Remembering Ken Goyer

/0 Comments/in ,
https://paulneevel.com/hp_archive/pix/kengoyer.jpg

On the front porch of the house he built in West Eugene, Ken Goyer shows an example of the Six Brick Rocket Stove

Photo by Paul Neevel for the Eugene Weekly

I think about Ken making the lightweight, insulated bricks from Bailey Hill yellow clay for the Uganda submerged double pot stove in 2002. Exposing the sides as well as the bottom of the pot(s) to flame and hot gases increased fuel efficiency. The Rocket combustion chamber, also made from Ken’s recipe (clay and sawdust) was a 5” in diameter, 12″ high cylinder, placed under the first, larger pot. 

We tested the stove using one pound of wood. 6.6 pounds of water in the first pot (12″ diameter) boiled in ten minutes. We had a great week of sunny, windy weather and it was great fun to work with Ken and Peter Scott (Burn Stoves), who was about to go to South Africa. 

I met Ken when he was doing “Ken’s Ten-Buck Tune-Ups.” He first saw open cooking fires when he went to El Salvador in 1992 to help Sylvia Gregory with her women’s empowerment project. With funding from Rotary Club, Ken directed construction of brickmaking kilns for refugee camps near Lira in Uganda and Gulu in Darfur. He helped to start Aid Africa and is one of the inspirational people we miss and so fondly remember. He was one of Larry Winiarski’s best friends.

New on the Website! Improving Biomass Stoves, 2025

/1 Comment/in ,

The new Osprey funded book is a compilation of fifty-one updated newsletters, reflecting the current state of knowledge at ARC. 

Stove experiments fail to improve prototypes as often as they succeed. One of the great things about iterative development (testing effects of single changes in prototypes under the emission hood) is that you learn as much from failures as from success! Every day moves us forward. 

How to achieve close to complete combustion and close to optimal heat transfer efficiency are describable in single page summaries. 

Aprovecho is helping to manufacture biomass cooking and heating stoves that are clean burning enough to protect urban air quality and meet the Paris Agreement. Most of the stoves that we help to make are not this clean burning, but how to achieve cleaner combustion is better understood and less expensive to achieve.

The hope is that these short summaries will be more accessible and more fun to read compared to previous longer-winded attempts at communication.

Our lab is open to visitors and we try to be good hosts. After years of trying, the coffee is becoming more palatable. 

Come on by!

Aprovecho Research Center, 2025

/0 Comments/in

ARC started in 1976, almost 50 years ago. 

In 1982, the original cook stove consultants returned from global travels to Oregon, bought 40 acres of forested land at the end of a road, planted a garden and started talking to Dr. Larry Winiarski, (Oregon State University) learning how to improve combustion and heat transfer efficiency. 

Dr. Nordica MacCarty, an associate professor at OSU, is the Executive Director of ARC and continues investigations of how wood fires can better help humanity. She has worked at ARC off and on for 25 years. Rigorous science-based experimentation, field learning, publication of peer reviewed journal articles and market-based manufacturing and distribution intertwine as ARC matures.

Learning from experience, eating a thousand kinds of food, succeeding now and then, is always great!

Building Blocks to Health

/0 Comments/in ,

In 2018, the World Health Organization published the book “Air pollution and child health: prescribing clean air”. The report concludes, “Every day around the world, billions of children are exposed to unsafe levels of air pollution. The result is a global public health emergency.” 

The WHO suggested “prescriptions” to clean the air and protect health:

  1. Use clean household energy for cooking, heating, and lighting.
  2. While waiting for clean to be available, use technologies and fuels that reduce exposure such as low-emission biomass cook stoves.
  3. Minimize the time children spend around smoky fires.
  4. Increase ventilation or install a chimney.

A combination of interventions is usually most cost effective. 

ONE

  • Help to make clean burning stoves available.
  • Promote solar lighting.

