Towards a wood fueled pulsejet

[vturbine]

Ha, I was just thinking the same thing Joe while reading another article on the internet about the future of mankind. And then a "parallel" theme occurred to me. You wouldn't want it to be easy in one sense, the very fact that jam jars are fussy is what makes them so interesting. Maybe in heaven or on some planet with more oxygen, jam jars wouldn't be as entertaining, maybe they would be commonplace. I remember contriving an analogy of a beagle that liked to chase rabbits. Then I imagined him on an island overrun with rabbits; his interests would be defeated and he would soon tire of that activity. You can only chase jam jars/rabbits for so long. And yet you can use what a jam jar teaches you in so many ways. I don't think I will ever completely understand the fascination of jam jars or conversely why they become so boring at times. But there is something there that teaches you to be sensitive.

Mark, I'm in total agreement with this. I used to have a philosophy teacher now gone from this world, Richard Tristman, who once said, "The more rules, the merrier."

I didn't know what he meant by that when I was young, but I think I do now. The constraints foster discovery beyond themselves.

[vturbine]

The little "d" engine was somewhat of a puny simplified spin-off of GRIMs draft engine, was reasonably sure it could run off a small bottle. Was happy it did. Just used the little brass valve that came attached to the torch head for throttle ($10 brass propane torch from hardware store)

Developing the wood gas will be an important part of the process. Maybe more important than the engine design at this stage.

One approach may be to test a draft pipe by itself, use a small propane torch to create an updraft, and slowly bring the wood gas flow/flame on line, then reduce the propane. There should be a selection of pipe diameters that give good results to match your gassifier output. Try to make the pipe lengths 12.5 times the pipe diameter. Cover a wide range, so there is some feel for when the pipe is small and which pipes become to large, and which pipes support the best flow rates.


If memory serves, I recall running the big draft from the small 4" diameter propane bottles, without chilling, in poor conditions. Will test it this weekend. Days are reaching in the mid 90s to 100s deg.F. Humidity=crazy.

Joe

Wow that's pretty amazing about the big draft running on a camp propane canister. That must mean it doesn't need much fuel. Yet it gets so hot you don't want to be near it. I wonder why?

The large amount of radiated heat was one of the things I was a little concerned about. But thinking about it, maybe one of the causes is just that there is a large surface area in the big CC to radiate heat compared to other more conventional horizontal thrust engines of similar fuel consumption.

What you say about testing draft pipes against a gas generator makes a lot of sense sense. But then I'd have to build a gas generator instead of an engine first, and that sounds like less fun!

I guess the order I'd like to go in is:

find an engine I can start and run and throttle easily in a variety of weather
then figure out gas consumption, and design and build an appropriate size gas generator
then try to get it to run on wood gas
then try to add a diaphragm or piston and maintain good running
then add a linear alternator
then think about improvements to everything

reality is welcome to step in and stop me at any stage of the above!

EDIT:

I did locate my long propane hose. It's 1/4" ID and UL rated for 350 lbs pressure. Fittings are 3/8" male NPT at one end and 3/8" female flare at the other. I also found an old style tank connector, which has a 1/4" NPT male end. I bought at the hardware store a 3/8" ball valve, a 3/8" x 4" pipe nipple, a 3/8" x 1/4" flare adapter, a 1/4" flare nut.

I have a lot of 1/4" copper tube, some 1/8" also, and some finer stuff. I've also got some 5/16" stainless brake tube, and various sizes of steel brake line and nuts. I have a tubing flare tool and it can do double flares.

Nevertheless, I couldn't hook everything up after I got home. Typical. I needed a 1/4" x 3/8" reducer for the tank connector. I have never successfully made a single trip to a store for a plumbing job of any kind. I always have to go twice, and sometimes even three times to complete even a simple job. It's weird. Icould swear every time, I have a complete list, plus all kinds of backup/spare parts at home. But every time, there's one little part I forgot about. It's a 40 minute round trip to town here, so I'll try again tomorrow.

