METHOD FOR OPERATING AN AUTOMATED TWO-BURNER BIOMASS COOKSTOVE

Abstract

A two-blower automated biomass cookstove with sensors that dynamically adjusts air 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. A method for operating an automated two-blower cooking stove, the automated two-blower cooking stove having a combustion chamber, the housing having a primary air flow passage, a secondary air flow passage, a primary blower and a secondary blower, the 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 primary blower in communication with the primary air holes, the secondary blower in communication with the secondary air holes, the combustion cup base adjacent the primary air holes, the flame well adjacent the secondary air holes, the method comprising: detecting that rate of change of the temperature of the combustion cup base has exceeded a reference change rate, and if so: adjusting 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.

2. The method for operating an automated two-blower cooking stove of claim 1 wherein adjusting the speed of the secondary blower comprises: increasing the speed of the primary blower in a plurality of steps by a first set of pre-established increments over a transition time, increasing 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, and detecting that the temperature of the combustion cup base has reached a pre-established CHARFLIP temperature or that said transition time has expired, and if so: terminating the increases of speeds of the primary and secondary blowers.

3. The method for operating an automated two-blower cooking stove of claim 1 further comprising: detecting that the temperature of the flame well has fallen below a pre-established shutdown temperature, and if so: turning off the primary and secondary blowers.

4. The method for operating an automated two-blower cooking stove of claim 1 further comprising: detecting that the temperature of the flame well has fallen by a rate greater than a pre-established rate indicated in a configuration file, and if so: turning off the primary and secondary blowers.

5. The method for operating an automated two-blower cooking stove of claim 1 further comprising: determining 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: increasing or decreasing the speeds of the primary and secondary blowers until said current speeds meet the speeds indicated by said target flame level.

6. The method for operating an automated two-blower cooking stove of claim 5 wherein if said current speeds are lower than the speeds indicated by said target flame level: increasing the speed of the secondary blower in a plurality of steps by a first set of pre-established increments, and increasing the speed of the primary blower serially after each of said plurality of steps by a second set of pre-established increments.

7. The method for operating an automated two-blower cooking stove of claim 5 wherein if said current speeds are higher than the speeds indicated by said target flame level: decreasing the speed of the primary blower in a plurality of steps by a first set of pre-established increments, and decreasing the speed of the secondary blower serially after each of said plurality of steps by a second set of pre-established increments.

8. The method for operating an automated two-blower cooking stove of claim 1 further comprising: determining 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: setting the speeds of the primary and secondary air blowers at a pre-established level, and determining after a pre-established time interval has elapsed that the temperature of the flame well is greater than a pre-established shutdown 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.

9. The method for operating an automated two-blower cooking stove of claim 1 further comprising: determining 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: increasing the primary and secondary blowers to begin stepped increases of speed to speeds indicated in a configuration file.

10. A method for operating an automated two-blower cooking stove, the automated two-blower cooking stove having a combustion chamber, the housing having a primary air flow passage, a secondary air flow passage, a primary blower and a secondary blower, the 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 primary blower in communication with the primary air holes, the secondary blower in communication with the secondary air holes, the combustion cup base adjacent the primary air holes, the flame well adjacent the secondary air holes, the method comprising: determining 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: increasing or decreasing the speeds of the primary and secondary blowers until said current speeds meet the speeds indicated by said target flame level, and detecting that rate of change of the temperature of the combustion cup base has exceeded a reference change rate, and if so: adjusting 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, and detecting that the temperature of the flame well has fallen below a pre-established shutdown temperature, and if so: turning off the primary and secondary blowers.

11. A method for operating an automated two-blower cooking stove, the automated two-blower cooking stove having a combustion chamber, the housing having a primary air flow passage, a secondary air flow passage, a primary blower and a secondary blower, the 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 primary blower in communication with the primary air holes, the secondary blower in communication with the secondary air holes, the combustion cup base adjacent the primary air holes, the flame well adjacent the secondary air holes, the method comprising: determining 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: setting the speeds of the primary and secondary air blowers at a pre-established level, determining after a pre-established time interval has elapsed that the temperature of the flame well is greater than a pre-established shutdown 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, and detecting that rate of change of the temperature of the combustion cup base has exceeded a reference change rate, and if so: adjusting 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, and determining 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: increasing or decreasing the speeds of the primary and secondary blowers until said current speeds meet the speeds indicated by said target flame level.

12. The method for operating an automated two-blower cooking stove of claim 11 further comprising: determining 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: increasing the primary and secondary blowers to begin stepped increases of speed to speeds indicated in a configuration file.

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 a closeup view of the combustion cup of the combustion assembly shown in FIG. 2A.

[0019] FIG. 3A is an upper rear perspective view of the controller therefor.

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

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

[0022] FIG. 3D is an upper rear perspective view of the controller similar to FIG. 3A 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 executed by the microprocessor of the control system thereof.

