Kirk Harris tests his newest TLUD design under the Laboratory Emissions Monitoring System (LEMS) hood.

Having an emissions hood allows ARC to make more detailed observations. We try to do one ISO 19867 test every day, establishing an in-house culture of data driven inquiry. Now, having a hood isn’t necessary for creating amazing stoves. Larry Winiarski, Tom Reed, Paul Anderson, Kirk Harris, and many other people have spent happy hours tweaking prototypes that then worked better and better. But when you get to the point where it’s hard to see the smoke, visual inspection doesn’t work as well. In the modern world, health requirements are violated by fairly invisible amounts of PM2.5. Of course, the same thing goes for CO which is odorless and invisible.

That’s why we offer free access to serious stove developers. Kirk Harris recently visited the lab to tune up his latest TLUD. We have a nice, warm cabin for him and daily access to one of our two emissions hoods. The cafeteria is open and Kirk brings food to prepare. If we are lucky, we hear him playing his flute. Dale Andreatta makes an almost annual visit and then likely climbs some mountain and goes somewhere to watch trains.

Steps of scientific inquiry

  • Complete background research into the topic
  • Observe the natural process
  • Make a hypothesis based on the observations and test it

We’ve recently added 4 oxygen sensors and 4 temperature probes to the data generated every second for greater depth of detail. Detailed observations help to see if one set of information had an effect on another.  For example, when temperatures rose at 3” up from the floor of the combustion chamber did CO or PM2.5 change at the same time? Was a significant effect on CO or PM2.5 seen above a certain temperature? What happened with the temperature probe data taken at 4” up from the floor? And more and more. The process of learning is data driven which makes a black box theorist happy.

In so many ways, the detailed observation of what is happening in a biomass stove is in its infancy. Establishing a culture of daily data generation at our lab (3 hours) is getting us closer to having “observed the natural process.” And, it’s Christmas fairly frequently when a statistically significant relationship is observed.

The high mass CQC stove with Jet-Flame inserted from the side.
The Jet-Flame in the CQC high mass brick Rocket stove

I ask for help when moving the CQC stove. We built it on a piece of plywood and two folks can, with care, move it around the lab but it is heavy. The sand/clay/cement bricks are dense at 1.4 grams per cubic centimeter after being baked many times in the stove. Dr. Winiarski advised that, when possible, Rocket stoves should float in water at less than 1 gram per cubic centimeter.

For a long time, people have added sawdust and other lightweight materials into earthen mixtures to try to lighten up stoves. I ended up at Shengzhou Stove Manufacturer (SSM) in China because for hundreds of years ceramicists had manufactured (and sold in Africa since 1407) durable earthen stoves that weighed around 0.7 grams per cubic centimeter. Their amazing clay floats when dug out of the ground! It is full of diatomaceous earth. The Shens own a 100 year supply of clay in two mines next to the factory.

Why go to all of this trouble to lighten stoves?

The heat from the fire is diverted into the mass of the stove body and less heat is available to cook food. It is harder to start a hot, intense fire in a high mass combustion chamber. In a natural draft stove, this can be disadvantageous. The open fire has other problems but, out of the wind, the hot gases from the flames directly contact the pot and it’s common for open fires to have higher thermal efficiencies compared to high mass stoves, including Rocket stoves. Lightening the bricks helps to address this difficulty. Heat is still diverted into the stove body, but less. Well insulated, mostly metal, Rocket stoves successfully avoid most of these losses.

Indigenous cooks, experts at using fire, often use grasses and twigs to start a hot, fast fire in a high mass stove. You need to pour the BTUs into the stove to quickly prepare food. Speed to cook is almost always the first priority when talking to cooks around the world. When the SSM Jet-Flame is added to the high mass stove, the mini blast furnace immediately starts a hot, over 1,000°C fire that delivers relatively hot gases into the channel gap around the pot created by the pot skirt. (The CQC skirt creates a 5mm channel gap that is 7cm high.) 

The Jet-Flame creates a surprising result

The thermal efficiency in the first CQC/Jet-Flame test (see below) was 33%. The 5 liters of water boiled in 12.5 minutes. After the first 12.5 minutes of heating, the over 1,000°C fire started to heat up the mass and the water boiled more quickly in 10.2 minutes at 38% thermal efficiency. Three more short, but intense, heating phases resulted in the thermal efficiency incrementally rising to 41%, 42%, and 45%. The progressively hotter gases scraping against the sides and bottom of the pot in the small channel gap were more and more successful at transferring heat through the metal walls of the pot into the water.

When thermal efficiencies are in the 40% to 45% range, the performance of the high mass stove is similar to low mass, insulated Rocket stoves. This similarity was completely unexpected at ARC.

Results of five tests of the CQC Stove with Jet-Flame.
A woman sits next to two rocket stoves.
A woman sits next to two rocket stoves.
Firewood is stored between a pair of CQC’s TLC Rocket Stoves.

