Towards a wood fueled pulsejet

[vturbine]

Camping trip postponed because of severe thunderstorms and 2 days of rain -- leaving tomorrow, back Wed.

The throttling problem might be solved by putting a valve on the vacuum side of the fuel blower (if there is one) and reducing the draft to the gas generator. Response might be slow, due to continued pyrolysis, but may be okay for a stationary engine. This assumes a loose top on the gas generator that can vent if there is any pressure build-up, and outdoor operation.

[vturbine]

I got a couple free hours to work on the fan rebuild today. Drilled out all the rivets on the old blade wheel and removed the wheel from the shaft. It had been silver brazed to a shoulder there. I no longer trust that the temps will stay low enough for any braze. It held even though the aluminum blades melted last time, but I don't want to have to worry about it. So I cleaned off all the braze.

I worked on a mechanically attached hub machined out of 1.25" dia. bar stock turned it, faced it, and bored for the 5/16" shaft and drilled for two set screws. Also drilled and tapped to attach to the fan plate. As I was tapping the second fan hole after working hard with the deep set screw holes, I was thinking that I had never broken a tap. Ever. Knock on wood. How come people had so much trouble with taps?

Snap!

Wait a minute...... It's broken......uh, wait a minute......Uh I don't have another 10-24 tap......wait a minute......A little bit is sticking out, if I just get some needle nosed pliers on it......Snap, crackle.......wait, this can't be.....I can't make another part today, I don't have the stock or the tap........etc. The mind struggles with incomprehension of the simplest fact: It can't be. But it is.

Anyway, dredging up from the mental depths a trick tap removal remedy, I put a number 10 nut over the slight stub left of the tap, hook up the ground clamp, pull out a a special 1/16" 6013 rod from a box I just received, and set the amperage to 40A, and weld the nut to the tap right through the center hole.

Letting it cool, I gingerly applied a wrench to the now bloblike nut. It turned. Very easily. Too easily. Basically only the slag had held it in place. Miracle cure failed. Or it did three times with three nuts, since I didn't believe it the first time, and had to repeat the foolishness.

Well perhaps that works with bigger taps than a #10, or better welders than me, but I finally had to accept that I'd broken my first tap, and wrecked the part. and spent more time trying to solve that than it would have taken to make a new part. If I'd had the material and tap. Time to call it a day.

Sorry not to report progress here.

[vturbine]

I decided to weld the new hub onto the backing plate, although I knew this would distort it from the heat. I welded it in four places with 3/32" 6011 stick without burning through. The welds looked good so I put the plate on a flat hardwood board and used a planishing hammer to get out any big humps. Then I installed the disk and hub on a 5/16" arbor and chucked it in the lathe and set up a gauge against the face. Rotating the chuck by hand, I used a slotted bar to bend out the irregularities as best I could. I unchucked and set the disk on a milled iron surface and tapped some more, then re-chucked for a final round of checking and correcting,

It looked pretty good, so I cut out new vanes using some stovepipe metal (22 ga. I think) and bent them in the vise and drilled them. The vanes are slightly taller than the last batch, since I wanted to take up the clearance left by eliminating the second rotor plate. Vanes were scribed along the centerline of the bottom mounting leg and one rivet hole position marked. These were punched and drilled 1/8".

I mounted the vanes on the disk with a single rivet, and then rotated the vanes on the rivet until I could see the scribed centerline through the second hole in the main plate. Centering that line in the hole, I drilled a second hole in the vane, and then riveted it.

Everything went well, and I installed the rotor and shaft into the bearing housing, and gave it a spin. The bearings seemed okay, though perhaps a little less free than I'd expect for ball bearings. But they weren't noisy or rough, so maybe they'll run easier with a little use and heat. They and the whole spindle assembly were probably expanded a bit last time around. I can always replace them, since skate bearings come 8 to a set. I actually also have a set of 8 even better bearings if needed.

I mounted the bearing plate to the main fan housing and tried it with compressed air. It spun up pretty well, though subjectively a little less speed than when I had the double plate version. I hadn't measured that rate, but decided to now.

