Almost perfect!

Having unbiased villagers or Dr. Jim Jetter test Aprovecho’s Lorena stove might have helped to reduce our embarrassment when again and again the open fire was proven to be much more fuel efficient! Inventor’s pride is a well-known human frailty. Creating a truth-telling team including all the folks concerned with a stove project helps to address the inventor who is doing what feels natural and right, but can be misguided. It happens at ARC frequently!

The ARC team has found that an engineer/researcher may know more about the thermodynamics of a stove, but the expertise of cooks, manufacturers, distributors, retailers, and funders in the stove project need to be included in the decision making process from start to maturity. Test, test, test!

As Dr. Kirk Smith said, “You get what you inspect, not what you expect”.

Our advice is to test everything frequently from all angles and try to respond to problems without inventor’s pride. It’s not easy! Cognitive dissonance messes up judgement all the time. 

It’s easy to think, “I am intelligent, and make good decisions.” Admitting a mistake can threaten that image of self. It can be really hard to hear someone say, “Man, that Lorena stove is terrible! How could you have been so dumb?”

At Apro, we strive to use criticisms as a tool for improvement. Taking time to assess and define the problems, and consulting with our team about how to make improvements, moves us forward towards a more successful outcome.

Man driving tractor with front loader attachment, man watches in background

In 1976, Aprovecho was started in Guatemala after a terrible earthquake. The founders invented a stove called the Lorena as part of trying to help folks with their farms and forests. In 1981, Aprovecho came back to Oregon and bought 40 acres to learn how to maintain a forest, grow food, and make stoves. The hardware and software were OK but the wetware was not.

Profile photos of Carl Jung and Sigmund Freud

Sigmund Freud and Carl Jung broke up in 1913. Freud had picked Jung as his successor, but Jung made an unforgivable joke at dinner that ended their relationship. Freud was sure that the most powerful human motivation was infantile sexuality. Jung commented that eating must be at least equally important?

That was it!

Sure, stoves are interesting, but food is certainly more important. I lived on a ranch in Mexico for eight years and when the food ran out we weren’t lighting fires to cook. We were out farming, hunting, fishing, or gathering edibles from the desert.

Growing food has always been important at Aprovecho. So has maintaining the health and productivity of our forest/woodlot. Oregon is cold and too rainy in the winter, and warm and too dry in the summer, so we’ve had to learn how to adapt to this place and how to grow food productively.

Man in cowboy hat blows compost onto field
Man driving tractor with front loader attachment, man watches in background

We are lucky that our garden at Blue Mountain is bottom land and is easily accessible. We buy inexpensive compost made from food scraps by friends in Eugene and our neighbor, Butch, bought a rototiller for his tractor a couple of years ago that he uses, free of charge, to till our ½ acre garden. Butch also gives us unlimited manure from his cows, so friendship has made growing food a lot easier.

Being friends with the folks on our road increases our feeling of safety, and friendly neighbors can agree to growing a wide variety of foods from garden to garden. Being friends is important on lots of levels and when food is involved, breaking up, especially because of an ephemeral idea, is something to be carefully considered. 

Maybe better to share a slice of that good pumpkin pie?

 Happy Thanksgiving!

Man on tractor plowing a field, Aprovecho campus in background
Jet-Flame cross section

Dr. Larry Winiarski would remind me to imagine the languid rising of smoke from a cigarette when thinking about the velocity of natural draft gases in the Rocket stove.  I remember Larry saying that rising smoke is sexy, contemplative, and slow.

Sam Bentson, General Manager of ARC, and Chenkai Wang, Division Business Manager of SSM, spent months designing an inexpensive 2 Watt fan that developed a pressure of 0.75 inches of water column to blow high enough velocity air jets into a Rocket stove fire to increase mixing and combustion efficiency.

When Sam measures the dynamic pressure in the chimneys of household natural draft rocket cooking stoves he finds less than 0.01 inches of water column. Sam estimated, using the Archimedes principle, that a 10” inch in diameter chimney pipe at 700°C for its entire length would have to be 15 meters tall to generate 0.50 inches of water column. It’s amazing how powerful a little electric fan can be!

Jet-Flame cross section drawing
The 2020 Jet-Flame

Kirk Harris writes that he has wondered how an exceedingly small pressure variance could drive the tall flames that we see in some stoves. He envisions fire gas as having exceptionally low density, very light weight, with very low inertia.  Kirk thinks of fire as like a “hole in the atmosphere”, easy to push around. His stoves use static mixers and small velocity induced natural draft pressure differences to mix flame that has been divided into thin sheets. Using these approaches, the Harris TLUD stove achieves less than 1mg/min for PM2.5 when burning pellets.

The Jet-Flame, on the other hand, uses very high-pressure jets of air that blast up into charcoal and then mix wood gas and air as the jets pass through sticks on fire. The bottom air technique requires the equivalent pressure of a 15-meter-high, extremely hot chimney to lower emissions to about the same degree as the Harris stove. It is interesting to think of these two stoves side by side, representing quite different approaches to clean burning. The Harris stove is gently manipulating flame as easy to move around as a hole in the atmosphere while the Jet-Flame is dynamic, a bit loud, creating hot jets of air that drill holes in burning wood.

Testing in the laboratory and in the field

It is important to remember that in the Aprovecho lab, the 3 Stone Fire has used less wood and made less pollution than cooking fires and high mass stoves operated by cooks in the field. The fires in the lab tests were carefully made using dry and uniform sticks of Douglas fir fed into the fire in a controlled way to optimize the performance. Well-constructed 3 Stone Fires protected from wind and tended with care scored between 20% and 30% thermal efficiency.

Open fires made with moister wood and operated with less protection from the wind can score as low as 5%. The operator and the conditions of use largely determine the effectiveness of operation. Stoves have to be tested with careful repetition in order to achieve statistical confidence in the results. Because there are so many differences between laboratory and field results, it is difficult to use the results of laboratory testing to predict exactly how stoves will perform in the real world.

However, side-by-side comparisons can be used to generally estimate performance. An automobile that gets 40 miles per gallon on a dynamometer is more likely to use less gas driving down the highway than a car that only gets 20 miles per gallon in the same test. A cooking stove that used less fuel or made less pollution in a standardized test will, one hopes, translate into reductions in the field, but field surveys are needed to establish the actual performance. Field tests are essential to also learn lots of important things, such as if the cook likes the stove, whether the stove product will be successful in the market, and how much PM2.5 and CO is inhaled by members of the household.

In our opinion, no lab test can replace going into the field and learning from reality. And, being taught about stoves from cooks is one of the most fun parts of this job.