If I were considering pressure flow rather than use a pressure sensor I can just read the angle position of the Ari Fuel Ratio Electronic valve. So for instance I could say (if servo angle position is less than 45*) : Shake the Grate … (else, dont the shake the grate)
I could also add another condition using the temperature as well. So under certain angle plus low temp threshold. If both are true, the grate actuates. A different scenario could be used to actuate the hopper agitator as well.
Once the flow increases the servo will automatically adjust to compensate for the now richer gas and once past the 45* angle the grate will stop actuating. Simpler method with out added sensors, just some added code that would be very simple to do.
Keeping sensors clean could be an issue Though a possible way around this is to use a tube with water as a barrier between the gas. This way only only clean air trapped above the water would interact with the sensor
I don’t want the grate to actuate unless the char is spent and is incapable of producing the heat needed to crack tar. The only time the grate would move is if the temp drops below 900 degrees Celsius. The movement of the grate allows fresh char to move down and new reduction of the fuel above. This stops gas leaving the system below 900 degrees if char is reduced quicker then anticipated. The servo operated air inlet only allows for a oversized air inlet. This allows the unit to operate over the full rev range of the engine. A one size nozzle just the right size is why some builders have trouble operating their engines at certain speeds. Some build threads and discussions I’ve read say that the engine lags under 2000 revs then goes well till 3000 rpm then loses power again. Others say their build goes well below 2000 then won’t perform. I feel this is due to inlet nozzle sizing restricting the gasifier from performing at its optimum. Lots of threads talk about having specific velocity of air Moving through the system. The velocity of air is a result of pressure drop , air temp ,humidity and density. Altitude also plays a part but it is still Covered by pressure drop ultimately. Even a breeze blowing could affect pressure Drop. The one size nozzle approach will only supply the right amount of air to create the right pressure drop and therefore the right velocity in the reactor over a limited rev range. If the engine is revved over this range the pressure drop is increased and therefore the air velocity is increased. In this situation the residence time of the gas to crack tar is shortened. I have seen a few discussions here that mention a 1/2 second is needed to crack tar. Also if the engine is under the optimal rev range the air doesn’t have the velocity to keep the reactions happening and low quality fuel is the result. My solution is to have a nozzle that is oversized and control air velocity by maintaining a constant pressure drop at any rev or load. I’m sure there are many experienced builders and operators of gasifiers that can get a quality gas every time under every weather condition. I like the ability to start something and know that it will run well without minor adjustments if the weather changes.
Not sure about needing an oxygen sensor for the gasifier. Could you explain why I might need to use one on the outlet of the gasifier. The map sensor use I propose is to read the pressure ( should be below atmospheric ) in the gas delivery pipe from gasifier to the engine.
The input I need is the placement of the air inlet above the grate. Can’t seem to find any maths to calculate the distance it should be. The only solution I can come up with is choose a gas outflow rate and work out how long it would take the air to travel from inlet to the end of the char bed and work out the distance based on the half second residence time. This solution seems to simple and I’m not happy with it. Is there a ratio builders use for example The diameter or area of reactor equals a certain height needed for the air input.
Welcome Rodney,
As you probably discovered we’re all playing with gasification for different reasons. Some like tinkering and the building process - others are in it for the satisfaction of not being dependent on gasoline. Some even have a need to satisfy their squirrel genes by prepping and storing as much wood as possible (me).
My personal opinion is that with store bought fuel and store bought bells and whistles I could just as well use store bought gasoline. The DIY feeling would be gone. But that’s just me.
My “first build input” would be to identify your power needs. Secondly, build a gasifier to those specs. With the gasifier up and running you will soon be aware of what kind of assistance it may need.
In the DOW library section you can find the Imbert specs. As far as I know dimensions are for wood chunk gasifiers. You may need to go a little smaller if you’re running chips, but the tables will give you a hint.
The lambda calculation determines the ratio between the amount of oxygen actually present in a combustion chamber vs. the amount that should have been present to obtain perfect combustion. … If the mixture contains too much oxygen for the amount of fuel (a lean mixture ), lambda will be greater than 1.00.
The MAP is on the engine intake manifold . The oxygen sensor is on engine exhaust pipe . I added a $75 heat sink when I actually needed to replace oxygen sensor . lambda air valve servo is two feet below engine intake manifold .
