Turbines driven by pulse jets

Jets that defy normal classification

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Viv
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Re: Turbines driven by pulse jets

Post by Viv » Tue Sep 15, 2009 2:26 pm

Hi V

Thanks for taking the time to read it and I hope enjoy it too, that was really my goal, a it of fun and to start a discussion on basics, you seem to have pulled out of it all the main points and stated them very clearly.
In reply to a few points,
yes compressor input and efficiency is some thing that is all to often glossed over or entirely missing in posts, probably I am not the only one grinds their teeth about that ;-) the huge shaft horsepower required to spin up even a small compressor wheel normally comes as bit of a shock to people.
Maybe the only person to consider a stationary combustor from scratch so far has been Reynst, most of the others were based on traditional flight engine layouts including my own commercial design.
Capstone who produce small scale turbine power units for combined heat and light installations probably have the best economic price point nailed down for a successful marketable product, smaller outputs than what they produce is probably not worth it.
Agreed for specific designs optimized to a pulsejet output, I am watching your efforts to develop one with interest as you are to my mind doing it correctly.

Personally I prefer the Reynst pot as a turbine driver and have a few ideas jotted down for when I get time

And yes a bit of fun along the way too ;-)

Viv
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Re: Turbines driven by pulse jets

Post by vturbine » Thu Sep 17, 2009 4:37 am

Hi Viv,

To hopefully carry on a lively converation, the primary thrust :D of your treatment here seems to be that the inlet of a valveless pulsejet allows a loss of pressure that is not present in a ram combustor applied to a conventional compressor turbine. This is true . . . however, that valveless pulsejet does not have to turn a compressor to drive the turbine. It replaces the compressor. This didn't seem clear from your explanations. A ramjet combustion chamber, which you suggested was superior, requires a compressor, even in a vehicular turbine, unless pushed off of a cliff, or accelerated from rest in some other fashion.

My point is that a valveless driven turbine, while operating at lower pressure ratio, and accepting some inlet loss, avoids compressor and transmission losses. I don't know whether this will be at an advantageous level -- but suspect it may be possible for small stationary engine sizes. By the way, I don't believe that Capstone has defined the only commercial niche for small turbines at their lower size limit of 35 Kw, and note that their efficiency claims include cogeneration heat use -- that certainly would boost pulsejet efficiency figures as well. :D

My primary disagreement with your discussion came when you used an example of an air tank with two valves, one venting to atmosphere, the other, attached to a turbine wheel, and stated that a valveless pulsejet could likewise therefore only utilize 50% of the available pressure. It seems to me that a conventional turbojet engine also has an inlet hole and an exhaust hole, and by that logic would not go anywhere. It's what is going on inside any jet engine that makes a difference. Neither type is the analog of an air tank with two outlets. In fact a valveless pulsejet IS a compressor (that's its function), fed by fuel, with (like a piston compressor) pulsing directional output, and using as somewhat leaky valves, acoustic effects to give a balance of positive thrust. It's a very poor valveless pulsejet that has equal flow out both inlet and exhaust like a two hole air tank. In fact I've yet to find results posted in these forums of a valveless -- even an unbent linear -- with no effective thrust, though I'm sure it's possible (this ought to generate a slew of links to suitable candidates :lol: )

Finally, the Reynst engine, though a wonderful mystery, in my very humble and definitely inexperienced opinion, is basically a two holer with a concentric configuration, using fairly complex deflector shields to try to enforce separation between exhaust pipe and intake manifold -- whether this does actually prevent pressurizing the inlet and creating some suction in the exhaust at some stage in the cycle I'm truly unqualified to say. I'd want to build and test one myself before totally accepting the lore of this engine, just as I did with the Tesla disk turbine. But like a valveless, it does in fact have inlet and outlet, two holes, but like a valveless and conventional turbojet, should not therefore be reduced to an air tank analogy.
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Re: Turbines driven by pulse jets