[PyroJoe]

The CC isn't as hot running on the small bottle, no hot glow from the CC. Just a slow idle is the best the little tank can produce. The large propane bottles can bring the CC up to high heat toe fryer.

I also have that 40 mile round trip, find it useful to bring the pieces I have with me and assembly everything right there in the plumbing aisle.
Joe

[Viv]

Hi Viv,

Actually, heat output itself is not of interest, nor is thrust. Pulse amplitude and frequency are of interest. As are easy starting, simplicity, easy running, and well, small size would be a help. I'm open to any configuration that will provide these things, so a Reynst pot would certainly be included in the possibilities.

I like the draft engines right now because they clear themselves, provide their own starting airflow, and are apparently loud -- meaning I hope that pulse amplitude is good.

It also seems that a diaphragm power takeoff of some sort might be easier in an engine with a separate intake and exhaust, but that remains to be seen. Seems like one hole for both exhaust and intake has a lot to do already, and additional loads taken off the CC might disrupt timing and internal flow symmetry..

I have a few ideas for power take off -- In a two pipe pulse engine, I was thinking maybe a third closed pipe that had a diaphragm at the end, and tuned to return a peak to the CC maybe 360 degrees from the last peak. In other words at the next cycle. I don't know if that would work or make any sense - but I thought it would have the least negative effect on the cycle and yet allow varying work to be taken out of the system. I might be way off in that thinking. I don't know enough yet.

Viv, at this point personally, I'm just getting my feet wet in pulse engines, and trying out simple designs I've found here or that have been suggested by others to try to get a better understanding of what happens. No design type or shape has been excluded.

I haven't finished reading the Reynst book, and so haven't yet come across its output being tied to reciprocating elements rather than continuous flow actuation like a turbine or nozzle. I apologize if I have therefore missed a prior solution to what I want to do.

I also think control of the ring nozzle carburetion methods shown might be tricky with a gas -- particularly if the engine stalled, compared to a tube inlet. It does look like he needed to premix gas with air outside of the combustion chamber. Again apologies for not being sufficiently knowledgeable so far.

Hi Vturbine

Clearly you have a good grasp of the requirements to drive a diagram and realize too it is an energy damper to the acoustic system with its liabilities and benefits, with that said I fully understand your comment about getting your feet wet at the moment so do carry on and have some fun

I originally wondered if a true Reynst set up would be interesting as its got a piston to alter the CC volume for starting, that may help you with wood gas startup, the other benefit is the tuned acoustic tailpipe is separate of the basic thermal pots operation so you can create a new system tailored to your alternators (yes plural, you may want more than one).

You will need to do some thing with all that heat though as its a basic operating mode for the Reynst pots, thermal refrigeration or air conditioning maybe?

Viv

[PyroJoe]

It does idle weakly on the small bottle. Bottle does chill, position where the fuel is applied is tricky. Requires some fuel to heat the draft pipe, remember this was primary reason not to run on the small bottle (bottle starts to chill about the time the engine is hot enough to run, typically not a problem during 97 degree day).
Venturi fuel system will probably be as difficult as everything else combined.
Joe

[vturbine]

I originally wondered if a true Reynst set up would be interesting as its got a piston to alter the CC volume for starting, that may help you with wood gas startup, the other benefit is the tuned acoustic tailpipe is separate of the basic thermal pots operation so you can create a new system tailored to your alternators (yes plural, you may want more than one).

You will need to do some thing with all that heat though as its a basic operating mode for the Reynst pots, thermal refrigeration or air conditioning maybe?

Viv

Yes, Viv, I was thinking that multiple diaphragms might be a possibility in the future, but that would be at a more sophisticated stage. Even progressively positioned and phased. But that is the "complicated stuff." And as Joe rightfully points out, even carburetion will be a big problem to solve earlier on. If I think too far ahead into refinements, I'll end up like one of those Yahoo internet theorists who haven't ever turned a screwdriver. Maybe I am already, even this far along.

