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.”

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
CQC stove set up for testing under the LEMS hood

ARC is investigating how to optimize the performance of the SSM Jet-Flame in the CQC earthen brick stove. Forty six thirty-minute ISO 19867 Water Heating Tests were completed under the LEMS hood at seven fan speeds. Two 4 cm x 4 cm douglas fir sticks were burned side by side. Five liters of water in a seven liter pot were heated, and the CQC pot skirt was used in all tests.


Tier 4 ISO Voluntary Performance Targets:

  • Thermal Efficiency           40% to 49%
  • CO                                     <4.4g/MJd
  • PM2.5                               <62mg/MJd

Time to boil: The time to boil decreased with an increase in fan speed.

Thermal efficiency: The thermal efficiency stayed close to 35% in most cases and was higher at 3 and 8 volts (around 40%).

Firepower: The firepower rose to 6.8kW at 8 volts, starting at 2.6 kW at 2 volts.

Emissions of Carbon monoxide: Generally emissions decreased with increasing fan speed.

Emissions of PM2.5: 7 and 8 volts scored the best, at half of the result of 5 volts.

Combustion chamber temperatures: The mid combustion chamber temperatures rose with increases in fan speed from 382C to 730C.

Excess air:  Lambda fell as voltage increased from 4.1 to 1.9.

We recommend that the project do enough field testing to determine what settings are preferable to local cooks, remembering that higher voltages consume more power. In this way, the Jet-Flame/CQC stove can be tailored to regional cooking, keeping in mind the power output and use patterns of the CQC photovoltaic solar system.

Here’s what the flame looks like when varying the voltage:

Kabanyana Murabukirwa Domina and Jean Marie Vianney Kayonga in Rwanda
Kabanyana Murabukirwa Domina and Jean Marie Vianney Kayonga in Rwanda
Kabanyana Murabukirwa Domina and Jean Marie Vianney Kayonga in Rwanda

One of the roles of the ARC engineer is to give accurate technical information to the in-field decision makers who are directing the stove project. The folks on the ground have to make sure that cooks really like the stove, that the price is market based, that manufacturing is arranged for, etc. ARC engineers and the field team work closely together as the project evolves.

A New Project in Rwanda

In Rwanda, Kabanyana and Jean-Marie and their NGO, ENEDOM, are working with C-Quest Capital and ARC on a carbon credit supported Jet-Flame project. We met Jean-Marie through the internet and realized that he is well known in the sector. In fact, he knows many of our friends in Africa. Dr. Dan Lieberman at Global Health Labs sent Jean-Marie twenty Jet-Flames, and he showed them around to many of organizations, like the World Bank, that have large projects in the country.

Real World Use Guides Product Improvement

Moving the Jet-Flame to the side of the CQC stove
Moving the Jet-Flame to the side of the CQC stove

When we envisioned the Jet-Flame we imagined that it would be inserted into the fuel door of a Rocket stove. Mr. Shen at SSM directed the effort to manufacture the Jet-Flame and it includes a beautiful stainless steel stick support that also protects the fan. However, it only took several weeks of trails for ENEDOM to make a strong recommendation to move the Jet-Flame to the side of the CQC stove. Cooks in their homes were accidentally burning up the cord!

We gratefully thank ENEDOM for helping us make fewer mistakes. It’s another great example of trying to make sure that reality is in the product.

Home made CQC rocket stove (L) is easily improved with the addition of a Jet-Flame (L).

ASAT, the for-profit arm of Aprovecho, has been awarded a prestigious Tibbetts Award by the US Small Business Administration. The Tibbets Award is given for demonstrating significant economic and social impact from the R&D funding provided by SBIR (Small Business Innovation Research) grants. ASAT received EPA SBIR grants that enabled the research and development of:

  • The Jet-Flame that increases combustion efficiency (costs around $11). See:
  • An air cooled thermoelectric generator (water cooling is hard to install).
  • A low cost, easily cleaned electrostatic precipitator (90% reduction of soot).
  • The Integrated Stove. See:

We partnered with the Gates funded Global Health Lab to develop the Jet-Flame. They have recently supported sending Jet-Flame samples worldwide. C-Quest Capital (CQC) has completed several pilots and has plans to do projects in Africa, Asia, and India. A factory in Malawi is gearing up to build Jet-Flames and solar systems with carbon credits from CQC. 

Home made CQC rocket stove (L) is easily improved with the addition of a Jet-Flame (L).
The CQC home made brick Rocket stove is updated with the Jet-Flame in Malawi

“C-Quest Capital is committed to the Jet-Flame as a truly breakthrough technology. Our stoves in Malawi now use less wood, women save time cooking, and breathe a lot less smoke.”

Ken Newcombe, CEO, C-Quest Capital

The clean combustion of biomass adds homegrown power to the energy mix here in the USA and in other countries. Without the EPA SBIR this would not have happened! To learn more about the Tibbets Award, visit

sticks and charcoal start to combust in a rocket stove

The Jet-Flame was developed from combustion concepts used in fluidized beds and TLUDs.

Fluidized Bed

fluidized bed combustion diagrams

“In its most basic form, fuel particles are suspended in a hot, bubbling fluidity bed of ash and other particulate materials (sand, limestone etc.) through which (under air) jets of air are blown to provide the oxygen required for combustion or gasification. The resultant fast and intimate mixing of gas and solids promotes rapid heat transfer and chemical reactions within the bed.”

Top Lit Up Draft

diagram explaining how a top loaded up draft stove works

The TLUD uses under air flowing up through the fuel to transport wood gas into the hot layer of charcoal and flame above the fuel assisting more complete combustion efficiency.

Cleanly Starting the Jet-Flame

High velocity under air jets blow up into the lit charcoal placed on top of small sticks of wood. When the charcoal and wood are on fire, long pieces of wood are pushed into the made charcoal to start a Rocket Jet-Flame without making visible smoke. The sticks of wood are burned at the same rate as the continual production of charcoal creating a cleaner combustion process related to a fluidized bed and the TLUD.

sticks and charcoal start to combust in a rocket stove

Charcoal over wood is lit.

bed of charcoal in rocket stove

The charcoal becomes superheated with jets blowing up into the pile.

sticks burning in rocket stove

After 30 seconds, long sticks of wood are pushed against the burning charcoal creating flame.