C-Quest Capital recently announced a collaboration with Macquarie Group Ltd., a financial services company with A$550 billion in assets under management and 16,000 employees in 35 countries. The two firms will fund and deploy efficient cook stoves with pot skirts to one million rural households across Malawi, Zambia and Tanzania. CQC’s preferred rural stoves project standard is two stoves per household to decrease user fallback on three-stone fires.

USAID in-field testing in Africa showed that Rocket stoves with pot skirts reduced smoke emissions by 40% due to the use of less wood while cooking. Addressing health by increasing the air exchange rate in the kitchen and home is a fundamental component of this project. This is done by strategic placement of windows and doors, and promoting half-wall kitchens or well-protected external cooking spaces. A minimum of one visit per year by trained staff to each household to help repair, maintain, and ensure good use of the Rocket stoves is also essential to elevating adoption rates in the targeted areas.

Over the next decade, this investment will deliver over 40 million high quality carbon credits with verified Sustainable Development Contributions to the Voluntary Carbon Market. It is the first leg of a three-pronged program to transform the lives of low-income communities across Sub-Saharan Africa at scale. Ken Newcombe, CEO of CQC, comments, “Our hope is to include something like 100,000 Jet-Flames, assembled by Ener-G-Africa in Lilongwe, Malawi, in the project. Field tests have indicated that the Jet-Flame dramatically reduces PM2.5 emissions and exposure to cooks and their families, further protecting health. If the deployment doesn’t get to 100,000 sold by end of next year it’s not because of the demand – it’s because we couldn’t get the working capital and distribution channels to get the product to the market. Of course, we are exploring all possibilities.”

Sam Bentson and a Winiarski designed down-feed downdraft Rocket stove with added cooling fins.

We used to have problems with the upper portion of the sticks catching fire in Dr. Winiarski’s down-feed downdraft Rocket stoves. The draft had to be strong, and the sticks at the right moisture content and size/weight to burn up completely without any smoke back drafting up into the room. The vertical metal feed tube got too hot and could catch the top part of the sticks on fire, overcoming the draft moving into the stove. (Usually something like 3 MPH.)

When Sam Bentson and Karl Walter were making a 20 watt thermoelectric generator (TEG) for the EPA SBIR supported Integrated Stove project we had the same problem, until Sam added aluminum cooling fins to the top of the vertical feed tube, as seen above. The team had previously designed and built the cooling fins unit that Sam is holding in the photo to cool the cold side of the TEG. I was amazed how well cooling fins work!

But then I remembered how small the radiators are in automobiles with huge horse powers. I saw that Sam and Karl had added a fan to their radiator to make sure it could dissipate the 1.5 kilowatts running through the hot side of the TEG. Adding fins to parts of a stove that could use more dissipation of heat brings to mind several possible applications: the heat exchanger cylinder in the photo, a chimney that has high exit temperatures, or the outside of a metal combustion chamber to preserve the metal. But I would not use fins where they can get dirty! They don’t work, for example, on the bottom of a cooking pot where soot quickly fills the space between the fins. (I didn’t think of this before we tried it.)

Manufacturing pot skirts

In 2013, C-Quest Capital (CQC) began distributing and installing the TLC Rocket Stove (TLCRS), a high-efficiency, long-life metal and brick improved cookstove, to the rural poor of Malawi. Early learning has resulting in many upgrades to the stove to improve sustained use and a long life. Over the past two years, CQC has installed the TLCRS in 450,000 Malawian households. Beginning in January 2020, Ener-G-Africa (EGA), a Malawian entity formed by CQC and Malawian entrepreneurs, began manufacturing all the metal stove parts for CQC’s sub-Saharan Africa TLCRS program and has since produced more than 300,000 sets of parts.

Interior view of EGA Stove factory in Lilongwe, Malawi
Stove Kits ready to ship at Ener-G-Africa’s factory in Lilongwe, Malawi

More recently, in February 2021, CQC placed irrevocable orders for the first 10,000 Jet-Flames from Shengzhou Stove Manufacturer in China, marking the first large scale commercial commitment to Jet-Flame distribution in the world. With CQC’s funding, EGA’s factory in Lilongwe is currently building the second solar panel assembly plant in sub-Saharan Africa and will begin manufacturing the solar panels, and eventually the batteries, needed for the Jet-Flame Kit.  CQC is hoping the superior cost and cooking amenity provided by the Jet-Flame will make serious inroads to the charcoal user market.

Through the growing partnership between CQC and EGA, the TLCRS will be installed on a two stove per household basis in three million households across eight sub-Saharan African countries in the next four years. Together, CQC and EGA are setting a new standard for cookstove projects in rural Africa. 

Manufacturing pot skirts
Welded pot supports
Parts ready for packing
Manufacturing area at Ener-G-Africa’s factory in Malawi