ARC just received a grant to hire full time assistance for the Regional Testing and Knowledge Centers (RTKC). Many of the RTKCs use our emission equipment. Jaden has just returned from Tanzania where she was setting up a new lab and Travis is going to Mozambique soon to do the same thing. Over 100 emission boxes have been sold worldwide.
It’s great to have a dedicated person available so anyone with a problem can get immediate help. The new hire will learn by testing every day, crunching the numbers with Jaden’s Python software, cleaning the equipment, calibrating it, etc. Sam and Jaden are here to help with complicated problems.
Maybe Travis, Kim and I can help with iterative development of improved stoves?
What a great year!
https://aprovecho.org/wp-content/uploads/2025/06/ethiopia_lab.png454600Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-09-25 14:56:522025-09-26 09:29:49What a Great Year!
It’s great to have colleagues whose opinions are trusted. Dr. Larry Winiarski was usually right, by which I mean, that when we built and tested his inventions they might not have been perfect but were significant improvements, good starting places for further development. I always appreciated talking to Dr. Tom Reed, inventor of the TLUD, for the same reasons. Hui Yang Shen, the head of Shengzhou Stove Manufacturer, has been an almost-always-right resource about manufacturing. In 1987, Dr. Sam Baldwin wrote a book on cook stoves that I still refer to frequently.
In the same way, Google’s Gemini AI has become an interesting resource for me. It has been fascinating to encounter such an accessible way to find another reasonable opinion. One question to AI every morning has become part of my routine although I don’t have time for more. Google AI gives many references for each summary and I try to at least scan them.
At ARC, we have the great advantage of doing experiments to learn. Reading what others have written is interesting, however I much prefer and believe that progress is faster when doing iterative development of prototypes under an emissions hood. As importantly, going into the field to do R&D with cooks, distributors, manufacturers, etc. is necessary to make things that work. Reading alone cannot get you to success but it is a sturdy third leg of the stool: Literature searches, lab and field R&D.
Glad whenever I get out of the box.
https://aprovecho.org/wp-content/uploads/2025/09/Untitled.jpeg300600Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-09-18 13:58:452025-09-18 13:58:46AI: Great but Stuck in a Box
In the middle of August, we had three stoves under development using the three emission hoods (two-forced draft, one natural draft). Sam and Travis built the natural draft hood to help improve heating stoves. Sam is thinking about making another one, number four, since we are working on more heating stoves and things can get a bit backed up.
During testing teams often trade observations during the day and sometimes, when the air temperature gets a bit elevated, I’ve heard folks exclaim: “WOW, FIRE HOT!”
What makes fire colder? Things like:
The air entering the combustion chamber (~30C in August)
Surfaces that absorb heat, like thermal mass or
Pots of water (~100C)
Thermometers are very helpful when trying to improve performance! Both combustion and heat transfer efficiency increase when temperatures rise. Taking a stove’s temperature(s) can facilitate making helpful changes in a prototype.
WOW, look at the temperature, IT’S HOT!
https://aprovecho.org/wp-content/uploads/2024/04/hot-4.19.24.jpeg4691200Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-09-10 12:09:222025-09-10 12:20:12Cleaning up combustion: TOO COLD!
The great thing about 12” high tincanium natural draft TLUDs is that they are cheap, short and powerful. Dr. Tom Reed had a dream that a billion TLUDs would protect health, save wood, etc. We wondered if an all Tier 4, affordable, stainless steel ND-TLUD might help?
The first step was to test the baseline ND-TLUD. It’s great for camping outdoors but not close to Tier 4 for PM2.5, CO and Thermal Efficiency. We are now trying three ways to achieve all Tier 4:
A nothing fancy prototype. Control primary and secondary air and don’t let flames touch the bottom of the pot.
A static mixer prototype.
A better concentrator ring prototype.
Usually when we make one change a day in a prototype and test the effects under the emission hood it takes about a month to get close to an “optimal” solution. Doing one iteration a day leaves us time to do all the other work here at the lab.
