## A few questions about a/f ratios and injection/ignition

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unclematt
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### Re: A few questions about a/f ratios and injection/ignition

Eureka!

I found a study done on a rotor very similar my idea except for the hub mounted impeller/combustor. It is here:

This is experimentation done on a 6.6 foot rotor, with cold cycle, and blown blade trailing edges and tip-jet nozzles. I read the whole thing, but here are some of their conclusions:

"Fundamental parameters were identified that determine the performance
of a fully pneumatic rotor system. Due to the combined characteristics of
pneumatic lift augmentation by circulation control and pneumatic reaction-drive,
the rotor lift is the same constant, essentially linear, function of blade pressure
regardless of rotational speed. This relationship results in lift equaling five times
the tip nozzle static thrust and is valid over the full range of operating conditions."

This is the same number I guestimated earlier. So if your static net nozzle thrust is 100 pounds, the lift generated by the rotor will be around 500 pounds. This is the kind of verification I was looking for on that question.

"The rotor rotational speed displays a self-limiting behavior. The
onset of the limiting speed condition is related to the optimum aerodynamic I efficiency condition of the rotor."

I encourage anyone following this thread to read this study. It is fascinating, and tells you a lot about tip-jet research in the 90's.

John: I will work on the pressure problem. I am looking at a wave rotor idea, as I have been studying them for over 5 years.

With regard to how combustion will react to a spinning flame tube, I offer the following thoughts: In my concept the flame tube is around the hub at a small radius, so centrifugal effects would be minimized. I have read studies done on jet turbines run on the tips of helo blades, and they discovered only 15% deflection out there due to centrifugal effects on the fuel being injected into the flame tube. My design has the burner almost at the center of the prop, so it should have little to no effect on the combustion process. And the pumping action within the blades will cause the flame tube to see a lower pressure at the exits into the blades than if it were exiting onto a turbine wheel. And I am fine with very lean fuel to air ratios as all I want from the hub is a lot of presurized air at high mass/flow rates.

However, I did want to ask about something: If the impellor feeds the flame tube, it never sees the combustion temps you mention, does it? And the combustion exiting the flame tube is entering the blades, whch could be coated with a ceramic coating to protect the metal, ar you could arrange air to blow down the walls of the inside of the blade duct (cooling the temps near the surfaces near the blade root). Given this, why would you be limited to a fuel to air ratios of 50:1?

racketmotorman
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### Re: A few questions about a/f ratios and injection/ignition

Hi

I started reading the report and theres too much difference between what you propose and this study to make it applicable .

Firstly they used cold air , .................where is your working fluid coming from ??

How is your working fluid compressed ??

Where is the horsepower for compression coming from ??

There's something I'm missing here ..............nearly 20 years of playing with turbines is telling me somethings wrong .

The air from the compressor passes to the flame tube where temps of >2,000 deg C are reached in the primary zone of the FT where air fuel ratios are "correct" at ~15 :1 , the metal temps at the primary end can be severe with nickel based alloys required , as the combustion gases pass down the flametube the dilution air cools the gases to an acceptable level for the turbine wheel to survive, ie 900deg C if an Inco turb wheel , with ~50:1 A/F ratio . .

There appears to be an enormous amount that you don't understand about turbines , hopefully those couple of books I recommended will help you to understand the massive task in front of you .

Cheers
John

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

racketmotorman wrote:Hi

I started reading the report and theres too much difference between what you propose and this study to make it applicable .

Firstly they used cold air , .................where is your working fluid coming from ??

How is your working fluid compressed ??

Where is the horsepower for compression coming from ??

There's something I'm missing here ..............nearly 20 years of playing with turbines is telling me somethings wrong .

The air from the compressor passes to the flame tube where temps of >2,000 deg C are reached in the primary zone of the FT where air fuel ratios are "correct" at ~15 :1 , the metal temps at the primary end can be severe with nickel based alloys required , as the combustion gases pass down the flametube the dilution air cools the gases to an acceptable level for the turbine wheel to survive, ie 900deg C if an Inco turb wheel , with ~50:1 A/F ratio . .

There appears to be an enormous amount that you don't understand about turbines , hopefully those couple of books I recommended will help you to understand the massive task in front of you .

