First build input needed

Just thinking about building my first gasifier. Fuel is to be wood chip but would like to build it so it can be run on a mixture of wood chip and sawdust eventually. I plan to use automation to overcome some of the difficulties of using a fuel mix like this. I have a tube 130 mm internal diameter and 400 mm long. I can add extra length if needed. I intend to use thermocouples and a map sensor to control temp and airflow.

Intend to use a flat plate that rotates with a scraper bar to hold the char bed at about 900 degrees. If the temp drops below this the plate will rotate and the scraper bar will empty the plate allowing fresh char into this zone. It may only move 1/8 th of a turn depending on temperature. The map sensor will maintain a .5 hg pressure drop within the system by utilising a servo to open or close a tap that alters airflow into the gasifier depending on Fuel load requirements. I intend to use a pipe with a wide slot pointing down as an air injector. I believe this can be oversized as air velocity is dependent on pressure drop and with pressure drop being maintained by opening or restricting air flow set by the map sensor
To put it simply if the woodgas required is 10 cfm the velocity of the air into the Gasifier is the same as if the woodgas required Is only 1 cfm per minute. The rotating plate maintains the movement of wood through the system while ensuring a high temp to crack tars. There will be no restriction in flow other then the rotating plate to time fuel flow through the gasifier. Fuel flow is governed by temperature in the char bed this way.
For a start if I can get a unit producing woodgas to flare off will be good then move onto running a lawnmower engine eventually.

My questions are is maintaining 900 degrees in the char bed enough or should it be higher. How much distance is required from air inlet to char bed. Any other thoughts are welcome.


Are we talking about C or F. You will need a minimum of 700 C at the grate to achieve gasification at all.

You dont need to make it all that complicated you can simply time your grate on a stationary system if that is your application as your engine RPM will be static, so it will be quite predictable. Your trying to fix the problem with your system verses preventing the problem. With your system it will be too late and processes will crash. You want to prevent temp and flow drops and a timed system will achieve this just fine and with simplicity.

Why are you going with direct woodgas system instead of charcoal? (just curious) what do you think the benefits are going direct gasification and what do you think disadvantages are to charcoal?

Going with straight wood eliminates a process. In a static operation a timed system may be passable although it would not be the best. I am into experimenting so I don’t mind pushing boundaries. A problem with timed systems is that the char may become depleted and therefore lose its ability to crack the tar. By using a feedback system based on temperature I can ensure the gas passes through a consistent 900 degree Celsius so all tars are cracked. Not sure why you feel the system will crash. The map sensor will consistently read and adjust the air inlet to keep pressure drop and therefore air velocity at close to optimal as possible. Reading through the forum it seems that all gasifiers have a problem reacting to load changes. While the map sensor will still have a slight delay due to air speed changes being delayed due to restrictions and other physics it will still allow the gasifier to operate at its best from idle right through to wot. The tech exists and is easy to implement. Instead of sizing a air inlet nozzle that delivers the right mix at a certain rev it’s easy to have a nozzle that can provide performance at wot and performance at Idle instead of wasting heat by having a less then optimal air flow rate. This build is just a proof of concept. If I can get a flare and management system to work next will be to see if I can get a lawn mower to run on it. If it successful I will look at a larger system. I have a homemade jet that burns 6.5 gallons of fuel per hour. Ultimate goal would be to attempt to run it on wood gas but first things first.


Your system will be an oscillating system a gasifier needs to be in balance with many processes happening inside. If you time you can quite easily maintain flows to keep things in balance. If you wait then your flow is going down and then suddenly opening back up and your processes will oscillate and can lead to them crashing. How would I know this? Probably because I have built over 300 machines over a 10 year span and I probably have the most advanced automation system to exist in this space in small scale systems.

Ok for charcoal, you are not really eliminating a process. Really these are two different fuels and two very different processing. Chipping fuel you will need to of coarse run your fuel through a processor, then you must screen it and this is especially important on a small gasifier. Generally will have a yield much less than you started with. This waste fuel is energy potential you can not use and wasted time and energy to produce it. Yes you could use it for a kiln to dry your fuel. but you are right back to adding a " process"

Charcoal on the other is much less labor intensive to prepare for a kiln. A charcoal kiln is very easy and cheap to build and there is no rule to how many you can make. You make tons of charcoal very fast with out fossil fuels involved into producing it.

Here are some benefits of charcoal. You simply are not going to produce tar number one. Charcoal runs very stable you dont really even need automation. The charcoal gasifier itself is stupid simple and low cost. And if you can think outside the box and integrate your charcoal process into a heating application this hands down makes it way more practical than a direct gasifier any day.

Take it from me as I am eating crow writing this post as I was very reluctant to adopt charcoal technology. I am now completely dropping direct woodgas systems completely from my product line. This is after 8 years of very rapid development with hundreds of thousands of dollars into it. Charcoal is by far better technology for small scale wood gasification. No direct wood gasifier is exempt from producing tar; If it can happen it eventually will. Unless you can say there is no way it can produce tar 100% then it is not exempt. Larger scale is more doable but small scale will be a challenge Im not saying it cant be done not at all.

