A pressurized environment for the PJ

[ace_fedde]

Now first come on with those 4 atm. PJ designs!!

Anybody?

So could we take two pressurized tanks, one enclosing the inlet side and the other enclosing the tailpipe side?
Nop, the inlet also spews out exhaust gasses and the tailpipe also needs fresh air…
So now what
I think I already have an idea…

Would this work?

Mind that I only took a lockwood for the simplicity of the drawing.
Fedde

[metiz]

how do you intend to maintain the pressure in those tanks?

[ace_fedde]

Metiz,

Remember where this thread was coming from?

To be continued....
In the meanwhile, people, post all your 4 atm designs here

Fedde

[ace_fedde]

O.k. can’t keep it to myself any longer. Here’s the idea.
Note: If this is a new idea it is an invention of Fedde C. Bleijs, The Netherlands, don’t you walk away with it! (I’m not talking to anyone particular)

As you see the pressure doesn’t cause flow in the PJ, if it did the PJ wouldn’t work (might work with little flow, ok).

At starting (with auxiliary power), the turbine vanes or nozzle are nearly “closed” while the compressor is pumping (to much) air in the system causing the pressurized environment. Excess air is redirected to the compressor inlet (or better to the turbine, after the nozzle, to reduce losses?)

When the PJ ignites and sustains a bigger flow towards the “hot tank” will be produced, trying to raise the pressure there.
The “nozzle” will open to maintain the desired pressure and the turbine will deliver sufficient power to the compressor to sustain. Left is torque or jet power.

Now remember the old fashioned turbojets. They had the multiple combustion chambers between the compressor and the turbine.
Now replace these CC’s with the pressurized PJ’s, will there be any advantage?
Keep in mind that in a turbo jet the whole of the combustion pressure is produced by the compressor. The combustion itself only produces flow.
If we use a PJ (o.k PC, pulse combuster), the PJ will be the last stage in compression. So the turbojet’s compressor can now be a bit lighter while we still end up with the same combustion pressure and flow. In fact flow might be a bit lower due to the intermittant combustion, but that is again partly compensated by the augmentors.

Am I far off? Possible, I just started messing with PJ’s and I’m completely not a turbine man. So please let me know what you think and/or where the flaws are.
And even if there’s no efficiency, it’s still a fun project to (try to) build!!

Fedde

[metiz]

Fedde

Dit ziet er heel interessant uit maar ik begrijp er geen reet van kun je een pm sturen in het nederlands die het op een andere manier uitlegt? gebruik ingekleurde plaatjes svp

[ace_fedde]

I didn't realize but I just designed pressure gain combustion:

http://74.125.77.132/search?q=cache:IC3 ... clnk&gl=nl

Ha!

Fedde

[ace_fedde]

Here is the same document with images.

Why make problems abou valves Use valveless
Time to call NASA? Larry, do you have the phone number for me please?
Fedde

[racketmotorman]

Hi Fedde

The average PJ already operates in a "pressurised environment" , you have to think in absolute terms .

A PJ designed for operation at ~34,000 ft ( atmospheric pressure ~3.6 psia ) , when operated at sea level at 14.7 psia would be in a 4:1 pressure ratio environment .

As for having a gas turbine supplying the "compressed air" , its possible , but the PJ would only be replacing the normal combustor in supplying heat input .

You'd probably need to have the gas turbine running first , then slowly reduce the normal fuel flow as the fuel to the PJ was introduced so as to maintain maximum turbine inlet temperatures ( TIT) .

Trying to change over from normal flametube combustion to PJ combustion would be a nightmare , any drop in TIT would see a reduction in pressure ratio/rpm and mass flow , and conversely any increase in TIT an increase in pressure ratio/rpm and mass flow if the the turbine stage was able to swallow the extra flow .

Using a valveless PJ would only be complicating matters I feel , thats why I used a valved engine to run my Turbo Prop PJ experiment .

If the running PJ contributed some extra "total pressure" downstream of itself and before the turbine stage , this would cause rotor acceleration , so trying to keep rpm at below maximum rpm ( N1 100%) whilst still trying to maintain a high pressure ratio from the compressor would be rather difficult.

