AUTOMATED TWO-BLOWER COOKING STOVE

Abstract

A two-blower automated biomass cooking stove with sensors that dynamically adjusts independent air flows and optimizes for the fresh fuel phase, but also manages air through a transitional phase, and then a char phase. The cookstove comprises a housing, a combustion assembly mounted within the housing; dual air flow passageways disposed at least partially within the housing for communicating air flow from outside the housing to a combustion cup, and a control system for automatically and dynamically adjusting relative air flow between the primary and secondary air flow passageways to optimize performance.

Claims

1. An automated two blower cooking stove comprising: a combustion chamber having primary air holes, secondary air holes, a combustion cup base, and a flame well, the secondary air holes disposed above the primary air holes, the combustion cup base adjacent the primary air holes, and the flame well disposed adjacent the secondary air holes, a primary air flow passage in communication with the primary air holes, a secondary air flow passage in communication with the secondary air holes, a primary blower disposed to blow air into the primary air flow passage, a secondary blower disposed to blow air into the secondary air flow passage, a primary temperature sensor disposed near the primary air holes for measuring the temperature of the combustion cup base, a secondary temperature sensor disposed near the secondary air holes for measuring the temperature of the flame well, a controller in communication with said primary and secondary temperature sensors and with the primary and secondary blowers, the controller configured to: detect, using the primary temperature sensor, the rate of change of the temperature of the combustion cup base, detect, using the secondary temperature sensor, that the temperature of the flame well is greater by a pre-established increment than the temperature of the combustion cup base, and if so: adjust the speeds of the primary and secondary blowers to speeds indicated in a configuration file for a target flame level set by a potentiometer.

2. The automated two blower cooking stove of claim 1 further comprising: a housing, an air jacket mounted inside the housing, the combustion chamber suspended from the air jacket, an air separator disposed between the air jacket and the combustion chamber, the space between the combustion chamber and the air separator defining the primary air flow passage, and the space between the air separator and the air jacket defining the secondary air flow passage.

3. The automated two blower cooking stove of claim 1 further comprising: the controller configured to: detect, using the primary temperature sensor, that the bottom combustion zone has reached a pre-established hot CHARFLIP temperature, and adjust the speed of the secondary blower to increase the amount of air blowing into the secondary air flow passage to optimize combustion at the flame well.

4. The automated two blower cooking stove of claim 3 further comprising: the controller configured to: increase the speed of the primary blower in a plurality of steps by a first set of pre-established increments over a transition time, increase the speed of the secondary blower serially after each of said plurality of steps by a second set of pre-established increments over said transition time, detect that the temperature of the combustion cup base has reached a pre-established CHARMAX temperature, or that said transition time has expired, and if so: terminate the increases of speeds of the primary and secondary blowers.

5. The automated two blower cooking stove of claim 3 further comprising: the controller configured to: detect that the temperature of the flame well has fallen below a pre-established shutdown temperature, and if so turn off the primary and secondary blowers.

6. The automated two blower cooking stove of claim 1 further comprising: the controller configured to: determine if the current speeds of the primary and secondary blowers are at pre-established speeds indicated in a configuration file for a target flame level set by a potentiometer, and if so increase or decrease the speeds of the primary and secondary blowers until said current speeds meet the speeds indicated by said target flame level.

7. The automated two blower cooking stove of claim 6 further comprising: the controller configured to: determine that current speeds are lower than the speeds indicated by said target flame level, increase the speed of the secondary blower in a plurality of steps by a first set of pre-established increments, and increase the speed of the primary blower serially after each of said plurality of steps by a second set of pre-established increments.

8. The automated two blower cooking stove of claim 6 further comprising: the controller configured to: determine that current speeds are higher than the speeds indicated by said target flame level, and if so decrease the speed of the secondary blower in a plurality of steps by a first set of pre-established increments, and decrease the speed of the primary blower serially after each of said plurality of steps by a second set of pre-established increments.