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

[0026] FIG. 7A-7B are detailed logic diagrams of the cold start protocol.

[0027] FIG. 8 is a detailed logic diagram of the hot start protocol.

[0028] FIG. 9A-9D are detailed logic diagrams of the fresh fuel phase, the transition phase, char phase and shut down protocols.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings. A system and method are now disclosed for clean combustion of biomass for cooking and heating, a control system operationally coupled to the cookstove, and sensor data reporting for generating carbon credits and tracks utilization and consuming biomass. 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, and then a char phase.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 is 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.

[0035] 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 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 skid plate cooling air holes 50. The passive and/or active cooling air keeps the enclosure temperatures low for safety of the user and prevents electronic components from overheating.

[0036] 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.

[0037] With reference 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 invention as well as auxiliary components. 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 may also 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.

[0038] 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 CO2 and H2O. 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 O2+C+heat.fwdarw.CO2. In the case of a hot coal bed, the combustion products of carbon, CO2 reacts with the hot carbon in a reduction reaction that generates 2CO according to this reaction CO2+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+O2+Heat.fwdarw.2CO2+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 O2+C+heat.fwdarw.CO2+C+Heat.fwdarw.2CO+O2+Heat.fwdarw.2CO2. 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 O2 molecule to generate the gas and one O2 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.

[0039] 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.

[0040] 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 mechanically connects to the adjustment dial 226 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.

[0041] 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 execute 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.

[0042] 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 temperatures 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 bottom 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 bottom 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, whether the fuel was fresh biomass or charcoal and whether or not the stove was successfully operating indicator lights 64 and wireless transmission module 66.

[0043] Referring now to FIGS. 7A and 7B, it is seen that the cold startup protocol 700 is used if the temperature at the flame well is at or close to ambient temperature. Typically, a temperature sensor in the controller, TC (PCB), is used as a reference. Ambient temperature suitably may be set at 5 C. higher than the temperature measured by TC (PCB). If it is determined that the top (secondary) temperature sensor (TC2) detects a temperature no greater than 5 C. higher than TC (PCB), at 702, the air blowers are run at a start up speed (e.g., Fan-Startup_Stg_1), at 704. After a set interval, e.g., Time-Startup_1, the top temperature sensor TC2 is checked to determine if it is greater than the startup temperature (Temp_Startup_1), at 706. If it is not, the controller checks to see if the startup timer (Time-Startup_1) has elapsed and the startup temperature has not been reached, at 708. If so, the controller checks to see if the startup attempt timer has elapsed, at 710, If it has not, the controller checks the potentiometer to see if it is off, at 712. If the potentiometer is not off, the process returns to running the blowers again, at 704. If the startup attempt timer has elapsed or if the potentiometer is set to off, the controller shuts off the stove at 714. Returning to 706, if the top temperature sensor TC2 greater than the startup temperature, the air blowers are set to a higher speed (Fan_Startup_Stg_2), at 716. The temperature at the flame well is checked next at 718 to determine if it is greater than a reference temperature (e.g., Temp_Startup_2), at 718. If it is, the blowers speeds are further increased (e.g., to Fan-Startup_Stg_3) at 720. If it is not, the protocol executes a similar set of checks as 708, 710, 712 to determine if the startup attempt timer has elapsed and if the potentiometer has been turned off, at 722, 724, 726.

[0044] With continuing reference to FIGS. 7A and 7B, the temperature at the flame well is checked to determine if it is greater than a reference temperature (e.g., Temp_Shut_Down+buffer_temp), at 728. If it is not, the protocol executes a similar set of checks, as at 708, 710, 712, to determine if the startup attempt timer has elapsed and if the potentiometer has been turned off, at 730, 732, 734. If it is, the controller instructs the blowers to begin ramping up to main program speeds over timer intervals, e.g., 30 seconds, at 736.

[0045] FIG. 7B (at 736) and FIG. 8 (at 754) indicate the gradual ramping of blower speeds over the course of some set time frame, here listed as 30 seconds. As indicated in FIG. 7B and FIG. 8, any time the controller moves from one program to another the controller slowly ramps the blower RPMs over a given time range. This slow RPM change substantially reduces harmful emissions produced by the stove.

[0046] FIG. 8 is a detailed logic chart of the hot start protocol. This is used if the upper temperature sensor is substantially higher than the reference temperature. This allows the user to refill and light the stove shortly after its last run. The difference between the hot and cold startup protocols is primarily how the control system decides the stove is lit and to proceed. The hot start protocol checks whether or not the upper temperature sensor is increasing or decreasing. If the upper temperature sensor is getting hotter, then the control system knows that the stove is lit and has a stable flame and will proceed to the fresh fuel phase detailed in FIGS. 9a, 9b, and 9c.

