NZ206115A - Solid fuel stove; combustion chamber exit located to give extended gas circulation in stove - Google Patents

Description

• / 206115^ 20611c 2092 ll NEW ZEALAND PATENTS ACT 1953 N.Z. PATENT OFF ICE 300CT1984 RECEIVED No.: 206115 Date: 1 November 1983 No.: 206116 Date: 1 November 1983 No.: 209212 Date: 14 August 1984 COMPLETE SPECIFICATION "Improvements in or Relating to Stoves" iLEt MASON & PORTER LIMITED a company incorporated under the laws of New Zealand of Mt Wellington Highway, Panmure, Auckland, New Zealand hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: _ 1 _ a This invention relates to stoves and has been devised particularly though not solely for use as a wood burning space tO O heating stove. <35 h-* It is an object of the present invention to provide a stove O which will at least provide the public with a useful choice. Accordingly the invention consists in a stove including a combustion chamber, an exit for combustion gases leading from 1 said combustion chamber, a fuel loading opening in said C: combustion chamber, a closure for said opening, said closure including a transparent panel, an air admitting means through — which air is supplied to the combustion chamber, a flue ^ connection through which products of combustion are conveyed om the stove to a flue,«-a—aombuution u h jun b m—exit from—ttre=" o #1 oombuatiuii diorobai^" a passageway between said combustion chamber exit and said flue connection, said air admitting means comprising an air inlet in a lower part of said stove leading to a duct means, the duct means including an upper duct passing along an upper part of said combustion chamber adjacent said d(iClii»u}£ loading opening and including air transfer opening or j^oitinps ■ Sd'i<L arranged so that air fromfair duct is passed into said ^ combustion chamber through said air transfer opening or openings b<meL y ' to pass downwardly over the transparent ^op-feion-of said door to the combustion zone of said combustion chamber.

To those skilled in the art to which the invention relates many changes in construction and widely differing embodiments Q / S and oppileotiowg of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

One preferred form of the invention will now be described *^\with reference to the accompanying drawings in which: r*. • 28JAWI987 Figure 1 is a rear perspective sketch of an interior view ■ showing the path of combustion gases; Figure 2 is a cross sectional drawing of a stove on the line II-II (Figure 1) according to the invention; Figure 3 is front perspective view of the stove shown in Figures 1 and 2; Figure 4 is a scrap view showing one way of providing a by pass opening according to a preferred form of the invention; Figure 5 is a diagram of a control system to provide a by pass during low fire conditions, and Figure 6 is as Figure 2 but showing an alternative combustion chamber exit.

Referring to the drawings, a stove according to the invention is constructed as follows: A combustion chamber 1 is provided within a casing 2, some walls of the casing also acting as walls of the combustion chamber. A fuel loading opening 3 is provided in the combustion chamber 1 and through which fuel is admitted to the combustion chamber and a closure 4 having a transparent panel 5 is provided.

The upper surface 6 of the combustion chamber 1 may have duct 32 may have openings therein leading respectively to the combustion chamber 1 and the part of a passageway 12 in which, under suitable operating conditions, secondary combustion may occur. The surface 10 of the combustion chamber 1 is separated from the upper surface 11 of the casing 2 by a space providing part of the passageway 12 leading from the combustion chamber exit 20 to a flue connection 13* A divider 14 is provided irvner and/or -«^e*1face 9 of the 206115 having an aperture 15 in which a manually operable door 16 operates to provide a bypass for combustion gases e.g. during lighting up.