9. The automated two blower cooking stove of claim 1 further comprising: the controller configured to: determine that the temperature of the flame well is less by a pre-established increment than the temperature of the combustion cup base, and if so: set the speeds of the primary and secondary air blowers at a pre-established level, and determine after a pre-established Time-Startup time interval has elapsed that the temperature of the flame well is greater than a pre-established shutdown reference temperature, and if so: increase the speeds of the primary and secondary blowers to speeds indicated in a configuration file for a target flame level set by a potentiometer.

10. An automated two blower cooking stove comprising: a combustion chamber having primary air holes, secondary air holes, a combustion cup base and a flame well, the secondary air holes disposed above the primary air holes, the combustion cup base adjacent the primary air holes, and the flame well disposed adjacent the secondary air holes, a primary air flow passage in communication with the primary air holes, a secondary air flow passage in communication with the secondary air holes, a primary blower disposed to blow air into the primary air flow passage, a secondary blower disposed to blow air into the secondary air flow passage, a primary temperature sensor disposed near the primary air holes for measuring the temperature of the combustion cup base, a secondary temperature sensor disposed near the secondary air holes for measuring the temperature of the flame well, a controller in communication with said primary and secondary temperature sensors and with the primary and secondary blowers, the controller configured to: detect, using the primary temperature sensor, the temperature of the combustion cup base, p2 detect, using the secondary temperature sensor, that the flame well is greater by a pre-established increment than the temperature of the combustion cup base, and if so: increase the speeds of the primary and secondary blowers to speeds indicated in a configuration file for a target flame level set by a potentiometer, and detect that the temperature of the flame well is less by a pre-established increment than the temperature of the combustion cup base, and if so: set the speeds of the primary and secondary air blowers at a pre-established level, determine after a pre-established time interval has elapsed that the temperature of the flame well is greater than a pre-established reference temperature, and if so increasing the speeds of the primary and secondary blowers to speeds indicated in a configuration file for a target flame level set by a potentiometer.

11. An automated two blower cooking stove comprising: a combustion cup for mounting in a housing, the combustion cup having an inside face and an interior cavity, combustion cup air holes and an inwardly extending peripheral shelf, the air holes disposed above the shelf, a diffuser having a central dome, a peripheral lip and a sloped upturned flange, said peripheral lip extending outwardly from said outer dome, said peripheral lip having diffuser air holes, said upturned flange extending from an outer edge of said peripheral lip, said upturned flange sized to fit closely within said inside face, said central dome, peripheral lip and upturned flange defining a flame well, in an assembled configuration, said diffuser removably inserted in said combustion cup, said peripheral lip supported by said peripheral shelf, said diffuser air holes in communication with said interior cavity, said peripheral lip disposed below said combustion cup air holes, said combustion cup air holes and said diffuser air holes in communication with said flame well.

12. The automated two blower cooking stove of claim 11 further comprising: a skid plate, said skid plate having cooling air holes, a housing mounted on said skid plate, an upper edge of said housing having ventilation slots, said combustion cup disposed in said housing, a lid mounted on said housing, an air gap defined between said combustion cup and said housing, said air gap in communication with said cooling air holes and said ventilation slots creating a passive air-cooling system for insulating the housing against heat emanating from the combustion cup.

13. A high efficiency automated low emission biomass cookstove comprising: a housing, a combustion assembly inside the housing, dual air flow passageways disposed at least partially within the housing for communicating air flow from outside the housing to said combustion assembly, and a control system for automatically and dynamically adjusting relative air flow between said primary and secondary air flow passageways.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1A is an upper perspective view of an automated two-blower cooking stove according to the invention.

[0016] FIG. 1B is an exploded view of the cookstove depicted in FIG. 1A.

[0017] FIG. 2A is an elevational sectional view showing the enclosure and combustion assemblies thereof.

[0018] FIG. 2B is closeup view of the combustion cup of the combustion assembly shown in FIG. 2A.

[0019] FIG. 3A is an upper perspective rear view of the controller for an automated two-blower cooking stove.

[0020] FIG. 3B is an upper perspective front view thereof.

[0021] FIG. 3C is an elevational side view of the user interface and controller assembly thereof.

[0022] FIG. 3D is an upper perspective rear view similar to FIG. 3A showing the controller assembly with the wireless transmission module removed.

