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Hi Guys , Nice forum!

I have in mind the construction of a Motorjet based on a kj-66 compressor(KKK). The compressor would be driven by a brushless motor capable of running between 50,000 and 70,000 RPM at 22.2v.
This concept would be possible?

A KJ66 turbine reaches 120.000rpm at its fullest potential and your idle is at 30,000 rpm; 60,000 rpm therefore imagine that would not suffice, why not install two motors / compressors side by side...?

My question is whether the result of this motorjet without rear disc-turbine, but with the same rpm this would be at least similar to that of a turbine... Or the dinamics of the gases expansion changes completely ?

Regards,

Daniel

you will be surprised how many hp's you need to drive the compressor...

Fedde

So you're telling me that it is not feasible?

dfidalgo wrote:So you're telling me that it is not feasible?

Check out this link:

http://www.youtube.com/watch?v=6DNOk5hXD60

Probably not quite the same as your concept since only the temperature is raised, not the pressure.

OTOH it looks to work very well!

Bill

hinote wrote:Check out this link:

http://www.youtube.com/watch?v=6DNOk5hXD60

Probably not quite the same as your concept since only the temperature is raised, not the pressure.

I already knew, only one EDF with afterburner... But this only serves to attach a cool visual, nothing more
What I seek is a real turbine, but simpler with fewer moving parts (=Motorjet) , even if the performance is not the best.

Hi

The EDF in the video will be producing a total pressure rise across its axial compressor ( fan) stage , not as high a total pressure rise as you would get with a centrifical comp (KJ66), but thrust output has a square root component of pressure , so more horsepower required per pound of thrust , but less fuel per pound than a lower pressure ratio EDF .

The only difference between what you want to build and the EDF unit is the centrif comp vs an axial comp , a centrif comp will flow less air but will have a higher pressure for the same horsepower electric motor .

Assuming the centrif comp produces a 1.3 PR and a~ 30 deg C air temp rise at you 60,000 rpm you'll be needing maybe 7 Kw of power from your electric motor .

I wouldn't consider using a centrifical comp for this engineering exercise , its the wrong sort of compressor wheel , an axial wheel is "better" for low pressure applications with limited power supply .

Cheers
John

Thanks John, this was precisely the information I needed to know. 7kw is a lot of power, so the project is dead at birth.
One last question: With a edf running at about 70,000 rpm will I get any power gain? Or is it just a fuel burner?
With the Edf I'll need some special combustion chamber or a flame holder?

Regards,

Daniel

Hi Daniel

An "afterburning" EDF will be a fuel burner , but there will be a thrust gain , you'll have to be careful about "thermal choking" because of the very low pressure ratio , the very fact that the temp will rise during combustion requires a static pressure drop as the air/gases expand and accelerate out of the combustor .a classic example of thermal choking is Mark Nyes Thermojet from Junkyard Wars http://www.gas-turbines.com/thermojet/index.html , you may find that to get full combustion of all oxygen that you'll need a cone shaped combustor with a large outlet .

You need to think of this exercise as fitting an afterburner to a standard gas turbine engine , you need to measure the total pressure (pitot tube) downstream from the EDF fan in its original jetpipe and with its original jet nozzle in place , once you have this total pressure reading along with the thrust produced you can then calculate the required sizes of afterburner and its nozzle, the EDF should be allowed to produce the same total pressure with the afterburner as without it to get optimum thrust results.

The thrust gain will be equivalent to the change in the square roots of the absolute temps , eg sq rt 288 K =17 , sq root 1500 K 39 , so a 2.3 times increase in thrust possible for a temp rise of ~1200 deg C

You could build a "dump style" afterburner , checkout Yahoo DIY Gas Turbines Group > Files for more details , this doesn't require any special flameholders , the "dump" step produces the necessary "flameholder"

Cheers
John

John,

I have to thank you again for giving me valuable information. Now I see that things are not as easy as they seem ... I liked the idea of aftertburner dump, it seems a good starting point. For now I registered in yahoo groups and I am awaiting confirmation from the moderator.


Best Regards,

Daniel

Hi Daniel

See you over there

Cheers
John