[0047] Referring now to FIG. 8, the hot startup protocol begins, at 702, by determining if the top (secondary) temperature sensor (TC2) detects a temperature greater than 5 C. higher than TC (PCB). If it is, the blowers are set to run at a first level (e.g., Fan-Starup_Stg_1) at 740. If a change in the temperature at the flame well is not positive, the protocol determines if determine if the startup attempt timer has elapsed and if the potentiometer has been turned off, at 744, 746, and shuts the stove off, at 748, if conditions are met. However, if the change in the temperature at the flame well is positive (at 742), the protocol instructs the blowers to run at a higher second level (e.g., Fan_Startup_Stg_2), at 750. The protocol periodically checks the temperature at the flame well to determine if it is greater than a reference temperature (e.g., Temp_Shut_Down+buffer_temp), at 752. If it is not, the protocol executes a similar set of checks as at 708, 710, 712 to determine if the startup attempt timer has elapsed and if the potentiometer has been turned off, at 754, 756, and turns the stove off, at 748, if conditions are met. If, at 752, the temperature at the flame well is greater than a reference temperature, the protocol instructs the blowers to begin ramping up to main program speeds over timer intervals, e.g., 30 seconds, at 758, and begin executing the main program logic.

[0048] During startup the user may manually shut the stove off to re-attempt lighting the stove. Once the stove enters the fresh fuel phase, the stove cannot be turned off manually unless the manual override feature is used. This prevents the user from turning the stove off at a stage where a lot of smoke would be produced.

[0049] The fresh fuel phase is optimized for combustion of fresh fuel. The fresh fuel settings will be used until the lower temperature sensor gets hot. When the bottom of the combustion cup starts to get hot, there is very little fresh fuel left and the transition phase protocol is required to continue with clean combustion. Data is stored during this phase to record what blower speeds were used to estimate combustion rate of the fuel for accurate tracking. The section in a dashed line box details logic of how blower speeds are managed during power setting changes. During typical operation, there is a lag in combustion behavior after a blower speed is changed and can result in more emissions due to improper air and fuel ratio. When increasing the blower speeds, it is best to increase the primary air first to give the primary air more time to produce more gas before increasing secondary air. introduce extra air at the top to burn any excess gas produced in the blower speed transition. When turning the blowers down, the primary blower speed is decreased first to keep the secondary air relatively higher during the transition. If you do not implement this, then there will be flare ups when decreasing the blower speeds since the thermal inertia of the higher power setting will continue to produce gas at a higher volume than the secondary air can combust at the new blower speed. When increasing the blower speeds there is a lag in gas production and the excess secondary air may extinguish the flame or increase emissions by lowering the combustion temperature.

[0050] FIG. 9 is a detailed logic diagram of the transition phase protocol. The transition phase is initiated when the lower temperature sensor becomes hot and will proceed until a specified time has elapsed, specific temperature or heating rate is measured on the lower temperature sensor. For the duration of operation, the controller senses and records information from sensors placed on the battery and on the controller itself (PCBA). At any time throughout operation the controller will activate a buzzer when the detected temperatures exceed the reasonable value for the aforementioned components (see FIG. 9A). If the temperature sensor for the battery exceeds the value set in the controller, then an additional program executed by the controller whereby the charging circuit for said battery is opened automatically to disengage the charging circuit. The objective of this functionality is to halt any progressive heating of the battery sensor as a result of battery charging.

[0051] FIGS. 9A-9D illustrate the primary cooking protocol 900 that regulates the input and output of the blowers to attain the desired cooking outcomes. FIGS. 9A-9B diagram the fresh fuel protocol. FIG. 9C is a detailed logic diagram of the transition phase protocol. FIG. 9D is/are a detailed logic diagram of the char phase and shut down protocols. The char phase begins when the blower settings are optimized for clean, efficient and effective combustion of charcoal. Generally, the blower speed ratio is reversed where the bottom blower is much higher than the top. The char phase protocol is used until the upper temperature sensor drops below a specific temperature or at a specified rate. Then the stove goes into its off state to prevent excessive CO generation. There will always be a little charcoal leftover after the top flame extinguishes and the heat generated after that is very low and uncombusted CO is very high. Data is stored during this phase to record what blower speeds were used to estimate combustion rate of the fuel for accurate tracking.