[0023] FIG. 4 is a simplified block diagram of the control system for an automated two-blower cooking stove according to the invention.

[0024] FIG. 5 is a high-level flow diagram of software protocol to be executed by the microprocessor of the control system thereof.

[0025] FIG. 6A-6B are a more detailed flow diagram of the software protocol depicted in FIG. 5.

[0026] FIG. 7 is an upper perspective cross-sectional view of the housing thereof.

[0027] FIG. 8 is an upper perspective cross-sectional view of the combustion assembly thereof.

[0028] FIG. 9 is an exploded view of the combustion assembly shown in FIG. 8.

[0029] FIG. 10A is a cross-sectional view of the combustion cup and diffuser thereof.

[0030] FIG. 10B is an elevational cross-sectional view of the tapered combustion cup and the air separator thereof.

[0031] FIG. 10C is a closeup view of a portion of the combustion cup shown in FIG. 10B.

[0032] FIG. 11A is an upper perspective view of the air plenum thereof.

[0033] FIG. 11B is an exploded upper perspective view of the air plenum shown in FIG. 11A.

DETAILED DESCRIPTION OF THE INVENTION

[0034] Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings. A system is disclosed for clean combustion of biomass for cooking and heating, a control system operationally coupled to the cookstove, and sensor data reporting that generates carbon credits and tracks utilization and biomass consumption. Clean means biomass technologies for cooking, including biomass stoves, that meet the definition of Clean as defined by the World Health Organization, which definition is accessible on the Internet at https://www.who.int/tools/clean-household-energy-solutions-toolkit/module-7-defining-clean. In accordance with the present teachings, a two-blower automated stove with sensors is taught that dynamically adjusts air independent air flows and optimizes for the fresh fuel phase, but also manages air through the transitional phase, and then the char phase.

[0035] As noted above, biomass stoves such as the TLUD are a known solution for generating heat cleanly relative to a three stone hearth, charcoal cookstove or other biomass cooking apparatus and method. TLUD cookstoves achieve decent emissions and efficiency while also being convenient and granting access to renewable fuel sources. However, TLUD cookstoves are less convenient, have higher emissions and have a limited heat range compared to liquid or gas cookstoves. Further, many cookstoves are unable to reliably report usage data for market feedback and carbon credit reporting.

[0036] Many TLUD stoves only use a single variable speed blower and a fixed ratio of primary and secondary air with no sensor feedback, this results in a stove that runs well only for a narrow range of heat outputs and only during the fresh fuel phase of combustion. Because of the limitations of food types that may be cooked with a biomass pellet stove, users will often defer to dirtier or less sustainable fuel types such as charcoal, liquid propane gas, and kerosene, even when biomass pellets are available. To expand the impact of sustainably produced biomass pellet stoves, the stove itself must be generally practical and accommodate all cooking requirements that one might expect from an open flame stove.

[0037] Hence, it would be advantageous to provide a biomass cookstove that efficiently and effectively converts biomass to clean useful heat for cooking or other applications while generating reports for credible carbon credits and customer usage data. These features have great potential to unlock a global transition from unsustainable cooking to sustainable fuel sourcing and, with correct agricultural/forestry practices, serve as an accelerant of regenerative cooking fuel deployment.

[0038] In accordance with the present teachings, a two-blower automated stove with sensors is disclosed that dynamically adjusts air independent air flows to optimize fuel combustion during the fresh fuel phase, an intermediate transition phase, and a carbonized fuel (char) phase.

[0039] An automated low emission high efficiency biomass cookstove 10, as seen in FIGS. 1A-1B, comprises a housing assembly 12, flame well 14, cooking implement (e.g., a pot) 16, adjustment dial 18, lift handle 20 and user interface 22. With additional reference to FIG. 2, it can be seen that a combustion assembly 24 is disposed inside the housing assembly 12. The housing assembly 12 comprises a housing shell 26, top lid 28, user interface 22 and skid plate 30, and a combustion cup 32 having a combustion cup base 33. Primary and secondary air flow passageways 34, 36 are disposed at least partially within the housing for communicating air flow from outside the housing 26 to the combustion cup 32 and comprise a control system for automatically and dynamically adjusting relative air flow between the primary and secondary air flow passageways to optimize performance of the stove.

