Steam turbine turbo charger idea.

[Troy R. Legner]

Gentlemen,
I have been thinking about utilizing the heat generated by a pulse jet to drive a steam turbine driven turbocharger. I would like to put this out here for all of you to put in your opinions and suggestions for the concept.

The idea of throttling a pulse jet seems to be eluding us. I am thinking that this concept may open the door for throttling.

Reasoning for this concept:
Pulse jets have a very sensitive internal geometry. If you hinder the cycle of the combustion in any way, you may lose the thrust. It is best to leave the base engine design alone. The engine will have to be able to start under its normal operating parameters. The flash boiler will then begin the compression of air. I believe that there should not be a boost condition until a working model can be produced to show how the engines geometry would have to be modified to accommodate it. I think that an ignition system that continually sparked would have to be in place. The idea is that if the fuel or air were decreased below what was needed to operate the engine the momentum of the turbo would keep the engine going by keeping the flow going. This should mean that it would pop pop at a lower thrust to idle it. There are many variables to consider. As you think about it you will see all of the dynamics that are taking place.

General concept description of a pulse jet steam system:
The boiler would be a flash type boiler. It would consist of a water feed pump/ accumulator/ pressure relief valve that would pump in a known amount of water to flash into steam. The flash boiler is somewhat independent of the temperature needed because a given amount of water is injected to flash to steam. The pressure may vary given the temperature, but that may correlate to the speed of the engine. I have a design idea that will accomplish this in mind. The water would enter the boiler and flash into steam. This steam would drive a small dual entry redirecting impulse turbine which is located on the back side of the compressor. This would drive the compressor. The exhaust from the turbine would be slightly condensed and evacuated into the jets thrust.

What’s you opinions?
Troy R. Legner

[Mike Everman]

did you get the Reynst book? His combustors are all about making steam, and not so much about thrust. First impressions are the tankage of water on top of the combustor fuel you'd have to haul around, but let's just say this is on a fresh water speed boat! ;-P
I like the idea, steam turbines would be very interesting to some of the folks around here, like Bill Hinote. He could talk knowledgeably about the efficiency of such a thing...

[Troy R. Legner]

Gentlemen,
My thinking of a flash boiler is due to the amount of heat produced and the volume of steam that can be produced. I believe that a standard boiler design would boil too fast resulting in the loss of steam through the relief valve. The flash boiler also offers an advantage of size. It would take less space and added weight than a conventional boiler.
The pressure fluctuations of my design are utilized to operate the feed pump.
My immediate questions to the forum are the volume of water to inject per boiling cycle. This is a little tricky given that I do not know the actual efficiency of the boiler. I do am also not sure of the flow rate of the nozzles. At this point in the early stages of development I would guess at an operating pressure of 150 to 200 psi. This is due to being able to test the turbine on compressed air.
I am reasonably sure that the temperature of my engine alone is around 1200 degrees F. It takes it a few seconds to get to that temp. I can over design the boiler to maximize the temperature produced for calculating purposes. This should insure good use of the 1200 degrees. It should also require less water to produce the desired volume of steam at 200 psi. The feed water valve design I have in mind also acts as an accumulator. The volume of the accumulator is also dependent of the steam production.

This is not a real complicated concept. The turbine is of a design we called a Terry turbine in the US Navy. I have seen this design used on a small scale. It worked quite well and machining it is not very difficult. I built one 15 years ago.
The turbo installed on a pulse jet is much more feasible than the complexity of a turbojet engine design. The nozzles can be throttled to accommodate the air flow desired. Over design it and under drive it.
The engine classification still remains a pulse jet engine.

Thank you,
Troy R. Legner

[Mike Kirney]

I think a closed-cycle flash boiler would work great in this application. Assuming that this machine will be used in a rapidly moving vehicle, you could use airflow to cool your outlet steam duct for increased power across the turbine. I can't see why your idea would not work Troy, but you would have to build your pulsating duct out of thicker metal and you would probably burn an outrageous amount of fuel very quickly. Your valves might have to be quite thick (too thick to flap?) to hold back the added boost pressure between pulses, although maybe you could put a wastegate between the turbo and the valves to relieve this.

[Troy R. Legner]

I would probably not want to go with much boost. I would rather go after the throttlability aspect. I will cover my thoughts on boost later today.
The exhaust from the turbine would be routed along a tube to the tail where it would be fed into a special made venturi. This would pull a vacuum on it. This would increase the differential in pressure to improve performance of the turbine. This type of turbine acts off of pressure. I thought about a radial flow reaction type turbine design. They are not referred to with much popularity. I do not think a correct blade geometry can be achieved to utilize the steam expansion through it. The blade geometry falls in place with this design. I believe I could get more power out of a radial flow turbine because It could use more steam flow. I am guessing at using a bucket turbine. I know more hands on knowledge about this type.
Troy Legner

[Viv]

Hi Troy good to talk to you again, I remember you have been nocking this idea back and forth for a while now, it sounds like you are getting nearer giving it a try.

I have been lost too the pressure jet forum for a while so have been doing some side ways research on these engines, my question is what type of nozzle would your turbine use? a simple sonic nozzle or would a supersonic nozzle be better.

Viv

[Troy R. Legner]

I haven't thought about the nozzle in that much detail. It is really a small drilled hole that is in a shoe with corresponding bucket blades. The size will probably be somewhere in the size range of .020"
The steam enters on one side of the bucket and is redirected 180 degrees where it enters a fixed set of buckets that redirect it back to the turbines blades. It does this cycle 6 times.

