Rocket Stove Mk II / TLUD — Stainless Square-Tube Core + Pot Skirt + Chimney
Packs into itself, cooks on twigs, and burns clean when run right. Top-lit updraft gasifier core (TLUD) inside a rugged, field-serviceable shell.
What You’re Building
- Core: 4″×4″ (102×102 mm) stainless square-tube TLUD canister with primary-air grate and a preheated secondary-air ring for clean flame.
- Pot Skirt: stainless ring with a controlled 11–15 mm gap around the pot for high efficiency.
- Chimney: 1 m detachable 4″ round stainless flue + spark arrestor screen.
- Packable: chimney nests; skirt clamps flat; spare fuel can fits over core.
TLUD = top-lit; air from below; pyrolysis zone moves down; hot secondary air burns wood-gas at the top for low smoke.
Specs (target)
| Fuel | Twigs/pellets, dry biomass (≤3 cm dia) |
|---|---|
| Power | ~1–3 kW (load & fuel dependent) |
| Core | 304 SS, 1.6–2.0 mm wall (16–14 ga) |
| Skirt gap | 11–15 mm (12 mm default) |
| Chimney | Ø 100 mm × 1 m, SS, spark screen |
| Weight | ~6–8 kg assembled |
Bill of Materials (Parts to Buy)
Metals & Core
| Square tube (core) | 304 SS, 4″×4″ (102×102 mm), length 330 mm, wall 1.6–2.0 mm |
|---|---|
| Square sleeve (air jacket) | 304 SS, 5″×5″ (127×127 mm), length 160 mm (top section), wall 1.0–1.6 mm |
| Perforated grate | 304 SS plate 2–3 mm, perforated Ø6–8 mm holes, 35–40% open |
| Top plate | 304 SS sheet 1.6 mm, with pot-support tabs (3–4 pcs) |
| Pot skirt | 304 SS sheet 0.8–1.0 mm, forms ring (height 120 mm) + 3–4 standoffs (12 mm) |
| Chimney | Ø100 mm SS flue, 2× 500 mm nesting sections + clamp |
| Spark arrestor | SS woven mesh 304, 1/2″ (≈12 mm) to 3/8″ (≈9.5 mm) grid, cap ring & hose clamp |
| Insulation (opt.) | Bio-soluble ceramic fiber blanket, 10 mm, for around upper core jacket |
Hardware & Misc
| Fasteners | M5/M6 SS bolts, nylock nuts, fender washers; SS pop rivets 3.2 mm |
|---|---|
| Air slider | Small SS angle + 1.0 mm sheet for primary air shutter (with slots) |
| Legs/base | 3× SS angles or tripod base plate (folding) |
| Handles | 2× spring SS handles (stay cool) |
| Finish | Edge trim, high-temp anti-seize (bolts), labels |
| Tools | Cutoff saw w/ SS blade, drill + step bit, deburring tool, riveter, clamps, files, respirator, gloves |
Avoid galvanized steel in the hot gas path (zinc fume hazard). Use stainless in flame areas.
Cut List
| Item | Qty | Size (mm) | Notes |
|---|---|---|---|
| Core tube (4″×4″) | 1 | 102×102×330 | Deburr; this is the fuel canister |
| Grate plate | 1 | 96×96 | Perforate Ø6–8; sits 20 mm above bottom |
| Primary air ring | 1 | 102×102×20 (strip) | Forms intake frame for slider |
| Secondary jacket (5″×5″) | 1 | 127×127×160 | Slides over top; heats secondary air |
| Top plate | 1 | 130×130 | Center cut-out 105×105; tabs for pot rests |
| Pot-skirt sheet | 1 | 360×120 | Roll to ring Ø ~ 300 mm (adjust to pot) |
| Skirt standoffs | 4 | 12×20×1 (L-tabs) | Sets 12 mm gap |
| Chimney sections | 2 | Ø100×500 | Nesting; top gets spark screen cap |
| Legs/feet | 3 | 25×25×250 (angle) | Foldable or removable |
Printable Diagram
Print at 100% (A4/Letter). Dimensions in mm.
Secondary air jacket covers only the upper ~160 mm of the core. Drill 3–4 rows of small jets near the top inside edge to inject preheated air.
Assembly — Step by Step
- Prep & Deburr. Cut the 4″ square tube to 330 mm. Deburr all edges. Mark a line 20 mm up from the bottom inside wall for the grate ledge.