[0040] As seen in FIG. 2A, the combustion assembly 24 is nested inside housing 12. The primary air blower 38 conveys air through the primary air flow passageway 34 into the primary air holes 40 for primary combustion of fuel in the combustion cup, such as biomass. Primary combustion is what generates the gas that is combusted at the top of the combustion cup 32. The secondary air blower 42 conveys air through the secondary air flow passageway 36 into the secondary air holes 43 (see FIGS. 8-10B) for secondary combustion in the flame well 44. Secondary combustion generates the visible cooking flame in the flame well 44 at the top of the combustion cup 32 by combustion of the gases produced from primary combustion. The diffuser 46 directs the gases that have flowed upward from the primary combustion outside the combustion cup 32 to the flame well 14 to mix it thoroughly with secondary air to substantially improve combustion having lower emissions. Enclosure air flow 48 is driven by heat convection and enters the cooling air holes 50 in skid plate 30 and exits through ventilation slots 51 at the top of the housing 26. The passive and/or active cooling air keeps the enclosure surface temperatures low for safety of the user and prevents electronic components from overheating.

[0041] FIG. 2B is a high-level representation of components of the fuel combustion that occurs in the combustion cup 32. Fresh fuel 200 is disposed at the bottom of the combustion cup. The top level of the fuel is undergoing pyrolysis, at 202, the product of which is combusted in the primary combustion area, at 204. Pyrolysis and combustion product a layer of char 206 atop the fresh fuel, and gases 208 which flow upward into the flame well 44 defined by diffuser 46 for secondary combustion 210.

[0042] With reference now to FIGS. 3A-3D, a controller 52 housed in user interface 22 (see FIGS. 1A-1B) includes a microprocessor 54, user start switch 56, blower terminals 58, power source 60, temperature sensor terminals 62, indicator lights 64 and wireless transmission module 66. The controller is an automation device that processes sensor signals, manages electrical flows and executes the program for operating the cookstove and auxiliary components. The controller manages the speed of the blowers and the ratio of the speeds of the two blowers to optimize combustion. The controller microprocessor may be a Programmable Logic Controller (PLC), microcontroller-based bespoke controller such as an STM32 with a custom PCBA, off the shelf computer or any suitable programmable controller that can communicate with power electronics, motor controllers, variable frequency drives, PWM modules and any necessary electronic components via digital and analog communication protocols. The controller also may include a wireless data transmission module and indicator lights to provide information to the user as well as the distributor, manufacturer, carbon credit entity or any party that may find value in stove data reports such as a marketing team. The wireless data transmission module also supports firmware updates. The controller includes a power source which may be a battery, thermoelectric element, and/or connection to shore power or any suitable electrical power source compatible with the microcontroller. The controller includes firmware that operates the cookstove and generates the sensor data report that may be converted to carbon credits. A K-type thermocouple with high temperature insulation able to withstand the surface temperatures of the mounting surface would be suitable for use as the temperature sensor.