Heh, my big problem right now is I don't have a 3/8" x 1/4" pipe reducer.

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

I'm also guessing that high throttle (and heat) levels are an advantage to a thrust system, while possibly lower levels will work as well or be advantageous in a oscillating power takeoff system. As Joe is saying, the draft engine can basically tick over, and I bet the pulse intensity is still good. Fuel efficiency may favor a low mass flow in this type of system.

[Viv]

Hi V

I can see your thinking about how to drive those alternators and thats a good thing, have you thought about doing some theoretical modeling using Graham's NUDIS program? some notable (or just plain vocal) people have used Graham's work to produce optimized engines on the forum, for you it would allow you to start work on what kind of pressure differentials you can expect to drive the diaphragms.

The heat by product comes with the territory I am afraid, its a thermo-acoustic driven system after all the only other thing maybe would be a catalyst conversion to hydrogen (if thats even possible) and then power a fuel cell to generate the electricity (still some heat).

Viv

[vturbine]

VivL Nudis maybe some day, but for now, working with metal and fuel.

IMHO the heat generated is only partially used for acoustic generation. Most is wasted

OTOH waste heat can be used in many ways. I can think of quite a few off the top of my head. Wrap a coil of 5/16" tube about 25 feet long around the CC and insulate around that with a vermiculite inside a sheet metal jacket. Apply water pressure at one end from a garden hose and probably generate enough steam to run a 1 HP flash steam engine. Not that I'm interested in doing that. I suppose you could also inject preheated water and gain thrust in a thrust engine, or one used as a gas flow generator for a turbine.

You can also get electricity direct from heat using a thermoelectric Peltier effect device, which uses bismuth teluride to generate a potential.

Or wrap single half loops of fine SS tubing around the CC and feed these into the displacer chamber of a hot air engine.

Or investigate differential cooling on the tailpipe to possiblt boost pulse amplitude via hot air engine effects. The last is the only one above of interest to me since I'm shooting for a pure system without additional "engines", but anyway, there is lots to investigate about not only reducing waste heat, but using it.

But again, back to nuts and bolts. I got the reducer, here's what I have so far for a propane feed.

PyroJoe, I'm getting closer to a bigger draft engine. Everything I hear about it seems like what I need. Of course that's what you and Grim suggested from the start. But I'm glad I got practice, and understanding (and a little more confidence) with the other engines.

By the way, I did run the big snorkeler a few times today -- conditions were a little better even though it poured rain last night. I was able to try my longer snorkel -- got the loud BRAAAAT at first, then whittled that height down in two .25" steps, and got what seems like pretty good running, considering the still too high humidity. I need to water cool it better now if I want sustained runs on methanol. I really like the sound of that engine. Wish I could get it to run for a long time. I'm sure I will, if only because the weather will eventually get better.

I also got your J pipe draft running for extended periods on methanol, though not consistently locked in. Lots of in-between gurgles and rumbles but the flame didn't go out so I could try different positions. It seemed to like an extreme forward angle on mine -- unlike yours, less than 45 deg. from horizontal. I got some long runs that way (for me). I also tried larger and smaller holes on my second pipe cap, but the stock 5/16th in. hole ruled. Mine also seemed to like a bit of fuel -- ran better that way than when low on meth.

[PyroJoe]

The big snorklers make the sweetest thub-thub-thub. Really enjoy when they run for extended times.

The propane setup looks good. Is that short piece of copper tubing a injector or will a injector be added?
Usually need about 18" of tube to keep the hands from crispy crittering.
Even so, monday mornings reveal patches of hair missing or curled short on the tops of the hands. Signs of the addiction. ha

Propane can be frustrating for the first couple of weeks, after then it becomes second nature, the feel of the valve and the hiss of the injector.