Since some difficulty may be encountered in maintaining a flue temperature which is high enough to inhibit the deposit of creosote and/or other such material in the flue when the stove is set for low fire (i.e. low heat output) conditions, the present invention envisages the provision of means to provide a direct by pass to the flue for a proportion of the combustion products at least under low fire conditions. Accordingly the door 16 preferably does not completely close the aperture 15 so that there is a permanent gap through which some products of combustion can pass even in normal operation. In the preferred form therefore, the by pass door 16 is arranged to leave an opening 17 (Figure 4) leading from the aperture 15 even when the door is in the fully closed position. As an alternative, the door 16 may be provided with finger openings 18 which pass right through the door 16. These finger holes may be used to remove the door when access to the flue is required, the hinges being hooks adjacent the lower edge of the aperture 15 on which the door 16 rests by gravity. As a further alternative a stop could be provided to prevent the door 16 from fully closing. A still further alternative is described below.

The main exit for combustion gases is through the combustion chamber exit 20 from the combustion chamber 1. The exit 20 is provided in a lower part of the combustion chamber preferably at about the level of burning fuel and lying between one-quarter Zb6 1 p Xo and three-quarters of the height of the combustion chamber 1 and preferably lying below a plane at the half height of the combustion chamber. Thus the exit 20 is preferably in a lower part of the combustion chamber rather than being in an upper part thereof.

The combustion chamber exit 20 is shown in the drawings to be below the half height level 21. The combustion gases could if desired pass directly through exit 20 to the flue connection 13 but preferably baffles 22 (figure 1) are provided with the baffles 22 engaging with the rear wall 23 of the casing 2. If desired divider 14 and/or baffle 22 may be partially formed as wings or rib extensions extending from adjacent parts e.g. baffles 22 may be provided as wings extending from the back 23 with appropriate joint lines. Thus the flue gases leave the combustion chamber 1, pass through the exit 20 and then pass to each side of the baffle 22 and forwardly over the hot upper surface 10 into the passageway 12 as shown by the lines 24 and a barrier 25 is provided between the two baffles 22 and extending to the rear wall. In this way a flue gas path of considerable length is provided which assists in the transfer of heat to the casing and consequently to the room being heated. To provide air admission means to admit combustion air to the combustion chamber 1 a duct 32 is provided and the duct 32 preferably is in the form of four tubes in the form of a rectangle, the inner faces 33 of the tubes defining the loading opening 3 leading into the fire box or combustion chamber. Part of the side 3U of the lower transverse tube of the duct 32 may be sloped as shown 206 11 106 i 20921 to assist free flow of down coming air in the combustion chamber 1 as shown by the arrow 35. Additionally primary air admission holes may be made in the side 34. In a lower front face of the duct is provided an air inlet comprising an opening or preferably a plurality of openings 37 leading to ambient atmosphere and it will be seen that the ducting is such that at least some of the air will pass from the openings 37 into the interior of the duct and up both sides 38 of the ducting to air transfer apertures 39. The provision of the two vertical tubes 38 of the duct 32 assists in giving a balanced or symmetrical air flow. The duct 32 is exposed in part to the combustion chamber so that the incoming air is heated before admission to the combustion chamber. The apertures 39 are arranged so that air from the duct 32 passes through the air transfer holes 39 and passes down the interior surface of the transparent panel 5 of the door 4, as may be seen by the arrowed path 35 in Figure 2.

To assist in controlling the air flow, a pivotal flap 40 is provided which is controlled by a manual lever 41 and this is connected through a bi-metal element 42 and a link 43 to an arm Qa 44 connected to a pivot rod 45 to which the flap 40 is fixed.

" Although not shown, bi-metal »42 is covered by an outer covering nKfH ' to shield the bi-metal element from draughts. The arrangement is such that even though the manual lever 41 is moved fully in a direction which diminishes the combustion air supply, the flap 40 will not move to a completely closed position if the stove is cold. Also the flap 40 has one or more bleed holes (not shown) 20611 2ma to provide sufficient air under low fire conditions. However as the stove warms up, the bi-metal strip 42 is modified in its disposition to substantially completely close the holes 37• When the stove is set for maximum output with the flap fully open, should the temperature rise excessively, the bi-metal element 13 will deflect to reduce the flap opening and thus diminish the air supply to reduce the stove temperature.