I good test is to produce both fuels first before you build and see what you think is most viable and learn to crawl before you run.


Thanks for your experienced input. I’ll stick with wood as it can be easily obtained already chipped. Another reason for using the automated rotating plate is opens up the possibility of using fuel that is not a specific dimension. Provide the char will pass out the bottom onto the plate to be wiped off by the scraper bar any size fuel should work. A mixture of wood chips and sawdust should be ok which opens the door for more fuel types to be utilised. Can you explain why the system will oscillate any more then a standard gasifier. All gasifiers oscillate depending on load. The map sensor and controlled airflow will allow microsecond adjustments which should even out the oscillation better then a standard gasifier The temperature controlled fuel flow should maintain a constant temp to crack the tars. From what I’ve read here the gas needs about 1/2 a second to crack the tars at above 900 degrees Celsius. It’s very possible that my system could produce a high amount of bio char but I don’t see that as an immediate issue. Bio chars are very expensive here in Australia. The production of bio char could be reduced by having a wider rotating plate but that may also increase tar production.

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Its fairly simple. Think of the solid fuel inside your unit and the layers of process. When drop fuel out the grate everything above drops down. Go back to the top of the hearth now. Raw fuel just dropped into your hearth cooling it immediately, gas is not fully processed and water is not cracking. That water is now migrating into your hopper along with tar. This is now saturating your fuel and the hopper walls. Now your fuel is sticking and hanging up. Your reduction is now cooling and not able to process the raw pyrolysis gases with tar now building up in this bed make it more restrictive.

If you just time it and make subtitle movement you can very easily maintain constant flow and temperature.

Your fuel size will be dependent on your build of what it can process. fuel density moisture content will also have huge effects. Soft wood you can run high MC hardwood needs to be dryer.

To better control things we use an electronic automixture system. I have a tutorial right here on the sight to build it.

You definitely are a wood gasser. Just like many of us we tend to want to improve it before we build anything: If its not broke dont fix it: however we can certainly improve this technology. But you need to first really identify what actually needs improvement and many of us developers are already there doing it. The automixer, auto grate, hopper vibrator agitator are really all you need to make the system stable.

You can certainly add your system along with the timed system though.

My temp controlled system has the same drawback as your timed system. Both drop fuel into the zone and cause the problems outlined as far as I can see. I think both systems have an advantage over the ww11 gasifiers as they relied on manual shaking / stirring or the vibration of the road to move fuel into the zone. Does your timed system allow for changes in load and therefore higher fuel reduction rates. The advantage of utilising heat to time fuel movements is the heat is always constant in the char bed to crack any tars. A timed system that doesn’t allow for load changes may allow temps to drop below optimal in the char bed as increased load will lead to faster fuel reduction and the loss of the chars ability to maintain heat output. Have I got the right thought here or have I missed something.


On a stationary gasifier its not an issue especially if you have the electronic air fuel mixture. Your going to need this no matter what you do if you want to walk away from the machine.

No the timed is only making subtitle flow movements and is not so much dropping the fuel its keeping it loose and from packing the grate.

Once you detect a pressure or temp drop its already too late. You want preventive measures not corrective measure for a stable system.

I should add and this was sort of proprietary. But the grate system on the wood gassers was too parts a rotating grate and static grate with choke plate just above that. The reduction tube skirt had slots cut into it at the bottom and the rotating grate fit inside this. This is where the gas actually left the reduction and not the rotating grate. The rotating grate was only there to hold the fuel up and this was very passive grate system so it was not subject to gas flow issues ever. The timed grate simply kept things flowing. You are going to consume a pretty static volume of fuel regardless of load.

If you feel your set up will work dont let me stop you. I hated it when people told me Nah you cant do that it will never work!! lol Yeah well I did anyways and guess what a lot of stuff did work and thats when I chucked a lot of literature in the garbage.

But Im just trying to offer a simpler way that I know works from lots of experience.


Appreciate your input. Honestly can’t see the difference between your timed movements verse my temp controlled movements as both can be as subtle as the programming of the microcontroller allows. The map sensor would be located on the output side so any delay in its operation opening or closing the air inlet valve would still possibly be quicker then a gasifier can react without such a system. Optimising air flow seems to be one of the biggest drawbacks to operating a gasifier. The speed at which air moves through the system is the biggest key to maintaining optimal temperature and time to fully complete the process. Having a set inlet valve doesn’t seem to be the best option as velocity of air is dependent on pressure drop. Maintaining the correct pressure drop means that the gas is optimised. If excess air can enter through a slight miscalculation in nozzle size the system is not going to create the right gas composition and also limits gas quality. I watched your videos when you automated your engines air flow ratio based on o2 readings. Every time you changed loading the airflow and velocity of that airflow was affected and became suboptimal. The map sensor would detect these changes in pressure and change the inlet setting even before the gasifier felt the change in pressure. A well tuned pid system could elimate these subtle Changes.