The little J drafts can handle alot of fuel for the tiny CC. If a longer intake could be used and the tailpipe become hot enough, one might just lock in.

If the draft engines are not sufficient for operation, there could be a PLAN B, but it is more complicated and more severe.

Joe

[vturbine]

The propane setup looks good. Is that short piece of copper tubing a injector or will a injector be added?
Usually need about 18" of tube to keep the hands from crispy crittering.

Joe

Oh yeah there will be a longer injector added. The needle valve above goes on the short length and then the long injector. I just hadn't installed the needle valve yet when I took the photo because...........

uhhh, it turned out to be a 3/8" and the tube I meant to attach it to was a 1/4". So again, it's wrong

On the other hand, I found an older 1/4" needle valve on another obsoleted experiment, so now I just have to find new ferrules and compression nuts, which I'm sure I have around here someplace..................

[PyroJoe]

No worries on the needle valve, that can be added later if needed.
I generally use the lone tank valve on my setups.
Joe

[vturbine]

I'm rebuilding the half size miniPJ'sbigdraft. This time rolling the CC out of 16 GA MS, instead of a ready-made SS canister, flame welding (no braze), fabricating the cone out of sheet instead of trying to stretch the tube.

I also looked at Grim's oval draft again, and might do that one too if I get some 1-3/4" exhaust pipe.

Also considering the pipe Ugly Stick, but maybe mounting vertically as a draft. Or possibly elbowing the exhaust pipe up.

I found the ferrules and compression nuts and made up the needle valve, and tested the whole rig for leaks with soap. Ready for propane.

[vturbine]

Well, I didn't have the pipe I thought I had for PJ's new mini draft, and did have the pipe I needed for Grim's oval draft engine, so I started on that one.

I decided to try to learn gas welding -- I've never done that, just stick welding and brazing. I did some practice pieces first with a Victor #0 tip, and then went ahead and welded the vertical seam on the oval shaped CC. It went a lot better than I thought, and I think I'm going to like gas welding a lot. It's kind of like brazing, but you can actually see the work a lot better. Temps aren't really a lot different, and you don't need to flux all the time. I like it!

First seam on Grim's oval draft

I then used the CC as a guide to cut out the end pieces and gas welded the bottom one on.

I also made up a hole cutting guide from a learger piece of tubing. Here's a mockup of how that's used -- it would need better clamping if this were a real cut. Actually, this is really the bottom of the CC. I'll be cutting the holes in the other end piece and welding in the pipes before I attach it to the CC. I think it will be easier to do good welds that way.

The end is on -- showing a hole cutting guide

I've made a few of these hole burning guides, mostly out of washers and scrap. They need to be the diameter of your cutting tip wider than the hole diameter you want to cut. So if your tip is 1/4" (6mm) in diameter, and you want to cut a 1-1/2" (38mm) hole, you need a guide that's 1-3/4" (44mm) in diameter

Various homemade guides

[GRIM]

Hey Looking good ,

Yes Gas welding is very rewarding , just takes some practice ,

One thing I might mention is that Pyro Joe made one of these and found it worked better with a shorter inlet stack ,
I cant remember exactly how long he made it , but found in my files a modified drawing , attached ,

JOE CAN YOU REMEMBER ?

For flaring the inlet and exhaust you might take a look at this ,
viewtopic.php?t=4538&start=240#p56183

Not perfect flares but plenty good enough for experimenting,

As for fuelling, I found the injector pushed in a hole in the corner worked really well , but it will also run just fine with a Rossco down the inlet , I just found it a little harder to start that way ,

Good luck and keep us informed on how it goes ,

[vturbine]

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. When you add the flare in it's almost identical to 110mm to the flare (or cone). I'm probably going to try to make the cone.

I did see that flare tool -- very cool!

Here's what I've been looking at (in png form with inch dimensions added -- hope that's okay to put up.)

Original dwg with inch measurements added