Compressed air ran the turbine at 2700 RPM, which seems roughly what you would expect if 4000 RPM would require a half horsepower motor to drive it as a fan. My shop compressor is a typical portable shop single cylinder 110 volt type, not a big 220V stationary. Though rated at 2 hp "peak", the motor is simply not capable of that from the actual consumed wattage, I'd call it a one hp "true". Then add in the losses of the compressor in friction, and heat, and then the 25 feet of 3/8 hose I have on it, and finally the blowgun at the end with its safety hole, and the distance to the mouth of the fan, and non-seal with it. I'd be surprised if the equivalent power leaving the nozzle was 1/8 hp.

This multiplying of inefficiencies, by the way, is why most Tesla turbines built by amateur experimenters never run anywhere near projected RPM on compressed air. People figure a 2 hp compressor should drive a 2hp rotor. But 2hp sure isn't delivered to the turbine nozzle. You have to figure a tenth or even less of the compressor motor's rating to be realistic.

Anyway, 2700 RPM seems in the ballpark for this air driven setup. Looking forward to seeing how it does on the pulsejet.

[vturbine]

The pulsejet/turbine running. Spinning disk on shaft is half black for tach readings.

Ran it! And finally some video, too. Here:

http://www.youtube.com/watch?v=3v0tolKhXb4

First nice day (non-raining) after the effects of some hurricane or other. This has been the coolest wettest summer ever. I sure hope we don't have that kind of thing this winter, or we'll have snow drifting to 8 feet and 20 below zero for sure.

Anyway, making hay while the sun shines, here's the first test with the steel blades. Notice the blades were glowing red even after the turbine was swung out of the exhaust path.

Blades glowing in outlet.

I'd say the engine was at "cruise" throttle I didn't want to burn or distort anything up on this first re-trial. The CC is a nice red, but nowhere near yellow hot.

CC Color

Checking with the tach, as it passed 2000 RPM I noticed it started ticking from contact of the rotor probably with the case from heat expansion -- this put on quite a bit of drag, but it managed to kick past it anyway after a bit of wear and push on up to a peak of 3000 RPM -- it seemed to like settling at 2700 RPM, coincidentally (or not) the same peak it had with the compressed air test.

In the video you can see me feeling around the inlet for escaping gas. There was lots of it! I could feel the pressure through heavy welding gloves. The outlet of the pulsejet is smaller and round compared to the inlet of the turbine, which is rectangular. The turbine is also about 1/4" above the pulsejet outlet. So, if we don't interfere with combustion, sealing the outlet/inlet should really give it some additional boost. That plus getting rid of the rotor drag, and probably better bearings and lubrication should see it up at least to the proposed 4000 RPM and possibly beyond. Unless 2700-3000 is a sort of equilibrium plateau speed at which the centrifugal fan forces tend to oppose inflow rapidly increasing resistance.

I wonder whether the escaping gas was not only exhaust backflow from a loose inlet, but also a result of that centrifugal counterflow -- like what I found when spinning the fan with compressed air?

There was definite outfltow through the normal turbine exhaust at the center of the housing. This could also probably be improved with a venturi outlet rather than a simple hole.

Anyway, not bad for a crudely fashioned turbine, and wild performance estimate/calculation, run off of a pulsejet, apparently witrhout harming the pulse combustion. In fact, at least by ear, I couldn't tell any difference when the turbine was swung over the pulsejet. Perhaps you guys with audio analyzers will confirm this. This computer doesn't have that ability (no XP) my other one does, but it's down for now.

woohoo!

[GRIM]

CONGRATULATIONS
Very very good , and excellent vid , I ran va , and couldnt detect any visible difference in the frequency , theres two strong peaks, one about 130Hz and one about 270HZ they dont appear to change much ,

this is just way cool, cant help thinking what will happen with the square to round transition ,
btw i have a program to generate templates of these , if you want, just send me the dims and i will send you a template back in .pdf

thanks for posting

[vturbine]

CONGRATULATIONS
this is just way cool, cant help thinking what will happen with the square to round transition ,
btw i have a program to generate templates of these , if you want, just send me the dims and i will send you a template back in .pdf
thanks for posting

Thanks Joe! I just measured the turbine inlet and if I lap the transition piece over the outside of the inlet and rivet it in place:

1.) The ID of the rectangular end of the transition piece should be 2" x 2.125"

2.) If you can, would you give me 3/8" tabs for the overlap, then start the transition? If not I can just add them by drawing it in.