Cheers
John
John, I think perhaps you have misunderstood my design. The combustion exhaust is not used to turn a turbine AT ALL, only drive the reaction nozzles/jets at the blade tips. The only turbine present is the impeller that is used to compress the air for combustion in the hub. As I stated earlier, that impeller is turned by the torque generated by the jet-tip nozzles through mechanical means (which I also described earlier). So there is no concern about diluting the gases so the turbine wheel can survive because there is no such turbine in my concept. The only concern about materials being effected by hot gases is in the blades and nozzles themselves, which can be coated with protective ceramic thermal coatings to address that concern.

racketmotorman
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### Re: A few questions about a/f ratios and injection/ignition

Hi

OK , no turbine wheel to extract power to spin the comp .........................it won't work !!

Cheers
John

racketmotorman
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### Re: A few questions about a/f ratios and injection/ignition

Hi

Heres some concrete numbers that'll help .

The Garrett TV84 turbo I used for my bike build http://www.racketmotorman.turbinebuilde ... hp?album=3 produced a 4:1 PR at excessive rpm , by running at excessive temperatures ( TITs) it produced 110 lbs of thrust from a mass flow of 1.8 lbs/sec at ~1800 ft/sec when using a 78mm dia jet nozzle with efflux temps of ~700 deg C , TOTs were ~800-850 C .

Assuming that jet nozzle was at the end of a 6 foot prop ( 3 foot arm ) , that would give 330 ft lbs of torque , assuming ~2600 rpm , now hp = torque X rpm divided by 5252 = 163 hp .......................BUT wait .... we have to take into account the jetnozzle velocity as it spins around to get a net figure for thrust , at 2600 rpm the jet nozzle will be travelling ~816 ft/sec , we need to subtract our 816 from the 1800 , lets say 1,000 ft/sec is the net velocity , thrust is now only ~60 lbs and torque 180 ft lbs, horsepower is reduced to ~90 hp ....................the bike has been dyno'ed at 115 rear wheel horsepower .

With a mass flow of 1.8 lbs/sec - 108 lbs/min and a high >900 C TIT lets assume an overall 50:1 A/F ratio , so ~2 lbs of fuel /min or 120 lbs /hour , that works out at a bit over 1 lb of fuel per horsepower per hour , about right for a lowish compression turbine engine

If this engine had used the prop tip efflux method rather than a freepower turbine , it would have been producing 90 hp rather than 115 hp for the fuel burn rate , so SFC would have been worse by nearly 30% .

Forget your project , .............it might spin around but its not a commercial proposition

Cheers
John

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

Hey John,
I appreciate all of your comments as they give me areas to focus on when searching for solutions. I am a little concerned with comparing the jets you are used to working with to what I am suggesting, as they are 2 different animals. I have been considering your last post, and after reading through many experimental and theoretical studies on the matter, I now realize the prop/fan itself is the 2nd turbine in the engine, though it takes a diffrent form than what you have worked with.

I acknowledge there are some challenges, but after taking a look at ejector nozzle technologies utilizing entraining shrouds, I think this may still be viable. I have seen studies estimating thrust augmentation using this method as high as 1.8, as well as noise reduction. I am also exploring other ways to increase power and efficiency, and will post more as I flesh them out, so you can shoot them down.

racketmotorman
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### Re: A few questions about a/f ratios and injection/ignition

Hi

LOL......Its not going to be too hard to shoot holes ....................the concept is flawed because of basic thermodynamics and energy transfer inefficiencies .

Have you considered the need for a variable pitch prop in your system ??? .....................you'll need one, otherwise your starting power requirements will be enormous , ..................the Garrett TPE331 turboprop engine is a direct drive single shaft turbine engine that requires ~50% rpm just to idle , that ~20,000 rpm on the turbine rotor and 50% of prop max rpm .

You're correct in assuming your prop will be the "turbine" but its a very inefficient "half stage turbine" thats running very high efflux velocities which is a no no if you are wanting decent fuel efficiencies , what you envisage is something like the old pure jet engines when compared to modern high bypass fan engines .

Once you have a pressure ratio of 1.89:1 across your nozzles they choke and will require a CD nozzle , with all its complications, for further expansion .

If you only wish to run a 1.89 PR your SFC will be low because of the low expansion ratio , theres simply no way around the maths, you can try , but they'll beat you in the end

There has been multi millions of dollars spent on aircraft propulsion systems , if there was a better way , it would already have been done .

Cheers
John

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

I found a method to capture energy from the combustion stream, while still only using a single turbine wheel, that I can incorporate into my concept. Take a look at patent #6807802 for an idea of what I am talking about. It also makes it possible to use higher fuel to air ratios without worry of melting things down, or using a lot of bypass air for cooling purposes, and increases efficiency even further by transfering heat from the exhaust stream to the incoming air.

