US20080276924A1

US20080276924A1 - Wood burning stove

Info

Publication number: US20080276924A1
Application number: US11/801,711
Authority: US
Inventors: Lowell A. McMillan
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-05-11
Filing date: 2007-05-11
Publication date: 2008-11-13

Abstract

A wood stove defining an upper combustion chamber and a lower fire box having two inwardly and downwardly angulated opposed fuel chutes for gravitational feeding of fuel to the fire box for extended burning. A rectilinear air channel spaced apart from a back wall of the stove, and structurally attached thereto, provides a channel for combustion products and byproducts to pass from an upper inner portion of the stove adjacent a chimney port downwardly to the fire box to pass through the primary fire zone for more complete combustion of the combustion products and combustion byproducts to enhances heat production and reduce wasting of smoke generating particulates and vapors.

Description

II. BACKGROUND OF INVENTION

IIA. Related Applications
There are no applications related hereto heretofore filed in this or in any foreign country.
IIB. Field of Invention
This invention relates to stoves and furnaces, and more particularly to a stove having a downdraft air feed and a fuel supply hopper.
IIC. Background and Description of Prior Art
Combustion is the rapid oxidation of fuel with the release of heat and light. Byproducts of combustion are vapors, including partially combusted fuel, and carbon particulates that are wasted to the atmosphere.
Combustion occurs in two stages. First, volatile gases are liberated from the fuel. Second, the volatile gases are oxidized when they are ignited in the presence of oxygen. The heat released in the oxidation liberates more volatile gasses from the fuel. Ignition of the gasses leads to more oxidation which generates more heat. The process continues so long as there is fuel and oxygen.
Oxidation only occurs when the temperature is high enough to ignite the volatile gasses. In a stove where solid fuels are combusted, temperatures are sufficiently high to ignite the volatile gasses only in a limited area known as the primary fire zone which is the area in a fire where the flame is blue in color. Above, below, and adjacent the primary fire zone temperatures are not sufficient to ignite the volatile gasses, leading to incomplete combustion.
Incomplete combustion generates large quantities of carbon particulates and vapors that are wasted to the atmosphere. Carbon particulates and vapors are the “building blocks” for smoke. The more particulates and vapors released, the more dense the smoke. Conversely, complete combustion of the volatile gasses generates fewer carbon particulates, fewer vapors and less smoke while increasing the efficiency of the stove and increasing heat generation.
Complete combustion occurs when the temperature is high enough to ignite all the volatile gasses and hydrocarbons for a sufficient amount of time for ignition and oxidation to occur. One method to increase the percentage of combustion is to “re-burn” the combustion products by directing the combustion products back into the primary fire zone where the temperature is the highest and where ignition of the volatile gasses, vapors and carbon particulates occurs.
Air typically moves into the primary fire zone from below or laterally thereto because the heat generated by the oxidizing fuel causes gaseous expansion in and above the primary fire zone. The rising heat and gasses create updrafts. As the heat and gasses move upwardly a low-pressure area is created below the fire into which air is drawn to further feed the fire. Commonly this air enters the low-pressure area through adjustable vents defined in a bottom portion of the stove. Adjusting the air flow into the stove by opening and closing the vents regulates the rate of fuel consumption, by limiting the amount of oxygen available for oxidizing the volatile gasses.
Prior art discloses various methods and apparatus to circulate air into the primary fire zone of a stove including electrically powered and mechanically powered fans as well as strategically positioned air vents. Unfortunately, known methods and apparatus use fresh air rather than combustion products. Further, known methods and apparatus require moving parts and energy sources, such as electricity, which makes such apparatus prone to break downs, operating inefficiencies, needing regular maintenance, and causing higher manufacturing costs.
My stove overcomes these drawbacks by providing a wood burning stove having a lower fire box, an upper inverted triangular combustion chamber and a re-burner channel communicating therebetween. One end of the re-burner channel is adjacent an exhaust port in a top portion of the combustion chamber, and the opposing end is in the fire box adjacent the primary fire zone.
When heated combustion products rise upwardly from the primary fire zone they cool by being removed from the fire. This cooling is accentuated by the inverted triangular shape of the combustion chamber where the volume inside the stove proximate to its top portion is greater than the volume proximate to the fire box. After the somewhat cooled combustion products, including gasses, carbon particulates and vapors, rise into and collect in the upper portion of the combustion chamber, the combustion products must pass outwardly through an exhaust port which has an orifice smaller than the top of the stove. Alternatively, the combustion products must pass outwardly through orifices communicating with the re-burner channel.
The entry orifices to the re-burner channel cause a venturi effect where higher pressure inside the combustion chamber forces the combustion products through the smaller orifices at a higher velocity. After the combustion products pass through the orifices the venturi effect dissipates and the combustion products cool further because pressure and velocity have decreased. The cooled combustion products move downwardly through the re-burner channel as additional heated and fast-moving combustion products enter the re-burner channel at its top portion, and as the fire the fire box sucks air from below to continue oxidizing the volatile gasses liberated from the solid fuel. The downwardly moving combustion products in the re-burner channel exit the re-burner channel at its bottom end and re-enter the fire box adjacent below the primary fire zone and are drawn into the primary fire zone where temperatures are the highest and ignition and oxidation is ongoing. The result is an additional portion of the combustion products are combusted by passing through the primary fire zone more than once which decreases the amount of these materials being wasted to the atmosphere. The process also recycles previously heated air which increases heat generation.
My stove is small, carries a fuel supply for extended burning time, generates high heat and re-burns air and combustion products to more completely combust fuel providing a more efficient, long burning, near smokeless and high heat generating wood burning stove.
The configuration of my stove with its inverted truncated triangular shape with gravity powered fuel chutes opening to the top and the absence of fuel doors that pivot outwardly from the stove also make my stove more user friendly for persons who may have physical disabilities, such as being confined in a wheelchair. The absence of an outwardly swinging fuel door allows persons in wheel chairs to approach the stove, fuel the fire and tend the fire without having to navigate around a hot open door, and risk burning fuel falling out of the stove.
My invention does not reside in any one of the identified features individually but rather in the synergistic combination of all of its structures, which give rise to the functions necessarily flowing therefrom as hereinafter specified and claimed.