3.) The round end of the transition piece should have a 1-3/4 OD. Because I'm going to weld this end, I think I'll be using .063" thickness material, so I guess the ID would be 1-5/8.

4.) The length of the transition itself (excluding the overlap tabs) should be enough to yield the equivalent of let's say an 8 degree taper, which I think is about 4-3/8" long.

FYI, the round end will be welded to a standard exhaust flange. I'll put another one on the pulsejet exhaust and put a single bolt through them, so I can again start the engine with the turbine to the side, and rotate it into position.

I hope that's not too tall an order Joe, for your program!

Thanks for the help

[GRIM]

There you go ,
this is in two halves , ie two seams , these are tough to make in this small size so the two halves is easier
have fun ,

[vturbine]

Wow, that was quick!

Thanks, I hope to be able to get to it today after other work and chores. Will post when I do...

[PyroJoe]

Good job!

Any patents filed on a hampster wheel of fiery death?
(still working on my gasifier)

[vturbine]

Good job!

Any patents filed on a hampster wheel of fiery death?
(still working on my gasifier)

Oh, man, another missed opportunity....I only filed for a better mousetrap.

I'm working on a cheddar trip wire going to the gas tap, and striker. Any suggestions for these?

Also noise abatement? I don't want to wake up the entire house when I get one of them squeakers.

I'm also working on a semi-automatic clip that holds 25 marshmallows that feed the intake for a group camp-out game. Participants stand in a circle around the exhaust and try to catch the incendiaries on a pair of graham crackers.

This thing is going to fill a lot of needs....

[vturbine]

Seriously, no patents. Period.

Make a better one, Joe, and everyone else. Shouldn't be hard to do!

But, please post your experiments. I'm as interested as you are.

[Rossco]

Mate, this is very cool!
I was getting a nervous tick wanting you to crank it up, although i do understand some small need for more than one run.
[subliminal](bigger engine, bigger engine, bigger engine!) [/subliminal]


Impressed by the revs considering your mentioned ineficiencies. On top of wanting MORE POWER as always, i would be very interested to see some load on it, even if just gloved finger pressure. Did you do this at all? Would like to hear your thoughts on the torque. (not putting the concept down at all, just getting a feel for what you have here)

In regard to centrifical reverse flow, how do you plan to tackle this and is there a way to design this reaction type turbine around it? is curved blades a complete cure? How much of this effect in a sealed system before it overloads the combustor???
This will be your rev. limiter, although a. your combustor liked the back pressure in previous tests, how far can you push this? and b. Unloaded auto rev. limiter is kinda cool (if at the desired rpm). Dont judge the power of your system solely in regard to this (hence the torque q.)
Im sure you have been thinking on these same type of questions... throw them out here, and we will hit extra questions back to "help" some more

Pyro, Gasifier? Started a thread? Can we shoehorn another tangent into this forum?
I may have some contributions to this topic, looking at starting into this myself.

Rossco

[vturbine]

Mate, this is very cool!
I was getting a nervous tick wanting you to crank it up, although i do understand some small need for more than one run.
[subliminal](bigger engine, bigger engine, bigger engine!) [/subliminal]

Heh, I'm sure you'll remedy that situation once you get going on this!

Well, I have really no budget to spend on engines -- must use what I have on hand, and for bearings, I have some roller skate bearings, and they fit a 5/16th shaft -- so that limits the power you can get out of a turbine. Everything else mounts up in cost and complexity if you try to go big -- at least for me -- I've got limited amounts of sheet metal, etc.

Also remember -- I've got only a few weeks experience with pulsejets, so give me a few years to catch up with you guys

Impressed by the revs considering your mentioned inefficiencies. On top of wanting MORE POWER as always, i would be very interested to see some load on it, even if just gloved finger pressure. Did you do this at all? Would like to hear your thoughts on the torque. (not putting the concept down at all, just getting a feel for what you have here)

Nope, what you saw in the video was it. I'm not interested in torque when I'm not at least at projected RPM. I want to get the RPM and reliability up there before that. However, just to turn those blades at 3000 RPM takes, in my opinion, just as much power as a fan of those proportions turning at that speed. I don't see how it could be less. Of course shaft torque is zero at any unloaded max speed. I don't want to characterize this one until I see where the max speed ends up.

