A vehicle gasifier uses 3-5 mm steel for the reactor, 1.5-2 mm steel for the outer shell and 40-50 mm gas piping welded at every joint, because vibration loosens bolts and a gas leak is lethal. Match each material to the temperature of the gas it carries: steel or stainless in the hot half, and aluminium or rubber only after the gas has been cooled below 40 °C.
Part of Vehicle Gasifier Design
The metals and sealing materials suited to a gasifier on a moving vehicle, matched to the gas temperature and the vibration at each part.
Match The Material To The Temperature Of The Gas
| Part | Gas or surface temperature | Carrier’s material | Note |
|---|---|---|---|
| Reactor (firetube) | 800-1,400 °C inside at the throat | Thick steel, 3-5 mm; extinguisher tank or small pressure vessel | Throat and nozzles need a sacrificial or stainless ring |
| Outer shell | Warm | Thinner steel, 1.5-2 mm; a 200-litre drum works for larger vehicles | Carries the insulation and shielding |
| Hot gas line and cyclone | 300-400 °C | Steel, welded | No rubber, no aluminium |
| Cooler, filter, mixer | Below 40 °C after cooling | 40-50 mm steel or thick aluminium tubing | Aluminium is acceptable only here |
| Flexible joint | Cool side | 15 cm of heat-resistant silicone hose or a bellows | Silicone is rated near 200 °C, not for the hot line |
The temperatures are the carrier’s figures. Structural steel loses roughly half its strength by about 600 °C (recalled), and aluminium melts at about 660 °C, so neither is a hot-side material. Silicone hose is rated to roughly 200 °C continuous (recalled), which is below the 300-400 °C of the gas leaving the gasifier.
Why Welded, And What Welding Cannot Do
The carrier says to weld every joint because vibration loosens bolts and a gas leak is lethal. That is right for the runs of pipe. It leaves no way to open the cleaning stages, so the cyclone pot, the filter housing and the drains need a gasketed flange or a clamped lid that is tested after every opening, using soapy water on a low-pressure air test.
On a suction gasifier a leak mostly draws air in: it dilutes the gas, and a flammable mixture can form inside the line. During the start-up blower, or after the engine stops while the unit is hot, the same leak pushes gas out. Both are reasons to test, not to assume.
Corrosion And Tar
The condensate is acidic, since wood pyrolysis produces acetic acid and the liquid is typically around pH 2-3 (recalled), so the lowest parts of the cooler and the drains corrode first. Use steel thick enough to survive some loss, avoid galvanised steel anywhere that is heated, and do not use a drum that held oil or chemicals without cleaning it, since residue can burn or explode when cut and welded.
Method
- Choose the sheet and pipe thickness from the table, adding thickness at the throat and the drain points.
- Weld all runs and make the seams continuous.
- Fit gasketed flanges at the points that must open, with a heat-resistant gasket.
- Put aluminium and silicone only downstream of the cooler.
- Test the finished gas path with air before the first fire.
Common Mistakes
- Thin metal at the throat. It burns through in hours.
- A rubber joint on the hot line. It chars and leaks.
- A bolted joint on a long vibration path. It loosens.
Safety
A materials failure on a vehicle is a carbon monoxide leak beside the driver
Producer gas is about 18-22% carbon monoxide by volume. A cracked joint or burnt-through nozzle on a moving vehicle releases it near the cab. Never run the unit in a garage, shed or enclosed yard, and stop and leave the vehicle at the first sign of headache, nausea or confusion. Do not cut or weld a sealed cylinder that held fuel gas or extinguisher charge without venting and flooding it with water first. See Carbon Monoxide Risks.
What’s Next
- Learn next: Vehicle Mounting — fixing the unit to the vehicle
- Combine with: Reactor Chamber Construction — building the reactor from these materials