I am no longer using this set up , the lambda air valve servo was to small and I blew a fuse somewhere and it stopped trying to work , it did try to work .
I have not had issues with range limits with except of too low rpms not keeping the system hot enough. Nothing you can do here other than making the unit smaller. But then you limit the upper range. That may not be an issue for built to specific engines, but if you want to run a range of engine sizes it is. l would say machines that have this difficulty are not size correctly for the engine or it operating RPM range.
Two things factor your air to fuel ratio. one is pressure and the other is gas energy density. Your touching on one but you are going to have grate packing and this is why you will need the grate agitation. This alone will change air volume entering the hearth.
What you are proposing for air metering into the heath is not as straight forward as you may think. The jets are only going to allow so much air in at certain velocity based on the engine demand. Generally this is self regulating if you have this designed correctly this is not needed. Higher demand you will want higher velocity to penetrate the fuel in the hearth. controlling air inlet to supply these jets wont change this. The idea is to get the hearth as hot as possible with as little oxygen input as possible. This is the beauty of the Imbert as this is self adjusting based on demand. This is the part of the system that is not broke and does not need to be fixed.
The oxidation process is just that it is not the heart of the gasification process. Here all we are doing is freeing the molecule chains off the feed stock and trying to simplify those chains to simpler chains prior to entering the reduction process. The better you do this here, the easier it is for your reduction process to work. As Koen has note pay attention to the exothermic and endothermic reactions. Make a log as you experiment. What you wan to see is a big temperature differential from heath core temperature to the gas exiting the grate. The higher this differential the higher performance of your reduction process. What this translates too is that your reduction process is absorbing heat as it reacts with the raw gas. The higher the reaction the more heat is absorbed.
If you really want zero char yield then you could oxidize the char bed. This will need to be metered and need to be very low velocity. This will combat the endothermic heat absorption while producing producing gas to add back in the process. If done right you could pretty much eliminate the need for grate agitation. But this is way beyond a first time build.
Build it simple first and learn a bit. Your going to find what some have experienced will not be what you experience. There are so many things to factor and tons and tons of variables.
There is much more too this than just your gas / air flows. Generally all problems that come after gas flow tuning come from raw fuel flows. But then again kinda hard to tune this with out tuned raw fuel flows. You may encounter fuel flows not able to keep up with consumption. Sticky wet fuel hanging up in the hopper, moisture saturating fuel media. You may find the unit works great at start up and then slowly degrades in performance. Wet fuel does not run as hot as dry fuel. Use dry fuel. Improperly sized fuel will not flow as well as correctly sized fuel. Your gasoline car will not run on grease. Putting wet unprocessed fuel into a gasifier is like putting watered down grease into a gasoline engine. First lesson here is make good fuel first; create a standard and if your fuel dont meet that standard dont run it.
My experience in building my jet taught me about fluid flow and how to control it. The assumption that one size nozzle can do the job correctly is false due to pressure and density affecting flow thru an orifice.The gasifier has several obstacles that change the fluid dynamics so it’s harder to fully calculate. Just some simple maths to explain my approach. If your engine requires 10 cfm of wood gas per minute at wot the nozzle has to be sized sufficiently to allow the correct amount of air to enter the gasifier. The nozzle would have to be sized using the elevation ,temperature and humidity. If the engine is at idle a nozzle sized for the correct wot air intake allows too much air in which allows cooling and formation of tars. If the air flow is adjustable using a set pressure drop all other variables are compensated for. Fluid dynamics determine that all fluids attempt to even pressure out which guarantees a fixed sized nozzle will allow excess air if Atmospheric conditions or engine conditions change.
I built two charcoal gasifiers with about 3 inch pipe , which is too small and about six feet tall , which is too tall and I cap the bottom with mortar , concrete . one pipe has 3/8 hole as nozzle other has 1/4 threaded pipe as nozzle , Both have 1 inch outlet on top cap connected to 1 1/4 inch sump pump hose . Both work .
Good Day RodneyW.
Everything you say is correct for fluid flows (gasses and liquids) thru orifice deliveries.
My experiences with gasoline carburetors said there could be a benefit to adjustable needle restriction from the back side of the air nozzles.
