Towards a wood fueled pulsejet

[GRIM]

Hi Grim, looks almost like the 3" cone was cut off -- that would have been 110mm -- pretty close to 115mm. Did PyroJoe try your cone on top of the inlet? My guess is the cone works at the original height, while cone-less probably prefers a little lower height. Here's what I've been looking at (in png form with inch dimensions added -- hope that's okay to put up.)

Hi, no problem, yes Thats more or less what I discovered with that style of inlet , the "inlet length" basically finishes where the cone starts to expand , but with all the cone and the downturned ring present ,as previously mentioned there is some kind of weird lens effect ,

That particular engine is very tolerant , an inch here or there doesnt seem to make any difference , in fact at one time I had it running with a 10 foot vertical exhaust to send the noise up over the house, so dont worry too much about a few milimeters here and there

[vturbine]

Downturned ring?

Is that the line at the top of the cone? I was wondering about that -- thought it was just an anomaly in drawing the cone opening -- apologies, obviously intentional. Well, that's getting a little too far beyond my skills at this point. Maybe I'll do the cone-less at 115 mm with flare -- if PyroJoe agrees that was the height he found worked.

Seems like I may have it finished by tomorrow evening if there's no cone. I suppose I could always add it later anyway if desired , the way this works out as an addition, rather than a mod. It would probably just fit right into the flare.


Edit:

The bad (or at least scary) news is, the stoichiometric mixture on wood gas is 1 to 1. Not even sure how I can do that. I'd need an injector the size of the inlet, wouldn't I? Seems nearly impossible without screwing up the cycle.

Tee into the inlet pipe? Or increase the inlet diameter with a concentric inner fuel pipe, w/sealed end, perforated length? Area of inlet around fuel pipe = to original inlet area?

I don't know, this was probably nuts from the start.

Even more editing:

With such a large volume of fuel needed, probably pre-mixing with some air would help what looks to be a big mixing problem, though that increases the feed volume even more.

I seem to remember comments somewhere in this forum about the feed ring on a true Reynst pot premixing fuel and air before the actual feed at the lip. Seems there was some question about why this was necessary if the purpose of the internal vortex was mixing. With premix also, you'd need a big inlet hole and Reynst pots do have large inlets.

[PyroJoe]

She is looking good!
Cut the inlet to 4.625" length on mine, was a little easier to start that way, and could pulse at a lower throttle.

1:1 sounds a wee bit rich.

Joe

[GRIM]

Is that the line at the top of the cone?

Yes , However I would forget the cone and ring for now and just get it up and running on a straight inlet, and yes it would be a very easy add on if desired , the ring is no more than a washer shape bashed in using a hammer and large socket,

The bad (or at least scary) news is, the stoichiometric mixture on wood gas is 1 to 1. Not even sure how I can do that. I'd need an injector the size of the inlet, wouldn't I? Seems nearly impossible without screwing up the cycle.

Or maybe two inlets , one air one fuel , assuming that the gas is at atmospheric pressure , who knows ? maybe different length inlets , I am getting into deep water now , I dont know why but The logan sprang to mind , I can see a logan with two inlets at 90 degrees to each other , logans are supposed to have good mixing caracteristics I believe ,

Heres one I built a while back , terrible video , runs fine needs some air for start , huge thrust from the inlet ha ,

[PyroJoe]

Well, looking at this, it may very well be 1:1

http://www.gengas.nu/byggbes/49.shtml

Counted on at least two inlets, maybe 3 to assist the Venturi effect. Do we know the temperature of wood gas used in the 1:1 ratio?

Guess I need to build one just to see what it can supply, plenty of dead mesquite brush in the local landscape. Do we have a set of gassifier plans to work with?

Joe

[vturbine]

Well, looking at this, it may very well be 1:1

http://www.gengas.nu/byggbes/49.shtml

Counted on at least two inlets, maybe 3 to assist the Venturi effect. Do we know the temperature of wood gas used in the 1:1 ratio?

Guess I need to build one just to see what it can supply, plenty of dead mesquite brush in the local landscape. Do we have a set of gassifier plans to work with?

Joe

Great, PJ! I had a feeling you might get interested in building something.

For a gas generator the Gengas design is a good one, but kind of complicated to construct compared to Brenton Pope's version, which I kind of like.

Let me find that reference --- back in a sec..........

Here:

http://www.angelfire.com/ak5/energy21/woodfire.htm

I was hoping that for pulsejet use, all of the filtering (and hopefully, cooling as well) could be eliminated, and the combuster feed off of raw gas generator output.

That would be in fact the major advantage of a pulsejet over any other kind of engine for this purpose.

I haven't had a chance to work on Grim's jet yet today. Just got through a 4 hour job interview. Gotta get my mind off of that. Metalworking will do it.

