Champion (2021) average energy emission factors (g/MJ) from ISO high, medium, and low tests.
Champion, Wyatt M., et al. “Cookstove Emissions and Performance Evaluation Using a New ISO Protocol and Comparison of Results with Previous Test Protocols.” Environmental Science & Technology, 2021, 55, (22), 15333-15342. DOI: 10.1021/acs.est.1c03390
Lab testing can quickly compare emissions from stoves. The EPA and ARC labs now measure the climate emission factors, not just PM2.5 and CO. It has been proven that only field tests show real world performance. Together, lab and field tests help to move stoves forward as we get closer to market driven stoves that please cooks, successfully cook food, use a lot less fuel, and protect health/climate.
The above chart contains a lot of information. Some takeaways are:
Wow! The Three Stone Fire (TSF) was pretty bad! 943g/MJ for PM2.5, 15.5 g/MJ for CO.
Charcoal made ~90% less PM2.5.
The Carbon Monoxide (CO) from charcoal was only a bit higher than the Three Stone Fire (19.2g/MJ).
LPG did so well! (Too bad that we are entering the end of the fossil fuel era).
The forced draft pellet stove looked great, as well. (PM2.5: 30g/MJ, 2.2g/MJ CO)
Black Carbon (EC) is much worse than CO2 for climate change. Many of the stoves, except the Rocket stove, successfully reduced Black Carbon.
R&D has shown that the Rocket stove requires successful forced draft mixing at high temperatures to decrease emissions of Black Carbon and potentially address climate.
When the emissions factors are summed and converted to global warming potential the forced draft stoves have the potential to generate large amounts of carbon offsets.
https://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-02-09 16:07:592024-02-09 16:29:55Moving Forward: Thanks to Jim Jetter’s EPA Lab!
Dr. Sam Baldwin describes the use of a pot skirt in his book “Biomass Stoves: Engineering Design, Development, and Dissemination (1987).” Changes in the length and diameter of the channel gap (between the pot and the interior of the skirt) result in dramatic changes in heat transfer efficiency.
“In fact, the channel efficiency, defined as the fraction of the energy in the hot gas entering the channel that is transferred to the pot, is extremely sensitive to changes in the channel gap. For a 10cm long channel, the channel efficiency drops from 46% for an 8mm gap to 26% for a 10cm gap. Thus the stove and pot dimensions must be very precisely controlled.” (pg. 45)
If stoves are to be compared, these types of variables must be controlled. The use of a standard pot, or pots, without pot skirts will result in performance scores that are significantly reduced. If a pot skirt is used on testing pots it should be identical in all aspects. Again, the use of a standard pot(s) seems to be required.
https://aprovecho.org/wp-content/uploads/2023/12/12.29.23-pot-skirt.jpg11101408Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-12-29 18:22:422023-12-29 18:22:43Pot Skirts – basic theory
“The concept of black boxes has been around since the early days of systems theory though some attribute the first use to the field of electrical engineering.
It is a simple concept and has a straightforward definition: we know the inputs and subsequent outputs to a system but the internal workings of the system are not visible to us.
Black boxes approaches focus on input and output rather than the details of how inputs are transformed into outputs”.
The results of experiments guide the subsequent experiments. For instance, adding secondary air jets into flame is shown to decrease PM2.5. Guided by the result, further investigation in a prototype under the emission hood determines the most successful application by varying parameters.
Random Experimental Design
In a Black Box (where the situation is complex and not understood) randomized approaches to experimental design can be effective and efficient.
https://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-11-30 17:25:332023-11-30 18:02:16Iterative Development of Stoves and Black Box Theory
Written decades ago, the lab based tests for both biomass heating and cooking stoves were designed to achieve statistical validity by controlling variables. Because many real world variables were removed from the heating and cooking stove protocols, the results were known not to predict real world performance.
Automobiles are currently tested on a dynamometer instead of being driven around town. EPA estimates are based on dyno tests designed to reflect “typical” driving conditions and driver behavior. Even so, The EPA warns customers that actual mileage will probably be significantly different.
