Shut a wood gas vehicle down by switching to petrol for the last 2 minutes so the engine clears itself of gas, closing the gasifier’s air inlet and the gas valve, leaving a vent to the flare open until the unit is cold, and not opening anything while it is hot. Then drain, clean and inspect on schedule, because a gasifier that is left dirty makes tar next time.
Part of Operating Procedures
Shutdown ends a run safely, and maintenance keeps the gasifier, cleaning train and engine in a state that makes clean gas on the next run.
Shutdown, From The Carrier
- Switch back to petrol for the last 2 minutes of driving, which clears wood gas from the engine.
- Close the air inlet to the gasifier, which starves the fire.
- Close the gas valve.
- Let the gasifier cool naturally. Do not open it while hot: hot charcoal exposed to air ignites violently.
What The Carrier Leaves Out
A hot bed keeps giving off gas for a while after the air is shut; the carrier does not address this, and the following is my reasoning from the physics, not a sourced procedure. Closing every valve traps that gas in a hot vessel. As the unit cools the gas contracts, and any leak draws air in, leaving a flammable mixture sitting over a hot bed. A hot restart or an opened lid in that state is where flashbacks and tank explosions happen. So:
- Leave a vent path to the flare open and lit, or at least open to the outdoors well away from people, until the unit is cold.
- Treat any restart before the unit is cold as a hot restart: blower on first, flare lit, lid never opened, and no one near the unit.
- Do not close a hot unit up in a shed or vehicle for the night.
Ash And Cooling Time
I have no figure for how long a vehicle unit takes to cool, and it depends on insulation and fuel load. The corpus charcoal safety article says an ash pile that looks cool can still hold dangerous heat for days (Safety Practices); treat the ash pit the same way, and empty it into a metal bucket outdoors only when the unit is cold.
Maintenance Intervals: Parent And Carrier
| Task | Stationary parent | Vehicle carrier |
|---|---|---|
| Shake grate, remove ash | every 4-8 hours | not stated |
| Drain condensate | daily, after shutdown | drain regularly |
| Fabric filter | clean or replace every 50 hours | change every 200-500 km |
| Cyclone | clean every 200 hours | empty pot every 100-200 km |
| Air nozzles | inspect every 100 hours | not stated |
| Hearth constriction | check for erosion every 200 hours | not stated |
| Whole unit | inspect every 500 hours, welds and worn parts | not stated |
At an average 60 km/h, 200 hours is 12,000 km, against the vehicle’s 100-200 km; the schedules differ by 60-120 times for the cyclone and by 6-15 times for the filter. They cannot both be right for the same hardware. A vehicle sees more load swings and a smaller cyclone, which could explain a shorter interval, but I cannot source a figure, so base the interval on what you find in the pot and the filter and shorten it whenever you find tar.
Method: After Each Run
- Complete the shutdown and let the unit cool, vent open.
- When cold, outdoors and upwind, drain the condensate into a catch can and shake the grate gently.
- Empty the cyclone pot, check the filter and the suction gauge, and look at the nozzles and hearth ring.
- Test the joints with soapy water after anything has been opened.
- Write down hours and kilometres, so the intervals are based on your own record.
Common Mistakes
- Opening it hot to look inside. The gas flashes and the charcoal re-ignites.
- Putting water on a hot gasifier. It makes steam, and water on hot char makes more fuel gas.
- Skipping the drains. Condensate then freezes, rots the steel or floods the line.
Safety
A cooling gasifier still holds carbon monoxide and a flammable mixture
Producer gas is about 18-22% carbon monoxide by volume, and a shut-down unit can still hold it for hours. Never park or leave a hot or lit unit in a garage, shed, lean-to or enclosed yard, or sleep in the vehicle. Never open the lid or ash door of a hot unit: gas, charcoal and air can flash into your face. Do not use water to put out a hot gasifier. See Carbon Monoxide Risks.
What’s Next
- Learn next: Emergency Procedures — when something fails mid-run
- Combine with: Grate & Ash Removal — the ash side in detail