Summary , running a PJ in a pressurised environment should be possible , having a gas turbine supplying that environment ,.... problematic , and one has to ask ...... for what ?? maybe a slight increase in potential thrust output from the gas turbine engine , but with a huge amount of complication, internal frictional air/gas losses, increased weight and frontal "envelope" .................not worth all the trouble (

PJs are PJs , gas turbines are gas turbines , combining the two .....................interesting in theory .............but in the real world , not practical ...............just my personal opinion .................LOL.....I'd be happy to see someone shoot it to pieces though , I tried... I failed )

Cheers
John

Cheers
John

[ace_fedde]

John,

I'll answer you but first let me show what I found the last hour or so:

http://books.google.nl/books?id=Ksn4Z1_ ... t&resnum=7
Go down to figure 14.5

NASA TM-2005-213854[1].pdf

(1.58 MiB) Downloaded 491 times

42810[1].pdf

(896.81 KiB) Downloaded 462 times

Rob Miller AIAA-2009-1063[1].pdf

(931.47 KiB) Downloaded 494 times

Fedde

[ace_fedde]

John,

Thanks for your reaction by PM and now in the thread. I already knew your PJ-prop project and I read your contributions to Luc's "pressure gain now proven" thread.
Then I didn't know what pressure gain combustion meant though
Now I know! Appearantly I designed it with this project!
But also I don't know much about turbines . I understand though everything you wrote, I’ll have to let your information work in the back of my head to find out what it means for my project and how problems can be avoided.

As said I don’t know much about turbines. You do!
That's why I would like to ask you the following more practical: Regarding to (modified?) turbo charchers, is it possible to use variable guiding vanes as a nozzle, so that (high) pressure is maintained in a system (my system, or an exhaust)?
Is there anyway (apart from the rpm)to control the centrifugal compressor, so that flow and pressure can be controlled?
What max pressures can be (efficiently) produced with a turbocharcher's compressor?

Thanks! Fedde

[racketmotorman]

Hi Fedde

I'll try to answer these .....

.......Regarding to (modified?) turbo charchers, is it possible to use variable guiding vanes as a nozzle, so that (high) pressure is maintained in a system (my system, or an exhaust)?

Variable nozzles in a turbo would allow you to "tune" the turbine stage more easily than fixed A/R scrolls , closing the vanes to create smaller throat areas will increase gas velocities and generally increase rpm and pressures from the compressor

..............Is there anyway (apart from the rpm)to control the centrifugal compressor, so that flow and pressure can be controlled?

The turbine stage flow areas do a good job of controlling compressor flow , there has to be a matching of flows for the engine to perform well .
Compressor rpm/tip speed controls pressures to a large degree , whilst the turbine stage areas control flow, compressors can only flow efficiently over a limited range at high pressures , at mid range ~2:1 PR the range can be wide , but it narrows at high rpm/pressures , just the nature of the beast .

It is possible to have variable compressor inlet vanes to aid in "part load" control of flows , but more complication .


...........What max pressures can be (efficiently) produced with a turbocharcher's compressor?

This varies with compressor design and Trim numbers , generally low Trim numbers give higher pressures without inlet choking problems , a low Trim comp of <50Trim will produce better results than a 60 Trim wheel , but generally speaking, a Pressure Ratio ( PR) of ~3.5:1 is about the point where efficiencies start to drop off badly and would be considered about the max pressure ratio one would use for a gas turbine build even though the compressor map might go to >4:1 , theres very few turbos that will efficiently compress air at 4:1 , though I use 4:1 on my bikes TV84 comp but at only ~69% efficiency , ideally you need >70% effic , and with a low Trim wheel efficiencies of ~74 -75% at 3.5:1 PRs are achievable on large flow wheels .

Compressors with highly swept back exducer blading will give best efficiencies but at reduced pressures for a given rpm/tip speed .......its a trade off .

A number of the RC micro turbine engines now run to a 3.8:1 PR , but efficiencies will be starting to drop off by this point , affecting SFC .

Cheers
John

[Mike Everman]

some nice bits here:

[Viv]

Hi Fedde, hi John

Fedde, forgive me but you seem to be worrying about what types of pulse jet to use in your idea and to be more specific the mechanics of your idea rather than starting out with the basics of your idea! how do you think it works is my first question, the research you have done is good and commendable, from a quick read I noticed that a lot of your questions are answered by that research, first amongst those in the first paper you found is what is pressure gain combustion.

Viv

[Viv]

some nice bits here:

Hi Mike

Yep the NRL paper is probably the best explanation out there and closest to his idea, I was going to give him that last though

Viv

[ace_fedde]

Viv,

Hi Fedde, hi John
.... how do you think it works is my first question, ....
Viv

I wrote that down in dutch for Metiz in the meanwhile (might be dubble dutch to you ). I'll translate it, and adapt it a littlebit that also newbies (like me, ha) would understand, and post it.

But you have to be patient. I'm a bit busy now with packing for a trip to the Balkans. But don't you worry, I'll be online there as well.

Mike,
Great stuff, really helps me! Thanks

Fedde