[Stoves] (no subject)

Thu Oct 10 16:48:52 CDT 2019

Dear Kevin

Perforating the grate is important to getting the charcoal to burn properly, that is well known. The number of holes and spread is debatable of course and is affected by the power lever sought.

Root problems for charcoal stoves are (1) ignition (far too much smoke and (2) takes too much time; cooking power control is rudimentary - close a door and create terrible combustion conditions; (3) when the fuel starts to burn down, it tends to got to a state where the flame goes out but the "burning" continues. That happens when (4) the fuel particles are far enough away from each other that they don't keep each other alight. In this condition (smouldering) the fire produces very high CO.

The condition can be put off (delayed) if the pieces of charcoal are continuously nudged together to maintain a better quality flame condition.

Using a metal grate on small stones placed on an insulating (vaguely) clay base will help with the last issue (4) in that the metal and the gap will combine to preheat the primary air and keep the pieces burning well for longer. The standard cheapie stove in Lusaka is about $1.50 and has numerous small holes in a metal plate that supports the fuel. This helps in the same manner without clay materials. It suffers from several other design issues however so it is not a great stove. In many the cooking power is uncontrollable. Etc. Issue (5) is that the minimum amount of charcoal needed to sustain good combustion is related to the fuel depth. A large amount of fuel spread out thinly over big plate is terrible for a) ignition and b) having good combustion at different power levels.

The IKJ clay-lined JaKo has design issues and aeration is just one. The Pebbles-And-Plate will help. The depth needed to hold the fuel and create a unable gas and contain a flame prior to letting the hot combustion gases touch a cold pot is already far too shallow decreasing the height available will make that problem worse. The result will be higher CO (an inefficiency and a danger) but people blame the fuel not the stove for high CO.

Addressing the issues 2-5 simultaneously an attempt was made in Mozambique to create the Maputo Ceramic Stove, funded by DGIS, managed by ProBEC/GTZ 2005-2010. The result is the MCS which is/was available in Maputo and then central SADC countries in an all-metal form.   This uses (uncontrolled cooking tests monitored in homes) 42% less fuel across the board from expert cooks to incompetent hackers.  It was made originally from ceramic materials because of cost. Secondly, no skill existed to work metal as is available in east and central Africa.

The issue of getting the fuel to come together was addressed by making a bowl-shaped chamber instead of flat. If you made a perforated metal bowl and placed it on the stones and placed all that on a deeper ceramic body, it would address issue 4. If you could arrange for preheated secondary air t o flow horizontally over the lip of the bowl into the fire, it would dramatically reduce the CO and create more heat (free). Following your nose you'd end up with an MCS if you have instruments to guide you.

At this stage in your product development I think you need absolute numbers not final relative fuel as a guide. If it is better. Why and how to optimise it?  Most charcoal stoves have far too much air flowing through them. Limiting that improves fuel efficiency and when burning purchased fuel, people care a lot. So saving 50% of fuel over a not that great to begin with stove is good, but how does it compare with a really good stove. Context matters. If claims are being on principle then it needs absolute performance comparison. Essentially it is providing fuel aeration, a lack of which is a problem that shouldn't exist.

Good luck with your efforts. If it works, use it. Understanding can follow. Sometimes it doesn't follow, but it still works. That's OK too.

Regards
Crispin
From: info at sun24.solar
Sent: October 11, 2019 1:39 AM
To: stoves at lists.bioenergylists.org
Reply to: stoves at lists.bioenergylists.org
Subject: [Stoves] (no subject)

Listmates,

Has anyone tried this?

We seem to have significantly increased the efficiency of charcoal jikos by putting a bed of rocks on the jiko's grate and putting second metal grate on the rock bed.  The charcoal goes on the second metal grate.   2-3 cm rocks work.  It works in all metal jikos and clay jikos that we've tested.

Our testing is early and unscientific, but consistent.  25-50% less fuel used.  Here are three reports.  The Sierra Leone report has good photos at the bottom.

Sierra Leone<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F12MvBKjxq6PCGCcCHAjSYSeVXXvl7jWjD%2Fview%3Fusp%3Dsharing&data=02%7C01%7C%7C3962888aec1e4f20ff3e08d74da8d5c7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637063259869051564&sdata=wqC0rGNu1gBMaAV3gb9NeuqMod5wpqoAeoX28UVIrmg%3D&reserved=0>

Uganda<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1zQIY49E1vrfjYl7t5V_shvw70d67QirGWUrbW51tDxo&data=02%7C01%7C%7C3962888aec1e4f20ff3e08d74da8d5c7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637063259869071574&sdata=yhlthne56Ufk9TWMqzfyzOlgkccdEDi0PvJERsyP%2FyM%3D&reserved=0>

Kenya (very few rocks)<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1MPwHCwKEVqJvuybKB5Yj39nr8fbcopBP&data=02%7C01%7C%7C3962888aec1e4f20ff3e08d74da8d5c7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637063259869081591&sdata=n7t0MH%2BSE2mi%2B%2Bk7HjKQja0ND6ofOLX6merX4NEZOzs%3D&reserved=0>

(The report authors are untrained and not native English speakers.  Especially the Kenya report contains many errors. Please focus on the consistent final conclusion that a rock bed and second metal grate significantly reduce firewood usage.)

This may be a very low cost, very easy way to greatly improved the efficiency of charcoal jikos.  I'd like to hear if there is already a body of work on this.  Here is my rough drawing:

[20191010_133359.jpg]

Thank you,
Kevin

Kevin McLean, President
Sun24
https://sun24.solar<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsun24.solar&data=02%7C01%7C%7C3962888aec1e4f20ff3e08d74da8d5c7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637063259869101600&sdata=yuOyAsWMLHTp0qJpFew42%2Fdw3OfIoP1lWQLAnCojncE%3D&reserved=0>  Sun24 Cookstoves Overview<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F1ZryS7gQ1q3zKLZPM2KcXdtIHbOYQp4PbloPqMvrlZ5Y%2Fedit%3Fusp%3Dsharing&data=02%7C01%7C%7C3962888aec1e4f20ff3e08d74da8d5c7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637063259869111599&sdata=7ZbY9iJ3x%2BiSt7Icv%2Ff2UGsMeh4%2F%2BOVe234YEtQxxlo%3D&reserved=0>
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             [https://docs.google.com/uc?export=download&id=13teZQbnv_6ek6JkEy-4n0yyUVTrl3M2W&revid=0B8zNcWsuiuj3N2RuVFFYL3EvdElxR1lDcm9QQVlaL0F4VnVFPQ]         [https://docs.google.com/uc?export=download&id=11k6wcaMcCbykOoLu-Qo4n6Kbdhplk_er&revid=0B8zNcWsuiuj3ejdsRjRXQWU2OW4rVUpwMUx0Q0U0eXgxcStBPQ]

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