I made this stove based on mix of Kazimirov's stove (ru) idea, tiny gasifier stoves design widely showed @youTube and some spirit of rocket stove.
Making this stove I took into account
- the need of preserving the heat in the wind (key feature)
- portability (not backpacking, but so small that it can be constantly carried in the car trunk in case bag)
- price and
- low fuel consumptions.
- 3 x 2L cheap aluminum pot (1 for burner, and two cookpots for soup and tee respectively)
- 2 x 2.5L aluminum pot (casing)
- 1 x aluminum pan (coal/ash collector)
- 3 х kitchen 16mm tube railing (tripod stand stucked in the ground)
- 3 x M5 threaded rod: M5 too small, I'll recommend to use bigger (M8)
- 6 x М5 (M8) cup nut (put it to ends of every threaded rod)
- 6 x M5 (M8) wing nuts (3x for tripod mount leveling, 3x for ash collector gap tuning)
- X x M5 (M8) large washers
- Y х M5 (M8) ordinary nuts
WARNING: don't use any (especially DIY) gasifier stoves indoor or in closed areas: all of them emit a lot of CO and tar pairs which will be dangerous in closed spaces. If you have some factory producted gasifier stove check your manual is it consists some notes on usage in closed areas. I have no such stoves, but knowing US law tenacity I think you must find some warning note.
Step 1: Structure
Oven consist of two parts distanced by 3x threaded rods:
Casing made from two pots with bottoms fastened together. Doubled bottom has large through hole forming diaphragm which passes hot gases from lower case half with burner to high case part with cooking pot. Diaphragm assembled by two ordinary nuts clenching drilled case pot bottoms together. Diaphragm zone consists of diaphragm itself and area above the smoldering fuel.
Internal (flying) burner and outer case divided by ~1cm gap between walls and between burner edge and diaphragm. Burner with perforated bottom suspended on 3 threaded bars going through the entire oven using two nuts on every bar clenching drilled burner bottom at required position.
Air moves in gap between case and burner upward by convection, and heated air injects via gap between top edge of burner and case into diaphragm zone mixing with wood gas. Wood gas mixture burns in diaphragm zone and in gap between cooking pot and top case gives heating over all pot surface, and no heat losses.
Fuel smoldering (top down gasification) and charcoal post-burning require air flow from bottom of the burner. This is done by perforating burner bottom by 1-2cm holes.
This oven can be equipped with (optional but very useful) ash collector made from alu pan. Gap between panand lower edge of casingforms fresh air flow blows into oven. This gap can be tuned by 3 wing nuts. In storage mode this wing nuts must be tightened by hand to prevent ash eruption out of badcleaned oven.
All oven structure strung on threaded rods. I used M5 rods, but they are too flexible being heated, so use M8 or even M10 rods. Rods goes thru holes drilled in pot bottoms in vertices of an isosceles triangle. Size of this triangle must be agreed with your smallest cooking pot size -- cooking pot stands on the ends of thread rods covered by cup nuts. Every cup nut should support cooking pot in point near pot bottom edge, but on flat surface (it's critical), so drill rod holes on circle with diameter 10-15mm smaller then you smallest cooking pot flat surface diameter.
Oven fuel capacity and heat rate can be tuned by length of threaded rod enging. Gap between casing and cooking pot fixed by size of your selected pots. But you can play with distance between diaphragm and bottom of cooking pot. Smaller gap will limit fuel consumption, but don't make it too small preventing burning goes out. Larger gap will increase burning gases flow thru diaphragm making heating stronger -- combustion will be emitted in gap between case and cooking pot, and heating surface will be much bigger.
But if diaphragm and ash collector gaps too large you will get lot of sooted smoke since wood gases will not burn completely. This soot effect especially noticeable when burning resinous wood such as cherry or apple wood. If you take off your pot burning cherry wood, you'll see boiling tar on top case walls and a huge amount of soot on your cooking pot. I experimentally found the right combination of ash collector and diaphragm/pot gap sizes and size and area of perforated burner bottom to burn cherry wood, but it highly depends on pots geometry. You can try to add some tuning jigs into construction, if you are worried about control of air flows and burning process.
On photo you can see pan cover bolted to ash collector: it is surplus detail, you don't need it. This is remnant of my unsuccessful attempt to make the air flow control. I made some hollows and forced to shut them down.
The same photo shows how to make tripod leveling using only 3 wing nuts. But I recommend to use 6 nuts to control leveling and ash collector gap separately.
Please note me what online service I can use to draw detailed schemes of oven internals: I tried draw.io but this thing is not I want to use.
Step 2: Ignition, Went !
- get two long cross bars and put it over diaphragm hole -- it will be automatic breaker at end of ignition, and first draftstarter fuel portion will fall into burner
- put some thick and thin bars over draft breaker
- short thick logs are main fuel tank -- it will burn long and slow, giving large charcoal pellets
fill up the "hydrazine" firestarter
Wait until some burning fuel drop into burner and preheat it. You'll notice firedraft will be increased dramatically. Hot burner will preheat inlet air and make forced convection airdraft into diaphragm burning area.
Add some additional wood (can be longer) thru diaphragm if you need long cooking.
Wait until all burner will be filled by fuel for long cook, or only partially if you need some tea. No fuel should be at top cover part. Put there cooking pot prepared with water and potato, with pot cover installed.
If you have good tuned gaps and good enough wood for fuel (you can test burner prefilled with shavings and sawdust as you do with ordinary TD gasification stove), you'll get fast oven for long bushcraft or outdoor "dacha" garden. It has fast ignition stage with forced humming airdraft, and fairly economical cooking mode.
Step 4: Some Tips on Rocket Stove
I've done some modeling how to expand Rocket Stove with air preheater, see images.
We should add flat heat interchange plates longer than typical rocket stove tube. This will add gap between rocket tube edge and bottom of top casing (flat in this case but often spherical due to usage of old gas ballons).
Also we add some holes to RS tube to put some air in earlier stage (RS has high gas flow so we need some time to mix additional air into RS flame flow and make some afterburning).
All additional construction covered by additional covering tube with length smaller then main RS tube.
So in result we have rocket stove with double step afterburning:
- main afterburning in mid of RS flame flow and
- final afterburning just before going into the upper housing