Drive a wood gas vehicle gently with the revs kept up and downshift early on hills, because the gas an engine can swallow, and so its power, rises in proportion to its speed, while a closed throttle or long idle drops the gas flow, cools the gasifier throat and makes tar. Expect 40-60% of rated power, check the fuel every 30-45 minutes, and keep the cab ventilated so that drowsiness is read as a carbon monoxide warning and not as tiredness.
Part of Operating Procedures
Driving technique on producer gas: gear and rev choices, fuel checks and the signs that the gas is going wrong.
Revs Are Power, Because Gas Flow Follows Revs
An engine’s intake volume is proportional to its speed, and so is the gas it can take in. For a 2.0 L engine at full throttle with gas 47% of the mixture and a volumetric efficiency of 0.8 (the same assumptions as Downdraft Gasifier Sizing for Vehicles):
- At 2,000 rpm: gas = 0.47 × 0.8 × 0.03 × 2.0 × 2,000 = 45 m³/h.
- At 3,500 rpm: 0.47 × 0.8 × 0.03 × 2.0 × 3,500 = 79 m³/h.
- Ratio: 79 ÷ 45 = 1.75, the same as 3,500 ÷ 2,000.
So at full throttle the engine’s available power on gas rises roughly in proportion to rpm. On petrol the torque curve rises and falls, but on gas the supply limit dominates, so the engine pulls best at higher revs and lighter load. This is the carrier’s rule: keep the RPMs up, downshift earlier on hills, accelerate gently.
What To Watch While Driving
- Power: 40-60% of petrol power (Power Output Derating). Plan overtakes and hills accordingly (Speed & Power Reduction).
- Gas temperature: if it rises above 50 °C the engine loses power; increase cooling. Check the cooler and its fan.
- Fuel: check the hopper level every 30-45 minutes.
- Misfires and loss of power: the carrier reads these as tar clogging, meaning the gasifier is running too cold.
- Your own state: yawning, headache, sleepiness, nausea or clumsiness in the cab is a possible carbon monoxide leak. Stop.
Idle, Descents And Stops
A closed throttle cuts the gas flow. At idle a 2 L engine draws only about 7 m³/h of gas against 68 at full throttle, a ten-fold turndown, and a throat loaded that lightly runs cold and makes tar. So:
- Avoid long idles on gas; at stops longer than a few minutes, switch off or switch to petrol and restart the sequence later.
- On a long descent, expect the gas flow to drop; the carrier notes that dual-fuel capability, switching to petrol for starting and hills, makes the vehicle much more practical.
- If the engine stalls with the unit lit, stop outdoors, run the blower to the flare, and do not restart on gas until the flare is steady.
Method: Refuelling On The Road
- Stop outdoors, upwind, and well away from buildings and people.
- Keep the blower running or the engine drawing so that air moves down into the hopper, not gas up out of it.
- Open the lid at arm’s length with the face turned away, add the fuel quickly and close it.
- Expect a puff of smoke or gas, and possibly a flash at the lid; never lean over it.
Common Mistakes
- Lugging in a high gear. Low revs mean low gas flow, tar and stalls.
- Idling at the roadside to rest. The gasifier cools and the cab fills with exhaust.
- Refuelling with the face over the hopper. It is the highest carbon monoxide point.
Safety
Drowsiness in the cab is a carbon monoxide warning
Producer gas is about 18-22% carbon monoxide by volume and a leak at a joint reaches the cab. It is odourless; the early symptoms are headache, nausea, clumsiness and confusion, and they destroy the judgement to stop. Keep windows open or the cab vented, never drive with someone asleep beside the unit, and never idle or park with the gasifier lit in a garage, shed or enclosed yard. A hot bed full of gas can flash at the hopper lid. See Carbon Monoxide Risks.
What’s Next
- Learn next: Shutdown & Maintenance — ending the day safely
- Combine with: Range & Fuel Consumption — how far a hopper takes you