Heart dimension

Hearth Dimensions.
Must ask because I do not understand, the size of the heart, must depend on how fast the air should go through, to maintain a temperature so that the tar is split or burned?
Does this have anything to do with the number of hp an engine has or does it depend solely on how many liters the engine has?
I think it should depend on how many liters the engine has and at what speed you want to ride?


Hi Jan,
Good question. IF you are planning on building an Imbert or any gasifier
the answer is a definite , YES. The Law of Conservation of Energy, “ENERGY
IN EQUALS ENERGY OUT”. I have experience in the imbert build.
The imbert design dimensions START with the ENGINE HORSEPOWER (energy out) so
the gasifier unit (energy out) will produce enough gaseous energy
to support that HP demand. These are PROVEN DIMENSIONS!
Other than that I can’t offer anything other than that all gasification
dimensions are dependent upon the energy demand of
the engine HP, displacement. ENERGY IN EQUALS ENERGY OUT. This is
the MOST IMPORTANT aspect of designing your unit. All too often folks
build with what is on hand with very mixed, unpredictable results, often
disappointing for sure. You can avoid all that.
Anything other than using these parameters will waste your time, effort
and the results will have you scratching your head and kicking your ass!
Go to the Small Engine Section and check out, “My first small engine run”
for an in depth study of my build. It will answer a lot of questions.
Good luck, feel free to pick my brain.

But if you design a gasifier according to hp, I will make a gasifier that is made to be at a much higher rpm than I do in reality.
Which will cause the gasifier to produce tar (probably).

Look at what hp you engine makes at the highest rpm you want to run on woodgas.

If you can’t find a hp curve for you engine lock for the peak tourqe which should be at a lower rpm and calculate the hp from it.

What engine do you have in mind?

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Use a work loaded engine operating between 1200 to 3000 RPM as your need-fuel design guidelines.
Modern specification fuels of gasoline, deisel and motor grades of propane can support an IC engine from an idle unloaded power to 80% of that engines maximum possible capability.
Call this a 20 to I power ratio fuel flexibly range.

Wood gasifiers built from “available” lay-about materials usually do well to only fuelgas supply at a 4 to1 usable power ratio range.
Better proven designs; with purposed selected materials; and this can be stretched out to maybe a 10 to 1 usable power use range.

A very, very few very advanced features woodgas systems. Operated by superior operators. Using best-use inputs woods have verifiable proven actually can, and will, operate at a 15 to 1 power capable range.
And these experienced operators never claim commercial pump grade fuel use equivalencies.

Only fools think that woodgas can be made to Be-Just-Like highly developed and purified spec grade motor fuels.

Ha! Ha! After all. Anyone ever drinking local-yokel made moonshine from Anywhere knows: you drink for the likker Kick. Not for the just-like Label taste.
Steve Unruh


Sorry this may be bit nitpicking…
I don’t think those fuels have a turn down ratio, sure a small engine with a huge carburator will run bad but some caburators have a much better “turn down ratio” like the predator or q-jet and when it comes to electric fuel injection so it has more to do with what the ecu can handle, most stock injection systems will not have the resolution to controll big injectors on low load, but better systems can handle bigger injectors and use multiple rows if needed.

A turn down ratio of 100 to 1 should not be a problem and has more with what power range the engine has then the fuel delivery.

If we think about woodgas then it is really bad motor fuel, it just happens to be easy and cheap to produce, low flame speed, low energy for volyme and can’t be stored in a practical way.
But it’s sure fun to make the best of it :smiley:.


Exactly what kind and size of engine are you going to gasify
and what will you be using the engine for? Without this info
we are just flapping in the breeze, so to speak!


I am going to disagree with some of what has been said. I did NOT start with ‘‘horse power’’. Horse power can be figured in many ways which can give different values for the same engine. I start with the ‘‘engine displacement’’ and the ‘‘RPM’’ that the engine will be run at. This is a time consuming process and you have to rely on some established standards.so, as Pipe has said there is a table you can go to and get figures that have been consolidated from the various builds that were manufactured during WWII. TomC
PS. I’m talking Imbert style gasifire. WK style is a different world.


Yup its all about the volume the engine is going to pull and the volume the gasser will output producing acceptable fuel grade gas.


Hi pepe I think you mean Jan Axelsson and sure some more specific engine Spec would help, but it’s also intresting atleast for me how people have calculated These number.

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I can be wrong but is not hp better to size to then engine volyme?

The ford flat head has a displacement of about 4000cc and ~100hp a ohv 2000cc engine may have the same power as the side valve engine.

You dont want to calculate the dimensions via hp. A 1l engine can have 20 or 200hp, but is still a 1l engine. What you want is calculate the amount of gas that enters your motor every second. The formula is

Rpm(:1000)x3xdisplacement=gas volume in l/s.

So, per instance, on my 2.3 l engine driveing at 2500rpm it looks like this

2.5x3x2.3=17,3l/s of gas or a good 1000l/min. This is your upper gas demand. There are further formulad on D.J.s website.

But in general l dont bother much with precise mesurments any more. Imberts can be forgiving allso. You can build a voriety of different hearth specs as long as you have the RESTRICTION in the right dimension!!


But does not the volumemetric efficiency have part in it?

A engine with a VE of 65% will fill less then a engine with a VE of 110%.

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Ofcorse. This formula predicts the filling ratio of 0.7 l belive. Wich is realistic for most engines suckin on gasifiers.


Sorry I thought restriction and heart were the same. there is the restriction that I mean.

Heres what gek recomends, then you have the sizing chart on this website for the v type of imbert.

One of my books recomends a restriction of 3.675 inches for a 2.0l engine, 3.15" for 1l and 4.2" for a 3l engine.


Sounds about right. But still, engine size doesent say everything. Engine design and geometry play a big role in wood gasification. Per instance, my mercedes likes to drive in the in the 1700rpm neighbourhood, no point in reving much over 2300rpm as there is not much power gained for the amount of gas sucked in. My 1.6l chevy liked to run above 2500rpm. Quite dead under 2000.

Now, the difference in displacement is 0.5l, BUT! The gas consumption is exactly the same in realistic driveing conditions! Meaning, no matter the difference in engine size they will require identical hearth dimensions.


What Kristijan said.
1, 2, 3 liter…50, 100, 150 hp …at idle they all breathe eq to a chainsaw, and you suddenly find yourself completly off the chart. I see no reason to deal with decimals to do with WOT. The most important thing has to be to be able to make good gas at idle. Soon enough you will find out about the maximum performance.
Driving habits, speed, terrain, fuel size, fuel humidity, insulation, hopper condensation, air preheat, system pressure drop and many others…they are all just as important variables as the restriction size.
Look at the Imbert chart as a rough estimate. I would say start off on the small side. Better safe than sorry. Lack of power is not a disaster. Tar can be. Use restriction and nozzles which can be changed out.


What JO said !!

Building a gasifier without the ability to easily change the internal dimensions is like having a belt with only one notch in it.


Thanks Jim, it’s starting to resemble what I read too. Am a little scared of tar and when I read this which only refers to hp, I become thoughtful.
And should I start a new one, I would like to know what I do, and do not have too big restriction, and also reasonably right with nozzles.