Entries by Kim Still

  Improving Heat Transfer Efficiency (HTE)

HTE Design principles: Increase temperature and velocity of gases, exposed area in pot(s), radiation, proximity of gases to pot(s) without decreasing velocity. Use dry wood. Doubling temperature, velocity and area doubles heat transfer efficiency! Doubling radiation is much more effective! Wood Moisture Content: This is often a critical variable. Ideally, wood should have a moisture […]

Health: Reducing PM2.5 by ~90%

Although airtight biomass heating stoves in the USA on average emit a lot more smoke than Southern Hemisphere cook stoves per unit of time, legally mandated chimneys move it outside where it is diluted enough to generally meet WHO standards. That’s great! Anyone who uses a wood burning heating stove knows that a chimney is […]

The Icy-Ball : A Heat Driven Refrigerator

That’s an Icy-Ball (and a younger Dean) in a photo from ARC in 1994. Dr. Larry Winiarski and I built 18 somewhat scary prototypes and eventually made ice. We had replicated a pre-rural-electrification 1920s ammonia/water absorption refrigerator. A fire heats the water/ammonia mixture and separates the ammonia out of the water (it turns into gas at […]

A Hospitable Chinese Environment for Improved Cookstoves

Information summarized via Google AI: In 2026, the Chinese carbon market (CCER) is generally a more hospitable environment for cookstove projects—defined as traditional improved biomass stoves that lack advanced digital monitoring—compared to UN or Western voluntary markets.  While international markets now demand costly digital “metering” and stricter methodologies, the Chinese domestic market offers more flexibility for […]

Tier 3 Biomass Stoves

To reach multiple, interlinked Sustainable Development Goals, the UN advises that “the share of the population mainly using improved cooking solutions like low-emission biomass stoves reaching Tier 3* or better needs to increase to 35 percent by 2030.” (ACHIEVING UNIVERSAL ACCESS AND NET-ZERO EMISSIONS BY 2050: A Global Roadmap for Just and Inclusive Clean Cooking […]

Don’t Let The Flame Touch The Pot

As we iterate changes in natural draft TLUDs and Rocket stove prototypes, trying to reduce emissions while maintaining high thermal efficiencies, one design principle keeps on suggesting itself: Don’t let the flame touch the pot. The pot is ‘cold’ and if the flame has not burned itself out and contacts the surface, we instantly see […]

Early Rocket Stove Research at Aprovecho Still Rings True

Early Rocket Stove Research at Aprovecho Still Rings True A summary of Global Modeling and Testing of Rocket Stove Operating Variations, Nordica A. Hudelson, K.M. Bryden, Dean Still Department of Mechanical Engineering, Iowa State University, Aprovecho Research Center, 2001 In the summer of 2000, Aprovecho’s current Executive Director Nordica MacCarty spent a couple of months […]

Cook Stoves for Ethos

An open fire Jet-Flame? We have been at Shengzhou Stove Manufacturer this November working on cookstoves for display at the annual ETHOS conference including: If stove projects do not have capable stoves, then project goals will not be met in the same way that some carbon credit projects fail to meet their impact goals when […]

A Clean Open Fire?

Illustration from: Birzer et al. (2013) “An analysis of combustion from a top-lit up-draft (TLUD) cookstove”, Journal of Humanitarian Engineering 2(1):1-8 DOI:10.36479/jhe.v2i1.11 When Dr. Tom Reed and Dr. Larry Winiarski added short, narrow chimneys above the fire in TLUDs and Rocket stoves, they increased draft and created laminar flow flame in the tubes that could […]