The best rocket stove fuel is dry sticks 1 to 3 cm in diameter, broken to 20 to 30 cm lengths; split kindling, dry bark strips and bamboo are good, and larger split wood of 5 to 8 cm burns less efficiently. Logs, wet wood and green wood smoulder and clog the stove. Thin sticks work because they have far more surface for their volume, so they heat and burn quickly.
Part of Rocket Stove Design
A rocket stove’s chamber is small, so fuel size and dryness decide whether the gases burn completely.
Thin Dry Fuel Burns Fast Enough To Keep The Chamber Hot
The overview grades fuel:
- Best: dry sticks 1 to 3 cm diameter, broken to 20 to 30 cm lengths.
- Good: split kindling, dry bark strips, bamboo.
- Acceptable: larger split wood (5 to 8 cm), but less efficient.
- Poor: logs, wet wood, green wood.
Worked Example: Why Thin Sticks Burn Faster
The side surface of a long cylinder per unit volume is 4 ÷ d, where d is the diameter.
- d = 1 cm: 4 ÷ 1 = 4.0 per cm
- d = 3 cm: 4 ÷ 3 = 1.33 per cm
- d = 8 cm: 4 ÷ 8 = 0.5 per cm
A 1 cm stick has 4.0 ÷ 0.5 = 8 times the surface per volume of an 8 cm split. More surface per volume means gas leaves the wood faster, so thin sticks heat the chamber quickly, and large pieces can only release gas at the rate their surface allows.
Worked Example: How Much Fits The Opening
Using the tin-can prototype’s 8 × 10 cm opening, 80 cm². Four 2 cm sticks have a cross-section of 4 × π × 1² = 12.6 cm², which is 12.6 ÷ 80 ≈ 16% of the opening. The rest is air space. That is why the overview says never to pack the magazine.
Method: Preparing Fuel
Step 1: Gather dead, dry branches.
Step 2: Break them to 20 to 30 cm lengths.
Step 3: Store under cover, raised off the ground.
Step 4: Test. A dry stick snaps cleanly; a damp one bends and is cool to the touch.
Common Mistakes
- Using green wood. It steams and smokes.
- Using treated or painted wood. Toxic fumes.
- Using big pieces to save effort. They smoulder; see Complete Combustion vs Smoldering.
Safety
Fuel that burns badly makes carbon monoxide
Wet and oversized fuel burns incompletely, and incomplete burning makes carbon monoxide, which has no smell. Treated, painted or glued wood also gives off toxic fumes. Cook outdoors or exhaust to the outside. See Carbon Monoxide Risks.
What’s Next
- Learn next: Starting & Feeding — using the fuel
- Combine with: Coppicing & Fuel Management — a renewable supply of sticks