Post by Viv » Thu Sep 17, 2009 1:13 pm

Hi V

One of the biggest problems in trying to deal with this is that simple analogies break down very quickly as you have correctly pointed out, but you have to start some were and its why you will have seen Fedde and I trying to keep to the "simple" theme but maybe not always succeeding, one of the starting points for this thread was the belief by some that a valveless pulse jet could replace the compressor of a normal gas turbine and it could output the same amount of work! its not going to happen as we all know but this is why I used the simple air tank analogy to get across the inherent low pressure ratios available and gave a reference for a good book on thermodynamics for further reading ;-)

Small heat and light units are of interest to me as is wood fuel to power them, Capstone has a nice market niche carved out but there are others too and yes as they are a heat light unit they do focus on the numbers a bit but that the marketing types running free I assume, have you noticed Volkswagen are getting in to cogeneration too now with a IC engine powered unit? some thing they are calling Swarm Power, very interesting distributed power generation concept.

I like your main argument against the simple air tank analogy but I have to then think maybe apples and oranges is going on a bit ;-) the turbine has maybe a 100 SHP tied up driving the compressor wheel that stops the air leaking back out the turbines inlet, I don't see any thing similar happening to prevent stuff leaking back out the valveless intake ;-) thats really the main point of the air tank analogy, stuff leaks out the intake and gets worse if you restrict the exhaust trying to extract work, there are limits to how much work you can get before the inlet loss becomes a problem, again simple analogy only.

The Reynst is another kettle of fish but has definite advantages I think for a compressor fed turbine output arrangement, size being a big part of that and the ability to run phased pairs.

Viv
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Re: Turbines driven by pulse jets

Post by vturbine » Thu Sep 17, 2009 10:17 pm

Hi Viv,

I'm not sure which turbine you are talking about for the 100 shp figure, so it's hard to talk about comparisons between compressor turbines and pulsejet turbines in that example.

I naturally do think that one can describe the action occurring in a pulsejet attached to a turbine as taking the place of the compressor (and combustion chamber, as well) -- since I did in my last post :D . However, a better analogy of the compressor type than a fan compressor is a piston type, with somewhat leaky acoustic driven air valves and pistons.

And in the sizes of a few kilowatts may have many advantages over a shaft driven compressor (true microturbines) for stationary engines. I have little doubt that the large aircraft turbojet engine as we know it will NOT generally be replaced by a pulsejet as we know it -- at least without an alteration in the nature of the physical world. Always a possibility either by fundamental discovery or external manipulation, but so far, remote in this field. :D .

One of the current fundamentals of a turbojet aircraft engine is that the turbine's purpose is to turn the compressor. If we didn't need a compressor, we probably wouldn't need a turbine on an aircraft. A turbine can be viewed by an irreverent person (certainly not me...) as a kludge for the compressor. I'm of course excluding turboprop engines, which do absorb power from the turbine beyond compressor requirements.

In a stationary engine however, a turbine is the transmission between air flow and shaft power for whatever external purpose we have in mind. Because it can be run from a pulsejet, a mechanical compressor is not required. It becomes a pure transmission, and that transmission can be optimized to output requirements rather than compressor requirements. This is a big deal, I think. Not only elimination of the compressor power draw but a reduction of transmission losses.

I don't have any proof -- just a suspicion so far. I have constructed a frighteningly crude turbine :lol: And I have no illusions that it could not be bettered by a monkey with welding gear and a little training. The blade shapes, bearing types, materials, housing, inlet and exhaust shapes probably couldn't be much worse, and the "scientific" assumptions, "calculations", and certainly, my incorrectly built version of a low thrust pulsejet could probably be improved upon by 95% of the readership of these forums. Sorry, I don't mean any connection between the monkey analogy and the readership -- maybe I should put that in a separate paragraph..... :D

But anyway, I remain hopeful that better minds will certainly be able to exceed my own performance envelope.

Now Reynst, because I love to think about, and often question, that engine type. Hope you don't mind our discussing it a little more deeply here as a turbine driver.

