"Fat Boy" 12/118 thrust engine

[racket]

Hi Ron

I've ordered a new fuel pump , ~6 lpm flow at the pressures I use , I can get rid of the PWM and its crazy "earthing" problems and 24 volt requirement and go back to a simple 12V system and a needle valve "dump" throttle ............I really want to hear this engine on full throttle, even if only for a few seconds at a time :-)

Cheers
John

[turboron]

John, can you share some more information in your PWM earthing problems.

Thanks, Ron

[racket]

Hi Ron

The PWM I'm using supplies "full" 24 V positive power to the fuel pump and the "control" is on the negative , this makes for "interesting" times if for any reason the pump is earthed out , it suddenly goes to full power/flow , this happened in early testing of the fuel pump/PWM when I activated the starter motor, somehow a circuit was completed with the fuel pump and it went to full flow, once I made sure the pump was completely isolated there weren't any more "surprises" , but theres always the opportunity of an "earthing" through the pump's metal body .

Another problem I have is I've got two flow controls , the PWM, and a needle dump valve from the original pre PWM days , this complicates the setting of prestart fuel pressure .

I'll be very happy to put the PWM back into its box and quietly hide it in the back of my cupboard never to be used again, I'm not a great fan of "electronics" on a test stand , if they start to play up theres no way of me testing them, unlike a simple mechanical device like a needle valve.

Cheers
John

[turboron]

John, I always get some key insight from you. The insight being that electrical controls and safety switch get in the way of development. When we are involved as the control then we can adjust on the fly. If the control is driving all kinds of crazy stuff happens. When I was starting up chemical plants we always need some wire cutters to get the plants up and running.

[racket]

Hi Guys

New fuel pump installed and some testing done to check flows and try and find a suitable spoolup setting .

With pump activated and my dump throttle v/v wide open the pump is outputting ~10 psi of pressure , one turn in and it rises to 12.5 psi , 1.5 turns ~15 psi and 2 turns ~20 psi , so a nice fine adjustment for idling conditions , with the old pump I had half a turn out from fully closed for idling , it was a bit "touchy" trying to set a steady flow to hold a P2 setting when taking readings.

Now with 2 turns in and 20 psi on the pressure g/g , when the v/v for supply to the engine is opened pressure drops to ~11 psi and ~1500 ml/min are fed through the injectors , probably a "safe" setting for first spoolup attempts , .......... maybe next week :-)

I've also swapped the T2 probe for a shrouded one to see what difference there is, just in case theres been radiant heat giving a false reading .

Cheers
John

[turboron]

John, what does v/v and g/g mean? I have not seen these terms. Also, can you provide details on the fuel pump? I would like to know the type, manufacturer, rpm, voltage, price etc.

Fat Boy rocks.

Thanks, Ron

[racket]

Hi Ron

v/v valve , g/g gauge , my bad , shouldn't abbreviate in my postings.

Pump www.ebay.com.au/itm/201380681232

Cheers
John

[racket]

Hi Guys

Took the engine out for a test run yesterday with mixed results, the new fuel pump worked OK but the removal of the exhaust diffuser tipped things backwards a tad too far ,

The first spoolup went off without any problems though a little slow getting up past 30,000 rpm on the starter motor , once the starter was removed , and despite the addition of a bit more fuel, the rpm decayed and the run needed terminating .

Two more spoolup attempts made but neither successful , the starter motor became too hot to handle so I packed up and went home .

Its "interesting ??"that the engine worked, up to a point , with the smaller jetpipe on it , but not with the larger one which should have minimised any downstream "blockage" ............I'm gunna have to have a good long think on this before pulling the engine and making some internal mods ( NGV and/or turb wheel )

Cheers
John

[monty]

John,

Sorry to hear about that. Could the back pressure from the nozzle reduce the turbine PR and prevent choking somewhere in the stage, thereby allowing the engine to run? Just a thought.