To predict real world performance, each car could be driven around town by enough people until a meaningful average was mathematically determined. Cook stove tests could also rely on field tests generating complicated data resulting in accurate predictions. However, doing real life testing for every manufactured car or stove has been thought of as rather cumbersome.
Another approach might be to have regional survey data inform a predictive model. The model teaches the dynamometer how to test the car. Stove use could be modeled in the same way, so lab tests get closer to predicting what actually happens when cooks use wood to make meals.
Making a model probably didn’t seem to be worth the trouble in the past. However, things have changed. The harmful emissions from cars and biomass stoves damage health and contribute to climate change. Actually knowing what a new car or stove will do when used should help to create better technologies and reduce pollution. Any kind of predictive testing seems like a great idea!
https://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-07-06 15:36:462023-07-06 15:38:27Predictive Testing of Cars and Wood Stoves
Yesterday, two fine fellows who manufacture stoves in southern Oregon visited our lab. One of the very competent guys had just installed a Corvette engine in a Jaguar, for fun.
We quickly got on the same page when the ARC staff showed them how an emission hood (with both real time and gravimetric measurements) enables quick experiments to improve performance and achieve clean burning.
Anyone involved with racing (or fixing cars) knows how a computer helps to tune a modern car. The biomass emission hood allows folks to tune stoves like race cars.
Testing for development means that the testing of a manufactured product will have known results.
You win the race.
https://aprovecho.org/wp-content/uploads/2021/02/vroom.jpg7341200Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-06-08 15:11:482023-06-08 15:11:49Emission Testing: Tuning a Stove Like a Race Car
The Jet-Flame pushes jets of primary air into the fire to aid combustion.
When a wooden stick is burned a lot of smoke is produced but the made charcoal at the tip of the wooden stick does not make much smoke. Rocket Stove: Push the sticks in slowly so the charcoal at the tip is burning. TLUD: Charcoal covers the slowly burning fresh wood.
If the stove begins smoking, the solid wood is being turned into gas too quickly, too much wood gas is being produced and un-combusted fuel is escaping. Rocket Stove: Pull the sticks back until just the tips are burning. TLUD: Reduce the primary air.
Mixing the smoke, gases, flame, and air reduces emissions. Rocket Stove and TLUD: Cut up the laminar flames with static mixing devices or jets of primary or secondary air. Aim the jets of secondary air into the flame and adjust the velocity of the jets to completely cover the burning fuel. Primary air jets can also achieve close to complete combustion. Excess velocity in primary or secondary jets is detrimental when it reduces the combustion temperature.
For close to complete combustion the temperature in the combustion zone needs to be 850C or above. The woodgas and air and flame have to be thoroughly mixed. The residence time needs to be 0.2 seconds or more. Reduce the amount of woodgas entering the combustion zone until close to complete combustion is achieved. Biomass fuels with 15% or lower moisture content are easier to burn.
It is necessary to tune the stove under an emissions hood to achieve close to complete combustion. Change one variable at a time and test until significance is achieved.
https://aprovecho.org/wp-content/uploads/2020/12/12.30.burning3.png578898Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-02-24 17:27:292023-02-24 17:27:31How To Achieve Close To Complete Combustion of Biomass
The SSM Jet-Flame in the C Quest Capital 15 brick stove
The Journal “Energy for Sustainable Development” has just published Aprovecho’s most recent research paper, “Retrofitting stoves with forced jets of primary air improves speed, emissions, and efficiency: Evidence from six types of biomass cook stoves.” It was authored by Samuel Bentson, David Evitt, Dean Still, Dr. Daniel Lieberman and Dr. Nordica MacCarty (Energy for Sustainable Development 71 (2022) 104–117)
Incorporating jets of forced air into biomass cook stove combustion has been shown to potentially decrease harmful emissions, leading to a variety of designs in recent years. However, forced draft stoves have shown mixed success in terms of real world performance, usability, and durability. The Shengzhou Stove Manufacturer Jet-Flame forced draft retrofit accessory was developed by the Gates funded Global Health Labs and ARC, to implement forced jets of primary air at a low cost into a wide range of types of cook stoves using a small 1.5-W fan housed in a low-cost cast iron body to be inserted beneath the fuel bed of a biomass cooking fire.
