Matt, thanks for that description. Does air flow through the gap between the nozzle and the coupler?
With the fire close to the chamber wall, does the wall get pretty hot?
Will the nozzle survive without water?
So many questions, lol!
3 Likes
Hi Chuck the Hexoloy carbide was installed way back in 2018 and i must have over a thousand hours on it ,yes really if not more and never a drop of water , the build up of slag on a vertical nozzle does actually help to protect the nozzle , i can run for months and months without having to tip my barrel over to get to the bottom of the 55gal drum to be able to reach in and clear a fist size build up of slag .
I always know when to clean out due to much slower light up times , i also find it helpful to put a rod up through the nozzle after shut down or right before light up and that help push away anything that may hinder the nozzle blast and help light up .
Dave
8 Likes
That is a really rugged and simple system Dave. The hours are truly impressive.
Do you have ballpark conversion numbers, lbs/kw/hr?
What sized engine are you running with what sized nozzle, since 2018?
It seems like the 10mm nozzle that you put 120 hrs on would be high velocity (assuming a 200cc and up engine), and would have produced a lot of slag. If you only get a fist sized clinker after a ton of hours then the nozzle/slag conglomerate must be acting like a diffuser and slows down the air so that minimal slagging occurs after the first hour or so.
2 Likes
Hi Chuck , i always intended to make notes of what’s what but i am lazy and forgetful and i really do walk away once its running and forget about it till i hear the engine spluttering .
The main engine that’s been run since 2018 on a approx1 inch id Hexoloy nozzle mounted in a vertical fitting from the bottom of a large 55gal drum that is sat on top of a table to allow around 16 inches of room underneath to allow for firing up and cleaning of the nozzle with a rod
this has run a GX390 7.5KW inverter generator that in turn charges up a battery bank through a 80 amp inverter charger .
Dave
5 Likes
On the slag formation i think i may have posted photo’s of what it looks like after many months of run time in the bottom of the drum , maybe if you go back in time on this post i may have updated the life of these nozzles .
Dave
Found it post 359 are the photo’s of my slag volcano
1 Like
I remember those pics.
Image from Dave’s post 359
The slag dynamics look complex, maybe partially blocking the nozzle most of the time?
Looks like the air flow tends to divert it to the sides where it builds up until the whole ‘volcano’ is tall enough there is no where else for the slag to go.
For my particular design focus (obsession?), I suspect the nozzle flow is more diffuse because of the partially obstructing slag, which then slows the formation of slag.
At a rough guess, I’d say my small downward angled nozzles would produce the volume of slag in your picture every forty hours.
Obviously it doesn’t matter very much as yours works very well.
Is it safe to assume the gasifier breaths easier and starts up much faster after a cleanout?
3 Likes
Here is a table from this document that interests me:
For my little test generator at 212cc;
**with a 70% cylinder fill ratio at full throttle
**at 3600 rpm
**at a 50% air/gas ratio
I should be drawing about 8 cubic meters of gas per hour.
If you look on the chart you’ll notice that puts me at a pretty steep part of the conversion efficiency curve.
Add in all the real world factors (filters, moisture, less than premium fuel) and I think you can assume even worse numbers.
My take away (and real world experience) is that you can lose 10-20% conversion efficiency pretty easily with small engines without a high velocity nozzle.
Maximum efficiency isn’t my focus, but the margin you gain over all the real world variables is… a 10% increase in conversion efficiency makes operation much less finicky.
I could just move to bigger engine too I guess:)
But I want really long run times.
With long run times I can use a smaller battery bank.
Longer run times makes living with a gasifier more practical (convenient).
Edit: The chart is on pg 79 in the pdf
4 Likes
Dave, can you record your gallons/liters of charcoal per kilowatt hour?
Just an approximation would be fantastic.
You are the benchmark for stationary gasification with small engines I think:)
Oh, and charcoal size?
Matt, do you have lbs/kilowatt/hour ballpark numbers?
I’m sure your customer base will soon have the highest aggregate real world numbers. Can you share them as they come in?
4 Likes
Nope it is just dead space between the two. The front of the machines are double walled. The 1 inch pipe couple is a full couple and is welded from the inner wall and then assembly welded on the outer panel. This gives this area integrity and so far we have had zero issues. Our demo now has a few hundred hours on it. If it were to fail I think we would have seen by now. Plus I have ran both our 8750 and 9500 in tandem together to push the unit to its max. It can run both around 850cc together, but this is pushing temps to the limit. So I have adjusted our max engine displacement on that unit to 500 cc maximum. Basically if I can not hold the exhaust hose with my hand then the unit is being overdriven.