Monty

[racket]

Hi Monty

LOL............I really have no idea whats going on , something is very marginal , a slight change in flow rates between differing jetpipes/diffuser exhausts is tipping things one way or the other.

Probably a change to a "standard" G Trim turb wheel is the first option , it'll soon point out if its just a "weak" turbine wheel thats causing problems , extra gas deflection will increase power but at the expense of mass flow , hopefully the surge slot will keep flow under control.

Cheers
John

[turboron]

John, I remember that you installed a compressor pre-swirl IGV to reduce the mass flow with some success. If you install a G trim turbine wheel will you take out the compressor pre-swirl?

Thanks, Ron

[CH3NO2]

Hi John,

You put on a diffuser and it reduced operational performance. Then when you removed the diffuser and replaced it with a convergent nozzle the engine came closer to idle sustain operation? That really is bizarre. One thing we can be sure of is a convergent nozzle will reduce flow velocity and Reynolds number upstream of it.

How is turbine performance affected by Reynolds number and choked flow?
Could reduced flow velocity be causing flow reattachment in an area where there will otherwise be flow detachment?

Tony

[racket]

Hi Ron

Nope , the preswirl will remain , it effectively increases turb wheel speed relative to comp speed , the comp diameter is still a bit more than my "ideal" 10% bigger than the turb wheel .

Cheers
John

[turboron]

John, a backward bent impeller would require a greater rpm for the same pressure ratio while offering an efficiency increase. The downside is higher blade stress.

Thanks, Ron

[racket]

Hi Tony

I really don't know the answers :-(

Yesterday I started doing some "comparison shopping" , getting the turb Corrected Flows and comparing them with exducer areas from the larger Garrett wheels( GTX50 and 55) and it looks like they flow 1 lb/min/116 sq mms , which extrapolated out to a 112 mm exducer gives me ~85 lbs/min Corrected or ~160 lbs Actual - 2.65 lbs/sec , which is OK if theres a reasonable static pressure exiting the exducer , I can get my flow into the turb wheel its just getting out thats the problem

The GT6041 turb stage with its 119 mm exducer and Corrected Flow of ~94 lbs/min with the 1.47 A/R scroll produces 1 lb/min/118 sq mms , so I think I can be able to use those numbers as rough guides for "performance" turbos , but the turb map for my TV91 wheel with a 106 mm exducer and a 1.70 A/R scroll has a Corrected Flow of 90 lbs/min or 1 lb/min/98 sq mms of exducer

Years ago with the TV84 turbo I used in my bike , I had neither a comp or turb map , but eventually came to the conclusion that I had a mass flow of ~1.8 lbs/sec , but I was able to use scrolls with A/Rs from 1.23 up to a very fat 1.84 A/R which was a huge doughnut , the rectangular port in the "foot" was the "throat" in that scroll , the cross sectional flow area increased downstream of the foot , yet the engine ran well with it and produced max thrust.

The fat scroll would have been producing very low gas speeds which the turb tips must have been impacting and forced to accelerate the gases probably producing nil input power to the wheel , the power was being produced by a choked exducer ................it was a "sick" combination , but it still worked ............the ideal combo would have been a 1.39A/R on the 110/96 mm turb wheel driving the 88/118 mm comp .

My current thinking is to get the replacement wheel installed , do some runs , then start to increase the radial clearance on the exducer to "unchoke" it , hopefully increasing the mass flow to a level that the comp is happy with , its going to be a juggling act getting the various pressure drops through the stage parts sorted out , I've never been able to find any info on the Net about the actual pressures at different stations through the radial inflow stage .

Does the NGV have precedence, or the turb exducer , or is it a 50/50 split of required pressure drop , will one choke before the other , theres turbocharger information but they assume an outflow pressure near ambient whereas we want several psi of static pressure along with several more psi of dynamic velocity pressure .................LOL, I might just have to sit in front of this screen a bit longer looking for answers :-)

Cheers
John