Looking forward to sharing test results!
https://aprovecho.org/wp-content/uploads/2025/09/image.png231280Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-09-04 15:34:292025-09-04 15:40:20Lowering Emissions in a Short, Natural Draft TLUD
When Dr. Larry Winiarski and I lived for a season at Rancho San Nicolas in Baja California Sur, Mexico we wanted to be helpful. We built cook stoves, solar cookers and other delightful inventions that we found interesting. But Larry was an insightful fellow and he started to listen to folks and ask them what problems they wanted to solve.
We had such a great time at the ranch, people were so nice, but Larry learned more than I did because he was born in Honduras and was more fluent in Spanish. It took me a couple of years to be able to understand what folks were saying. Speaking the language is important for many reasons!
After a while, Larry and I started working with the rancheros making rat proof boxes from available wire reinforced cement. Steel would have been great but was much too expensive and you couldn’t get it anyway. Rats were eating so much food and storage was a major problem. Stoves were great but homemade rat proof boxes took off like hot cakes.
We started making boxes and became more helpful. Folks loved Larry anyway but now he wasn’t just good company. After a couple of years, I started fixing holes in boats.
https://aprovecho.org/wp-content/uploads/2025/08/rodent-proof-box.jpg300400Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-08-27 09:11:112025-08-27 09:20:19Learning From People
Over the past 3 years, thanks to three grants from Fire Capital, Aprovecho has been working with CSIR (Council for Scientific and Industrial Research) in Ghana to expand their lab capacity. We have focused on teaching stove design principles through co-developing a stove retrofit for boarding schools in Ghana.
During the recent in-person workshop, Jaden visited the lab to help with the building of the prototype and plan for its installation at a local school. This prototype will go over an existing stove at the school, increasing thermal efficiency and reducing indoor emissions. With user, manufacturer, and lab result feedback, CSIR will finalize their design and give stoves to ten schools for a larger impact study.
The LEMS in Bangladesh
Sam went to Bangladesh to update their lab and provide training. The Bangladesh University of Engineering Technology in Dhaka now has a lab that can test cookstoves according to ISO 19867 standards. This provides a useful development tool for the area as well as way to teach the next generation about cookstove development. Sam observed that while urban and peri-urban areas had access to gas and electricity, households couldn’t always afford it, highlighting the need for clean biomass stoves even in areas with access to alternative fuels.
Sam also visited Life Green Energy, a stove manufacturer focused on forced draft stoves. Together, they developed a local Jet-Flame prototype aimed at saving fuel and reducing emissions. The prototype was able to burn green wood while other brick stoves could not. More development is planned to improve the product.
Aprovecho and Oregon State University paired with SunFire (Malawi), KIRDI (Kenya), and CSIR (Ghana) to conduct a total of 720 thermal efficiency tests on traditional wood and charcoal stoves. The goal was to compare the baseline efficiency of stoves with UNFCCC (United Nations Framework Convention on Climate Change) default efficiency, which had recently changed.
We developed a new test protocol, the UCET (Uncontrolled Cooking Efficiency Test), which measures thermal efficiency on any meal cooked. We found that the average thermal efficiency was between the new and old UNFCCC defaults. It was also found that firepower, pot/pan size, and cooking method are strongly correlated with efficiency.
https://aprovecho.org/wp-content/uploads/2025/08/UCET_test.jpg473600Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-08-13 11:55:502025-08-13 12:00:44What’s Cooking at Aprovecho
When I asked Google AI, “Is flow more laminar in a smaller diameter tube?” it immediately responded:
“Yes, thanks for asking! A smaller diameter tube can promote more laminar flow for a given flow rate. This is because reducing the diameter of a tube increases the Reynolds number, which is a dimensionless quantity that helps determine whether flow is laminar or turbulent.”
I had been noticing that the chimney also increased draft in a TLUD we have been developing, lengthening the rising column of flame.
As a rule of thumb, Dr. Winiarski advised that flame should burn out before it touches the bottom of the pot. Yellow flame is very hot (around 1,100C) which is great, but sufficient mixing and residence time are also needed to burn up smoke.
Have you also experienced that lifting the pot off of the top of a TLUD can reduce the emissions of PM2.5?