[0052] With reference now to FIG. 9A, a diagram of the fresh fuel phase protocol, after the hot or cold start protocol is executed successfully, at 902, the controller determines the setting selected at the potentiometer, at 904. Before setting the blowers at fresh fuel phase levels, the controller checks if the temperature of the PCB is greater than a reference temperature (e.g., 65 C.) or if the battery temperature exceeds a reference temperature (e.g., 55 C.), at 906. If either condition is true, a buzzer is activated at 908. If not, the buzzer is not activated, at 910. In either event, as seen in FIG. 9B, a configuration file is checked to determine if RPM levels are at levels indicated for the potentiometer setting, at 912. If they are not, the controller instructs the blowers to adjust speeds to meet the correct speed levels, at 914. The controller presents the question whether the desired power settings for the blowers are higher than the currently measured power settings, at 915. If they are, such that the power settings for the blowers need to be increased, the secondary (top) blower primary (bottom) blower is increased first, followed after a small delay (e.g., 2 seconds) by the primary (bottom) blower, at 916. If not, such that the power settings for the blowers need to be decreased, the primary (bottom) blower is decreased first, followed by the secondary (top) blower after a small delay (e.g., 2 seconds), at 917.

[0053] While or after the blower speeds are being adjusted, the controller checks to see if the temperature of the combustion cup base has reached a set high temperature (e.g., CHARMAX), at 918. If the CHARMAX temperature has not been reached, the protocol checks to see if the potentiometer has been turned off at 919 (FIG. 9D). If the CHARMAX temperature has been reached, the protocol checks whether the combustion cup base has reached a higher temperature (e.g., CHARFLIPPED), at 920 (FIG. 9C).

[0054] With reference to FIG. 9C, if the temperature of the combustion cup base has not reached the higher CHARFLIPPED temperature, the controller determines if the change in temperature (DeltaTC1) is greater than a reference change rate (e.g., Charflig_Trigger_DeltaT), at 922. If it is not, the protocol dictates that the blower settings should be those from the configuration file, at 924, checks to see if the temperature of the flame well is below a shutdown temperature (e.g., Temp_Shup_Down), at 926, and if it has not, returns to the potentiometer check at 904 (FIG. 9A). If it has, the protocol returns to the Startup Sequence, at 928 (FIG. 9C). If, at 922, the temperature of the combustion cup base has reached the higher CHARFLIPPED temperature, the CHARFLIPPED status is changed to TRUE, at 930, and the protocol moves to settings for the Transition Phase, at 932.

[0055] The controller then periodically checks to determine if the temperature of the combustion cup base has exceeded a set higher temperature (e.g., CHARMAX), at 934. If it has not, the protocol returns to checking if the temperature of the flame well is below a shutdown temperature, at 926. However, if the temperature of the combustion cup base has exceeded the higher temperature, the CHARMAX status is changed to TRUE, at 935, and the blower speeds are ramped from CHARFLIP transition settings to char phase blower settings, at 936, before returning again to check the potentiometer settings, at 904 (FIG. 9A).

[0056] With reference to FIG. 9D, at 919, if the potentiometer is not set to off, the protocol determines if the temperature of the flame well is below a set shut down temperature (e.g., Temp_Shut_Down_Char), at 938, and if it is not, checks to determine if the temperatures at the primary and flame wells are falling at less than a set end rate (e.g., TC1_End_Rate, TC2_End_Rate), at 940. If they have not, the protocol dictates that the blower settings should be those from the char phase blower settings stored in the configuration file, at 942, and returns to the potentiometer check at 904 (FIG. 9A). If, however, at 938, the temperature of the flame well is below a set shutdown temperature the protocol returns to the Startup Sequence, at 928. And, at 940, if the temperatures at the primary and flame wells are falling at less than a set end rate, the protocol checks to see if the potentiometer level was changed recently, at 944, before returning to the Startup Sequence, at 928. If, at 919, the potentiometer is set to off, the controller turns off the stove, at 946.

[0057] 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.

Operation

[0058] The 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 a 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 temperature sensor. When the upper temperature sensor 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 temperature sensor. 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 temperature sensor 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 temperature sensor will decrease in temperature and the control system will turn the blowers off and execute a shutdown protocol whereby the controller gradually reduces the RPM signal to the blowers until they are at zero and combustion is brought to a halt The user may then remove the combustion cup and dump out the remaining ash and charcoal and start the process over again.

[0059] Upon entering the automatic shutdown phase the program returns to startup in case the user desires to continue using the stove. The controller will choose the hot start protocol and adjust blower speeds accordingly. The user places a fresh load of fuel into the combustion cup and upon ignition the stove will restart itself. If the user declines to continue cooking but does not concomitantly shift the control dial to the off position, both the cold startup sequence and the hot startup sequence will each automatically shut off the stove upon the program timing out.

[0060] 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: [0061] a) delivering consistent low emission profiles (meeting Tier 4 and Tier 5 ISO Standards for all criteria), [0062] b) superior fuel economy (30% longer cook times on the same fuel load) and [0063] c) sufficient turn down ratio for versatile cooking (targeting a 5:1 ratio, from 30 cooking eggs to boiling large pots of water)

[0064] This can be achieved through implementing simple computer controlled air management using temperature sensors and multiple fans to dynamically adjust combustion conditions.

[0065] 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.