Updating a 9-year-old “Clean Combustion” YouTube Video

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The great and upsetting thing about YouTube videos is that they don’t go away! A lot of this old video now seems incomplete:

Our understanding of how to come closer to complete combustion has changed and includes details missing before. The following describes a hopefully less wrong set of design principles. David Evitt is currently deep diving into clean combustion and who knows what details will be added in the next few years?

Nine years ago, we thought that close to complete combustion could be achieved by forcing all gases and smoke into flame for a sufficiently long amount of time.

  1. Today we add that the air/fuel ratio in the combustion zone needs to be air rich.
  2. We add that the flame/gas/smoke/air mixture needs to be thoroughly mixed. 
  3. We add that the temperature in the combustion zone needs to be above 850°C to allow short residence times to become effective.
  4. We add that at a minimum of 850°C the residence time needs to be more than 0.2 seconds. Longer is better.
  5. Wet wood, un-preheated air jets, and mass tend to reduce temperatures to below 850°C.
  6. Optimized heat transfer efficiency helps to reduce harmful emissions since less fuel accomplishes tasks.

Video: Harris Natural Draft TLUD Swirls

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Kirk Harris has been investigating TLUDs for decades and, as far as I know, his natural draft TLUD burning pellets achieved the lowest natural draft recorded score for PM2.5:  0.7mg/minute at high power (Lawrence Berkeley National Laboratory). This video shows Kirk in China at Shengzhou Stove Manufacturer where Mr. Shen built a copy of his stove to start the process of possibly manufacturing it.

The fascinating aspect in the video is how fast the flame is swirling, keeping the flame below the level of the pot and increasing dwell time.

Adding a fan shaped static mixer between the hole in the concentrator ring and the bottom of the pot has become commonplace in various TLUDS since Kirk invented the technique. We recently added a fan shaped static mixer in a natural draft TLUD to get rid of creosote. The tars were burned up in the hot, swirling flame.

Keeping the flame below the cold surface of the pot is always helpful and can be achieved with the Jet-Flame and in both natural draft and forced draft TLUDs.

To last long enough for commercial/carbon success, the combustion chamber has to be made with cast refractory ceramic. Making the static mixer and combustion chamber from cast refractory ceramic dramatically increases longevity. The Oorja stove in our lab has lasted for about 20 years!

I imagine Dr. Tom Reed smiling in heaven as the stove community moves closer to optimization with:

  • clean burning pellets 
  • a well-engineered TLUD 
  • a refractory ceramic combustion chamber 

Dr. Kirk Smith and The Breathing Space Project

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Dr. Kirk Smith, a hero

ARC worked closely with Dr. Kirk Smith (1947-2020) when we helped to include emissions in the Water Boiling Test, used to evaluate biomass cookstove performance, for the Shell Foundation. We included the first “Tiers of Performance” with a simple approach that divided stoves into two categories: improved and unimproved. It was great to know Kirk and I admired him tremendously.

Kirk was a professor at the University of California at Berkeley and was, in my opinion, the most effective advocate for the billions of people afflicted by breathing smoke. Kirk and ARC continued to work together during the Breathing Space project in India. Here is a video that ARC helped to produce in 2009, which describes the project. 

The goal of Breathing Space was to introduce the Rocket stove into India. We hoped that the Rocket stove, after being re-designed by women in 18 villages, would “go viral” and protect health. Eventually, Envirofit become the distributor and project manager. Envirofit and the Shell Foundation worked together to bring Rocket stoves into markets worldwide.

In 2011, Kirk Smith announced that switching to LPG seemed more likely to protect health. By 2017, Envirofit was including LPG and gas stoves in their catalog of options. Trying to create and disseminate truly clean burning biomass stoves had proven to be difficult and a more successful, wide scale intervention was needed. Although people liked it, the combustion efficiency of the Rocket stove just was not good enough. The Justa stove with chimney (with Rocket combustion chamber) that Kirk tested in Guatemala leaked, and when many stoves were in use the outside air became smoky. Maybe gas stoves, even though the fuel is not renewable, had a better chance to succeed?  

What would Kirk Smith recommend in 2022?

Can market driven biomass stoves (with hay boxes, solar stoves, pot skirts, SuperPots, Jet-Flames, etc?) successfully address health and climate change? Maybe we should keep working and find out?

I think that Kirk would not object.

