Tag Archive for: Rocket Stove

From: EPA’s Lab Test Results for Household Cookstoves, Jim Jetter, 2012 

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Since 2012, optimized biomass cook stoves have been tested at ~50% thermal efficiency

The temperature of the hot gases flowing past the surface of the pot is increased by

  1. Creating as much flame (1,100C) as possible in a low mass, insulated combustion chamber.
  2. Decreasing the distance between the fire and the pot without making excess smoke.
  3. Not allowing external air to cool the combustion gasses.

In convective heat transfer, the primary resistance is the surface boundary layer of still air immediately adjacent to a wall. 

Increasing Temperatures, increasing exposed Area, increasing Radiation, increasing Velocity in a 6mm to 7mm channel gap (10cm or higher) pot skirt has been shown (up to 5kW firepower) in a 24cm or larger diameter pot to result in ~50% thermal efficiency. Reducing losses from the exterior of the pot skirt with refractory ceramic fiber insulation also increases thermal efficiency. 

60% thermal efficiency has been demonstrated in the lab.

Helpful links:

From: EPA’s Lab Test Results for Household Cookstoves, Jim Jetter, 2012

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Key findings compared with the 3-stone fire:

  • Most stoves that were tested had better thermal efficiency, but some did not.
  • Compared with the 3-stone fire, many stoves that were tested had better combustion efficiency, but many did not.
  • A natural-draft TLUD stove (ARC) had very high efficiency with processed, wood-pellet fuel with low-moisture content.
  • Some forced-draft (fan) stoves had very low emissions – but not all fan stoves did.
  • Most natural-draft stoves that were tested showed a bigger improvement (lower emissions) over the 3-stone fire with high moisture fuel than with low-moisture fuel.
  • A natural-draft TLUD stove (ARC) had very low emissions – but required processed, wood pellet fuel with low-moisture content.
  • Two rocket stoves were tested at a “medium power” level – and had lower emissions (per energy delivered to cooking pot) than at maximum power.
  • Charcoal stoves had high emissions of CO and high emissions of PM during start-up.
link to Rocket Stove 2020 YouTube video

New Rocket Stove 2020 Video: Carbon Neutral Fuels

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How can burning wood, agricultural waste or even cow dung be a carbon neutral energy source? How do you start a fire without making a lot of smoke? How can a metal skirt around a cooking pot help with fuel efficiency? Dean Still has the answers for you in this new video.

Find out more about the Jet-Flame combustion accessory used in this video at www.jet-flame.com.

YouTube Video explains the importance of mixing for clean combustion

New Rocket Stove 2020 Video: Mixing

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In this video, Dean Still explains why mixing air into flame is important for cleaner combustion. He uses several Rocket Stoves to demonstrate the effects of both natural draft and forced draft secondary air jets. Which style is more effective? Watch to find out!

For a simple way to add mixing to a Rocket Stove, check out the Jet-Flame.

Sad cooking pot on a stove

TARP-V: Optimizing heat transfer efficiency

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Two cooking pots
Mind the Gap!

Here are the TLUD (Top-Lit Up Draft Stove) derived heat transfer principles that ARC designers use when designing and improving stoves. They are just as important for Rocket stoves as TLUDs:

T: The temperature of the hot gas contacting the pot or griddle should be as hot as possible.

A: Expose as much of the surface area of the pot or griddle to the hot gases as practical.

R: Increasing heat transfer by radiation is important. Move the zone of combustion as close to the surface to be heated without increasing harmful emissions.

P: Optimize the proximity of the hot gases to the pot or griddle by reducing the channel gap without reducing the velocity of the gases. Reduce the thermal resistance with appropriately sized channel gaps under and at the sides of the pot. Match the firepower to the channel gap size and to the size of the pot or griddle.

V: In convective heat transfer, the primary resistance is in the surface boundary layer of very slowly moving gas immediately adjacent to a wall. Increase the velocity of the hot gas as it flows past the pot without reducing the temperature of the gases. As a rule of thumb, heat transfer efficiency can double when the velocity of the hot gases also doubles (N. MacCarty, et al, 2015).