Reducing draft by removing the concentrator disk/chimney this week has allowed flame enough time to burn up more smoke in a relatively short TLUD. At the same time, thermal efficiency has been reduced when short flames dance playfully on top of the larger diameter combustion zone (with a larger Reynolds number).
https://aprovecho.org/wp-content/uploads/2025/08/pyrolysis-stove-diagram.jpg388500Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-08-06 13:56:572025-08-06 14:11:41Concentrator Disk/Chimney in a TLUD
Looking at the photo it is easy to imagine why field-testing is needed to show whether an intervention is actually saving fuel. Real life is complicated and is not replicated in a lab.
The use of a Water Boiling Test to determine if new stoves are saving fuel has historically been questionable. WBT’s tend to underestimate fuel use compared to field tests. (Hernández, 2014; Teune et al., 2020, Bayer et al., 2013).
Water Boiling Tests are great for international stove comparisons when variables are controlled. WBTs are also useful to investigate how stoves might be improved and to experiment with iterative changes that could improve heat transfer and combustion efficiency.
Luckily, we were assured at ETHOS 2025 that only field tests would be used from now on to calculate fuel savings for carbon credits.
When data from field testing was replaced with lab-based results it was such an obvious mistake!
Of course, any type of testing needs to be done carefully by a third party.
https://aprovecho.org/wp-content/uploads/2025/07/5703178844_856986299e_c.jpg535800Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-07-30 15:42:442025-07-30 15:42:45Carbon Credits and Fuel Savings?
In my opinion, the WBT* cannot be used, especially in the lab, to improve a biomass cook stove because all of the important field variables are not represented.
A successful cook stove needs to be evolved from field tests, as we did in Southern India for the Shell Foundation. Cooks in eighteen villages kept on changing the Rocket stove until it was acceptable, useful, and even likable. It took a while but it was a lot of fun and a great introduction to Southern India!
The WBT, with severely limited variables, can be useful in the lab for international comparisons of stove performance. The same pots, same amount of water, same fuel, same procedures and protocols limit the confounding variables in an attempt to isolate the stove as the reason for perceived differences.
As we did in India, both field and lab data can inform stakeholders. The successful stove has to please cooks, retailers, distributors, etc. and, at the same time, meet project goals such as reducing adverse health effects. We used the WBT in the lab and the CCT* in the field. Marketing tests, as suggested by Baldwin (1987) were very important, as well. We learned right away that the stove had to cost ~$5 to capture sustainable market share.
The lab based WBT is best used to inform researchers how stoves might be improved. Then, iterations in prototypes are tried in the field including cost, weight, color, height, firepower, fuel used, etc, etc.
This combined use of the WBT, CCT, and KPT* for stove development was suggested in the International Stove Standards, (1985).
*Water Boiling Test “The Water Boiling Test (WBT) is a simplified simulation of the cooking process. It is intended to measure how efficiently a stove uses fuel to heat water in a cooking pot and the quantity of emissions produced while cooking.” – The Water Boiling Test Version 4.2.3
*Controlled Cooking Test “The controlled cooking test (CCT) is designed to assess the performance of the improved stove relative to the common or traditional stoves that the improved model is meant to replace. Stoves are compared as they perform a standard cooking task that is closer to the actual cooking that local people do every day.” – CCT version 2.0
*Kitchen Performance Test “The Kitchen Performance Test (KPT) is the principal field–based procedure to demonstrate the effect of stove interventions on household fuel consumption.” -KPT version 3.0
The size of the hole in the middle of the flat plate, usually round, that seals the top of the combustor in a TLUD stove has important functions. The flat plate forces air jets/flame to travel horizontally in an attempt to completely cover the fuel bed. The diameter of the round hole has a dramatic effect on firepower. When it is too small, the fire can even be extinguished.
As with other variables, iterating changes in a prototype under the emissions hood can determine the compromise that best meets project goals. Larger holes in the concentrator result in higher firepower but can also increase emissions. In a 5” in diameter stove, a 3” hole in the middle of the concentrator is commonplace.
In the StoveTec FireFly lantern, developed at ARC, a small hole in the concentrator ring (1.5”) forces the flame into a narrow, vertical cylinder used for illumination. While the firepower is very low, so are the health-affecting emissions per minute.
https://aprovecho.org/wp-content/uploads/2025/07/concentrator-ring-image-7.3.25.jpg6731200Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-07-03 13:47:082025-07-03 14:05:00The Concentrator Ring in a TLUD