And yes, of course I know I will need a mechanism to adjust blade pitch.

racketmotorman
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### Re: A few questions about a/f ratios and injection/ignition

Hi

Its just another unworkable system ...................theres "millions" of them out there in the Patents Office .

My last posting on this subject , all the best with your project

Cheers
John

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

For those who would like more info on this advanced turbine impeller that I want to employ in my concept:

http://www.p2pays.org/ref/20/19269.pdf

I couldn't find any recent info about this, so it may be as John said it was. Still, if it works it would allow me to do away with the mechanical coupling between the rotor and the impeller, and create more power and efficiency while making my device simpler with fewer moving parts. The guys that came up with it are working at Los Alamos, and won several awards for this idea, so I will try to contact them tomorrow and see what is up.

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

I have been doing more research, and have come across quite a bit of material about air entraining nozzles which could be employed in this concept. You can read one such piece here:

http://etd.gatech.edu/theses/available/ ... 08-164716/

If a single rotor could contain both compressor and turbine, and perform with good levels of efficiency, I still think it is possible to pull this off. That rotor would sit in the hub, surrounded by the annular combustion chamber. The blades, of which there would be between 4 and 8, would each have a "tip-jet" . Please don't think that "tip-jet" only refers to a combustion unit at the end of the blades. The tip-jets I refer to are simply air-entraining nozzles which discharge the high temperature, high flow combustion gases generated in the hub.

At least one company is trying to use tip-jets in the development of a VTOL rotor, but high sound levels remain yet to be overcome. As a part of my concept, I knew from the begining that some way would have to be found to overcome this problem. Hypermixing nozzles have been shown to have some effect, as well as ducts and shrouds. For more on the hypermixing nozzles, look here:

http://ntrs.nasa.gov/archive/nasa/casi. ... 001877.pdf

I am also considering a shroud that could not only contain and reduce some of the side noise, but also redirect the exhaust from the tip-jets to align with the main rotor thrust flow. I am hopeful this will augment the thrust from the tip-jets to the rotor torque, as well as directly to the main thrust, at least as much as the shroud weighs. And hopefully to the extent it will augment static thrust in general. To avoid tip clearance issues, I am hoping to bury the rotating blade tips in an annular passage in the shroud, with stator fins inside that the jet exhaust could act against, as well as redirect the exhaust flow as previously mentioned.

As far as I know, all of this has never been put together in a single device. Perhaps for good reason. lol

more later
Last edited by unclematt on Mon May 10, 2010 1:12 am, edited 1 time in total.

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

By the way, does anyone know of David Platts? He once worked for LANL, but his email has changed so I was unable to find out about his invention, the single rotor turbine. If anyone know his contact info, please let me know. thanks!

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

unclematt wrote:By the way, does anyone know of David Platts? He once worked for LANL, but his email has changed so I was unable to find out about his invention, the single rotor turbine. If anyone know his contact info, please let me know. thanks!
I was able to contact him today

unclematt
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### Re: A few questions about a/f ratios and injection/ignition

http://defense-update.com/20111114_unma ... -2012.html

Here is a system that performs almost as I described earlier in this thread, using a gas turbine to generate high velocity air to tip-jets on blade ends. My concept uses the single rotor turbine design gas generator, while this system uses a more conventional gas turbine. But the general concept seems to be feasible...

sockmonkey
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### Re: A few questions about a/f ratios and injection/ignition

unclematt wrote:http://defense-update.com/20111114_unma ... -2012.html

Here is a system that performs almost as I described earlier in this thread, using a gas turbine to generate high velocity air to tip-jets on blade ends. My concept uses the single rotor turbine design gas generator, while this system uses a more conventional gas turbine. But the general concept seems to be feasible...
While producing cyclic control on such a helicopter rotor seems problematic, it seems ideal for turboprop planes since collective wouldn't be hard and it looks especially suited to something like the V-22 Osprey. The current version needs heavy interconnected shafts running the length of the wings to provide redundant power, but mounting both engines in the fuselage and running a pair of tubes for compressed air to the wingtip rotors would weigh a lot less than the gears and shafts as well as moving the jet exhaust to blowing back between the twin tails instead of straight down where it erodes the landing pad a creates a safety hazard to anyone next to the thing.