Your timed grate is pretty much like my idea for a rotating plate with a wiper bar. It will be set below the end of the burn tube and wide enough that the fuel and char will not just pour through. For a 1 inch chip size it could be approximately set About 11/2 inches below and 2 or 3 inches wider then the burn tube. This way it would only hold the fuel within the tube much like your design.


Here is what your going to find. The new guy generally- wants to re invent the gasifier. The old guy thats built a machine is going to try get you to build a successful machine but in the easiest possible way. And in your case you are already talking computers and this will be over some folks heads.

So you may find discouragement and this can be for good reason. As you may find your initial plan is not going to work as planned. However you should also not be discouraged to try new things. If we dont try then we dont advance. Some are happy with cumbersome and simple. Me Im like you that is unacceptable.

My automation is now very fast and now the machines have touch screens and are fully 100% controlled from them. The machine does it all on its own based on your input.

The code for the automixer is much faster than it used to be. You may just want to try building that first. What you are proposing wont really effect performance it just dont work that fast. But I think you will improve efficiency instead.

Thanks. I’m not easily discouraged and failure just means try again.


You actually want as much as possible char consumed = less Tar and better quality gas.
The best cracking temperature is around 1200ºC for the glowing carbon to stay most effective…

I think you might be a great tinkerer with newest tech and i am pretty sure you will encounter some nice things where you have to rethink the obvious :grin:

energy /shaftpower from woodgas with an IC engine… you’ll have some fun with it, at least we all do…

Your topic title “input needed”
focus on the glowing charbed and how to keep that balanced ( exothermic with endothermic reactions)
Understand the behavior of your fuel ( from raw to ashes, it changes shape and volume )
Be aware of restricting builds / mass flow / gas flow / filter, the less restriction= more gas to your engine.

There are a lot of wise people here on DOW, tons of experiences, all eager to give you the best advice they can, find time to read into their builds.

Last 2 cents: pay max attention to your fuel, saves you a lot of headache and good fuel leads to good results ( shit in = shit out principle)

thumbs up for good idea’s, keep sharing your experiences, show us your builds


Good morning RodneyW.
There are at least FOUR different designers/developers using chipped wood fuels you will not be able to find on the DOW.
Canadian Gregg Manning. He really only does larger systems than you propose.
USA new englander Stephen Abbadessa (sp). He does do raw wood chipped small systems.
Netherlander Dutch John. He did tiny to medium, then large woodchipped systems.
Plus two more I’ll explain later.
What these three can teach you about using wood chips for fuel is to at the chips making stage make better chips!!
Use a different chip maker capable of this!! Standard Arborist chip/grind-up-all systems are what create the problem in the first place. Free they should be. Agony to then sort this out to the useable component. Just do not use. Landfill trash. Inoculated, fully rotted converted making eventual soil adamant inputs stocks.

And StephenA. does his internal double row downward angled air jetting completely different from anyone else. He evolved this specifically for his specific made wood chips.
Active DOW member Canadian Arvid Olsen (tritowns), builds uses Stephens systems.

The next two are The PowerHearth slit throat. Don’t want to say names as that always seems to be in dispute.
And the Drizzler system. Evolved it seems to wood pellets now. But has been used by some for dribbling in wood chips.
Oh. And the actual dedicated sawdust pac Ray Risler Missouri gasisfer systems. The active DOW member using these, Doug Brethower, with his own book, “Angel Fire”.
Much to be learned from these too.

The Power Hearth supposedly used multiple points pressures sensing and controlling points.

So please continue on.
I think you are onto something there.

Ha! We can not all be charcoal’tiers.
Australia mostly in wildfire restrictions like us here western states USofA - charcoal making is difficult to do without tripping multiple fire watch hammer downs. NO FIRES at all, folds in charcoal making too.
And Motor-heads like me like to get edge tread using; and are not afraid of tars clean ups.
Just use engines easy to partial open up and quick de-tar, de-carbon.
Use non-interference engines. Ones specifically design so a valve down open cannot touch the piston.

Steve unruh


Hey, I heard my name!

Hope all is well with everyone. Hey Steve hope you and yours are well.

My advise would be stop typing and build something. Much easier to offer advice on something we can see. Just make it air tight where it needs to be and adaptable.

Good luck in your build, look forward to seeing what you do


I don’t know crap about gasification so I am no help. I just build things that others say will work. I’m just butting in to find out where in the system the MAP sensor will be located. My experience with MAP and MAF sensors is they are extremely intolerant of any kind of contamination. I’m thinking there will be a lot of contamination in the gas stream of any system, Wood chip or charcoal. I’d definitely stock up on cans of cleaner.


GM-Style 3 bar Map Sensor Kit needs 12 Volt supply - Custom - w/Connector .
Keep it above the tar , Mine came lose and filled up with tar and I needed to buy another . You did not mention oxygen sensor and lambada ?