown in detail in Figure 4.

The rotor 14, and hence the grating 9, is rotatable about a vertical axis by 450 by means of a lever 15, attached to a further boss 1 6 extending downwardly from the rotor 14 and rotatably mounted in a central aperture in the bottom plate.

As will be clear from Figure 3B, the grating has a downwardly extending skirt portion 1 7 which has four projections 18 mutually spaced apart by 900.

Each projection 1 8 is of the same angular extent as the space between adjacent arms 1 9 of the rotor 14 and, when the grating and rotor are bolted together as shown in Figure 1, each projection 1 8 fits within a respective space between two adjacent arms 19, thus defining four apertures 20 spaced apart by 900. Co-operating with these apertures, as will be explained below, are four similarly-shaped and spaced apart apertures 21 in the core 1.

Mounted on the left hand side of the casing 7 (when seen in Figure 1) is a boss 22 in which is rotatably mounted a shaft 23 carrying, at one end, a pinion 24 and, at the other end, an impeller 25.

The impeller 25 is generally disk shaped and is equipped with a plurality of radially extending upstanding blades 26. The impeller 25 is turned by hand by means of a handle 36 attached to a gear wheel 27 rotatably mounted on the casing 7 and in mesh with the pinion 24. Turning of the handle 36 causes the impeller 25 to rotate and draw air from the exterior of the casing via arrows E, F through a hole (not shown) in that side of the casing 7 opposite to the impeller, thence around the exterior of the core 1 and into a chamber 28 formed by a partition 29 via arrows C, D. The resultant air flow across the core 1 has an insulating effect on the core and preheats the input air to the impeller giving improved efficiency.

Air in chamber 28 is passed into a generally annular chamber 37 which surrounds the core 1 at the level of the apertures 21.

The stove is used by piling material to be burned onto the grating 9 and setting it alight, or by feeding already-ignited material through aperture 35 in the top plate. Once the stove is burning, further fuel may be periodically fed through the aperture 35 and the tapered top section of the core 1 acts to facilitate the flow of smaller fuel to the grate while retaining larger pieces as a conglomerate at the top. Depending upon the prevailing conditions, air for combustion can be supplied either naturally or by forced draught, or both. The choice of the mode of operation is dictated by the position of the lever 1 5 which in its extreme positions, 450 apart, causes the arms 1 9 of the rotor 14 to either completely block the apertures 5 in the bottom plate of the core 1 or to leave them completely open.The apertures in the bottom plate are oriented such that, in the first (blocked) position the arms 19 of the rotor 14 lie directly over the apertures 5, thus effectively closing them off. In this same position, the apertures 20 formed between the skirt of the grating and the rotor are in registry with the apertures 21 in the core 1, thus allowing air from the annular chamber 37 to enter the air chamber 11. In the second (open) position, the arms of the rotor lie over the lands between apertures 5 thus leaving the apertures 5 fully open and allowing air for combustion to be drawn into the chamber 11 through the bottom plate 6 by natural draught. In this same position, the projections 1 8 on the skirt of the grating block the apertures 21 in the core, thus closing off the annular chamber 37.The two positions of the lever 1 5 are illustrated by letters A and B in Figures 1 and 2 of the drawings, letter A representing the forced draught mode of operation, and the letter B representing the natural mode of operation.

The stove can also be used at intermediate positions of the rotor, depending upon the particular circumstances of use.

It has been found that the stove described above is capable of burning a very wide variety of fuels including domestic and other combustible rubbish, unseasoned and damp wood or horticultural and agricultural waste. Control of heat intensity can be readily achieved by varying the natural or forced air flow into chamber 11 by moving the lever 15, thus enabling fairly fine control of the heat output for use when cooking.

Control of heating intensity is also determined by the rate of rotation of the impeller -- the faster the hotter. The rotor control wouid be employed primarily in the natural draught position for passive conditions when the core is well stocked with ignited fuel - slow cooking. The tray-like top plate 3 of the stove is convenient for placing a cooking vessel or vessels to be heated.

Ash removal is achieved by agitating the lever 1 5 backwards and forwards which causes ash and unburnt debris to fall out through the apertures 5 in the bottom plate.

During use the action of the core is such as to produce an area of intense concentrated heat which ensures that complete combustion takes place. This is fueled by a tapered gravity feed which forms the upper core body.

An example of possible sizes is 10" overall height, the casing 7 being approximately 12" square with the area available for cooking vessels being about 9" in diameter.

Claims (5)

1. A cooking and/or heating stove comprising a generally cylindrical container whose axis is approximately vertical in use, a grating positioned in said container so as to define an upper combustion chamber, open at the top, and a lower air chamber into which air for combustion is drawn, a hand-operated air pump and valve means for allowing combustion air to be drawn into said air chamber either from the exterior by natural convection, or from said air pump.

2. A stove according to claim 1 in which said valve means is operable between two positions: (i) a first position in which the inlet to the air chamber for natural draught is blocked while the inlet for pumped air is open; and (ii) a second position in which the inlet to the air chamber for natural draught is open while the inlet for pumped air is blocked.

3. A stove according to claim 2 in which said valve means is operable to define a variety of intermediate positions between said first and second positions in which the two inlets are both partially opened in order to cater for different conditions of use.

4. A stove according to either one of claims 2 or 3 wherein the inlets to the air chamber are such as to allow natural draught to enter (when the valve means allows) through one or more apertures in the bottom of the cylindrical container, while pumped air, generated by said air pump, is passed to an annular gallery surrounding the container in the area of the air chamber, a plurality of apertures being provided between the gallery and the air chamber, such apertures being regularly spaced about the circumference of the container in order to provide an even distribution of pumped air into the air chamber.

5. A cooking and/or heating stove substantially as hereinbefore described with reference to the accompanying drawings.