[0043] Operating under the protocol managed by the controller, the biomass cookstove facilitates roughly three distinct thermochemical phenomena: pyrolysis, reduction and combustion. Pyrolysis is the heating of a material in absence of oxygen, this thermally breaks molecular bonds creating smaller molecules often in vapor form. Smoke is a typical aerosolized product of pyrolysis familiar to most people. Combustion is the heating of a material in the presence of oxygen resulting in an exothermic reaction of molecules generating primarily CO.sub.2 and H.sub.2O. In the typical wood fire, wood is being pyrolyzed by the combustion occurring around it. Because the wood is engulfed in flames, oxygen is scarce at the material surface, but heat is being transmitted, driving pyrolysis. When one watches wood burn, one is typically watching the pyrolysis gases (smoke) combusting, not the solid material. This changes in the char phase of a wood fire in which the solid carbon of the char is combusting with oxygen according to the following reaction O.sub.2+C+heat.fwdarw.CO.sub.2. In the case of a hot coal bed, the combustion products of carbon, CO.sub.2 reacts with the hot carbon in a reduction reaction that generates 2CO according to this reaction CO.sub.2+C+Heat.fwdarw.2CO. A blue flame on the surface of the coal bed is due to the CO combusting with oxygen after being created by reduction according to the following reaction 2CO+O.sub.2+Heat.fwdarw.2CO.sub.2+more Heat. During the Fresh Fuel Phase, a small amount of primary air 34 is used to combust fuel and generate heat to drive pyrolysis of the fresh fuel, then secondary air 36 is used to combust the pyrolysis gases. The amount of air needed to generate the pyrolysis gas is relatively small compared to how much air is needed to fully combust the pyrolysis gas, so fixed ratio TLUD stoves will have more secondary air holes 43 than primary air holes 40 with a shared forced air source. During the Char Phase, each oxygen atom required to generate combustible gas needs to be matched with two oxygen atoms to combust them. Combining the reactions together and balanced O.sub.2+C+heat.fwdarw.CO.sub.2+C+Heat.fwdarw.2CO+O.sub.2+Heat.fwdarw.2CO.sub.2. To support the secondary air requirements of the wood gas phase, the secondary air holes 43 of combustion cup 32 are located above the primary air holes 40 as seen in FIG. 2. Because it requires one O.sub.2 molecule to generate the gas and one O.sub.2 molecule to combust the gas, the primary air blower 38 must run at a rate calculated to supply sufficient combustible gas in the proper proportion for combustion throughout the fresh fuel, transition and char phases. Consequently, there must be a method to change the blower speeds to match the combustion phase. This is accomplished by monitoring the temperature of the combustion cup base of the combustion cup 32 using the lower temperature sensor 68. Since the fuel burns from the top to the bottom, the primary (lower) temperature sensor will not read a high temperature until the flame front in the primary combustion zone is near the base of the combustion cup and the fuel in the base of the combustion cup is also very hot. The fuel is very hot because it has undergone pyrolysis and will be in the char phase when the lower temperature sensor detects a certain temperature or rate of temperature change of the combustion cup base, referred to herein as the CHARLIP temperature. This trigger temperature or rate varies based on how much fuel was put into the combustion cup in the beginning. The control system will vary the trigger temperature or trigger temperature change rate, or trigger temperature change second derivative (the rate of change of the rate of change) depending on how long it takes for the primary temperature sensor to achieve the CHARFLIP temperature. Trigger temperatures and signal temperatures will vary between stoves and fuel types and so anyone skilled in the art will be capable of extracting these values through testing.

[0044] With reference now to FIG. 4, the cookstove receives biomass as a fuel and is managed by the control system 70 which generates sensor data reports and loads them on to a database 72. Sensor data reports can be queried from the database to a carbon credit registry 74 or any destination that will yield accredited carbon credits. A power source 76 connects electrically to the controller. The controller may comprise a charge controller circuit and charging port, such as a USB-C port or any suitable electrical receptacle or plug. The microprocessor 52 is electrically connected to the top temperature sensor 78, lower temperature sensor 68, primary air blower 38, secondary air blower 42, battery 80, transceiver 66, speed sensor 82 and 84, memory 86 and firmware 87, and mechanically connects to the adjustment dial 18 and user interface 22. The speed sensors may be integrated into the blowers to detect blower RPMs, or measure air speed in the primary and secondary airflow paths.

[0045] As seen in FIG. 5 and discussed more fully below, when the user turns the stove on at 90, the controller will determine if the user has turned on the stove at 92. If it is determined that the cookstove has been turned on, the controller will operate the stove according to the cooking protocol, at 94, and upon completion will either shut off the cookstove automatically or the stove will be manually shut off, at 96. During stove operation sensor data is recorded in memory. If it's time to send a data report, at 98, then the report is sent to a database, at 100. It then checks to make sure that the data was received correctly, at 102, using an appropriate protocol, at 104. After confirming the data was received correctly, the memory is cleared, at 106, to make sure the onboard memory does not fill up. The report timeframe should be less than it would take for heavy use of the stove to fill up data by some safety factor.