I have thought about this idea for a few years. It's becoming clearer as I go along. I am posting it now because It is now a much more compact design that has a better potential in my mind. I read last year about small RC planes that ran on steam engines using flash boilers. I have tried to email them, but did not get a response.
Troy Legner

[hinote]

I haven't thought about the nozzle in that much detail. It is really a small drilled hole that is in a shoe with corresponding bucket blades. The size will probably be somewhere in the size range of .020"
The steam enters on one side of the bucket and is redirected 180 degrees where it enters a fixed set of buckets that redirect it back to the turbines blades. It does this cycle 6 times.

Troy Legner

Hi Troy:

Maybe you ought to look at the nozzle issue some more--I think it's important (although maybe less so in a multi-stage turbine).

Also look at compounding before your final decision.

I'm not much of a turbine guy in re: steam so these are just suggestions.

Billl H.

[Troy R. Legner]

What would you recommend for the nozzles? The bucket turbine is not usually compounded. These types of turbines are always a single wheel. They are used on pumps and air blowers. I would like to do some tests using compressed air to figure out the nozzle diameter.
The radial flow design I thought about can be compounded. I put a little thought into a axial flow compounded design. The blades are much more involved to machine. I have tooling that I can produce it on a manual milling machine, but it is a time consuming job.
I think that if I were looking at large boost conditions, I would consider the impulse/reaction type designs. They are a little more complex in design with the expansion of steam throughout the blades. I am trying to keep it as simple as possible. I will look into adding nozzles to the Terry turbine before going to a axial or radial reaction type design.
Troy L.

[Troy R. Legner]

I will consider designing the turbine to be compounded. The axial and radial designs are staged.
I incorrectly worded that in my last posting.
You have made me think about the low pressures I would want to run on.

I will strongly look into stacking turbine wheels to recover my torque lost due to lower pressure. I am thinking of making the turbines out of bronze. This would never function in a high pressure system, but might work well in this application. This will make machining them easy. This is just a prototype design to prove a theory.
If any of you see problems with this reasoning please fell free to tell me. I have a lot of respect the wisdom found here.

Troy L.

[Al Belli]

A simple to machine turbine wheel can be made by ballmill drilling a series of angled holes from both sides of a disk.
The nozzles can be finished to size by using diemakers tapered pin reamers, which also gives a nicely tapered inlet to the nozzle outlet.
The turbines can be staged, but the nozzles in each following stage must be larger to compensate for the pressure loss in the preceeding turbine.

Al Belli

[Troy R. Legner]

Thank you for your idea.
What I had in mind will involve a narrow woodruff key cutter that is say 1/4" in diameter and 1/32" thick. This will cut scalloped pockets, tangent to the wheel. The steam will be directed tangential to the wheel. For example, there will be about 95 blades on a 1 7/8" dia. wheel. The nozzles would be in shoes that have 6 matching scallop’s. When the steam enters the turbine it enters the wheel then is redirected back into the shoe which redirects it once again back to the turbine. It repeats this 6 times to maximize the steams flow. The turbine would almost resemble a worm wheel gear. I will try and take a picture of a turbine I made years ago.
Troy L.

[marksteamnz]

Aye, well, hmm.
Small turbines are inefficient unless spun at high speed and with tight clearnaces ie Lear Bus Steam turbine 5" wheel turning 100,000rpm. Usual rule of thumb is less than say 300hp it's better to use a steam engine (pistons). The turbine design and it's horrendous steam consumption at http://www.steamcar.co.uk/ is regarded as a joke on the Steam car bulletin boards.
Monotube boilers can be made to run a constant pressure and temperature but usually need decent control gear, a simple bypass doesn't cut it with out temperature control as the the steam temperature makes a big difference to engine efficency. At 150psi in the small scale you are describing you would be lucky to achieve 5% of overall heat in to power out. That may not be a problem for you but increasing pressure and steam temperature will reduce the plant size and increase cycle efficency but it makes controls more critical.
Any more steam cycle stuff is probably off topic for this forum.

I will consider designing the turbine to be compounded. The axial and radial designs are staged.
I incorrectly worded that in my last posting.
You have made me think about the low pressures I would want to run on.

I will strongly look into stacking turbine wheels to recover my torque lost due to lower pressure. I am thinking of making the turbines out of bronze. This would never function in a high pressure system, but might work well in this application. This will make machining them easy. This is just a prototype design to prove a theory.
If any of you see problems with this reasoning please fell free to tell me. I have a lot of respect the wisdom found here.

Troy L.

[Troy R. Legner]

I knew that those types of turbines are inefficient. I did not realize that bad. All I can hope for is that the massive heat produced can feed it. I might consider building the turbine and testing it to see what It will do. The axial flow is too much for my brain to efficiently design aside from making it look like a large machine. There is a turbine called a "quaisie turbine"? or something like that. I am going to look into its design.
Thanks for that info. bad news is better than no news. I started thinking about compounding turbines the more I thought about it. Directly driven to the compressor brings the rpm's down.
Any suggestions of a better turbine type you have would be considered.

Troy L.

[marksteamnz]

Troy I'm no turbine expert particularilly in small sizes. You could look at Reliable Steam's web site http://www.pioneer.net/~carlich/ for ideas but first I'd really recomend trying to get hold of a copy of Experimental Flash Steam by J H Benson & A A Rayman.
Lots on model steam powered hydro planes = over 80mph on teather plus some turbine ideas.
I'd have to say having messed with monotubes and high performance steam plants for over 25 years I believe it to be more difficult to get information on and to build a satifactory light efficient steam powerplant than any PJ. As well there is also a lot more gunna's* in the light high efficency end of the steam world than there is in the PJ world (Sssscary thought!) so you have to be carefull about what info you collect. Me? I gunna build a steam outboard and gunna get the steam gocart going properly!!

*(gunna = going to. origin Australia as in "I gunna do it one day")