11/127 manned flight engine.

[jetric]

I'm sure that Andy could of got you a set of NGV vanes machined up out of inco and posted them to you?
Have you tried putting a restricter into the throat of the intake in front of the inducer tips to increase the axial velocity so the inducer angle matches up with the flow. All high pressure ratio centrifugal compressors that I've seen have a relatively small inducer diameter such as on the BMW/RR T312 which is capable of 60psi P2 with a titanium comp wheel and a diffuser running supersonic (you can see whitness marks in the oil staining of shock waves on every leading edge of the diffuser vanes!).

Jun 27, 2024 17:19:18 GMT -5 racket said:

Hi Richard

I generally use Inco , but its not so easy to source here in Australia , even more so since Covid disruption , hence my stainless use this last rebuild of the NGV .

Yep , I lost my way with the engine because of the new compressor wheel , the original compressor wheel/s worked OK with the turbine wheel size I have, but they were incapable of coping with any sort of decent compression ratio without stretching their bores .

The new wheel with its very high inducer angle simply wants to bite off more air than the turb can chew , this has created all sorts of problems , my early comp wheel was off a normal diesel engine turbo , this one is a racing tractor pulling wheel with unknown design requirements that was probably meant for 80+psi of boost , no matter what I try , I can't prevent the whole engine and test stand shaking when the engine is running.

Andys engine uses a comp with 10 degrees less inducer tip angle , its "normal" , so behaves as expected .

Ideally I need a much larger turbine wheel, but that then creates tip speed problems for the wheel , currently my comp tip speed is up around 1950 ft/sec with turb at ~1660 ft/sec , but another option is a larger flow wheel at lower pressure ratios from the comp , but finding an available turb wheel could be a challenge , I have contemplated a third stage Allison C20 wheel with tip laby seal removed , but its RPM is limited :-(

It seems a shame to have a beautiful comp wheel that can't be allowed to do what it wants to do , it has some unique characteristics that need exploring , like an inducer that has angles that will bite off more air than its throat can swallow without there being shock wave compression as with fan engine blades ........... I've got a highly strung race horse kicking the crap out of its stall wanting to run , but I'm not able to accommodate it :-(

Frustrating business R and D.

Cheers
John

[racket]

.
Hi Richard

The IGV stator set at a 20 degree preswirl seems to keep the worst of the surge under control whilst limiting the amount of air being dumped from the surge slot, theres actually a vacuum at the slot at full power .

A lower Trim would be a big help , at ~53 Trim this is normally a good size , the comp efficiency is very good when calculating from the temp rise across the stage .

I've "repaired??" the damaged NGV vane by piggy backing a section of 2mm stainless over it , it ain't pretty but any vane is better than no vane I guess





The rest of the vanes have been massaged to bring them back into some sort of shape and throat size .............It'll do , its only a prototype after all .

I'll grind the turbine wheel tomorrow and she'll be ready to go back together

Cheers
John

[racket]

Hi Guys

Turbine wheel reshaped



Bit less blading , but at least they're now all the same

Time to start reassembly

Cheers
John

[racket]

Hi Guys

Engine back together and mounted on the test stand, where it can sit until I decide what I'm going to do next .

Cheers
John

[racket]

Hi Guys

Crappy cold wet weather here so been doing some "research".

Decided to have a look at the Build Thread for my 12/118 engine jetandturbineowners.proboards.com/thread/612/fat-boy-118-thrust-engine?page=56 and found some info on "excessive" exducer shroud clearances that were used to increase mass flows , pic of original and revised jetpipe/shroud postimg.cc/ThWn76kB .

I'd forgotten about these experiments , but the results were OK www.youtube.com/watch?v=68Io36GsaSk&ab_channel=racketmotorman 203 lbs of thrust :-)

It might be advantageous to do something similar with the current engine, most turbo setups use wastegates to dump exhaust gases , so the turbine stage should be able to power the comp with less than the full mass flow .

Currently something is restricting the flow even when theres no jet nozzle attached .

Might be time to do some numbers :-)

Cheers
John

[racket]

Hi Guys

Nice sunny day , so time for a test run this arvo , oil tank heater on , all batteries charged .

