richardm
Senior Member
Joined: June 2022
Posts: 268
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Post by richardm on Apr 8, 2024 8:15:28 GMT -5
It's because you are taking the power for your fuel pump at the starter motor terminals, the voltage drop at the starter motor terminals will be substantial when you turn on the starter. Run separate wires for the fuel pump direct to the battery terminals. Richard S. But If that same set up work before then look at the batteries.. Theres a very large drop in fuel pressure as the starter is activated , I'm going to explore setting up a bespoke 24 volt power supply for the fuel pump. I'll do some testing of options tomorrow . Cheers John
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Post by racket on Apr 9, 2024 0:15:13 GMT -5
Hi Guys
Put the fuel pump onto a dedicated 12V battery and alls well , fired straight up , so at least I know the changes to the jet nozzle weren't the problem .
I don't know if my neighbours appreciated the spoolup to idle , but it was only a minute :-)
Recharge all the batteries and I'll be ready to take it out of town for a full throttle run .
I did a fuel pressure test once it was hooked up to its battery and found some changes , normally I have the dump back to tank valve adjusted to provide a 20 psi pressure head prior to opening the engine supply valve, when I opened it and fuel was forced through the injectors in the engine the pressure dropped to 10 psi , which is what should happen ,recently my pressure has been dropping to virtually nothing on the gauge , undoubtedly whats been the problem, the longer the starter was activated the lower the battery voltage and the lower the fuel supply to the engine, no wonder it wouldn't spoolup .
Cheers John
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Post by racket on Apr 10, 2024 2:59:42 GMT -5
Hi Guys
Completed a test this afternoon .............nice 11 second spoolup , like old times :-)
On only 12V the fuel pump didn't supply enough to get to 4 Bar P2 , but thrust still ~220 lbs , the airflow was being restricted , lots of "chuffing" from the comp and more surge slot pressure .
I'll collect numbers off the videos tomorrow
Cheers John
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Post by racket on Apr 10, 2024 4:04:57 GMT -5
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Post by racket on Apr 10, 2024 4:23:08 GMT -5
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Post by racket on Apr 10, 2024 4:42:08 GMT -5
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Post by racket on Apr 11, 2024 19:42:45 GMT -5
Hi Guys
This spoolup fueling issue has me baffled , but I want to throw this out to anyone that might know more about electrics than this dinosaur .
The test the other day produced a very fast spoolup , so I went back and looked at old videos of the spoolup when I first fitted this stronger starter and found it took a few seconds longer with the brand new starter .
Now to reduce spoolup speed there needs to be more power supplied by the starter which would mean sucking juice from the batteries at a greater rate .............perhaps to such a rate that the fuel pump was being starved of power .
Is it possible that the new brushes in the starter have worn in and are able to transfer more power ??
Cheers John
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Post by enginewhisperer on Apr 12, 2024 0:21:13 GMT -5
that's definitely possible (brushes wearing in) usually they start off with a pretty flat end profile and wear into the commutator shape a bit over time - so they'd increase in contact area.
The bearings and gearbox might also have freed up a bit?
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richardm
Senior Member
Joined: June 2022
Posts: 268
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Post by richardm on Apr 12, 2024 4:29:58 GMT -5
Yes new brushes will wear to a perfect fit I happened to change brushes on my lathe dc motor and it this was obvious . Initial noise after replacement turned down . And running the motor in reverse sounds different also as the brushes have a little play and "seat" differently if running in the opposite direction of their main use.You can ear turning the shaft by hand. May be it would help to open your starter again and clean up the commutator slots that are probably full of carbon dust from the new brushes seating in. I would also put the rotor in a lathe and give the commutator a little clean up with some fine sanding paper or even a light cut if deep grooves are showing . www.youtube.com/watch?app=desktop&v=VHjGc_qjNcE www.youtube.com/watch?v=ewqGrlf7Nr8You wrote " to reduce spool up speed" Did you mean spool up time ?
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Post by racket on Apr 12, 2024 15:53:58 GMT -5
Yep , spoolup time , theres ~3 seconds improvement
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richardm
Senior Member
Joined: June 2022
Posts: 268
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Post by richardm on Apr 12, 2024 16:54:15 GMT -5
Ok then since nothing comes from nothing your starter is pulling more amps at the expense of the other equipments. Would be interesting to clamp an amp meter to the starter positive cable to see how much it draws.
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Post by racket on Apr 12, 2024 18:37:48 GMT -5
LOL...........if I had an Amp meter :-(
Its drawing heaps , the starter gets hot to handle very quickly.
I'd sooner the spoolup is as quick as possible , less chance of doing damage from overheating the turb wheel .
I've gotta have a good think on things , theres been so many different tests with different bits added and removed that I'm getting lost.
Running a 5:1 PR should mean a choked NGV , but with a choked point , what happens downstream can't affect things upstream of it, unless what is done downstream removes the choke , I'm getting the feeling that its a fine line between one and the other at the moment .
A challenging scenario :-)
Cheers John
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richardm
Senior Member
Joined: June 2022
Posts: 268
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Post by richardm on Apr 13, 2024 5:05:50 GMT -5
Just curious. Isn't a 5: 1 PR too much for a single stage centrifugal comp? I mean I have no doubt that your engine achieves such a PR but Im thinking about "strange things" that happen then Like boundary layers separation , shock waves maybe etc You know what I mean.
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Post by racket on Apr 13, 2024 5:57:54 GMT -5
Hi Richard
Yep , shock waves are my current "unknown", just how much compression is there across a shockwave ??
I looked at some numbers for my comp today and with the high inducer tip angle , to reduce incidence to zero between blade and incoming air at the RPM I'm running , the air going in would need to be at ~900 ft/sec and the relative tip velocity is ~M-1.5 , so well into transonic conditions over a large portion of the inducer.
But the throat area of the inducer can't swallow the amount of air that the inducer is biting off at the density available .
So is there an increase in density across the shock that then allows the inducer to swallow what is being bitten off ................I don't know .
LOL.........to answer your question about 5:1 being too great a PR for a single stage comp , nope , some of the tractor pulling guys use 100psi of boost from a single turbo , 7.7:1 PR :-)
Cheers John
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richardm
Senior Member
Joined: June 2022
Posts: 268
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Post by richardm on Apr 13, 2024 8:59:55 GMT -5
Those are impressive numbers for a PR! I was referring to what I know about centrifugal gas turbines and jet engine I ve read the the RR NENE reached a max of 4:1 PR But that raise another question in my mind: Those high PR turbos are feeding a piston engine wich ,I guess , implies a quite different mass flow and pattern. I mean a jet engine is basically unrestricted flow trough compared to a piston engine Could this explain the higher PR ? Higher pressure at a lower flow?
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