TWO

  • Forced draft stoves can burn up a lot of the smoke.
  • An adjustable Pot Skirt forces the hot gases to scrape against the sides of the pot as well as the bottom reducing fuel use by about one-third. That results in one-third fewer emissions!
  • A light weight, abrasion resistant Rocket combustion chamber can burn up ~ 50% of smoke compared to the open fire. 
  • Winiarski designed stovetops can increase heat transfer efficiency by ~8%.

THREE

  • Promote reduction of exposure to family members, especially to women and children. 

FOUR

  • Doubling the air change rate reduces smoke in half.
  • Locate the fire under a window on the low pressure side of the house.
  • Cook outside.
  • Chimneys have been a part of traditional houses for centuries.
  • Cook with a chimney!

Applications of Pulling Woodgas Through Burning Charcoal

/0 Comments/in ,

We experimented at SSM with a “Horizontal TLUD”

As seen above, the draft of a Rocket stove can pull woodgas horizontally through made charcoal. The tips of the sticks turn into hot charcoal.

Secondary air is pre-heated in the circular annulus before entering the fire in front (or above) of the made charcoal, as in a TLUD.

Primary air is adjusted by covering the fuel entrance. More air makes a bigger fire.

PM2.5 is dramatically reduced when conditions are well adjusted under the emissions hood: (850C for 0.2 seconds, etc.)

Recently, we have been trying the same approach in pellet and log burning biomass heating stoves.

It is so interesting to switch back and forth between heating and cooking stoves.

Solvable problems make life great!

Green sign reading Sure, Light Up

Wow! The clean biomass future is now!

/0 Comments/in , ,
https://centralboiler.com/media/3755/inset-afterburner-320px.png?width=320&height=200

Central Boiler combustion chamber

Last week Dean and Travis went to the Hearth, Patio & Barbeque Association Expo in New Orleans to get updated on the latest heating stove technologies and to meet and talk to stove companies. Three days was a short time but we made many friends and learned a lot!

The CENTRAL BOILER outdoor log and pellet furnaces stood out as one of the newest innovations. It can be imagined that in a sustainable biomass future, heating big buildings (even high-rise apartments?) with logs or pellets might be as useful as freestanding stoves heating rooms. The same (bigger/smaller) clean burning combustion systems deliver renewable, home-grown heat to occupants in bigger/smaller buildings. Maybe pellets could be poured down the same delivery chutes that are used for heating oil in New York City buildings?

Admiring the automated house-sized furnaces on display at the Expo made the possibilities seem so much better defined. 

See: centralboiler.com

Wood Heating: Heating Design Load

/0 Comments/in

Burning wood slowly (and cleanly) can be a big part of the challenge when improving heating stoves. Air tight, insulated houses do not need big fires to stay warm. If the fire is too large, the house gets hot and folks are opening windows!

What firepower is needed to keep a house warm but not overheated?

“If you build a small, tight, well-insulated home — in other words, a green home — it won’t need much heat. Since typical residential furnaces and boilers are rated at 40,000 to 80,000 BTUH, they are seriously oversized for a super-insulated home, which may have a heating design load as low as 10,000 to 15,000 BTUH.” www.greenbuildingadvisor.com/article/heating-a-tight-well-insulated-house

15 thousand BTUs per hour is equal to about 4.4 kilowatts. (Burning ~2 pounds of dry wood per hour in a stove with a good heat exchanger.)

The required firepower of the heating stove is dependent on the losses from your house. Old-fashioned houses can require big fires to replace constantly lost heat. 

The Green Building Advisor says that it is most cost effective to reduce the air leaks first and then increase the amount of insulation in a home. 

Matching needed firepower to your heating design load should factor into your decision of what stove to buy. It is not difficult to do an energy audit of your home.

www.energy.gov/energysaver/home-energy-assessments

An Easier Institutional Stove?

/0 Comments/in ,
https://www.appropedia.org/w/images/e/ef/Libhubesi_stove.jpeg
Libhubesi stove (photo: New Dawn Engineering)

Institutional-size stoves like this Lihubesi stove frequently use a sunken pot or pot skirt to increase heat transfer efficiency.

