At a recent Maker Faire, I had the opportunity to see a fascinating exhibit - a small tractor powered by wood gas. This project intrigued me so much that I decided to dive deeper into this interesting technology and share with you how such a wood gas propulsion system actually works.
What is Wood Gas?
Wood gas is produced through incomplete combustion of wood in a closed gasifier with a limited air supply. This process is called pyrolysis. The resulting gas is a mixture of carbon monoxide, hydrogen, methane, and nitrogen. Although it has a lower energy value than gasoline, it is a fully viable fuel that can power a modified combustion engine.
How Does a Wood Gas System Work?
Gasifier and Gas Collection
The heart of the system is the gasifier, where the actual gas production takes place. The process begins with igniting the wood and heating to the proper operating temperature (800-1200°C). After ignition, the air supply is restricted to create a reducing atmosphere in which quality wood gas is produced.
Gas Cleaning
Raw gas is hot and contains impurities, so it must pass through several cleaning stages:
- Cyclone separator - uses centrifugal force to separate solid particles. Gas enters tangentially into a cylindrical vessel, where heavier particles fall away and clean gas rises upward.
- Cooler - reduces gas temperature to approximately 40°C. During cooling, tars and moisture condense.
- Multi-stage filtration - combination of coarse filters (wood chips), textile filters, and sometimes water or oil scrubbers.
Path to the Engine
The cleaned gas is led to a mixer, which replaces the classic carburetor. Here it mixes with air in the correct ratio. The entire system operates primarily on the negative pressure created by the engine during the piston's intake stroke. This negative pressure (0.05-0.1 bar) transfers through the entire system back to the gasifier.
Combustion Engine Modifications
To operate on wood gas, the engine must be modified:
- Increase the intake manifold diameter due to lower energy density of the gas
- Adjust ignition timing (advance), because wood gas burns more slowly
- Increase compression ratio for better efficiency
- Use more durable materials for valves and valve seats
Operating Phases
Operating a wood gas system has several phases:
- Starting phase (10-15 minutes)
- Igniting wood with open air supply
- Waiting to reach operating temperature
- Operating phase (1-2 hours)
- Partial closure of air supply
- Stable production of quality gas
- Refueling phase
- Adding fuel when performance drops
- Possible during operation with some systems
Suitable Fuel
For reliable operation, choosing the right fuel is crucial:
- Hardwood is best (beech, oak)
- Moisture content below 20%
- Piece size 3-7 cm
- Avoid softwood and chemically treated wood
Practical Operating Aspects
Operating a wood gas system requires regular maintenance:
- Checking and cleaning filters
- Monitoring temperatures in various parts of the system
- Removing tar and ash
- Checking seal integrity
- Ability to quickly switch to gasoline in case of problems
Conclusion
Although wood gas is not currently the primary energy source for vehicles, it remains a fascinating technology with potential for crisis situations or experimental purposes. Engine performance on wood gas is about 40-50% lower than on gasoline, but it represents an interesting alternative and reminds us that even seemingly outdated technologies can be very useful in certain situations.
If the topic of wood gas has caught your interest, you can look for other maker faires or technical museums, where functional examples of this technology can occasionally be seen.