This research sought to quantify the potential efficiency and emissions performance impacts of the Jet-Flame when installed in six different types of biomass cook stoves (three open or shielded fires and three rocket stoves) versus the natural draft performance of each. The effect of the operating fan voltage was also measured. A series of tests following a modified ISO 19867-1:2018 protocol were performed in the laboratory using the Aprovecho Laboratory Emissions Measurement System (LEMS) equipped with additional oxygen and temperature sensors.
Results for each stove, carefully tended with a single layer of sticks, showed that the global average PM2.5 reduction with the Jet-Flame was 89% relative to the natural draft cases, with larger relative improvements seen in the most rudimentary stoves. CO was reduced by a global average of 74%, reaching Tier 4 or 5 for all stoves. Thermal efficiency was also improved by 34% when calculated without taking into account the energy content of the remaining char (or 21% with char), illustrating the value of burning char to provide cooking energy rather than leaving it unburned in the combustion chamber as is common in many natural draft stoves. Time to boil was also reduced by 8%.
In addition, adjusting the voltage of the jet-flame assisted in modulating firepower, possibly improving the usability of the stove.
https://aprovecho.org/wp-content/uploads/2020/08/jet-flame-in-cqv.png520352Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-10-14 16:31:422022-10-14 16:32:49Jet-Flame Research Results From Six Types of Biomass Cookstoves
In 2009, The New Yorker published an article about the Rocket stove entitled Hearth Surgery: The quest for a stove that can save the world. One year later, USAID funded field tests in Africa showed that the insulated Rocket stove was not cleaner burning than the open fire. The Rocket with skirt saved 40% of the fuel to cook and emissions were only reduced by that amount.
Not a Planet Saver, yet!
The insulated Rocket combustion chamber raised temperatures but as Dr. Winiarski realized at the time, flame, air, and gases were not adequately mixed to achieve sufficient combustion efficiency. Larry knew that the Rocket was smoky but it was simple to make and with a pot skirt saved fuel. He wanted to provide folks with a stove that was helpful and he realized that it wasn’t perfect.
Larry’s idea went viral worldwide and continues to be a favorite on the internet and in many low- and middle-income countries. Millions of Rocket stoves are manufactured and sold yearly by factories large and small.
Going viral is great but can have a downside especially when the initial products are not technically mature. It’s normal for first generation products to be improved as time goes by. The process of development continues in 2022.
https://aprovecho.org/wp-content/uploads/2016/03/Sidefeed-1.jpg276187Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-08-19 13:25:292022-08-19 14:02:59A Recent History of the Rocket Stove: 2009
A major accomplishment of the past few years has been the creation of thirty Regional Testing and Knowledge Centers (RTKCs). Many of these facilities rely on emissions equipment and training from Aprovecho Research Center. They are usually created as an addition to a university in a developing country, and were initially funded by large development organizations such as the Global Alliance for Clean Cookstoves.
Once a month we’re turning our newsletter over to Sam Bentson, to tell you more about their activities:
Hello to everyone at the Regional Knowledge and Testing Centers (RTKCs), and to our newsletter readers, from Sam Bentson, General Manager at Aprovecho!
Sam was recently in Ghana and Senegal and then visited
the Instituto de Investigación y Desarrollo de Procesos Químicos (CPC) in La
Paz, Bolivia helping with stove testing and their LEMS emission hood. La Paz has the highest elevation of any
government city in the world at an altitude of 3,650m!
The atmospheric pressure at CPC in La Paz is 20Hg. Our
lab in Oregon is 241 meters above sea level where the atmospheric pressure is 30Hg.
Sam and the CPC staff determined that at their high elevation, and with the
voltage applied to the Jet-Flame motor increased to 8V, the mass flow in the
Jet-Flame was 82% of the mass flow measured at the ARC lab.