While testing the institutional-size Alpha Limited TLUD, ARC staff conducted an experiment to see if a skirt is strictly necessary with a very large pot. A 58cm in diameter pot was heated by the six-inch in diameter Tom Reed Alpha Limited forced draft pellet stove with an added 0.75 constant cross sectional area Winiarski stovetop.  

A complete stovetop was also made that increased heat transfer efficiency to the entire bottom of the pot. As-hot-as-possible gases are directed to flow as closely as possible to the surface without reducing their velocity.

The bottom of the 60 liter, 58cm in diameter pot (used in institutional stoves in Africa) had an external surface area of 2,640 square cm. The slanted Winiarski stovetop created a 5mm gap at the outer edges of the pot (See above).

The seven inch deep, Alpha Limited FD-TLUD stove ran for 82 minutes using 2.03 kg Douglas fir pellets. 20 liters of water boiled in ~60 minutes when a lid was placed on top of the pot. (A higher firepower stove is needed to boil 60 liters in a reasonable period of time).

The single test results were:

efficiency_with_char_                          57%          

firepower_with_char_high power        4.80 kW

CO_useful_energy_delivered_            1 g/MJd       

PM_useful_energy_delivered_            15 mg/MJd     

Summary

When pots have sufficient bottom surface area, using a Winiarski stovetop can result in high thermal efficiency. After one hour, the highest temperature of gases in the 5mm channel gap under the outer edges of the pot was 111C. Adding a skirt to the sides of the pot would not be help very much when gas temperatures are this low. 

Perhaps cooks would appreciate institutional stoves without sunken pots? 

Let’s see what happens?

Misty sunset at the Aprovecho campus

Working in a Forest

/0 Comments/in

Schoolhouse Creek, filled with late winter run off, rushes along next to the Cafeteria building

The Aprovecho lab is in a green forest, eight miles east of Cottage Grove, Oregon, a town of ~10,000 people.

Working in a forest to design, manufacture and sell clean burning biomass cooking and heating stoves makes sense.

Heating and cooking with renewably harvested biomass is easy to imagine when surrounded by a forest.

Eating food from our gardens, grown with fertilizer from animals we enjoy, means that we know a lot about the food we eat.

Learning more about burning biomass cleanly enough to join solar, wind, hydro, and geothermal as sustainable energy resources, is intrinsically optimistic work.

We hope that you can visit our stove lab at Blue Mountain one of these days! Contact dean@aprovecho.org

Secondary Air Injection

/0 Comments/in ,

S

Dr. Reed’s Alpha Limited stoves

Lefebvre, Vanormelingen, and Udesen examined secondary air jets air in cylindrical TLUD combustion chambers and described the most successful patterns and penetration depths. They reported that air jet penetration lengths approaching the middle of flame in a cylindrical combustion chamber resulted in a maximum reduction of PM2.5. An increase in the number of jets also created more thorough mixing. They advised that it was important to have the jets meet in the middle of the flame, but with minimal necessary force, to ensure highest temperatures and highest velocity of hot gases to the pot. (Lefebvre, 2010) (Vanormelingen, 1999) (Udesen, 2019)

It has been interesting to test Tom Reed’s larger Alpha Limited stove. More powerful secondary air jets forcefully meet in the middle, forcing the flame to create a cyclone that plunges down into the cylindrical combustion chamber. As reported in last week’s newsletter, in one 94-minute cold start high power test with Doug fir pellets, the larger WoodGas stove and insulated SSM SuperPot, achieved 58% thermal efficiency with a white filter and very low PM2.5.

Perhaps downward cyclonic mixing, caused by more powerful secondary air injection, might be another clean burning technique when combustion temperatures stay high enough? 

The Winiarski stove top that was added seemed to reinforce the downward cyclone. Larry always pushed better heat transfer efficiency in his pot supports, etc.

Tom probably invented using very little primary air and a lot more secondary air in forced draft TLUDs. So much easier to improve performance since Tom and Larry did a lot of the work!