Video: Lighting a Fire With The Jet-Flame – No Smoke

The Gates funded Global Health Labs and ARC/SSM invented the Jet-Flame

Global Health Labs, Shengzhou Stove Manufacturer and Aprovecho teams show off the Jet-Flame
Global Health Labs, Shengzhou Stove Manufacturer and Aprovecho teams show off the Jet-Flame

Shengzhou Stove Manufacturer manufactures the Jet-Flame (jet- flame.com) that is being field tested in over 30 locations. Our lab helped to create this accessory that is designed to reduce emissions while increasing thermal efficiency and reducing time to boil. 30 pre-heated primary air jets shoot up into the fire resulting in increased molecular mixing and elevated temperatures. Smoke is reduced by about 90% compared to an open fire.

A forced draft stove can be very clean burning, but start up may create a lot of PM2.5. This is because the cold combustion chamber can allow a higher percentage of the smoke and Carbon Monoxide to escape unburnt. David Evitt, COO of ASAT (the for-profit arm of ARC), invented a method for lighting the Jet-Flame that can be a lot cleaner.

  • Wet 30 grams of left over charcoal with 10 grams of alcohol.
  • Place the small pile of charcoal on top of the holes in the Jet-Flame.
  • Light the charcoal.
  • Turn on the Jet-Flame.
  • Push the tips of the sticks of wood against the pile of burning charcoal.
  • Keep on pushing the sticks into the fire as the tips are consumed.

Here’s a video showing how we light fires in the lab:

Forced Draft and High Mass Combustion Chambers

Years of experimenting with stoves at ARC taught us that a high mass combustion chamber absorbs a lot of heat that could be going into the cooking pot. That led us to presume that efficient combustion chambers had to be lightweight, which are harder to make. Once we started experimenting with forced draft, we were surprised to learn that adding forced draft (FD) to a TLUD or a Rocket stove increases the temperature of the gases and largely overcomes the negative effect of a high mass combustion chamber.

The Oorja FD-TLUD and the FD-CQC mud brick stoves generate temperatures of around 1,000°C in the combustion chamber. The option to use a high mass combustion chamber lowers cost and dramatically increases durability when designing forced draft, health protecting, affordable, clean burning, carbon neutral stoves.

The combustion chamber in the pellet burning FD-Oorja that we have in the lab is made from castable refractory ceramic and is over 20 years old. The retail price of the 400,000 British Petroleum Oorja stoves sold in India was around $18. The CQC Rocket combustion chamber is less expensive and is manufactured from sand, clay, and cement. With the addition of forced draft via a Jet-Flame, it reaches Tier 4 for  thermal efficiency and PM 2.5.

To replace health protecting stoves that use natural gas (a fossil fuel) it seems likely that FD-TLUDs and FD-Rockets can be built with lower cost and 10 year durability combustion chambers. The renewably-harvested-biomass fueled stoves need to be manufactured and field tested, and there is a lot of ground to be covered (an understatement), but it’s great that harder-to-make low mass combustion chambers may not be necessary.

Primary Air Jets

Champion Forge, circa 1920

The blacksmith’s forge is probably the most familiar technology that blows jets of primary air up into charcoal or coal, resulting in the high temperatures needed to shape or melt metals. A forge needs air at high pressure (10” water column) to do its work. A fan (usually a radial pressure blower) capable of moving air against significant resistance is required. You don’t need a big volume of air. What is needed is pressure to keep the air moving and to create molecular mixing of the woodgas and flame.

The Jet-Flame stove accessory
The Jet-Flame Stove Accessory

The SSM Jet-Flame

The Jet-Flame uses the same technology as a forge. It required a year of R&D to create a low cost, 1.5 Watt fan that delivers sufficient pressure into a Rocket stove fire. Thirty 2mm jets of air at 0.4 to 2 inches of water pressure blow up into the charcoal under the burning sticks of wood. When the pressure rises and the vertical jets of air penetrate further into the charcoal and fire, the following effects are seen:

• Temperatures rise in the combustion chamber, resulting in higher thermal efficiency as hotter gases flow past the pot. The higher temperatures also result in lower PM2.5 and CO. However, proper metering of the fuel, mixing caused by turbulence, and sufficient residence time are as important for decreased emissions of PM2.5 and CO. With higher temperatures, the related measures of firepower and CO2 also rise, while the fuel/air ratio decreases – as the fire increases, more oxygen is consumed. Increasing the pressure also increases firepower even when a constant fuel load (usually two 4cm by 4.5cm sticks) is being burned. Larger sticks have a lower surface area to volume ratio and make less smoke. When the outer surface of the sticks are covered with charcoal, emissions decrease as well.

