Every now and then in histories of the 20th’s century’s earlier years, you will see pictures of cars and commercial vehicles equipped with bulky drums, contraptions to make their fuel from waste wood. These are portable gas generators known as gasifiers, and to show how they work there’s [Greenhill Forge] with a build video.
When you burn a piece of wood, you expect to see flame. But what you are looking at in that flame are the gaseous products of the wood breaking down under the heat of combustion. The gasifier carefully regulates a burn to avoid that final flame, with the flammable gasses instead being drawn off for use as fuel.
The chemistry is straightforward enough, with exothermic combustion producing heat, water vapour, and carbon dioxide, before a further endothermic reduction stage produces carbon monoxide and hydrogen. He’s running his system from charcoal which is close to pure carbon presumably to avoid dealing with tar, and at this stage he’s not adding any steam, so we’re a little mystified as to where the hydrogen comes from unless there is enough water vapour in the air.
His retort is fabricated from sheets steel, and is followed by a cyclone and a filter drum to remove particulates from the gas. It relies on a forced air draft from a fan or a small internal combustion engine, and we’re surprised both how quickly it ignites and how relatively low a temperature the output gas settles at. The engine runs with a surprisingly simple gas mixer in place of a carburetor, and seems to be quite smooth in operation.
This is one of those devices that has fascinated us for a long time, and we’re grateful for the chance to see it up close. The video is below the break, and we’re promised a series of follow-ups as the design is refined.
I’ve gone down the gassifier rabbit hole a few times over the years, though I have yet to build one myself.
They were apparently fairly common in England during WWII, especially for things like tractors, as gasoline was obviously highly rationed for war use.
The biggest downside from what I see is you either need to run the gassifier and use the fuel it produces immediately (I have seen one example from the WWII era of a car pulling a trailer with a gassifier running on it), or store the results in low pressure gaseous form, which is obviously extremely space inefficient. Because of the wide variety of molecules present in the gas, liquification is not really achievable, and even pressurization has major challenges.
Tar buildup is another major issue, as mentioned. But still, very cool tech. If I had more time and funds to mess around with this stuff I’d love to get a setup going someday.
The Germans tried it with tanks at one point towards the end…
How many trees per minute?
There’s a quite funny Swedish facebook group with some enthusiasts building an ecosystem around this. Incidentally, Sweden has a lot of wood, not to mention growing petrol and electricity prices.
First, they make their own coal, including some very large “cookers” or whatever they call it to make a lot of it, optimizing the burn. The coal apparently makes less of a messy/cloggy experience in the engine than pure wood. Then, they adjust cars to run on said coal, trying to optimize the design. Last time I checked they were making electricity from a generator powered by coal, trying to optimize that process . Haven’t checked in for a while, maybe they’re onto the next thing, whatever that would be.
On my To Do: Build a search light with syngas, an ancient style blowtorch and limelight.
If I wanted to routinely remove the heads of my engine to have it media blasted I’d have bought a direct injected BMW.