[0046] FIGS. 6A-6B are a more detailed flow diagram of the software executed by the control system with an emphasis on the stove cooking protocol in FIG. 5. The program begins when the user starts the stove at 110. Then the temperature sensors are read to detect whether the stove has been recently operated and is hot, or if it is cold, at 112. If the stove is hot, the Hot Startup Protocol is executed, at 114; if it is cold, the Cold Startup Protocol is executed, at 116. After the startup protocol is executed, the temperature sensors are queried to determine if the stove was successfully lit and there is a stable, hot flame, or if the flame extinguished and the stove needs to be relit, at 118. If the ignition is successful, the fresh fuel phase protocol is executed, at 120, to burn the fresh fuel optimally. During the fresh fuel phase, the temperature sensors are queried, at 122, to detect if the fresh fuel has burned to charcoal. When the base of the combustion cup reaches a specified temperature or rate of change of temperature, at 124, the transition phase protocol is executed, at 126, to optimize emissions and flame stability while the last bit of fresh fuel is converted to charcoal. When the base of the combustion cup reaches a specified temperature or rate of change of temperature, at 128, the char phase protocol is executed, at 130, to optimize emissions and efficiency. When the upper temperature sensor temperature drops, at 134, 136, the flame is extinguished, and the stove shuts down, at 138. During operation, the sensor data of blower RPM and temperature is recorded to accurately determine the amount of fuel being consumed and whether or not the stove was successfully as indicated by operating indicator lights 64 and wireless transmission module 66.

[0047] As seen in FIG. 7, the pot stand 140 rests on the top lid 142. The wind guard 144 is supported by the top lid 142 as well but may also be supported by the pot stand 140. The pot stand is manufactured from a suitable material and finish to withstand direct contact with flames while supporting the weight of a pot full of water. Steel with a high temperature coating, stainless steel or any suitable material may be employed. The pot stand also disrupts the flow of combustion gases. The pot stand 140 rests on the top lid 142. The wind guard 144 is supported by the top lid 142 as well but may also be supported by the pot stand 140. The pot stand should be designed to absorb minimum heat from the flame and cookware to prevent a reduction in thermal efficiency. The wind guard 144 prevents external airflows such as wind or circulation fans from blowing out the secondary combustion or reducing thermal efficiency by blowing the hot gases away from the cookware. The housing 26 is a structural component that supports the top lid 142 and transfers the cookware weight to the skid plate 30. The skid plate transfers the weight of the cookware and stove to the supporting surface such as a table or the ground. The housing also supports the user interface. The lift handle 20 is used to lift the cookstove. Skid plate cooling air holes 50 allow air to enter the assembly to cool the enclosure while also preventing pests and debris from entering the enclosure. The user interface 22 attaches to the housing and supports controller 52 and should be designed to absorb minimum heat from the flame and cookware to prevent a reduction in thermal efficiency. The adjustment dial 18 is mechanically connected to the controller and supported by the user interface 22. The adjustment dial 18 and user start switch 56 may be separate components or a combined component such as a potentiometer or rotary encoder with a switch feature integrated for the user to establish a target flame level, e.g., the volume of the flame. The wind guard 144 prevents external airflows such as wind or circulation fans from blowing out the secondary combustion or reducing thermal efficiency by blowing the hot gases away from the cookware. The lift handle socket 148 provides a mounting point for the lift handle and serves as a hinge so that the lift handle may be set lower to not obstruct the space around the cookstove. The battery 150 may be attached to housing 26, air plenum 182 (see FIG. 11B) or skid plate 154. In one embodiment, the battery may be held by a sheet metal piece spot welded to the housing for simplicity of assembly.

