"Fat Boy" 12/118 thrust engine

[racket]

Hi Ron

From my Cohen and Rogers readings so far , the mass flow need not be impacted , but pressure ratio is, due to reduction in overall rate of change of angular momentum, but thats easily fixed because I have plenty of rpm in reserve .

Cheers
John

[racket]

Hi Ron

Just completed some starter testing with freshly charged batteries ...........

started with "old pipe" installed with 70 psi oil pressure, max rpm 11,600 within ~7 seconds then a slow drop off of rpm to 10 secs cutoff.

Removed old pipe and tested with no pipe at all , max rpm 10,700 in similar time and with similar decay .

Fitted "new pipe" and obtained 10,800 rpm in similar times and decay.

Just to make sure it wasn't batteries fading I refitted "old pipe" and rpm back up to 11,400 , similar times and decay .

Starter motor getting too hot too hold after ~50 seconds of running from the several tests , fitted leather glove for one more try and rpm down to less than 10,000 , time to recharge batteries.

Conclusion...........the "old pipe" with its exducer shroud produces more turbine energy than the "new pipe", not a lot , but maybe just sufficient to allow the engine to get "over the hump" during a spoolup.

Gotta love R and D :-)

Cheers
John

[enginewhisperer]

That really must be a bit borderline!

[racket]

LOL..........yep , she's a borderline proposition that'll need coaxing gently to perform at its potential

[turboron]

John, love your "Gotta love R and D :-)" statement. R & D seems to be very addictive. The joy of accomplishment versus the agony of defeat. We have gas turbines and the women have babies.

Thanks, Ron

[racket]

Hi Ron

Heres an interesting Paper I found about IGVs on a turbo comp isromac-isimet.univ-lille1.fr/upload_dir/finalpaper/168.finalpaper.pdf ...........its encouraging :-)

Cheers
John

[turboron]

John, I am still struggling with the logic for use of an IGV to improve your starting performance. If you reduce the compressor pressure ratio the expansion ratio of the turbine in also less which says that there is no gain even if the mass flow is the same. What am I missing?

Thanks, Ron

[racket]

Hi Ron

What I'm aiming for is a reduction in energy input per rev of the compressor , this will then require more revs of the turbine wheel ( and comp) to achieve the same outcomes from the comp as before

Now a turbine wheels horsepower is simply, gas deflection times BLADE SPEED , if the turb blade speed component has risen therefore it has more horsepower despite the compressor wheel only producing the same compression as before and hence the same horsepower requirement .

I'm effectively changing the "gear ratio" between comp and turb from a 1:1, to a 1 :1.1 , its the same as dropping back a gear in your car when its struggling to go up a hill , more revs of the engine ( turb wheel) makes life easier .

With this big comp wheel I'm only designing for ~60,000 rpm at 100% N1 , but I'll have to maybe go to 66,000 rpm to regain the same output from the comp as before , that 10% increase in turb blade speed has to mean its capable of turning out more power , even if its only 5% , it'll help with the marginal situation I'm finding myself in with this engine .

LOL..........clear as mud :-)

Cheers
John

[turboron]

John, I bow to the master. I think your logic is sound based on my limited understand of turbine aero. I just need to get to your level of understanding on gas speed versus blade speed etc. All the real aerodynamics gurus talk about turning as a performance parameter. You are showing me what they are talking about.

Thanks, Ron

[racket]

Hi Ron

LOL............another way of looking at it is , its similar to the power required to spin a purely radial comp wheel vs one with very back swept exducer , the backsweep lowers the energy put into the air per rev , it needs more revs to achieve the same pressure ratio as a purely radial wheel of the same exducer diameter .

What I'm proposing is fitting a "backswept??" inducer on the comp to complement the exducer one, to further lower the energy input per rev , I've got plenty of revs to play with , that billet comp is good for 70 psi of boost in a turbo , and the turb wheel is normally spinning much faster when it has its 141 mm TV94 comp on it , I can increase rpm from 60 K to 70 K without any worrying stresses.

Now all I've gotta do is make the thing :-)

Cheers
John

[CH3NO2]

Excellent find John! isromac-isimet.univ-lille1.fr/upload_dir/finalpaper/168.finalpaper.pdf

Your logic on it sounds plausible.
The lower power requirement is offset by increased RPM. Increased RPM gives a higher pressure ratio... which may get the system over its starting hump.

Tony

[dieselguy86]

I hate to go off topic but Tony, is your site "name" the chemical formula for nitromethane?

[jetjeff]

Hi John,

Have you ever checked the direction of your exhaust with a metal flag, as Kamps talked about in his book (page 93 - 3rd edition)?

"A minor swirl angle of up to 15 degrees in the direction opposite to turbine rotation is normal. A greater reverse swirl usually indicates too great a reaction level (not sure what that means). Narrowing the cross-section of the turbine nozzle guide vane system whilst enlarging the rotor cross section should remedy the situation."

Regards

Jeff

[madpatty]

Nov 18, 2017 20:05:04 GMT -5 racket said:

Hi Ron

What I'm aiming for is a reduction in energy input per rev of the compressor , this will then require more revs of the turbine wheel ( and comp) to achieve the same outcomes from the comp as before

Now a turbine wheels horsepower is simply, gas deflection times BLADE SPEED , if the turb blade speed component has risen therefore it has more horsepower despite the compressor wheel only producing the same compression as before and hence the same horsepower requirement .

I'm effectively changing the "gear ratio" between comp and turb from a 1:1, to a 1 :1.1 , its the same as dropping back a gear in your car when its struggling to go up a hill , more revs of the engine ( turb wheel) makes life easier .

With this big comp wheel I'm only designing for ~60,000 rpm at 100% N1 , but I'll have to maybe go to 66,000 rpm to regain the same output from the comp as before , that 10% increase in turb blade speed has to mean its capable of turning out more power , even if its only 5% , it'll help with the marginal situation I'm finding myself in with this engine .

LOL..........clear as mud :-)

Cheers
John

Hello John,

I was going through this and had a slight doubt in the highlighted part here.

Isn't the gas deflection through the turbine wheel (Difference between the whirl components of the velocity inlet and outlet of the turbine) depends on the inlet actual velocity into the turbine which in turn depend on the velocity out of the NGV throats which in turn is a function of pressure ratio going inside the NGVs which is in turn is a function of total PR out of the compressor.

Now if you decrease PR at a certain RPM you also decrease the velocity of gases at the NGV throats and thus total deflection from the turbine and thus its total power producing capacity at that RPM.

Now when you increase the rpm of the compressor to bring back to the same PR, it increases the mass flow(which in turn requires more power from turbine to process). Now which effect is more empowering is what I am doubtful of.

Cheers.


 

[CH3NO2]

Nov 18, 2017 23:28:24 GMT -5 dieselguy86 said:

I hate to go off topic but Tony, is your site "name" the chemical formula for nitromethane?

Hi Dieselguy86,

Yes, I'm a propellant chemistry geek.

Tony