III. SUMMARY

My wood stove generally provides a peripherally defined stove body having a lower fire box and an upper inverted triangular combustion chamber with two inwardly and downwardly angulated fuel chutes therein. A re-burner channel communicates between an upper portion of the combustion chamber and the fire box and moves combustion products from the combustion chamber back to the fire box for re-burning.
In providing such an apparatus it is:
a principal object to provide a wood burning stove having a channel communicating between an upper combustion chamber and a lower fire box for combustion products to move downwardly from the combustion chamber back into the fire box for re-burning.
a further object to provide such a stove having a gravity powered feed system for extended burning time that requires infrequent operator attention.
a further object to provide such a stove that wastes less incompletely burned combustion products to the atmosphere.
a further object to provide such a stove that is more fuel efficient.
a still further object to provide such a stove that is handicap operable and handicap accessible.
a still further object to provide such a stove that is of new and novel design, of a rugged and durable nature, of simple and economic manufacture and one that is otherwise well suited to the uses and purposes for which it is intended.
Other and further objects of my invention will appear from the following specification and accompanying drawings which form a part hereof. In carrying out the objects of my invention it is to be understood that its structures and features are susceptible to change in design and arrangement with only one preferred and practical embodiment of the best known mode being illustrated in the accompanying drawings and specified as is required.

IV. BRIEF DESCRIPTIONS OF DRAWINGS

In the accompanying drawings which form a part hereof and wherein like numbers refer to similar parts throughout:

FIG. 1 is an isometric back, top and left side view of my wood stove.

FIG. 2 is a reduced orthographic back view of the stove of FIG. 1.

FIG. 3 is a reduced orthographic front view of the stove of FIG. 1.

FIG. 4 is an orthographic left side view of the stove of FIG. 1.

FIG. 5 is an orthographic right side view of the stove of FIG. 1.

FIG. 6 is an orthographic top view of the stove of FIG. 1 with the fuel chute covers removed.

FIG. 7 is an isometric partial cutaway back, top and left side view of the stove of FIG. 1.

FIG. 8 is an orthographic left side cross section view of the stove of FIG. 1, taken on line 8-8 thereon, showing the interior of the stove and the circulation of combustion products through the air re-burner channel.

FIG. 9 is an orthographic front cross section view of the stove of FIG. 1, taken on line 9-9 thereon, showing the fuel chutes, the inflow orifices to the re-burner channel and the rectilinear opening at the bottom of the re-burner channel within the fire box