[0048] Referring now to FIGS. 8-9, air plenum assembly 154 is attached to the air jacket 156 with means to prevent primary or secondary air from leaking through the joint. This may be achieved through a combination of a gasket, an adhesive suitable for the local temperatures, a precision metal-to-metal fit or any suitable method familiar to those skilled in the art. The air jacket 156 can withstand the radiant heat from the combustion cup 32 and air separator 158 over a long period of time. Most stainless-steel alloys are appropriate for this application. The air separator 158 with the combustion cup 32 forms a gap G, creating a path for the primary air flow. The air jacket 156 supports the combustion cup 32. The top temperature sensor 78 is received in a small aperture 162 in the air jacket 156 to secure it immediately adjacent to the combustion ring yet protected from heat eddies allowing it to be reliably heated by the radiant heat from the combustion cup but also not to interfere with the reinstallation of the combustion cup. The interface between the combustion cup 32 and air jacket 156 should be relatively free of air leaks. The air separator 158 is a sheet metal assembly that can withstand the radiant heat from the combustion cup 32 over a long period of time. Most stainless-steel alloys are appropriate for this application. The air separator 158 encloses the primary air flow 34, preheats the primary air before combustion, and locates the combustion cup 32. The interface gap 160 between the top flange of the air separator 158 and combustion cup 32 outside diameter and cross-sectional area must be sufficient to allow easy removal and reinstallation of the combustion cup 32 but also allow for differentiation between the primary and secondary air flows 34, 36. If the gap is too large, the primary and secondary air flows will not be differentiated, and the stove will operate much like a single blower TLUD. The correct gap can be determined for any stove geometry by computation of fluid dynamics simulation and empirical testing. The air separator 158 also supports the primary temperature sensor 68. The perforated plate supporting primary temperature sensor 68 also serves as a radiant heat barrier to prevent conduction of heat to the air plenum assembly 154 and therefore the primary and secondary blowers 38, 42. The diffuser 46 is a removable component that directs the gases to the wall of the combustion cup for optimal mixing with the secondary air flow. In the illustrated embodiment the diffuser 46 is supported by an annular shelf 164 (see FIG. 10A) of the combustion cup. The diffuser features a handle 166 that allows a tool to be used to remove it when it is hot. The diffuser 46 and combustion cup 32 face particularly high temperatures, combustion gases, pyrolysis gases, producer gas (CO and H2reducing agents) and oxygen, so must be constructed of a refractory material such as ceramics, Inconel, SS310, SS326 or any suitable alloy capable of long-term exposure to combustion temperatures and gases in presence of oxygen. Insulation 168 serves to slow migration of heat from the combustion assembly into the housing and electronic components. The Insulation must be of sufficient thickness to keep the electronics below their rated operating temperature even during hot days, next to a source of heat or in direct sunlight. The insulation should also be stable when subjected to the surface temperature of the air jacket 156. Suitable materials are ceramic wool, fiberglass or any insulative material that will not degrade, pyrolyze or combust when exposed to the temperature of the air jacket 156. The upper temperature sensor 78 and bottom temperature sensor 68 are positioned such that airflow does not impact the readings substantially. If improperly placed, the temperature readings will be changed by airflows and aggravate the performance of the control system. Upper temperature sensor 78 is placed between the neck of the air jacket 156 and combustion cup 32 such that airflow does not cool the sensor. Similarly, primary temperature sensor 68 is located in the center of the air separator which features a scalloped plate that directs airflow near the air separator wall and directly into the primary air holes. This creates a dead space where airflow is minimal at the location of primary temperature sensor 68.

[0049] As seen in FIG. 10A, diffuser 46 includes a central dome 170 surrounded by an annular peripheral lip 171 having openings 174 through which hot gases flow from the combustion cup 32. The diffuser includes an upturned tapered peripheral flange 198 to facilitate insertion of the diffuser in the combustion cup as shown. Tapered peripheral flange 198 also provides structural rigidity to prevent warping under thermal stresses and cycles. Central dome 170, peripheral lip 171, peripheral flange 176 and the walls of the combustion cup 32 form an annular flame well 44 into which the combustible gases flowing up from the combustion cup 32 are directed close to the secondary air holes 43 for more effective mixing of the primary and secondary gas flows. The combustion cup 32 has an annular shelf 164 which supports the diffuser 46. The diffuser handle 166 and combustion cup cleat 178 can be used to remove the diffuser 46 or combustion cup 32 using a tool during operation. The combustion cup has two rows of staggered holes for flow dynamics that are favorable to clean combustion. These holes may be of different diameters to optimize fluid dynamics for best mixing.

