Getting wood gas from a rocket stove

As I mentioned before when I did my rocket grill project, I wanted to find a way to take wood gas from the rocket stove and channel it to the side burner. Here’s some work I’ve done, though there is a lot more to do to get it working:

We see from the video that it is indeed possible to collect some wood gas from the rocket stove for combustion elsewhere. With some improvements, more gas should be able to be drawn off, certainly enough for a sustained combustion.

This has got me thinking about using a rocket stove to build a wood gasifier. Note the way the gasification grate is made. Here’s a video on how I built it for reference:

What would happen if we put a simple butterfly valve at the top of the heat riser. Start the stove as normal with the valve open. In a minute or two when gasification begins, the intake of a small engine is connected to the air intake of the grate (with the appropriate coolers and filters). As the engine is turned over, the butterfly valve is shut and the uncombusted wood gases are drawn through the air injection holes of the grate. From there, they pass through the coal bed, get cracked further, are cooled and filtered, and finally fed to the engine for combustion.

I see such a system as having a great potential for a small wood gas system. Wood can be added to the fire with no smoke production, start up times should be very fast, and construction is very easy.

It is a rough idea, but one I plan to develop as time allows. Let me know what you guys think in the comment section of the first video in this post. This would make a great open source project.

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Preparations for wood gas generator

I have yet to find a deal on a generator to convert to wood gas. Because of this, I’m going to have to build my own. Right now, my power back up system is made of a 24v computer UPS connected to two deep cycle batteries in series. These are maintained by grid power and give me up to 4 hours run time for my outdoor wood furnace. This is fine for short outages, but a good ice storm will leave me needing something better.

I recently picked up a couple of these alternators to use for my project:

24 volt 35 amp military surplus alternator
24 volt 35 amp military surplus alternator


At 840 watts, they produce more than the 650 I need to keep the wood furnace running at full heat output. I have a 3 hp small engine, which should produce adequate power even with wood gas to run this alternator.

The next phase of this project is to source the materials I will need to build a wood gasifier.  This project has been a long time coming, but now that I have a welder, construction should go smoothly once I have all the materials needed.

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Making biochar and cooking with a homemade rocket stove

It has been awhile since I did anything worth blogging about. Here’s my latest rocket stove build, designed to cook and make biochar:

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Most of the biochar I’m making is for a charcoal gasifier, though I probably will set some aside for gardening next year. Being able to use the wood gases released to cook food or heat a house increases the overall efficiency of such a system.

Here’s a couple snapshots of the rocket stove in case you are interested in building one yourself:

IMG_0369Note how the back is made with three hollow blocks. On either side at the base, you have another hollow block set slightly offset. The sides and front of the heat riser are made with solid blocks.

IMG_0370All the broken blocks you see in the above picture can be replaced with a full solid block. To get better results, level the dirt beneath the stove. If you have any concrete blocks or bricks laying around, see if you can build a rocket stove. I think you will be impressed.

This design is perfect for cooking with, since you do not have to continually push in fuel. I find that a small load of wood provides a hour of good cooking heat.

For those who have had questions on my rocket stove DVD, I have decided to simply upload the series to Youtube, due to lack of interest. I’m running behind on the project, so be sure you are subscribed to my channel.

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Some ideas on woodgas

It is always funny how few people have heard of wood gas. Wood gas seems to be a forgotten footnote in our history. Most notably, it was used throughout the modern world during World War II to power personal vehicles and public transit alike during the petroleum shortages caused by the war.

WWII era vehicle with wood gasifier. Click image for copyright information.

So whatever happened to woodgas? It was cheap, but it was inconvenient. So when the war was over and petroleum prices dropped, so did the gasifier units. Wood gas has several disadvantages:

  • Slow startup times – up to 30 minutes
  • Since wood has low energy density, the fuel takes up a lot of space
  • Gasifiers often were not built well and led to the engine drawing in tars, leading to problems
  • Petroleum became cheaper and was always a lot more convenient

Wood gas has some advantages too, some of which interest many people today

  • Wood is pretty cheap to aquire
  • Its price is not real dependent upon world markets
  • A proper gasifier with a good engine can produce lower emissions
  • It is a fuel you can produce yourself

Let’s run some numbers. First, a seasoned cord of oak weighs around 3000 pounds and contains around 27 million BTUs. A good gasifier will produce 20 million BTUs from this for useable fuel. This is equivalent to about 175 gallons of gasoline. I can get a cord of wood split and delivered to me for $100. I can do it myself for a small fraction of that if you don’t factor in my time. Today’s gasoline price is $3.09 per gallon, so the same amount of fuel energy would run me $540.75. There is one more thing to consider – gasifiers don’t like firewood, they prefer chunks of wood. Let’s say you spend another $100 to chunk the wood up – your energy cost is still less than half.

Now for the bad news – a cord of wood is a stack 4’x4’x8′, or 128 cubic feet. The equivalent in gasoline will fit in three 55 gallon barrels. Big difference in space. Let’s scale this down to everyday numbers. My car holds 16 gallons of gasoline. I would have to haul around a stack of wood 2.3’x2.3’x2.3′, or 12 cubic feet. 16 gallons is equal to a bit over 2 cubic feet.

Since gasoline is a refined fuel, all you need is a fuel pump to get it to the engine. The gasifier is your mobile refinery for wood and will take up space and weigh you down more. It will have to be lit and will produce volumes of smoke and will not be ready for use until that smoke sustains a flame. Then you can crank your vehicle over until it fires up. The whole process can take up to a half an hour.

Wood gasifier and associated filters and coolers. This has to fit on a vehicle to run it off of wood.

If you like cheap fuel and are willing to put some work into it, you can save a lot of money by switching to woodgas. Check out for a lot of useful information from people who have done just that.

I’m planning to go down a slightly different route and refine the wood into charcoal. The charcoal can then be used in a gasifier to produce charcoal gas, which is mostly CO. By injecting steam, you can produce a fair amount of hydrogen, making what is called water gas. There is less risk to tarring your engine by using charcoal gas as well as shorter startup times. I’m going to start small and build one for my wood cutting wood project before moving on to powering my vehicles.

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