V. DESCRIPTION OF PREFERRED EMBODIMENT

As used herein, the term “bottom”, its derivatives, and grammatical equivalents refers to the portion of my stove that is closest to a supporting surface such as a floor. The term “top”, its derivatives, and grammatical equivalents refers to the portion of the stove that is most distant from the supporting surface. The term “outer”, its derivatives, and grammatical equivalents refers to a side portion of the stove as opposed to the laterally medial portion of the stove.
My wood stove is constructed of sheet steel with welded seams and provides a peripherally defined stove body 10 formed by a lower rectilinear fire box 11, an upper combustion chamber 12 having an inverted truncated triangle shape with two angulated fuel chutes 28, 35 therein, and a re-burner channel 13 communicating between the combustion chamber 12 and the fire box 11.
The fire box 11 has a front 15, a back 16, a bottom 19 and two sides 17, 18 that are welded together at adjoining edge portions forming an open top rectilinear cavity. Two vertically spaced apart hinges 23 are structurally carried by side 17 of the fire box 11 at an edge portion adjacent the front 15. The hinges 23 carry an opening and closing ash door 22 that provides access to the fire box 11 through an orifice (not shown) defined in side 17. A known fuel grate 60 is carried in the fire box 11 spacedly above the bottom 19 to support solid fuel thereon. Configuration of the grate 60 allows ashes, solid combustion products and the like to fall therethrough. A latch 24 is carried by the ash door 22 opposite the hinges 23 to lock the ash door 22 in a closed position.
Plural spacedly arrayed air vents 20, each having an operator adjustable cover (not shown), are defined in the stove body 10 to control the inflow of air and plural spacedly arrayed stove feet 21 are structurally carried by and depend from the bottom 19 to support the stove body 10 above the supporting surface (not shown).
As shown in FIGS. 2 and 3, the combustion chamber 12 has an inverted truncated triangle shape and is peripherally defined by a front 25, a back 26, a top 27, a first outer side 29 and a second outer side 36. The outer sides 29, 36 are structurally attached, preferably by welding, to the front 25 and back 26 at adjoining edge portions so that the front 25 is spaced apart from the back 26. A planar top 27 defining rectilinear feed port 32, 39 in each lateral edge portion is structurally attached to upper most edges of the front 25, back 26 and outer sides 29, 36.
As shown in FIGS. 7 and 9, the outer sides 29, 36 also function as inwardly and downwardly angulated bottoms to fuel chutes 28, 35 while inner chute sides 30, 37 function as tops to each fuel chute 28, 35. Front and back edge portions of each inner chute side 30, 37 are structurally attached to inner surfaces of the front 25 and back 26 peripherally forming the fuel chutes 28, each of which defines a channel extending therethrough.
The inner chute sides 30, 37 are structurally attached at upper end edges to the underside of the top 27 while the lower ends are spacedly apart from one another forming a gap 59 therebetween spacedly above the fire box 11. The angulation of each fuel chute 28, 35, relative to vertical, is sufficiently steep to overcome frictional resistance between the inner surfaces of the fuel chutes 28, 35 and any wood fuel sliding downwardly therein (not shown) so that the wood fuel moves under the force of gravity into the fire box 11.
Feed ports 32, 39 defined in the lateral edge portions of the top 27 communicate with upper end portions of the fuel chutes 28, 35 respectively while lower end portions of each feed chute 28, 35 are within the combustion chamber 12 spacedly above the fire box 11 (FIG. 9).
A recessed lip 58 around the periphery of each feed port 31, 39 positionally maintains a feed chute cover 33 that is used to cover the feed ports 31, 39 and provide a generally airtight seal. A cover handle 34 facilitates user positioning of the cover 33.
A chimney port 14 is defined in the top 27 generally medially between the inner chute sides 30, 37 and provides an orifice for combustion products to exit the stove for wasting to the atmosphere.
Two re-burner channel inflow orifices 52 (FIG. 9) are defined in the back 26 of the combustion chamber 12 adjacent the top 27 and adjacent each inner chute side 30, 37.
A pivoting gate damper 40 is carried on axle 41 extending through and across medial chamber 61 adjacent the chimney port 14. A handle 42 communicates with the axle 41 allowing an operator to manipulate the gate damper 40 inside the medial chamber 61 to regulate air flow and fuel consumption. A counterbalance weight 43 is slidably carried on the handle 42 so that the damper 40 may be positionally maintained as desired by positioning the weight 43 closer to, or away from, the axle 41 and fixing its position with a set screw. (not shown).
The combustion chamber 12 and fire box 11 are structurally attached to one another, preferably by welding, along adjoining edges of the fronts 25, 15 and adjoining edges of the sides 29, 17 and 36, 18 respectively. Because the front 15 to back 16 dimension of the fire box 11 is greater than the front 25 to back 26 dimension of the combustion chamber 12, the back 26 of the combustion chamber 12 is not directly connected to the back 16 of the fire box 11, leaving a rectilinear opening (not shown) therebetween. Further, the top to bottom height of the back 26 of the combustion chamber 12 is greater than the top to bottom height of the front 25 of the combustion chamber 12. This difference in dimension causes bottom end portion 26 a of the back 26 to extend downwardly into the fire box 11. (FIG. 8). The lateral edges (not shown) of the bottom end portion 26 a of the back 26 are structurally attached to the inner surfaces (not shown) of the sides 17, 18 of the fire box 11 forming a rectilinear channel 47 a between sides 17, 18 and between the back 26 and the back 16 of the firebox 11.
The re-burner channel 13 is formed from a rectilinear back plate 44 having a top edge, a bottom edge and opposed side edges and two elongate rectilinear side plates 45, 46. Each side plate 45, 46 is structurally attached to one side edge of the back plate 44 along adjoining edge portions to extend perpendicularly therefrom.
Edges of each side plate 45, 46 opposite the back plate 44 are structurally fastened to the back 26 of the combustion chamber 12 forming a rectilinear channel 47 b between the back 26 of the combustion chamber 12 and the back plate 44 and medially between the two side plates 45, 46. As shown in FIGS. 2, 4 and 5, the top edge of the back plate 44 and upper end portions of the side plates 45, 46 are structurally attached to the top 27 forming an airtight seal therebetween. The side plates 45, 46 are laterally outward the re-burner inflow orifices 52 so that both re-burner inflow orifices 52 communicate with the re-burner channel 47 b. Bottom edge of the back plate 44 is structurally attached to top edge of the back 16 of the fire box 11 so that rectilinear channel 47 b communicates with channel 47 a between the lower end portion 26 a of the back 26 and the back 16 of the fire box 11.
