The gas cooler on a wood gas vehicle brings producer gas from about 350 °C to below 40 °C, which for 60 normal cubic metres an hour means rejecting about 7 kW and needs roughly 1.8-3.1 m² of tube surface, so the carrier uses a finned radiator in the airflow path or behind a fan, with a condensation trap at its lowest point. A salvaged car radiator or heater core is tempting but its narrow tubes clog with tar, so give the gas wide passages, a continuous fall to the drain and a way to clean it.
Part of Gas Cleaning for Mobile Use
The cooler is a finned heat exchanger on the gas line that condenses tar and water and lowers the gas temperature before the filter.
How Much Heat Has To Go
Following the method in Tar Removal (Cyclone & Cooling), with a specific heat of about 1.35 kJ per Nm³ per K (an estimate) and the vehicle gas flow of about 60 Nm³/h (mid-range of the carrier’s cruise flows):
- Sensible heat: 60 × 1.35 × (350 − 40) = 25,110 kJ/h = 6.98 kW.
- Condensing the water adds latent heat of about 10-30% on top.
- Mean temperature difference to 20 °C air: (330 − 20) ÷ ln(330 ÷ 20) = 111 K.
- Tube surface at an assumed 20 W/m²K (bare pipe, moving air): 6,980 ÷ (20 × 111) = 3.1 m². At an assumed 35 W/m²K (fins and a fan): 1.8 m².
A bare 45 mm pipe has 0.141 m² per metre, so 3.1 m² is 22 m of pipe. That is why a vehicle uses fins and forced air. The heat coefficients are assumptions, not measurements, so treat the area as an order of magnitude.
The Carrier’s Radiator, And Its Weakness
The carrier uses a section of finned radiator (a salvaged car heater core or small radiator) mounted in the airflow behind the grille or with its own fan, with a condensation trap at the lowest point. The need for airflow is real: a vehicle at a standstill, as at start-up or in traffic, has no slipstream, so the fan is not optional.
The weakness is the passage size. An automotive radiator or heater core has narrow flat tubes built for clean coolant, and gas that is condensing tar will foul them; I could not source a clogging rate. Prefer plain round tubes of generous bore with fins on the outside, laid with a continuous fall to the drain, and give the cooler a flanged end or cleanout so it can be rodded and flushed when cold.
The Trap And The Temperature
- Drain: a valve at the lowest point, kept closed while running, plus a catch can. Condensate is toxic and tarry (Moisture Separation).
- Target: below 40 °C, where the gas is still saturated at 7.3% steam by volume; colder is better for power. The carrier warns that gas above 50 °C costs power, which is consistent.
- Placement: after the cyclone and before the filter. Do not put the cooler in front of the vehicle’s own engine radiator without checking: 7 kW more heat is added to the air it uses.
Method
- Mount the cooler behind a shield, in clean air, with a fan wired to run during start-up.
- Slope the tubes to the drain and put the drain at the lowest point of the whole gas line.
- Insulate the hot pipe up to the cooler, so the tar does not condense early.
- Check the gas temperature after the cooler; if it exceeds 40 °C, add area or airflow.
- Drain and rod the cooler on schedule, cold and outdoors.
Common Mistakes
- Using a heater core as is. Its tubes plug.
- A cooler with a dip. Condensate lies in it and chokes the flow.
- No fan. The unit cools only when moving.
Safety
The cooler and its drain are carbon monoxide and tar hazards
The gas is about 18-22% carbon monoxide by volume. Draining or cleaning the cooler in a shed, garage or enclosed yard, or while the gas is hot or the unit running, is dangerous. Condensate burns skin and should not reach wells or streams. A tar-fouled cooler can ignite if air enters a hot system. See Carbon Monoxide Risks.
What’s Next
- Learn next: Fabric Filter Housing — the stage after the cooler
- Combine with: Compact Cyclone Separator — the stage before it