WASHINGTON, DC, April 22, 2021 — At the Leaders Summit on Climate hosted by President Biden, the U.S. government pledged to help countries achieve their climate ambitions through expanding access to clean cooking.

“Providing clean energy to households is critical to achieving global climate and sustainable development goals,” said Helena Molin Valdés, Head of the Climate and Clean Air Coalition Secretariat. “Smoke from fireplaces, cook stoves, and lighting is responsible for more than half of human-made black carbon emissions and millions of premature deaths from household air pollution. The Climate and Clean Air Coalition partners welcome the U.S. government’s re-engagement in the issue and look forward to cooperating to put in place solutions that improve lives and protect the planet.” 

The United Nations Foundation’s Clean Cooking Alliance

Would it be helpful to add climate metrics to the health-based ISO 19867? Currently, Scoring Tier 5 for emissions of PM2.5 and CO means that safety is assured in average households. As the score decreases from Tier 5 to Tier 0 the estimated amounts of ill health from breathing smoke and gas increase.

During ISO 19867 testing under an emissions hood, the fuel use, thermal efficiency and emissions of CO2, CO, and PM2.5 are measured and the data is used to determine a ranking on the voluntary tiers of performance. ARC multiplies lab data by a factor of three to estimate in field emissions. Usually in cook stoves, the CO2 has by far the largest effect on climate change. However, PM (black to white in color), CO, methane (CH4), non-methane hydrocarbons (NMHC), and nitrous oxide (N2O) also have varying amounts of climate forcing potentials. Currently, CO2, PM2.5, and CO are measured as a part of ISO 19867. ARC also determines the amount of black carbon in every test (using a filter) of PM2.5. Adding methane and non-methane hydrocarbons to the measured gases is not difficult. In fact, Sam is working on adding them to the LEMS right now.

The effects of inhaling particulate matter have been widely studied in humans and animals. They include asthma, cardiovascular disease, and premature death. Particles can also have an extremely strong effect on the atmosphere by absorbing and/or scattering the sun’s incoming radiation, depending on their color. The black particles have an approximate warming potential by weight of 680 times that of CO2 (Roden and Bond, 2006; Bond and Sun, 2005).

Total global warming impact, grams CO2 equivalent on a 100-year time-frame, per liter of water boiled and simmered for 30 minutes, normalized for starting temperature and fuel moisture content. Inclusive of CO2 and all PICs.

When we studied the global warming impact of five cook stoves burning biomass, CO2 was shown to be the major component, as seen above. At the time (2008), estimates of the various warming potentials were:

CO2….1  (IPCC, 2007)
CO….1.9  (IPCC, 2007)
CH4….25  (IPCC, 2007)
NMHC….12  (Edwards and Smith, 2002)
N2O….298  (IPCC, 2007)
PM – Black….680  (Roden and Bond, 2006; Bond and Sun, 2005)
PM – White….-50 (Estimate – Bond, 2007)

Warming potential, 100-year, CO2 equivalents

  • When biomass is harvested sustainably, the CO2 emissions from biomass-burning are considered to be greenhouse-neutral.
  • Although N2O is a strong climate-forcing constituent, emissions from the wood- and charcoal-burning stoves were very low, contributing less than 1% to the overall warming potentials.
  • The data suggests that there are biomass stoves that can be designed to (1) reduce the fuel used to cook, (2) reduce health-damaging emissions and (3) address climate change. The considerable differences in climate-changing emissions from the stoves in this study should be noted. Large-scale use of cleaner burning stoves might well reduce global warming effects, especially when the biomass is harvested in a “carbon neutral” manner. (N. MacCarty, D. Ogle, D. Still, T. Bond, C. Roden, Energy for Sustainable Development, 2008)

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: http://bioenergylists.org/stovesdoc/Still/Rocket%20Stove/Principles.html

When I went to UC Berkeley, studying psychology as an undergrad, lots of people made fun of Freud, Jung, and Adler who wrote (a lot) about divergent theories of what makes people tick. UCB liked to think of itself as a scientific institution, and facts are proven by statistical validity. Why should we believe speculation from the dear departed? I eventually agreed and I was intrigued by the big question: How do we know the truth?

The paradigm that captured my thinking was the BLACK BOX. In black box theory facts are like an elephant in a box. Scientists poke sticks into small holes in the box and one stick hits a toenail. A scientist exclaims, “Why, what is in the box is hard and slippery!” Other sticks hit the softer belly or the trunk, resulting in very different observations. Hopefully, after many experiments an accurate description of the elephant can emerge. (Although, what the elephant is thinking may well remain private.)

I was really excited by statistics!

If you’re trying to know the effectiveness of something, calculating the statistical significance can help. It gives you a measured amount of confidence in the hypothetical conclusion. At UCB we did experiments and 95% confidence was the minimum that students had to achieve to get an “A.” To achieve 95%, the sample size and the size of the effect had to be big enough.

Here’s the application to stoves

When we try to use found wood sticks from the forest in our experiments, one stick, for example, has two inches of bark on it. Another stick has three inches of bark and the two sticks make very different amounts of smoke. So, the variable of using sticks that emit different amounts of smoke makes it more difficult to know the truth: Did changing the air/fuel ratio, for example, result in the stove making less smoke? Using wood with no bark, we can achieve confidence in five to seven tests. We have to do a lot more tests when the fuel has added variables.

When trying to understand heat transfer or combustion efficiency in the lab (not what happens in the field) limiting variables has a great appeal to lazy researchers like me at ARC. So, we do not design stoves in the lab!

We realized quite a long time ago that we could only investigate heat transfer and combustion efficiency in the lab, and then with great relief go to an amazing place, work with wonderful people in a new culture, eat incredible meals, etc. in order to help a local team evolve a stove using found everything (and testing/statistics).

CQC stove with swinging door
CQC stove with swinging door
A door was added to the CQC stove to block some of the air entering the combustion chamber.

Last week we shared some thoughts about the importance of gathering detailed data and making direct observations when testing stoves. Here’s a question we recently considered.

Did a partial cover over the sticks entering the combustion chamber help reduce emissions in the CQC stove with Jet-Flame?

No, not in this preliminary test series, although lots of interesting things happened! Placing a swinging door over the fuel opening into the combustion chamber has often occurred to Rocket stove designers and it appears now and then in stoves. Dr. Winiarski liked the swinging door.  The thought is to get the excess air down by reducing the amount of air coming into the combustion chamber through the door. With sufficient but less excess air, the temperatures needed for cleaner combustion should rise.

Excess air did go down when a metal cover was near to touching the tops of the sticks in our experiments. It fell from an average of 2.91 times stoichiometric to 2.54. The average temperature in the combustion chamber did rise as a result, from 557°C to 596°C. The partial cover was doing its job. Firepower went up (4359 watts up from 4012 watts) and that might have helped with heat transfer efficiency. However, in this particular case, the thermal efficiency was unchanged (36% covered and 37% uncovered).

The positive changes in excess air and temperature also did not affect the emissions. PM2.5 (56mg/MJ-d covered and 55mg/MJ-d uncovered) and CO (2.63g/MJ-d covered and 2.72 g/MJ-d uncovered) were not changed enough to show a difference. Of course, using a Jet-Flame that is introducing lots of changes into the combustion chamber, including more excess air, probably makes this an unusual set of circumstances.

The swinging door may be great in a natural draft Rocket stove and as usual, Dr. Winiarski was right. It didn’t seem to be needed in this scenario. That’s OK with me, because the cover obscured the visual clues that help to tend a fire, and make tending more fun. I felt like I was flying a plane through the fog and was glad to land.