Also: For sizing I'd maybe use the Gengas rules of thumb (in fact I did when estimating early in this thread) for throat area of the cone in the Pope style generator. It looked like 4" dia. would do. 6" was recommended to avoid bridging in the Gengas tube, but the Pope version wouldn't have that problem because of its cone shape. You don't want the chips to flow out of the cone opening, so it can't be too large either.

[vturbine]

Didn't have much time this evening, but welded the intake to the top plate. I was able to clean up the weld on the inside face of the plate because it wasn't attached to the CC yet. Chamfered the inside corner very slightly (just broke the edge) and sanded it smooth. I'll cut out the tailpipe hole tomorrow.

I made up Grim's flare tool and flared the top of the intake. That went very easily. Then I cut the tailpipe to length and prepared the end for welding. I'll make up the injector tip with the three point style as shown. I have some .040" music wire to form the orifices.

The jet should be ready to run tomorrow afternoon.

[PyroJoe]

Still reading about Popes version, lot of good info there. Good field testing, with practical modifications and instruction. In the German text of Gengas there is also more information. Multitude of design considerations.

Hope all goes well tomorrow.

Joe

[vturbine]

Still reading about Popes version, lot of good info there. Good field testing, with practical modifications and instruction. In the German text of Gengas there is also more information. Multitude of design considerations.

Hope all goes well tomorrow.

Joe

I actually think that both of those are larger than we probably need, but I'm not sure.

Still, Joe, look what they are running with those two designs. So as a test rig, maybe something even smaller or simpler, was what I was thinking.

[PyroJoe]

The capacity to run a van and trailer at 80 km/hr requires considerable amount of fuel. Maybe a 4 or 5" throat gassifier would be a good start. Both the draft engine and gassifier can be slowly hewn to a more reasonable scale as the operating parameters become more stable and defined.
Joe

[vturbine]

Passed the water fill test, now to make legs and an injector.

[PyroJoe]

Looking good!

[ace_fedde]

Vturbine, Viv, Joe

Yes, Viv, I was thinking that multiple diaphragms might be a possibility in the future, but that would be at a more sophisticated stage.

I think you guys should really have a look (if you didn’t already) it this one:
http://www.aster-thermoacoustics.com/indexeng.html
No moving parts, creating high amplitude sound inside a tube, out of heat(differences).
It looks to me that it is possible to fit diaphragms or pistons at the other end to drive linear alternators. I think I’m going to contact that guy (he’s Dutch like me) to see if he’s interested to join the forum.

Yeah the heat generated is a problem because a lot of it is a waste in an acoustic take-off in this application. Maybe there is a way to use that heat to amplify the oscillator, just as there is an analogous thrust augmenter for a linear thrust application. Maybe some hot air engine principles can be used to reduce the waste heat. Again complexities I don't want to think about too much yet without even a working propane engine

And what, apart from the above mentioned, about your idea (and mine) to use that heat for making the wood gas? With the coaxial setup?
I really think that you don’t have to worry at all about waste heat.

The bad (or at least scary) news is, the stoichiometric mixture on wood gas is 1 to 1. Not even sure how I can do that. I'd need an injector the size of the inlet, wouldn't I? Seems nearly impossible without screwing up the cycle.

With such a large volume of fuel needed, probably pre-mixing with some air would help what looks to be a big mixing problem, though that increases the feed volume even more.

Mmm! That’s going to be interesting! You might use a augmentor at the inlet in the same way, but with a different purpose, as I designed for my PJ-turbine coupling:
A chamber, in your case fed with mixture, enclosing the “outlet” of the inlet and the inlet of the augmentor.
In that way you can split the feed for the inlet from the combustion gasses coming out of the inlet.
Few problems involved though. 1) not tested yet. 2) acoustical problems expected 3) part (half) of the mixture will leave through the augmentor and burn. (might feed your gas generator with that heat to)

Fedde

[vturbine]

Thermoacoustics have been around for a long time. There are many people commercializing it, and NASA also has done a lot of work on it. It is usually based on hot air principles using linear alternators for power out put. It is well understood by now.

This is different. My suggestion here, and the reason for starting this thread in this forum intends to use combustion gasses in a resonant system, not hot air, and does not have the problems of heat exchange that all closed fluid heat oscillators do. It does have its own set of problems the main one being that it must by necessity be an open system because of breathing and exhaust considerations.

I'm also the type of person who likes to try to accomplish things myself. I'm interested in talking with people here who are messing around in pulsejets with metal and fuel.

re.

And what, apart from the above mentioned, about your idea (and mine) to use that heat for making the wood gas? With the coaxial setup?
I really think that you don’t have to worry at all about waste heat.

There is a tremendous amount of waste heat generated in most puulsejets. It is a topic of interest to me at least.

[ace_fedde]

Mmm, burned your fingers today or something like that?

edit:
Mmm, totally forgotten what I commented here

Fedde