No jet nozzle or restrictions other than thermocouples , fully open 130 mm "pipe" to get some baseline numbers for when I start providing the exducer clearance gap to increase mass flow .

Currently I've got lotsa jetpipe pressure so I'll be using some of that to compress the extra flow even though that flow won't be producing its potential power in the turbine , so hopefully more mass flow at a slightly lower P4t.

Cheers
John

[racket]

Hi Guys

Well this afternoons test went off OK , but some strange numbers , even without a jet nozzle it produced ~250 lbs of thrust from the jetpipe from rather decent P4t pressures.

I'll put some video on Youtube , they're a tad long as I had some ignition/spoolup issues which required a a couple of attempts.

youtu.be/u9-ku82gu0E

youtu.be/vyc1obcbwlg

youtu.be/JqFOzcigrFU

Cheers
John

[slittlewing]

Thrust seems about right I think John! Not sure about the fact its with zero nozzling, seems your racehorse comp is doing its job Maybe a good reason to try your bypass idea via large Turb clearance to snout.
TOT's very high though, looked like >950 at 4.4bar.

For reference, I saw about 220lbs, 3.8bar Boost Dry Nozzle on my new engine which scales up about right to yours (113mm Turb Exit brought down to 100mmm Dry Nozzle).

Cheers

Scott

[racket]

Hi Scott

At least this test had jetpipe static pressure reading ambient throughout the test , whilst the P4t at 0.9 Bar meant very high velocities within the jetpipe , the gases should exit the exducer with maybe 0.5 Bar of static pressure plus possibly 1200 ft/sec of velocity , the 0.5 Bar then expands pushing the velocity up .

The static pressure probe at the NGV outlets registered 3 Bar at 4.5Bar P2 which would mean a pretty small pressure ratio across the NGV resulting in lowish velocities exiting the NGV and impacting the inducer , probably not impacting the right side of the inducer and producing torque but actually absorbing torque being produced by the choked exducer .

Your engine is behaving as it should, jetpipe 27% greater area than nozzle , with good thrust for its size , nicely matched comp/turb combo , whereas my comp is way too generous with its output potential .

I'll get the engine apart and start making some extra flow area at the turb , I'd like to see the red manometer go into "vacuum" so that I can reduce the IGV angles and get more air in the front ............interesting times ahead :-)

Cheers
John

[racket]

Hi Guys

Engine apart and exducer shroud machined out to produce an extra 3 mm of clearance , 128mm to 134 mm another 1234 sq mms - 1.9 sq ins of flow area , the exducer throats are ~10 sq ins so close to a 20% increase , this should make some difference .............good or bad :-)





Cheers
John

[enginewhisperer]

I remember you telling me not to do exactly that on a turbo many years ago

[racket]

LOL............OH !! ...........I wonder why ;-)

Guess I'll find out soon :-(

[racket]

Hi Guys

The numbers from yesterday



Looking at the numbers from the previous test with a tad of nozzling , the temps were higher along with the P4t and thrust , temps were sorta acceptable this time , considering the thermocouples were being exposed to 2,000 ft/sec gas velocities impacting them with resulting stagnation temp rise of perhaps 100 C degrees , if I average out the 4 thermo readings it comes to ~790 deg C , take off the stagnation component and it gets even better

Cheers
John

[racket]

Hi Guys

On inspection of the innards I found the same NGV vane damaged even though temps during this test were considerably lower than on the previous one , gotta work out whats going on :-(

Cheers
John

[racket]

Hi Guys

Decided to check the fuel injection , so set it up with the garden hose connected and 30 psi of pressure .

Water was going everywhere when the mounting wall was vertical as in the engine , so thought I'd try it horizontally , still problems, bit of crappy video youtu.be/oZbYljepBR0

Gunna have to sort this out as at full throttle theres 50 psi of pressure drop across the injectors , so there'll be a huge amount of spray going everywhere , no wonder my turb temps are all over the place .

At least I've got something to hopefully correct the situation , I'm also blanking off the holes between evap tubes as there could have been a "blow torch" entering one of them that was cutting my NGV vane in half .

Cheers
John