A Reynst engine as commonly referred to here in these forums seems to be a lot of different things. Mostly it is viewed as a tapered pot type engine with a single orifice and an internal focusing ring and lip feed. Drawings of a Reynst often show some other elements that seem to me to be rather critical. An intake manifold, a deflector shield, and a diffuser cone exhaust. Though concentration seems to be on building the pot with internal ring and attempting lip feed occasionally -- (these ARE logical building blocks because they are what is typically thought of as an engine) -- the intake manifold, deflector, and cone are usually missing.

The result is kind of like taking a 2 cycle engine and removing the same items -- intake manifold, ports, and tuned exhaust, and trying to get it to run briefly by squirting fuel into the cylinders. Yes it is an engine, and may run for a moment...but....

What I'd like to suggest here is that the lip feed and manifold, deflector, and diffuser cone are the entire fuel induction system. They cannot be separated. The cone and deflector and manifold must all work together to get a charge into the Reynst. Fuel and air will not flow (in appreciable amounts, or possibly at all) without the suction created by the cone, and the cone suction and timing is dependent on the acoustic energy from the exhaust. So, eliminate the cone and you don't draw the the quantity of air and fuel into the engine through the intake manifold.

If you keep it, unfortunately, sticking a turbine on top of the cone, as I did fairly easily with the draft pulsejet exhaust, probably isn't practical. The outlet is wide, meaning that you would need an axial rather than radial fan. These in my opinion will seriously interfere with pulsing and flow, and the typical vanes and blades will also perform poorly with that flow.

Not saying it will be impossible, but from here it looks hard to imagine as operable.
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Re: Turbines driven by pulse jets

Post by Rossco » Fri Sep 18, 2009 1:26 pm

V's,

Big end splash fuelled 2 stroke maybe, drip vaporiser like. "...squirting fuel into the cylinders", atomization? seems a little higher up the ladder for us monkeys.
(I for one liked the general whole community encompassing compliment/insult combination) ;)

Fuel atomisation(or other), metering, distribution, mixing and ignition. Then temperature control/management, then accoustic coupling and loading on an already maddeningly frustrating "simple" system seems like a long way away from the simplistic, fun engine most experimenters toy with these for!

"Not saying it will be impossible, but from here it"... hurts my head.

Linear drive... much nicer. Figures? (back on your thread)

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Re: Turbines driven by pulse jets

Post by vturbine » Sat Sep 19, 2009 2:24 am

Rossco wrote:V's,

Big end splash fuelled 2 stroke maybe, drip vaporiser like. "...squirting fuel into the cylinders", atomization? seems a little higher up the ladder for us monkeys.
Rossco
Heh, I meant as in an eyedropper with a little Missile Mist into a Babe Bee's exhaust port... uh strike that, probably means nothing to anyone under the age of 60, now. :D Used to be anyone over the age of 14 not so very long ago, if I remember correctly.... or a bit of Heet into the blowhole of a truncated Reynst, to catch up to 2009.

Rossco, man, you going to be the first to run a pulse turbine on plastic strapping? Now that would be a Youtube hit!
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Re: Turbines driven by pulse jets

Post by tufty » Sat Sep 19, 2009 9:52 am

Babe Bee's exhaust port... uh strike that, probably means nothing to anyone under the age of 60
HOI! I'm only 41.

<offtopic>
I think Cox were still making them well into the '90s, actually.
</offtopic>

Using a reynst as a driver appeals to me as well - even if it's not running a "tuned" exhaust, or if the additional back pressure of a turbine fouls up the tuning, which it almost certainly will, they still run. Much like the draft engine, in that respect, but with "both" holes pushing through the turbine.

Now, how to fuel a reynst on chicken shit?

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Re: Turbines driven by pulse jets

Post by vturbine » Sun Sep 20, 2009 7:03 pm

tufty wrote: Using a reynst as a driver appeals to me as well - even if it's not running a "tuned" exhaust, or if the additional back pressure of a turbine fouls up the tuning, which it almost certainly will, they still run. Much like the draft engine, in that respect, but with "both" holes pushing through the turbine.