Sigh. I was wrong.
Virtually no effect.
I think this was because of the factors that you are flowing into a variable pressure thermal dynamic area.
Specifically at low demand pulls on the charbed the heat still driving out gassing charcoal to then pressurize that area. From the nozzles perspective the down stream area.
It self limits flow.
High pull demand and this self-pressurizing does not build up and more flow is allowed.
So gasifers as enclosed systems introduce their own changing dynamic factors.
Heck. Shoot. Even the wood species of the wood char makes a difference. Hard to calculate for these dynamics. Cold flow values only gets you in a range. Easier to see-do, then on-the-fly compensate for these dynamics.
A bit like in carburetors the emulsification wells air bubbling slow heavy gasoline for a lighter weight faster reacting gasoline foam. The harder you pull the more air drawn to foam make; the more gasoline drawn in to be foamed, the better the emulsification. Jigger the air jets and fuel inlet restrictor jets based on results. Versus pre-calculating for results.
My point. It self regulates, dynamically.
Regards
Steve Unruh
Like Steve is saying an Imbert self regulates dynamically. The engine is your regulator and the jets are all ready set up for an operating range. I think you are missing how a gasifier works. The air “velocity” entering the gasifier only determines how much gas is stripped from your fuel. The volume does not necessarily determine this. The more you strip off the more gas is created. Heat is what tears off the molecule chains not air volume. Low velocity high volume can produce higher amounts of gas but the chains will not be cracked very well.
High velocity high volume will be more focused to a localized layer where combustion and heat is better focused. This results is better cracking of the molecule chains. You dont want a single jet you want an array to force the heat to central point.
What is more important is the velocity. If you can figure out how to control that to a range then you have something. But then you have some that will be complex. You dont want more air. You want more heat with less air. The less air the higher your energy density if you can produce the same heat for cracking.
So again only offering a better understanding, Your creative thinking is good.
Rather than do all this, it would be better to just charge battery bank get your spike power from that battery bank and if charging with DC load dont matter the gasifier and engine can run with out restriction. If you are using this for off grid this is the best way to use this technology. You dont want to run a gasifier constantly, it is not efficient and too much work. Only make the power you need and store it in your battery bank.
If you understand flows. then try to visualize flows under different load circumstances. The air leaving the jet inside the unit is not going straight across. It is arcing down ward and to the center. At higher load the less of an arc as the velocity is higher (more fuel is being oxidized increasing produced gas volume) At lower loads the velocity is less and arc drops faster oxidizing less fuel. Less gas is produced. Also factor and visualize eddy currents under this range of circumstances.
This needs correction. Too much air cannot be drawn in. Matt is trying to say this. The producer’s tuyeres loses air velocity as the engine goes from WOT down to idle. The oxidation reaction at the tuyere should show you orange/white color should you dare to look at it. As the air velocity slows, the color will shift down towards red. In the area immediately surrounding the oxidation zone the tar is being distilled out of the wood. As the velocity slows, the tar distillation zone moves closer towards the tuyere.
As an exercise, run your producer and then suddenly close the tuyeres, and stop the engine. Then dig out the layers of fuel and observe the different effects of the heat in the hopper.
Tar always forms. Even with char coal, there is a residual amount.
The danger that you are referring to comes not from the slowing of air velocity thru the tuyere. The danger comes when the velocity of the fuelgas across the incandescent char slows down. As soon as the char cools, the tar shoots right through into the filtration. There is a minimum velocity needed for the impingment of the fuelgas to knock the ash off the char and expose fresh incandescent carbon. Without that velocity, the ash insulates the carbon effectively cooling it.
You can see that too much air just causes more oxidation, and more heat. The case where this happens is blipping the throttle down from WOT to idle, and the flames start shooting out the tuyeres or the hopper lid comes off with a puff.
So a variable restriction, that reacts to throttle opening, to keep a constant velocity across the char bed (reduction zone) is what you trying to speak about.
Like Steve says tho…there are too many variables in just the different varieties of wood.
Matt is correct. Make your fuel first. Make a consistent dry fuel. What Wayne is doing is incredibly hard. In fact, he is the only one I know that makes engine grade gas from wood, and has done it successfully for years…thousands of hours.