In regard to centrifical reverse flow, how do you plan to tackle this and is there a way to design this reaction type turbine around it? is curved blades a complete cure?

Well this is really mostly an imaginary picture description (from me) and it only appears physically because of the open connection. Once it is buttoned up, nothing is going to come out the inlet, and all flow will have to go out the only outlet.

In fact the turbine will run up to the speed at which friction (both mechanical and aerodynamic) create enough opposition to create an equilibrium with applied power. What I referred to as centrifugal opposition will appear simply as aerodynamic friction. By the way, ALL radial turbines will generate reverse flow when the gas source is turned off, and all reach a max speed of equilibrium for a given amount of energy available. It's not unique to a bladed fan type turbine like this one. Most every turbine is a fan when power is removed from the blades and applied to the shaft.

How much of this effect in a sealed system before it overloads the combustor???

We don't know yet....isn't it wonderful?

This will be your rev. limiter,

I wonder. This fan will create MUCH more resistance as speed increases, in other words will require MUCH more power. Therefore, it seems likely that the fan will simply go a certain speed with this pulsejet and no more. I have a feeling that won't flame out the pulsejet. Or at least that's my hope. That's why I sized the fan to the pulsejet measurement I did with the manometer. They are (I hope) matched. And furthermore, that match was designed to also meet the speed requirements of an alternator without a transmission. And its inefficiency. See, I consider the turbine itself to be simply a transmission. So I set the transmission's input specs from pulsejet measurements, and set the transmission's output specs from alternator requirements.

I chose the straight radial centrifugal fan type over other turbine types, because to me, it seemed most appropriate for low speed transmission, with enough raw blade surface area to give lots of torque from a low pressure high volume source. And one that is pulsing.

It seemed to me that axial airfoils like a consistent flow, and we didn't have that. I'm a sailboat designer by trade. I understand high volume low pressure large area variable source propulsion. I applied that to the situation of a pulsejet. I made a rotary square rigged sailboat in a can. My kind of turbine.

Pyro, Gasifier? Started a thread? Can we shoehorn another tangent into this forum?
I may have some contributions to this topic, looking at starting into this myself.

Please feel welcome to add in here -- it could be a group thing -- working towards wood fueled pulsejets -- or if you feel like striking out under a different heading or in a different forum, that's great too.

[vturbine]

Now, here's another speed limiter, heh Uh, I pulled the cover off of the inboard bearing and whadya suppose I find? Solidified formerly melted snot. I mean plastic.

I suppose roller skates don't heat up all that much, so maybe you could get away making a roller bearing's ball cage with some miracle new age plastic, seeing as how plastic has invaded every other aspect of our lives in the drive to eliminate metals from the face of the earth.

Oh, to return to the days of fifty years ago when ball bearings were steel and plastic was merely a decor for furniture. You can't trust anything anymore.

Okay, here's a photo of two different skate bearings. The one on the left (green) is an ABEC 7 skate bearing. All steel. Including the ball cage. The one on the right (red) is what I thought was the same thing, purchased from a sporting goods store. Negatory. It has a plastic ball cage. In the center is the remains of the inboard bearing (formerly red) and bits of re-uncycled melted and re-snotigated plastic surrounding it.

That poor turbine. It had a lot of strikes against it. Imagine turning 3000 RPM with this crap inside.

Post Mortem

[GRIM]

Great pics ,
a quick one on bearings , try to get the bearings with steel chip shields , and the c3 designation ,
Bearing suppliers are usually the best place to buy from , and ball races are incredibly cheap considering the precision involved,

The chip shields will carry the designation zz or 2z and the c3 means a higher than normal (standard bearing)radial clearance, these are the ones to use in high speed hot locations ,

so the bearing number will look something like xxxx zz c3 ,

the bearings with rubber or plastic shields are fine for low temp operation but at speed and high temps the rubber burns and contaminates the grease not to mention the increased friction , vicious circle ,

and make sure they are almost a loose fit on the shaft an in the housing , that shaft WILL grow with heat , and that usually reduces internal clearance to zero , or worse , the rest is history ,

square rigged sailboat in a box ,