- Grate. Cut a 96×96 mm SS square from 2–3 mm plate. Drill Ø6–8 mm pattern to ~35–40% open area. Rivet or tack small tabs so it sits on the 20 mm ledge.
- Primary air slider. Make a window (≈90×20 mm) centered on one face, 10 mm above the grate line. Fabricate a slotted slider plate with a small handle; mount with two M4 screws & slots so you can meter air.
- Secondary air jacket. Slide a 5″ square sleeve (127×127×160 mm) over the top of the core, leaving a 10–12 mm annular gap around three sides. Seal the top of the gap with a small ring/plate; leave the bottom open so cool air is drawn up, heated, then injected near the top.
- Secondary jets. Drill Ø3–4 mm holes on three inner faces of the core, ~15 mm below the rim, every 10–15 mm. These jets admit preheated secondary air to burn wood-gas cleanly.
- Top plate & pot tabs. Cut a 130×130 mm plate with a 105×105 mm square opening. Add 3–4 pot-support tabs (10–12 mm tall) at 90° spacing. Bolt to the jacket so it’s serviceable.
- Legs / base. Bolt three SS angle legs or a skid plate under the core; target 20–30 mm clearance below for fresh primary air intake.
- Pot skirt. Roll 0.8–1.0 mm sheet to a ring that gives 11–15 mm gap around your pot (12 mm default). Rivet 3–4 standoffs inside the ring to set gap. Add three hooks or a band clamp so it sits concentric over the pot on the tabs.
- Chimney & screen. Fit two 500 mm sections of Ø100 mm SS flue with a clamp above the skirt. Cap the top with a woven SS spark screen (3/8″–1/2″ mesh) band-clamped inside the cap.
- Handles & pack-down. Mount spring handles on the core sides. Nest chimney sections together; the spare fuel canister can slide over the core for pack-out.
Operation (TLUD mode)
- Place stove outdoors on non-flammable ground, 3 m clear radius. Attach chimney + spark screen. Skirt on, pot ready.
- Load fuel loosely to the top (twigs/pellets). Add a thin top layer of kindling. Open primary air 50–100%.
- Light the top. After 1–2 minutes, visible blue flames should appear at the jets; adjust primary air until the flame is bright with minimal smoke.
- Set pot on tabs; drop skirt over pot (keep the 11–15 mm gap). Chimney carries fumes up and away.
- When the pyrolysis front nears the bottom (sound changes, flame weakens), remove pot briefly and either quench biochar (water/soil) or dump into a safe metal pan to cool.
Safety: outdoors only. Carbon monoxide is deadly; never use fuel-fired stoves indoors or in enclosed spaces. Keep a fire extinguisher handy; respect local fire bans.
Quick Fuel & Cook-Time Estimator
| Energy in fuel (MJ) | — |
|---|---|
| Useful heat (MJ) | — |
| Cook time @ power (min) | — |
Assumes dry wood ≈ 16 MJ/kg LHV; adjust for your stove & fuel.
Hazards & How Not to Get Owned
- Carbon Monoxide: lethal; never indoors, garages, or tents. Use outside with wind clearance.
- Sparks/Wildfire: always run the spark screen; clear 3 m of debris; have water/sand at hand.
- Hot metal: gloves, long sleeves, eye protection. Let parts cool before pack-down.
- Materials: avoid galvanized sheet in hot zones (zinc fume risk). Use stainless for flame path.
- Biochar quench: fully quench and stir; never store warm char in closed containers.
Tools
- Cutoff saw or bandsaw (SS-capable), drill + step bit, riveter
- Files/deburr, clamps, square, marker
- PPE: respirator, safety glasses, leather gloves
Hardware Notes
- Use SS fasteners in hot/smoky areas; anti-seize on threads.
- Rivets: SS 3.2 mm for skirt and jacket seams.
- Grate: aim 35–40% open area to balance draft & ember support.
Sources & References
- Micro-gasification / TLUD basics: GIZ/HERA & Energypedia manuals (Roth, Anderson). GIZ Manual · Micro-Gasification · Anderson paper
- Pot skirt channel gap guidance (efficiency vs burn rate): Aprovecho “Design Principles”. PDF · EPA copy
- Stainless 304 temperature resistance: Atlas Steels data · thyssenkrupp
- CO safety: EPA CO factsheet (2025) · WHO household air pollution
- Spark arrestor basics: HY-C explainer · Rock-Vent screen
- Avoid galvanized in hot paths (metal fume fever / ZnO): StatPearls · Overview