Take the low hanging fruit first.
Hi Rodney, buckle up and start building i would say…
My few cents:
1: turn down ratio of the gasifier
2: fuel reactivity / density
3: knowing the engine you want to use
4: knowing how to manipulate the engine so it delivers shaft power
5: knowing how to build into the “sweet spot” range for all of above
All what you mention does make sense and has been studied, build around over and over again.
Single nozzle gasifiers work just fine
Multi nozzle systems will work just fine
All will work just fine, if one is willing to learn and to understand what’s being build, how’s it intend to be used…
2 choices we can make:
a: we build a gasifier or b: we sit together in some armchairs and we talk about how it should be / could be build…
Gasification: i enjoy all of it, know a lot about it and have to learn even more
To ad in your simple math equations : the range in which the thermodynamic processes take place. exothermic and endothermic reactions do not have fixed points where as they fail or succeed. your fuel have a certain range, the engine has its own…
Now to start building a gasifier that fits the range of your fuel and your engine, your purpose
I have been thinking more about my original idea. With restrictions due to density and changing thermodynamics maintaining a .5 hg pressure drop will not work. Take the residence time for instance. Even half a second residence time will mean the map sensor is telling the air inlet servo to do something based on information on incoming air flows from half a second ago. The map sensor and servo will never sync into a smooth Operation as the original idea envisaged.
Next mad thought. I don’t want a grate. I want a flat plate that holds the ash in repose until the plate is rotated and the scraper bar removes some of the ash. This seems futile as well as I can’t work out how to sense when the plate needs rotating. Matt’s timed approach seems the easiest way to achieve this. But I’m thinking about a plate that continuously rotates and only has a very small gap to allow ash and gas out. I had even thought about holes in the side of the tube right at the bottom to allow the removal of gas. Applying fluid dynamics again this would allow for a larger area For gas escape The larger area means less velocity of the gas so that would mean less ash lifted that needs removing.
Started to build a blower unit out of an old turbo compressor and compressor housing I had laying around. Problems with my lathe so waiting on parts fir that now.
Matt fluid velocity is determined by pressure. By reducing inflow rates the velocity can’t deliver the volume required to fill the the area and therefore the pressure can’t rise and slow velocity. Velocity is a result of pressure drop. I am re thinking my approach here as it won’t work as I intended. I think it had merit though as controlling pressure drop maintains the right velocity without over supply of volume which as you stated cools the process limiting tar cracking.
There you go, yeah think in milliseconds things at the engine side are happening fast.
Yup your plate idea for the grate is how we build. The grate is solid except at the parameter and the skirt is the grate. this will redirect gas flows to prevent grate packing. If agitate with the idea of just that and not so much to drop the char this will keep flows going without excessive dropping.
Grate. Or, no-grate.
Grate, yes. Which type? Passive? Active? Just how active.
I will tell you true this.
If you no-grate; or go passive, barely movable grate (original Imbert) then you make a very narrow range fuel useable system.
You made a car that can only run on Premium fuel. Too many BMW’s, MB’s and others.
A much better flexible useable car does make more power on Premium, but can run just fine with a bit less power on the mid-grade and RUG fuel. Most Lexus, and other practical use cars.
We had a flex fuel Chrysler we drove for 18 years. No-ethanol gasoline to 85% ethanol gasoline. It sensed and self adjusted. Not even that much power difference. Huge fuel use difference. 40%. O’s stuffed fuels have less weight in H’s and C’s.
Raw wood fueled gasifier you should say screw fuel use efficiency and go for ability to use any, and all of your local trees and brushes woods.
And with the huge differences in coaling ability and ash content in woods, that my friends takes a command active grate.
And a command turn off gentle action one if you wish to use the fragile char types woods in many of the trees families. Most spruces. My predominate Douglas Fir is actually a spruce.
RodneyW. a continuous movement grate breaks and fine particle-izes up fragile char woods and turns your system into a severe clogging soots maker.
Continuous grate movement even with hard char forming woods will create a range of problems too.
So your grate question really depends on what purpose; and for who you are gasifier developing.
Ha! Ha! A command active grate can be as feed-back remote command automated as you please. Once you accept it as a system control point; verses just a pita flush-toilet waste system.