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

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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:

New Video: Test Kitchen 2021 Natural Draft Hood

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The old saying, “if you can’t handle the heat, get out of the kitchen,” is not lost on us when we are working in the test kitchen. It takes us a while to get the vertical and horizontal grid of Climate Solution Consulting’s HAPEx particulate matter monitors started and positioned. Then ARC’s PEMS-PC partial-capture based emissions sampler has to collect a zero point of the gasses in the atmosphere. Don’t forget the temperature sensors (where is that data?) and the wood. This is after reviewing yesterday’s work, discussing a plan for the day, and watering the garden. So, by the time the young scientist rolls into the test kitchen in the Oregon summer, currently home of America’s largest wildfire, it’s about 100°F and rising. But science must go on.

ARC’s four year old test kitchen is currently being used to test a natural draft hood of our design. Our experiment allows us to operate the fire without being exposed to the emissions from the fire. We used to use a vacuum cleaner as a positive pressure ventilator, but now we sit outside of the room and feed the fire through a glove box.  After seeing that the hood was effective enough to reduce the concentration of PM2.5 in the test kitchen to below 35 ug (averaged over 24 hr), we turned the hood around and made a video for you of us doing the water boiling test while enjoying a smoke free kitchen.

Enjoy the video (and know that those loud pumps and fans go with the bit about it being hot in the kitchen).

Please send your photos and stories of natural draft hoods! We don’t want to lose this beautiful technology.

-Sam Bentsen, Aprovecho Research Center General Manager

Video Overview of Clean Burning Biomass Cookstoves 2021

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It can be challenging to find the time to read a book so here’s a ten-minute video introduction to “Clean Burning Biomass Cookstoves” (2020), our recent updating of the 2015 edition. Download the book for free on the publications page. We spent a significant part of last year rewriting most of the book trying to put in one place pretty much everything that ARC has learned in the last five years. The plan is to do the same in 2025.

The summary includes:

  • The energy ladder and renewable biomass
  • Fire is investigated in the lab
  • Stoves are designed by cooks in the field
  • Factories tell us how to help them
  • Chimneys and air exchange rates protect health
  • A new outside air model helps to predict PM2.5
  • Increasing heat transfer efficiency! No problem
  • Residence time is shorter than previously imagined
  • Metering and mixing get us most of the way to cleaner combustion
  • There are great new stoves!
  • Let’s move faster
Intro image for YouTube Video

New Video: Rocket Stove 2021 – LEMS+ Realtime Combustion Analysis

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Watch what happens with PM2.5, CO2, Oxygen and more during a wood burning stove test in this real-time video from Apro’s Laboratory Emissions Monitoring System. The LEMS provides a display of what’s being recorded by the various sensors in the stove being tested, and in the emissions hood. In this video, Dean Still gives an overview of what the five lines on screen represent, and how they relate to each other as the fire progresses.

For more info about Aprovecho’s emissions monitoring systems, see aprovecho.org/portfolio-item/emissions-equipment.

Rocket Stove 2021 - Pot Skirts

New Video: Rocket Stove 2021 – Pot Skirts to Increase Heat Transfer

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In this video, Dean Still explains why a pot skirt – a sheet of metal wrapped around the cooking pot – is a simple yet important way to improve the fuel efficiency of a rocket stove. He also explains how to calculate the appropriate distance between the skirt and the pot. Stay tuned to the end of the video to find out who is causing all the ruckus in the background…

Helpful references:

simplified diagram of constant cross sectional area
Simplified drawing of the concept of constant cross sectional area.

This is a very simplified illustration of what “constant cross-sectional area” means. The top circle represents the cross-sectional area of a stove riser. The bottom ring shows the same area translated into the space around a pot. It’s important to keep the cross-sectional area that the hot gasses flow through consistent, so they don’t slow down. Hot, fast flowing gasses transfer heat most efficiently. 

graph helps calculate proper skirt gap for best heat transfer efficiency
Chart for calculating channel gaps, from Dr. Samuel Baldwin’s “Biomass Stoves: Engineering Design, Development, and Dissemination.” 1987, Volunteers in Technical Assistance.

This is the chart for determining efficient channel gaps, explained towards the end of the video. It was developed by Dr. Samuel Baldwin in 1987.

Here is the Ten Stove Design Principles poster referred to in the video. Many more helpful documents are also linked on the Publications page.

Thumbnail from Rocket Stove 2020 video about height and weight

New Video: Rocket Stove 2020 – Height & Weight

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Why is a heavy stove an inefficient stove? A tall combustion chamber makes a lot of draft to keep a fire roaring, how can that be a bad thing? What is TARP-V and how will it improve your stove? Dean Still has the answers for you in the latest Rocket Stove 2020 Video.

Here is the Ten Stove Design Principles poster. Many more helpful documents are also linked on the Publications page.

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.