Altitude had a big effect on boiling water and on the Jet-Flame!
CPC in La Paz, Bolivia from left to right: Libertad Mariana Casanova Velasquez, Dalia A. Borja, Sam Bentson, Jazmin Gidari Ruiz Mayta, and Karen Fabiana Paz Quispe
When Sam returned home, he started thinking about keeping in touch with all
of his friends at the RTKCs and to share reports of activities. We are starting
with CPC and highly recommend that anyone interested in doing research or a
stove project make use of this wonderful resource in Bolivia!
Testing the SuperPot on a three-stone fire, Batil Camp, South Sudan
ARC engineers rely on feedback from field testing to improve the real-world function of biomass cooking systems. Sometimes the news is challenging, but in this instance the news was very encouraging!
In 2014 the UNHCR (The UN’s Refugee Agency) conducted pilot testing of the SSM SuperPot in seven refugee camps in four countries in East Africa: Kenya (Kakuma, Dadaab), South Sudan (Yida, Maban), East Sudan (Kilo 26), and Ethiopia (Dollo Ado; Bambasi).
Kakuma: “Tests conducted in Kakuma overall yielded very positive results. The participants confirmed that cooking time is faster, fuel is saved, and water is conserved even if only by a scant amount. Participants agreed that SuperPot is a much better option than the regular cooking pots not only because of the efficiency but they are apparently also easier to clean, saving more energy and water.”
Dadaab: “Smoke expelled from the sides of the pan and does not enter the pot thus no change in the smell and taste of food. SuperPot cooks food faster and thus less firewood used. Less usage of firewood and faster cooking would mean less protection incidents, more time for infant/child care. With the SuperPot there was less heat loss and firewood consumption by wind as most of the surface was covered with the pan unlike the traditional pot.”
Batil: “Significant differences in cooking time were noted: for CSB++ (corn-soy blend flour) the Stovetec SuperPot cooked 8 minutes faster than the local pot; for cereal, there was a difference of 4 minutes. With pulses, super pot cooked faster by 5 minutes. Overall, Stovetec is time efficient. The fuel savings are particularly impressive.”
Yida: “Together, both tests saved women 20 minutes in overall cooking time. According to the participants, this time saved ‘can be used for other productive household economic activities or be dedicated to childcare which will effectively improve the nutrition and health status of the children and the entire household members.'”
East Sudan: “Testing was conducted at hospital kitchen inside Kilo 26 hospital complex by four people including two cooks and the HAI nutrition coordinator. 500g of lentils were cooked in 750ml of water in both pots on improved stoves. The super pot cooked the lentils in 27 minutes, as opposed to aluminum pot, which took 34 minutes, for a difference of 7 minutes.”
Assossa: “Results indicate that community perspectives are positive for the StoveTec super pot. The water boiled faster in the super pot by 3 minutes and the lentils were cooked 15 minutes earlier on kerosene stove, while also being 9% more fuel efficient than the regular pot. When testing CSB on kerosene stove, super pot was 4% more fuel efficient and saved 7 minutes of cooking time.”
Hilaweyn: “Tests were ran in Buramino Block 13 and Buramino Block 24 Line A with woman groups. In Block 13, the women tested cooking time for 500g of rice over an improved stove (with windshield). The Stove Tec pot cooked the rice faster by 8 minutes. In Block 24, women cooked 500g of lentils over firewood. Stove Tec pot out performed local pot only by 2 minutes. Neither water used nor fuel consumption were measured.”
Summary:
“Results indicate that the super pot is fuel efficient, effective in saving time, safe and well accepted by the community.”
Recommendation:
In their summary report, the UNHCR Food Security and Nutrition Unit advised “Procurement and distribution of SuperPot in select humanitarian contexts within priority countries according to needs of the most vulnerable households.”
https://aprovecho.org/wp-content/uploads/2022/07/7.11.22-Batil-Camp-SuperPot.jpg591725Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-07-11 15:37:572022-07-11 15:37:59Learning From The Field, Part 3