It will be seen that in intermediate settings of the lever the bi-metallic strip will respond to changes in stove temperatures by controlling the air supply and thus regulating the heat output of the stove. In this way some automatic control of air admission is provided.

The main combustion exit may alternatively be positioned at position 27 shown in Figure 6 and the air flow is then illustrated by arrow 28.

At least some observations we have made lead us to believe that a considerable proportion of the products of combustion rise towards the top of the combustion chamber, move forwardly and down again mixing with fresh air admitted from duct 32, before escaping through the exit 20 a proportion escaping directly through the exit 20 and into the passageway and a further proportion exit to the flue connection 13 through the opening 17 if the latter is provided. If holes 7 are provided some gase^s pass directly into passageway 12. It will be clear that there will be considerable mixing of air with the products of combustion enhancing the possibilities of complete combustion of unburnt gases.

As a further alternative in providing a by pass during low fire conditions a linkage is provided, arranged so that when the flap 40 is in its last phase of movement before being closed, the door 16 (preferably capable of fully closing the aperture 15) is partially opened from its fully closed position. Such a linkage is shown diagramatically in Figure 5 in which a manual control lever 50 is pivoted at 51 and is connected through a bi-metal member 52 and a link 53 to a lever 54 pivoted at 55 to open and close the air flap 40. A further link 56 is connected to an arm 57 which opens door 16 as flap 40 closes. To provide opening of olosun»- 16 only during later movement of flap 40 toward its closed position and to allow opening of the door for lighting up purposes5a lost motion device can be provided e.g. between arm 57 and link 56. The bi-metal _ s arranged to may be replaced by bell crank arm 58 and link 59 so that lever 50 directly controls door 16.

Although designed for burning wood on the floor of the combustion chamber, coal may be burnt by providing a grate with if necessary some air entry means which supplies air to below that grate.

At least one or more of the above constructions has the advantage that a tortuous path is provided for at least a significant proportion of the products of combustion enabling reasonable transfer of heat from such gases to the casing. Additionally because the outlet 20 is low down at the rear of the fire, some restraint of the rate of burning is achieved so o©r close flap 40 as the bi- heats up. If desired the link 56 2061 1 J; 20611 & 209212 that a slow combustion stove is provided. Further if the holes 7 are not provided most of the products of combustion which pass to the top of the combustion chamber are able to pass out through outlet 20 only after passing again over the top of the firebed, with admission of further air thus tending to reduce smoke emission and increasing efficiency by increasing the amount of combustible gases being burnt. Secondary combustion will probably take place in the top of the combustion chamber, or in the passageway 12 or both, and this is likely to be & koleS r enhanced by the provision of the •feol-e- 7. The secondary ' combustion increases the possibility of otherwise unburnt gases (^) being burnt to increase efficiency and reduce smoke emission.

One advantage of this construction in the preferred form is that the air admission is readily controlled and in the event of there being any momentary down draught it will be unlikely that smoke will pass from the fire out through the air openings 37 into the room. Also if the fire smokes heavily e.g. during lighting up when the flue is cold so that inadequate draught is created, there is little likelihood of the smoke flowing down the vertical parts 38 of the duct and out of the openings 37.

In addition where holes in the upper face 8 are provided <r*\ heated air is drawn into part of passageway 12 by the flue 'kB? draught to further facilitate or promote secondary combustion in that part of passageway 12.

The permanent by pass aperture 15 at least under low fire conditions: 1. Assists in improving draught. m\ 2. Assists in keeping flue temperatures up during low heat (low fire) conditions in order to reduce deposit of creosote and other such materials. 3. Hot gases passing through the opening will assist in igniting any unburnt gases passing from passageway 12.