• In a Rocket stove that has a large fuel opening, natural draft pulls room air into the combustion chamber. With forced draft adding more air, the average Lambda in a Rocket stove tends to stay above two times stoichiometric. The jets of air blowing into the charcoal result in higher temperatures as pressure increases resulting in temperatures over 1,000°C even at 2 to 5 Lambda. Secondary air jets blowing into the fire, on the other hand, have a cooling effect. In a Rocket stove with a Jet-Flame, the varying fuel/air ratios are not related to the emission rates of PM2.5 and CO.

• Higher temperatures caused by greater pressure also have detrimental effects. The percentage of black carbon is higher when temperatures/firepower/CO2 become elevated – hot yellow flames cause the formation of black carbon. The lifespan of affordable refractory metals is greatly decreased by very high temperatures such as 1,000°C. A durable refractory ceramic material is better suited to higher operating temperatures. Replacing metal combustion chambers with low mass, refractory ceramic was recommended by the 2011 DOE biomass stove conference. https://www1.eere.energy.gov/bioenergy/pdfs/cookstove_meeting_summary.pdf

• Lowering the firepower by adjusting the pressure in the air jets assists the metering of fuel to achieve a 3 to 1 turn down ratio. When the pressure is too high, the fire can be blown out when the charcoal has disappeared.  A layer of charcoal under the fire (or charcoal coating the sticks) helps to maintain the fire and lower emissions as charcoal emits much less PM2.5 compared to wood. The levels of CO tend to rise when the flame above the sticks decreases. The amount of flame above the sticks seems to be related to lower emissions of CO and PM2.5. The amount of flame above the burning sticks, the metering of the fuel, and the mixing of the wood gas are not as easily quantified as temperature and residence time but are as important for more complete combustion.

User Feedback Can Make For Unexpected Improvements

In our newsletter “Making It Real,” we described how feedback from the field in Rwanda suggested that the Jet-Flame’s power cord would last longer if the whole device was inserted from the side of the combustion chamber. (It was originally designed to go through the door, with the sticks placed on top.) So of course we ran some tests, and discovered more benefits.

Is the Jet-Flame, when inserted into the combustion chamber from the side of the CQC stove, as effective in reducing emissions as when it enters through the fuel door?  

Yes, performance seems to have even improved a bit. After testing the Jet-Flame with side entry, it seems that it’s better to get the hot metal out from under the parts of the fuel that you don’t want to heat up. To burn cleanly, natural draft Rockets like to burn something like 8cm of the end of the sticks. Instead of laying the entire length of the sticks on the heated metal of the Jet-Flame, the side entry only exposes a limited amount of the sticks to high temperatures.

As seen in the photo, the sticks are now supported by a white homemade high mass brick and only the tips are exposed to Jet-Flame heat well inside the stove. It’s nice how a suggested change from Jean Marie Kayonga in Rwanda ends up having some unexpected benefit, not just better protecting the cord. Thanks again, Jean Marie! www.Jet-Flame.com

The time to boil, thermal efficiency, temperature in the combustion chamber, CO, and PM were improved with side entry while firepower rose. Excess air fell from 3.38 times stoichiometric to 2.57. I liked operating the stove because the sticks seemed to burn more at their tips as Dr. Winiarski described in the Rocket Design Principles. See: https://bioenergylists.org/stovesdoc/Still/Rocket%20Stove/Principles.html

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

Looking at High Mass and Insulation

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.

Varying Fan Speed in the SSM Jet-Flame/CQC Stove

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.

Results

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

Making it real!

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 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 earthen 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.

We won the Tibbets Award!

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: www.Jet-Flame.com
  • 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: www.ssmstoves.com/project/m55/

We partnered with the Gates funded Global Health Lab to develop the Jet-Flame. They have recently supported sending Jet-Flame samples worldwide.

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 tibbetsawards.com.

sticks and charcoal start to combust in a rocket stove

Fluidized Bed Combustion, Top Lit up Draft, and the Jet-Flame

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.”   https://en.wikipedia.org/wiki/Fluidized_bed_combustion

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.