Caps 55 at the upper back corners of the fire box 11 are structurally attached to the fire box 11, to one side plate 45, 46 and to the back 26 of the combustion chamber 12 providing an airtight seal between the fire box 11, the combustion chamber 12 and the re-burner channel 13.
Having described the structure of my wood stove, its operation may be understood.
The stove is installed in compliance with codes and ordinances that regulate wood burning stove safety.
The fuel chute covers 33 are removed from the feed ports 32, 39 defined in the top 27 and pieces of wood fuel (not shown) are inserted elongately into each fuel chute 28, 35. The configuration of the fuel chutes 28, keep the fuel (preferably elongate pieces of wood) in elongate alignment. The bottom end portions of the pieces of fuel extend downwardly into the fire box 11 in an angulated orientation. After the fuel chutes 28, 35 are loaded with a supply of fuel, the covers 33 are replaced on the feed ports 32, 39 and aligned so that the covers 33 fit flush upon the recessed lip 58. The damper handle 42 is positioned so that the damper 40 is open and the set screw (not shown) is secured to keep the damper 40 open.
The ash door 22 and the spacedly arrayed air vents 20 are opened. A supply kindling, or other fire starter (not shown), is placed on the fuel grate 60 in the fire box 11 adjacent to and below the bottom end portions of the fuel extending downwardly from the fuel chutes 28, 35.
Depending upon environmental conditions, such as the temperature and humidity, it may be necessary for the operator to establish an air draw within the stove so that the stove operates properly. Igniting a piece of fast burning material and placing it in medial chamber 61 will typically initiate an air draft. As the fast burning material burns, air in the stove is heated, causing it to expand and move upwardly through the combustion chamber 12 and exit out through the chimney port 14. As the heated air within the stove moves upwardly, cool air enters the stove through the air vents 20 and through the ash door 22 establishing the air draw.
The supply of fine kindling or other fire starter is ignited with known means. The ash door 22 is closed and secured with the latch 24. The air draft, previously started within the stove provides oxygen to the newly ignited fire by drawing air through the air vents 20 which are open. The burning kindling heats the bottom end portions of the fuel extending angularly downwardly from the fuel chutes 28, 35, liberating volatile gases from the wood fuel. The volatile gases ignite and oxidize in the fire box 11 above the fuel grate 60. The oxidizing releases more heat which liberates more gases and the process continues, consuming the wood fuel. As the lower end portions of the wood fuel are consumed by the fire, gravity pulls the upper portions of the fuel down the feed chutes 28, 35 and into the fire box 11 to be burned. Gravity powers the self-feeding nature of the stove.
Expanding gases and heat generated by the oxidizing gases rise upwardly against the underside of the top 27. As the combustion continues, more heat and expanding gases, including vapors and carbon particulates rise upwardly into the medial chamber 61 increasing the pressure therein. A portion of the vapors, expanding gases and heat pass through the chimney port 14 and are wasted to the atmosphere. Because the chimney port 14 is areally smaller than the upper area of the medial chamber 61, pressure increases in the area adjacent and about the chimney port 14. Gaseous friction between the underside of the top 27 defining the chimney port 14 and the combustion products slows the passage of combustion products through the chimney port 14 which further increases the pressure in the medial chamber 61. The increased pressure forces some of the combustion products, including vapors, carbon particulates, heat and gases through the re-burner inflow orifices 52 into the re-burner channel 13.
The areally smaller re-burner inflow orifices 52 cause a venturi effect where higher pressure inside the medial chamber 61 forces the combustion products through the smaller re-burner inflow orifices 52 at a higher velocity. After the combustion products pass through the areally smaller re-burner inflow orifices 52 the venturi effect dissipates and the combustion products cool because pressure and velocity have decreased. The cooled combustion products move downwardly through rectilinear channels 47 b, 47 a which in combination form the re-burner channel 13 as additional combustion products enter channel 47 b through the re-burner input orifices 52 at its top portion, and as the fire the fire box 11 “sucks” air from below.
Because the re-burner channel 13 has three exterior surfaces, the back plate 44, and the side plates 45, 46, that are not directly exposed to the primary fire zone they are cooler in temperature than the fire box 11 and combustion chamber 12. This causes combustion products within the re-burner channel 13 to cool. As the combustion products cool they become more dense and move downwardly through the re-burner channel 13.
The oxidizing of the fuel in the fire box 11 draws air from all available sources including the air vents 20 and the re-burner channel 13. When the operator restricts airflow through the air vents 20 by closing the adjustments (not shown) thereon, the fire draws more air through the re-burner channel 13. The combustion products passing through the re-burner channel 13 contain carbon particulates, vapors and other combustion products that form smoke when released to the atmosphere.
Because the combustion products passing through the re-burner channel 13 enter the fire box 11 through the rectilinear orifice 53 adjacent below the primary fire zone, the combustion products pass through the primary fire zone again where they are again subjected to temperatures sufficiently high for ignition and oxidation. The result is a small but intense fire that provides more heat through substantially complete combustion of fuel, and a wood fuel stove that generates less combustion byproducts that cause smoke.
The foregoing description of my invention is necessarily of a detailed nature so that a specific embodiment of a best mode may be set forth as is required, but it is to be understood that various modifications of details, and rearrangement, substitution and multiplication of parts may be resorted to without departing from its spirit, essence or scope.
Having thusly described my invention, what I desire to protect by Letters Patent, and

