Charcoal zone heat need to be kept a minimum of 850C and up.
The “up” being determined by how your system walls and flow forming materials materials is able to handle the the extreme heat exposure duration. How bad of mineral ash fusing problems created. This begins at 1100-1300C.
Larry Dobson tried very complex cast silicon carbides for the flow erosion’s and heat/exposure resistance. Relatively BIG systems. Some he ran up to to 2200C. Then . . . he said his problems was thermal shocking. New relatively lower temperature fuel drop-in loadings would thermal shock, cracking the silicon carbide castings. Air-in super heating then became a necessity too.
MaxG said that high temperature capable ceramic castings cores WWII German experiences were found to be super sensitive to becoming surfaced scratched from metal poker rods. That micro-surface scratch then temperature migrating into a thru&thru gas leak crack. Your glass-top cooking stove ranges shattering problems.
On a charcoal system gasifier for his small (four-stroke single cylinder) inverter generator DavidB recently said he could only get enough engine power for usable electrical production by adding water (steam?) injection.
Gary Gilmore is the charcoal guy posting up using water drip; engine exhaust re-circulation, & waste motor oil drip, adds.
Ask, and I believe he will repeat that they all have worked for him.
That he has come to favor metered engine exhaust recalculation. It is always available. No reservoirs to keep track of; fear freezing; no water-mineral scale building-ups, clean. Engine exhaust is already pre-heated. And if close coupled directed/insulated the engine combustion produced water vapor is still in a vapor form.
Water for charcoal temperature moderation occurs three ways: water to vapor; vapor to true steam; the the hot HO2 steam molecule with hot charcoal C’s converting into H2 and CO.
Using the engine exhaust water vapor you greatly reduce thermal shocking problems; flash-to-steam 7000-to-1 volume flow crowd choking. And with the engine exhaust CO2 and trace CO, you can then KVL-like truly claim to be pollution burning. Engine exhaust carbons fuels contributing.
I am not sure you can count on there being much water vapor in the exhaust from a charcoal burner - unlike a hydrocarbon fuel we do not have a hydrogen source, we are burning pretty much straight CO, so the exhaust should be pretty darn dry. Even bone dry charcoal will have a tiny bit of moisture that it gathers from the air, so that will pass through, but we are talking about a few percent by weight, and you are probably getting most of the benefits from that the first time around.
EGR is a really simple way to keep the temperature down, but I dont feel like it is really unlocking the full potential of the charcoal fuel (in my humble opinion).
Carl you have a point, on dry exhaust when burning charcoal fuel in the engine, but there is nothing stopping us from adding a water drip to our exhaust system after the muffler. That would put just enough H2O moisture into the warm exhaust to be carried into the nozzle/nozzles and into reduction zone to be cracked into H2 for more power. A metal container could be inside the vehicle so it would stay warm and work in the winter months. And the water would just run out the exhaust pipe, if you forgot to turn the water valve off when shuting the gasifier system down.
This was how I was going to run my cross flow, double nozzle gasifier before Dana fell in love with my Subrau Outback that I was going to use. I really need to find Dana a newer Subaru for her. So I can finish my charcoal gasifier project.
Bob
I’ve thought for quite a while that the Subaru Baja’s would be a great platform. Basically an outback with a bed. My wife’s 03 outback has been pretty good to us… and fairly easy to work on as far as the ‘newer’ cars go.
I think you ask a very good question. I think that the temperatures you want to measure in this case might be too high for thermocouples. I’m working on an idea to maybe use one of those pistol type thermometers or similar technology. Not quite sure how to make it work yet. Blacksmiths and foundry men usually use color to determine the temperature of hot metal and thy become very accurate over time. I think you can learn to recognise the right color you need to make good gas.
Rindert
Good point CarlOR,
I do tend to think like a hydrocarbon fueler. Gasoline, propane, methane, kerosene, alcohols, diesel, woodgas all do have H components.
For just combustion temperature moderation though as found in the 1960’s any inert gas added works. Nitrogen. Argon. Krypton. Carbon dioxide. All of these were tried. But not cost effective for outside of Lab and Gov’mint costs-plus projects.
For automotive NOX reduction controlled metered in engine exhaust was found to be good’nuff.
Water/alcohols injection had been aviation/boosted pressure racing used for 50 years at that time.
Vehicle emissions regulations were tightened in the 70’s rewritten NOT allowing anymore any added/needed combustion modifying reservoirs of fluids or gasses. They’d learned that the majority of the users would ignore another depletion reservoir to monitor and buy replenishment’s for.
Took the advanced diesel emissions engineers and diesel engine manufacturers a decade and a half to finally get written exception for the D(iesel) E(xhaust) F(luid) reservoir systems. And only if they would design in electronic monitoring and engine de-powering systems to force users refilling compliance’s.
Skin this cat anyway you would wish. Realizing there is more than one way.
Using raw wood as this system was designed for: then “wood does it better” for char-bed heat moderation and excessive heat-to-enginegrade-fuel converting.
S.U.
Carl, thanks for the suggestions. Yes, the sum of the areas of my 6 nozzles is close to the cross sectional area of a 0.9" hole. But even if the cross sectional area is the same, I don’t think the 6 smaller ones would behave in the same as the one big one.
