FJK3 - 88mm DIY Gas turbine

[racket]

yep , gotta have a "soft" joint somewhere

[nersut]

I am considering a a new starting system for the FJK3, I have used vacuum motors with earlier builds.

For this build I am considering to use "direct" drive starter with bendix drive/clutch.
I have this small 0,4kW, 12 volt starter unit from a small 25hp 2-stroke Yamaha outboard engine.




I measured the startes no load speed to about 5700 rpm. powered by my DIY 4S Lithium-ion battery pack (15,76 volts ~ 60 % capacity).
The starter spins to about 8 % rpm. of the FJK3's max speed ~ 71.800 rpm.

Will the starters rpm. be too low for starting up the FJK3?
Maybe more voltage to avoid hung starts?
What is considered to be the minimum rpm. (% of max speed) for a reliable startup?


Cheers
Erik

[racket]

Hi Erik

Too slow :-(

Your idling rpm will be ~30,000 minimum , we can get away with a leafblower only supplying limited rpm initially , but once some fuel is added and rpm increase the leafblower still provides the same starting power unlike an electric motor which will favour its design rpm and power will drop off as rpm go past that point .

Thats a pretty low "no load" rpm , I get nearly 20,000 from my 12 Volt Nippon Denso auto starter armature running on 24 V , but max horsepower is ~10,000 rpm , this graph helps explain it postimg.org/image/72cobvglr/ , you might need a stepup gearbox like I had to make jetandturbineowners.proboards.com/thread/612/fat-boy-118-thrust-engine?page=26

Cheers
John

[nersut]

Aug 6, 2017 0:09:58 GMT -5 racket said:

Hi Erik

Too slow :-(

Your idling rpm will be ~30,000 minimum , we can get away with a leafblower only supplying limited rpm initially , but once some fuel is added and rpm increase the leafblower still provides the same starting power unlike an electric motor which will favour its design rpm and power will drop off as rpm go past that point .

Thats a pretty low "no load" rpm , I get nearly 20,000 from my 12 Volt Nippon Denso auto starter armature running on 24 V , but max horsepower is ~10,000 rpm , this graph helps explain it postimg.org/image/72cobvglr/ , you might need a stepup gearbox like I had to make jetandturbineowners.proboards.com/thread/612/fat-boy-118-thrust-engine?page=26

Cheers
John

Oh' bummer! I will try to find a suitable high rpm. electric motor.

[nersut]

I started to fabricate a tubular frame for the turbine.

The base is semi done, and here is the turbines location. Compact but there should be enough room for the accessories.
When finished it should look like one of those portable generators in shape.



The combustor has a slight downward tilt to the "colder side" for fuel drainage purpose.

I have a similar adjustable air pressure regulator to this in the picture below. I will try to use it to regulate the oil pressure (pressure dump).
It can handle pressure up to 10 bar & able to flow 550 liters of air/min. They should be able to handle oil as they also usually are paired with a oil/moisture separators.




Cheers
Erik

[enginewhisperer]

I have successfully used a car fuel pressure regulator for oil on my old turbine setup.

It was a Malpassi adjustable regulator.

[CH3NO2]

Hi Erik,
I've been researching the subject of starting motors too and came across these high power density electric motors that operate in the 12+V, 30K RPM to 60K max RPM with 2KW - 3KW surge power. If you can fit a Bendix mechanism they may be able to work as a starting motor without gearing.
And they are very small for their power capacity. 

1400 series

1900 series

Hi John,
Do these look feasible to you?

Tony

[racket]

Hi Tony

Yep , some are feasible ............but getting the right controller is even more important .

There are other guys on the Site that know more about electric motors/controllers who will hopefully get you on the right path , my rather pathetic attempts with RC type starter can't instil confidence in anyone :-(

Cheers
John

[nersut]

Tonight I had some time to make the transition piece from the compressor discharge pipe to the combustor, inlet diameter is about 100 mm & flared out. Nice & wide to slow down the air a bit.





I also cut a piece of the compressor pipe to make some space for the flexible joint, the gab is about 10 mm.

Here is a picture of the location for air delivery/distribution without the combustor outer casing.




Cheers
Erik

[racket]

Hi Erik

That looks about right , I think I only had ~6-8 mm gap between comp housing and delivery pipe , we only need to allow for a millimetre or so of relative "movement" between parts which is easily handled by the "rubber" pipe .

One thing to be careful of is security of the flexible pipe to make sure it can't move/creep as a result of repeated heating and cooling of the engine

Cheers
John

[CH3NO2]

Looks great Erik. Lots of work and thought going into it.

[nersut]

Aug 9, 2017 23:48:16 GMT -5 racket said:

Hi Erik

That looks about right , I think I only had ~6-8 mm gap between comp housing and delivery pipe , we only need to allow for a millimetre or so of relative "movement" between parts which is easily handled by the "rubber" pipe .

One thing to be careful of is security of the flexible pipe to make sure it can't move/creep as a result of repeated heating and cooling of the engine

Cheers
John

Hi John

Thank you for the tip, I will try to make something to keep the flex hose in place.

Cheers
Erik

[nersut]

Aug 10, 2017 7:04:59 GMT -5 CH3NO2 said:

Looks great Erik. Lots of work and thought going into it.

Hi Tony

Thanks, but I think it's more like "watch/read & learn" from the pro's in this forum & lots of questions to them

Cheers
Erik

[nersut]

Hi again

Another question, hole size & numbers:
The diameter of the combustor liner is about 170 mm.

I have already used about 10 % of the inducer area on the top dome.
So I still need about 23 % for the primary zone.

Does these numbers look okey?

• Primary zone (rest of the 23 %)
•     15 mm x 8 holes or
•     12 mm x 12 holes
• Secondary zone (33 %), 18 mm x 8 holes
• Tertiary zone (33 %), 23 mm x 5 holes

And a couple of rows of small holes for film cooling.


Cheers
Erik

[nersut]

I eyeballed & decided to use this following hole arrangement:

Primary zone (dome): counter-rotation swirlers
Primary zone: 12 mm x 12 & additionally 2 mm x 12 in between.
Secondary zone: 18 mm x 8 & additionally 2 mm x 8 in between.
Film cooling: 2 mm x 24
Tertiery zone 20 mm x 5 (I will bore the holes to 23 mm, need bigger drill bit).
Film cooling: 2 mm x 24







Hopefully the fuel will burn in a controlled way, fingers crossed

Cheers
Erik