Now, how to fuel a reynst on chicken shit?
What I meant was it ain't a Reynst without the axial fuel feed/manifold together with the diffuser cone, which last isn't only an exhaust thruster, but a means of creating low pressure in the intake manifold.

In my own possibly screwed up opinion, when an exhaust pressure pulse enters at the bottom cone, the cone causes its sign to invert and it acts to draw gas outwards or extract from the pot and manifold for that phase. This extraction draws air and fuel in through the horizontal hole (the slit -- or what I refer to as the second hole) as a slug of combustible mix. Likewise when the phase changes, the slug heads back home, only this time guided down the throat of the pot with the help of an exhaust deflector.

If you pull this set of contraptions off of a "Reynst, what you have is in my opinion, a jam pot -- nicely evolved with a tapered side and a guide ring insert, but just a jam pot, still. Not a true Reynst. That definition may just be me -- I'm sure thousands of "Reynst" builders may disagree. But anyway, sure, you can add a turbine to a jam pot. Good luck feeding it without the other jazz.

If you stick a pipe on top of a jam pot, what you have then is a "snorkel", an invention I attribute (rightly or wrongly -- or at least the name) to Mark, and in fact MY favorite pulsejet type of all. Just as a general like/dislike kind of thing. They sound so cool!

Maybe that's what you are thinking of adding a turbine to, in which case, I personally think a recoprocating element like a diaphragm or piston would make a lot of sense there, but I'm sure a turbine could be added there as well. Snorkels are tough to feed -- hence, probably the evolution of the true Reynst, but no reason you can't get a few enjoyable minutes out of it, with a fuel pool, and spinning a paddle wheel that I can see.

I would guess, with regard to gassified chicken doo-doo that the fuel isn't a problem, the means of supply to a jampot or snorkel is. A true Reynst or a draft valveless might be easier. Maybe the true Reynst would even be the easiest -- I'll even grant that, with its power induction and manifold. Most ordinary valveless pulsejets aren't as evolved in the fuel induction department, depending as they do on injection, not induction.

I think with the biofuels (biogas/methane, bio-diesel, woodgas) we need to increase our induction engineering knowledge for valveless pulsejets. Because these fuels all have various problems like low-pressure delivery, relative lower heat content (in the cases of the gasses), or the need for vaporization (for bio-diesel).

Now one more thing, unless you're a chicken farmer, or a corn farmer, (and even if you are, with the price of petroleum based, petroleum manufactuered, and petroleum transported fertilizers now skyrockting) biogas, ethanol, and biodiesel aren't going to do a whole lot for the energy situation, because they depend on multistage productions and conversions. They use up resources like farmland and fertilizer, and pesticides, require harvesting and processing, then conversion.

I like the prospects for woody biomass-- brush and woody waste grown on marginal non-farmland without fertilizers and pesticides a little better. Like Pyrojoe says where he is in Texas, we don't have tree chips, but lots of brush/sticks. It can be grown to reclaim mine waste land, etc, coppicing, whatever. Likewise where I am in Vermont, there is limited farmland, but lots of spontaneous growth of scrub everywhere a clearing appears. No need for seeding or cultivating, It pops up everywhere. Trees can be saved for lumber and forestation, but brush is certainly fair game. I chip mine -- hence the interest in chips.
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Re: Turbines driven by pulse jets