9 Likes
Hi Chuck , i am not very scientific about what mine does i’m afraid other than telling you that all of my charcoal is between 2mm up to 20mm in size its always the same and i load up the 55gal drum almost to the top leaving maybe 40mm from the gas out pipe , now that will run the large inverter generator on a full load for a max of 5 hours , i normally aim for 4 hours best run time and that leaves me with half the drum empty , as my nozzle is at least 5 inches from the bottom of the drum so i guess we are looking at around 25 gal for a 4 hour run time ,but that is as close as i seem to remember , as i have been playing with downdrafts for a few months but just recently we have had some real bad weather and so i have not made any more progress to anything .
Dave
8 Likes
I moved the 8.5mm tungsten carbide nozzle to the bottom of a 16 gallon tank, with 3 inches protrusion.
This nozzle:
Got normal behavior on startup. But the engine would only maintain full power for five minutes. You could hear it begin to clog. It ran another 25 minutes at three quarter power but I had to richen the mixture several times over that time. You could hear the engine bog and clear, bog and clear. The outlet temp rose as well.
I dumped it out and took a video;
https://www.youtube.com/shorts/O-6NXpZHRYQ
2 Likes
I think your nozzle size is creating too high of a velocity and is doing too good of a job penetrating the fuel. This was powering a 200cc engine?
Have you tried using this velocity in a cross-draft? I know in the Pegasus book you ideally want hot exit gas as a sign that the CO isn’t forming back into CO2.
1 Like
Here’s some images of the Pederick updraft. It uses a thick plate with nozzle hole orifices, but air comes in to a chamber to be pre-heated. Interesting that it has two or three nozzle holes.
I want to say the water drip actually gathers inside the pre-chamber to allow it to steam up.
But just based on the Pederick I think larger nozzle size is a benefit.
4 Likes
Hi Chuck yep that’s some hot stuff you got going on down there !
So that bottle shape is the Tungsten carbide ? what is the size and weight of it , can you get anymore ?
Have you tried one of the Hexoloy tubes yet ?
Dave
4 Likes
It formed a nice cap over the nozzle, lol!
212cc engine, 8.5mm nozzle ID.
Yeah, the high velocity nozzle is a slag maker… I just thought I’d give vertical a quick try. Obviously you want to avoid slag with a vertical nozzle.
One observation, the vertical nozzle was relatively cool compared to the 45 degree down angled version. Makes sense. It didn’t get red hot so the slag didn’t stick to the tungsten carbide.
I think I’m gonna have to use liquid cooled down angled nozzles for these high velocity slagging gasifiers.
I hope I’ve been clear as to why that is my objective;
I want to use small 200cc engines
The very hot reaction zone:
** gives better conversion efficiency
**has very fast startup
**is fuel quality tolerant
…all things leading to a positive experience with small engines.
3 Likes
Dave, the tungsten carbide sleeve/drill guide is a normally available part from placed like McMaster-Carr. I think they go up to .5 inch ID. Not cheap.
I used this part:
https://www.mcmaster.com/33455A587/
Yeah, I’ve used the silicon carbide (Hexaloy) nozzles. Since I’m running so hot they inevitably get slag on them and I’ve had them chip when trying to clean them.
They looked a lot like your 10mm ID picture you posted above, with the slag sticking to it.
I’m not sure anything I’m doing here is useful to anyone else since I’m doing the opposite of what most try to do with a charcoal gasifier, but tungsten carbide is undoubtedly a good choice for rugged nozzles.
2 Likes
Tungsten Carbide could make a pretty good nozzle tip for Mako style gasifiers. Maybe in the .5" ID size.
Are they already threaded? Also are they more brittle than steel? I know with Hexoloy nozzles I’d be afraid to use a poker to clear any bridging for risk of breaking one.
2 Likes
The drill bushings can sometimes be threaded, but mine was a simple cylinder that I swaged into a pipe.
I ground the OD so that it was .020 undersize about a quarter inch from one end, over a .100 area. Then I roll swaged a stainless tube over it. The depression makes for a pretty tight grip, unlikely to move even when the tube is at a red heat.
Maybe not the best way, but simple enough.
Another possible source of tungsten carbide nozzles is blasting nozzles. Lots of makes and models out there.
A search for Skat Blast tungsten carbide nozzle is a good start.
5 Likes
Chuck thanks for the info on the carbide you are using , i had a thought about what you are trying to do and what if anything can be done to stop the really fast build up of slag inside and around your sized nozzle , all i can think of right now is something Max Gasman suggested some years back about building a birdcage or a bell shape around a nozzle to prevent charcoal from falling to close to the tip of the nozzle to help keep the tip from over heating and slag building up , and if you think about it that is sort of how Matt has his nozzle inside a larger pipe to allow the protection of his main nozzle, not sure if there is something you could do to help your situation and save you from going up in size and then having to lower the velocity .
Dave
3 Likes
I was thinking about Max’s nozzle arrangement too, lol! Sounds like Matt has it dialed in, keeping the nozzle out of the glowing char as much as possible.
4 Likes