Claims

1. a stove for burning solid fuel comprising in combination:

a body having a combustion chamber at an upper end portion structurally connected to and communicating with a fire box at a lower end portion, the body defining a medial chamber;

the combustion chamber having a front, a back, a top and opposing sides, the top defining chimney port for wasting combustion products;

the fire box defining at least one air vent and an orifice having a door;

two inwardly and downwardly angulated opposing fuel chutes in the combustion chamber, each fuel chute having an upper end portion communicating with a feed port defined in the top, a lower end portion in the medial chamber spacedly above the fire box, and defining a medial channel extending therethrough for feeding fuel to the fire box;

a re-burner channel structurally carried by the back of the combustion chamber, the re-burner channel defining a rectilinear channel communicating between the combustion chamber and the fire box for passage of combustion products and byproducts therethrough; and

a recirculation in-flow orifice defined in the back of the combustion chamber proximate to the top and communicating with the rectilinear channel of the re-burner channel for combustion products and byproducts to pass therethrough.

2. The solid fuel stove of claim 1 wherein:

the combustion chamber has an inverted truncated pyramid shape, and

the fire box is rectilinear having a front, a back, opposing sides and a bottom that are structurally interconnected.

3. The solid fuel stove of claim 1 wherein:

the inward and downwardly angulation of the opposing fuel chutes provides gravity powered feeding of solid fuel into the medial chamber and the fire box.

4. The solid fuel stove of claim 1 wherein:

the re-burner channel has a back plate and two structurally attached side plates, the back plate extending parallel to the back of the combustion chamber and communicating between the top of the combustion chamber and the fire box, the two side plates structurally communicating between the back plate and the back of the combustion chamber to positionally maintain the back plate spaced apart from the back of the combustion chamber.

5. The solid fuel stove of claim 1 wherein:

the back of the combustion chamber extends downwardly inside the fire box spacedly below the bottom end portions of the fuel chutes forming a rectilinear passage between the back of the combustion chamber and a back portion of the fire box.

6. The solid fuel stove of claim 1 further comprising:

fuel chute covers for the feed ports defined in the top of the combustion chamber to seal the top end portions of the fuel chutes and prevent escape of combustion products and byproducts therethrough.