[0050] Referring now to FIGS. 10B-10C, it is seen that the combustion cup is tapered to make removal and installation much easier as shown by comparing datum line A with the wall of the combustion cup. As seen, the combustion cup 32 is closely nested inside the air separator 158. During operation of the stove, the combustion cup 32 heats to a high temperature and swells in diameter thereby reducing the radial width of the interface gap G formed between the combustion cup 32 and the air separator 158. As discussed above, it is important that the interface gap G must be of a sufficient diameter and cross-sectional area to allow differentiation between the primary and secondary air flows. The combustion cup 32 is therefore tapered to prevent it from binding during removal.

[0051] As seen in FIGS. 11A-11B, primary air plenum 182 is attached to the air plenum top plate 184 such that primary plenum air passages 186 are sufficiently isolated from secondary plenum air passage slots 188 thereby sufficiently isolating primary air flow passage 34 from secondary air flow passage 36. The air plenum bowl 190 is attached to the air plenum top plate 184 thereby encapsulating the primary air plenum 182. The nested plenums provide a few benefits; one is using space efficiently and the other is providing heat barriers from the combustion cup to keep the skid plate cool. Radiant heat will warm up the primary air sub plenum and primary and secondary air flowing around the sheet metal will actively cool the components such that any parts of the stove that the user may contact does not get too hot to touch.

[0052] The various embodiments of these concepts and methods are thermally efficient, effective for cooking and heating, user friendly, and able to generate reports for carbon credits, greatly increasing the relevance for clean cooking with sustainable biomass around the world. In short, a system and method have been disclosed for providing a significantly better clean cooking solution that combines the low cost of traditional fuels with the clean burning high performance of fossil fuels while using locally produced renewable feedstocks.

Operation

[0053] An automated two-blower biomass cooking stove according to the invention is a solution for combustion of solid fuels that is optimized for ease of use, low emissions, efficiency and usage reporting. Operating the stove starts with filling the combustion cup with fresh fuel and inserting the combustion cup into the combustion assembly. Then the user will start the stove using the user interface and light it making use of any variety of suitable methods likely based upon available accelerants. The preferred method is using about 30 mL of ethanol and lighting it with a match. From there the accelerant will burn, heating up the upper thermocouple. When the upper thermocouple triggers the control system to start the startup protocol the stove will either enter a cold or hot startup protocol depending on the temperature of the upper thermocouple. During the hot or cold startup protocol the blowers are set at a few speeds, starting relatively slow to prevent blowing out the Initial flame, then escalate to accelerate startup and keep emissions low and startup time short. After the upper thermocouple heats up enough, the control system will change the blower speeds to whatever the user has set the heat setting to. The control system will maintain these blower speeds until the user changes the heat setting or the transition phase protocol initiates. During the transition phase, the blower settings are such that the secondary air is relatively high compared to the fresh fuel settings and the primary air lower. This is because the rate of gas production increases relative to the primary air since the bottom of the combustion cup will get very hot and transfer heat to the fuel around the bottom of the cup. After the transition phase, the stove will enter the char phase where the blower speeds are optimized for clean combustion of charcoal. After the flame at the top extinguishes, the upper thermocouple will decrease in temperature and the control system will turn the blowers off and execute a shutdown protocol. The user may then remove the combustion cup and dump out the remaining ash and charcoal and start the process over again.

[0054] The innovation disclosed herein is based on the systematic application of the knowledge generated from decades of biomass stove research, combined with our team's expertise in biomass gasification system design and engineering. The intended result is a prototype small-scale biomass gasifier stove that will overcome the limitations of existing state-of-the-art stoves by meeting specific requirements: [0055] a) delivering consistent low emission profiles (meeting Tier 4 and Tier 5 ISO Standards for all criteria), [0056] b) superior fuel economy (30% longer cook times on the same fuel load) and [0057] c) sufficient turn down ratio for versatile cooking (targeting a 5:1 ratio, from cooking eggs to boiling large pots of water)

[0058] This can be achieved through implementing simple computer-controlled air management using temperature sensors and multiple fans to dynamically adjust combustion conditions.

[0059] While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.