I have come across an old post of a spreadsheet from @k_vanlooken showing how to calculate nozzle size. I wonder if he or anyone else has opinion about whether this would apply to my modification of Ben Peterson’s gasifier. This calculation is for a generator with a 196cc engine. Based on this, I plan to make each of the nozzles 1/8" in diameter.
I plan to drip water into the inner part of the air inlet, right beside the blast of hot air from the gas outlet in the heat exchanger. I’m hoping the dripped water boils quickly enough to make a difference.
Yes, the gas outlet is below the grate.
Hi Greg , can i just ask a question about your gasifier build ? , first off let me start by saying what i have seen of your build is really well done you seem to have gone the whole hog getting this machine together and it looks so nice , its late here and i have run out of time to re read the whole post and you have probably answered this already so forgive me , but isn’t this gasifier suited to wood rather than charcoal ? don’t get me wrong i am all for charcoal in fact its all i ever run my generators on , but for the amount of hard work thats gone into your machine and then to run it on charcoal seems a shame when a simple fire gasifier would have worked well for a first time build ,.have you ever run any raw wood through it ? , i would love to see a video of your creation running even if its just making a flare .
Dave
Just a comment about measuring high temperatures in the past.
I once worked in the vacuum heat treating department of a major heat treating company. We often had to measure temps in the 1800°F to about 2500°F range by looking through a porthole into the furnace. Yes, there were thermocouples in there, but, as many you know, it is sometimes very difficult to get the “exact” temp of a component that is a ways away from the thermocouple itself. (That’s why “soak” time is so important).
Anyway, we used an “optical pyrometer” to do this back in the 1960’s. Here’s an example of what they looked like then:
Basically a battery operated calibrated light bulb. You would point this telescope-looking device at the component under test and rotate a dial until the filament of the light bulb “disappeared” , becoming the same color as the part being viewed.
Then you read the dial, and converted the reading to the temperature. The conversion scales, IIRC, took into account the calibration for the light bulb, the effect of the furnace atmosphere,and the color shift related to the transparent material in the viewing port of the furnace.
Pete,
That’s exactly where I’m coming from. That old pyrometer was a total PITA, but it was good for training newbies to recognize specific colors associated with temperature.
Nowadays we have these pistol type IR thermometers that do something very similar in as far as they look at color. I think we could aim one of those through a nozzle, remote locate the viewing screen to the vehicle dash, and be able to monitor reaction zone temperature on the fly.
With this info one could adjust a water drip or EGR to reduce temperatures during high output. This would allow a wider range of safe gas output, or a larger ‘turn down ratio’ as we usually say it.
Just an idea.
Rindert
Hi Dave, Thanks for your observations. I built most of it during 2018 before I knew about the DOW group. I just followed Ben’s book. But I didn’t understand enough about the whole process to realize that I really wanted a small charcoal gasifier. So now I am modifying it to do charcoal, hopefully.
The modifications are easily reversible, and I expect to revert to wood gasification for a larger engine in the future, perhaps our 3.5 liter 1995 Plymouth Voyager minivan. But I want to start with something small and clean, and I do have 3 small generators and no big ones.
So yes, this gasifier is suited to wood with its heat recycling and probably lots of other features. But my little generator can’t provide enough suction to make it work properly with wood, so I’m modifying it to do the charcoal.
I expect to fire it up soon. I’m just waiting to receive the stainless steel plugs that I plan to drill out for 1/8" nozzles, as per the calculation in my post yesterday.
Hi Pete, Thanks for the suggestion. It sounds like a workable addition to a gasifier. My unit does have a nice sight glass. I’ll post the results here if I decide to use it.
Rindert, I think it is a great idea to have the temperature feeding back to control the water drip. The highest temp thermocouple I could find was this one, which I have installed - http://www.thermomart.com/kiln-part-instrument?product_id=220
The highest pistol type IR thermometer is this one, which I haven’t tried yet-
But I’m not sure how I would get the pistol type to automatically control the water drip valve.
This is what you might want to use coming from your probe, a read out device like this has other features on mine there is a read out and alarm settings this one is used for my hopper but I sure you could fine one for your application. When the temperature reaches a predetermined setting it trips the alarm. More water could be added to cool the nozzles down. It could be done automatically or manually.
Bob
Yes, the tricky part arises when you try and quantify those differences! I am also a bit of a numbers person, so I can understand the desire to measure everything, and arrive at the “right answer.” I wholeheartedly support you in finding good hard data, but I will also say that you can follow some very basic rules of thumb, and it will still work fine. If you are going to try and compile numbers, I would suggest you figure out some form of data-logger. I tried to keep tabs on like 5 or 6 variables once, and i spent the entire run scribbling down numbers.
I did not do rigorous testing, but I did see the start of a correlation with power output and nozzle airspeed. Sadly, its easier to make a hole bigger than smaller, so I noticed it as a loss of power when I enlarged the hole in my nozzle. Your screw-in nozzles will be convenient if you decide to test different sizes. I have used that spreadsheet too, and it should apply to any configuration of nozzles. There is also a chart floating around on here that talks about CO2 to CO conversion rates based on nozzle size and gas flow (ie nozzle velocity) and the differences are not huge. At some point the added drag of the system having to breathe through tiny openings is also going to counteract the richer gas that you should in theory be creating.
I think it would run fine in the current configuration, and will maybe run a little bit better with smaller holes. Only one way to find out