Claims (13)

1. , ^ V , •• " - ... 1- •-•*•.•;&;2'16115 206116 209212;WHAT WE CLAIM ISi;1. A stove including a combustion chamber, an exit for combustion gases leading from said combustion chamber, a fuel loading opening in said combustion chamber, a closure for said opening, said closure including a transparent panel, an air admitting means through which air is supplied to the combustion chamber, a flue connection through which products of combustion are conveyed from the stove to a "-rnHifti rn nhimtr'r nrii t iKl* rnm ^mjannt.i fta -nin ninK^ a passageway between said combustion chamber exit and said flue connection, said air admitting means comprising an air inlet in a lower part of said stove leading to a duct means, the duct means including an upper duct passing along an upper part of said combustion chamber adjacent said loading opening and including air transfer opening or openings arranged so that air from said duct is passed into Of said combustion chamber through said air transfer opening or openings to pass downwardly over the transparent pBrtio»of said 9 door to the combustion zone of said combustion chamber. o
2. 2. A stove as claimed in Claim 1 wherein said air admitting d means are disposed in a lowerl-fcwfee- and said duct means includes two side ducts connecting said lower duct to said upper duct.
3. 3. A stove as claimed in Claim 2 wherein said side ducts are disposed one on each side of said loading opening.
4. 4. A stove as claimed in any one of the preceding Claims wherein parts of the combustion chamber also form parts of a casing, wherein said passageway is formed by the upper surface of the combustion chamber being spaced below the upper surface of the casing to provide a space between these two sujr£a.ces, S ti - n - X 2SJAH 216115 206116 209212 parts of the casing, a divider and one or more baffles and/or barriers being provided between said combustion chamber exit and said flue connection so that the products of combustion passing along said passageway take a tortuous path from said combustion chamber to said flue connection.
5. 5. A stove as claimed in Claim 4 wherein said baffles comprise a pair of spaced apart baffles mounted between a divider separating said combustion chamber from parts of said passageway and a back wall of said casing and said barriers comprise a single barrier connecting the lower ends of said baffles and being mounted between said divider and said rear wall, the construction and arrangement being such that said passageway is divided into two parts between said combustion gases exit and said space.
6. 6. A stove as claimed in Claim 5 wherein openings are provided in the upper surface of said air admitting means and/or said divider of the combustion chamber said openings leading directly to said passageway.
7. 7. A stove as claimed in any one of Claims 4 to 6 wherein said divider extends downwardly rearwardly from said upper surface of said combustion chamber and includes a bypass aperture leading to said outlet for combustion gases, said bypass aperture having a bypass door manually operable to open the bypass aperture during lighting up of the stove.
8. 8. A stove as claimed in Claim 7 wherein said bypass door is formed or controllable so that at least during low fire conditions in said combustion chamber said bypass aperture is not completely closed off but there exists direct access between - 12 - 2n6115 2(16116 209212 said combustion chamber and said flue7for a proportion of the combustion gases. ws
9. 9. A stove as claimed in any one of the preceding claim^said air admitting means includes an air control flap, a manual control means for said air control flap and bi-metal element control means arranged to adjust the air supply to said combustion chamber according to the setting of said manual control means and according to the temperature of the stove.
10. 10. A stove as claimed in Claim 9 wherein said bi-metal element is mounted on the outside of the stove adjacent to the combustion chamber and covered with a cover to shield the bi-metal element from draughts.
11. 11. A stove as claimed in any one of the preceding Claims -fro- Q1 ■ wherein bleed holes are provided in said air admitting means to permit sufficient air to enter therethrough to maintain a fire under low fire conditions.
12. 12. A stove as claimed in any one of the preceding claims wherein said combustion chamber exit is disposed at about the level of burning solid fuel and within a space bounded by horizontal planes lying between one-quarter and three-quarters of the height of the combustion chamber.
13. 13. A stove when constructed arranged and operable substantially as herein described with reference to and as illustrated by the accompanying drawings. ' (k SON r/'/oU DATi'D T:'!3 1 b/'Y OF 'U. f\ f ;■> •• if t- --k , O /-.• J. R;\ u' i>r)M - 13 - • •• ? •••'? .••TLJCAfJT