Post by tufty » Sun Sep 20, 2009 7:48 pm

vturbine wrote:
tufty wrote: Using a reynst as a driver appeals to me as well - even if it's not running a "tuned" exhaust, or if the additional back pressure of a turbine fouls up the tuning, which it almost certainly will, they still run. Much like the draft engine, in that respect, but with "both" holes pushing through the turbine.
What I meant was it ain't a Reynst without the axial fuel feed/manifold together with the diffuser cone, which last isn't only an exhaust thruster, but a means of creating low pressure in the intake manifold.
I think the jury's still out on the absolute effect of the diffuser, but I'm certainly with you that it improves performance on otherwise "marginal" jars. It certainly allows running jars with larger-than-otherwise-feasible inlet holes. But I'm not sure I would dismiss any jamjar type combustor without the annular ring as being "non-reynst" - if you're getting that anal about things, then surely you should also discount non-variable geometry pots as well? Lipfeed of one type or another (Reynst had *many* variations on this) is a given, at least for me - I never managed to get a "bottom fed" reynst pot to run apart for the "first shot".
vturbine wrote:If you stick a pipe on top of a jam pot, what you have then is a "snorkel", an invention I attribute (rightly or wrongly) to Mark, and in fact MY favorite pulsejet type of all. Just as a general like/dislike kind of thing. They sound so cool!
Only if you do away with any direct "lipfeeding" and seal the tube to the top of the pot. Otherwise you have a reynst-style combustor exhausting into a (probably non-tuned) stack.

According to Reynst himself, his discovery of the effects of a tuned exhaust were purely fortuitous, due to one of his very long exhaust pipes splitting (coincidentally, or not, at one of the nodes). But his burners were running perfectly well with bloody great exhausts stuck on them.

Now, making a reliably running reynst pot with lipfeed isn't *that* hard, it's a question of engineering. Making one that runs into an exhaust is, again, "merely" a question of engineering. Finding out what happens with the back pressure of a turbine on top of (or in) the exhaust is experimentation.

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Re: Turbines driven by pulse jets

Post by vturbine » Sun Sep 20, 2009 8:15 pm

Glad to see you're so passionate about it!

Looking forward to seeing your work. :D
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Re: Turbines driven by pulse jets

Post by Viv » Tue Sep 22, 2009 2:00 pm

Hi V Hi Simon

Nice to see people having some fun in this thread but at the moment its a busy time for me, after a quick read of Vs and your comments about the Reynst pot I would simply answer that I would like to see the exhaust taken off and replaced with another pot running in active anti-phase as opposed to a tuned exhaust's passive phase support, the lip feeding problem is pretty academic really and superfluous in that setup so would be replaced with a pressure feed to say the vortex generator for instance (cools it too then).

Another comment I would make about Reynst pots is that with out the acoustic components to augment the cycle the pots primary running mode is thermal breathing, cooling the pot walls is critical to operation in this mode as people have demonstrated over and over again

But all good points in the rest of your posts I shall read more as I get time ;-)

Viv
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Re: Turbines driven by pulse jets

Post by vturbine » Tue Sep 22, 2009 5:17 pm

Viv, would it be feasible to use aluminum castings in a water cooled chamber in this case? I've been curious about that ever since seeing the water cooled section views -- I was curious about whether castings were used in the Reynst drawings I have seen. If so, I suppose they were cast iron?

I've even been tempted to make some patterns, though coring for the passageways and pouring thin sections is fairly high art. Still, not nearly as bad as a multi-cylinder engine block. I noticed some Reynst dwgs had a liquid cooled internal ring as well. Now that is fine casting work, and good seals to the rest of the castings required.

There could be some sleeving possibilities, though the opposite tapers at the bottom might mean a two-piece. Or even a pour-in-place mold with a steel liner as a permanent core. In cooled operation, if temps stayed reasonable the different expansion coeffs between steel and Al might still be do-able.

The opposed pots is a cool mental picture for me. I do like it.

Wondering where the turbine would be located, if you stick with the turbine theme? Really seems a natural for a reciprocating element.
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Re: Turbines driven by pulse jets

Post by Viv » Wed Sep 23, 2009 2:59 pm

Hi V

I had thought of using aluminum in the past but could never see a way to keep the surface temperature with in limits to stop erosion, the environment of a combustion chamber is pretty erosive to most metals as there is still a lot of very hot oxygen around, I have put 316 grade stainless and other grades in pressure jets as small test samples and they basically dissolve if not cooled properly.

Sleeving sounds like an option though, the Reynst pictures I thought looked to be cast from iron and that was the typical method in those days.

For reciprocating pots remember that waves go around corners much better than flows ;-) so with that said we would want to set the pots to flow towards the turbine while communicating pressure pulse to each other sideways perhaps

Viv
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