|
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
|
|
|
Post by racket on Apr 8, 2024 21:36:35 GMT -5
What sort of numbers do you have now ??
|
|
|
Post by racket on Apr 8, 2024 15:47:21 GMT -5
Hi Anders
You're getting some seriously gear in your workshop , nice :-)
Cheers John
|
|
|
Post by racket on Apr 8, 2024 3:54:16 GMT -5
Hi Ralph
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
|
|
|
Post by racket on Apr 8, 2024 3:50:50 GMT -5
LOL............back to the drawing board :-(
Could you post some closeup pics of the air delivery system to the combustor .
There is one other thing ...............the turbos heritage ............any chance theres something wrong inside ??
|
|
|
Post by racket on Apr 8, 2024 1:54:50 GMT -5
Hi Guys
Another unsuccessful attempt this afternoon :-(
Might have to be a bit "creative" to find a solution .
Cheers John
|
|
|
Post by racket on Apr 7, 2024 20:57:16 GMT -5
If you're running at surge , then the flow is less than design , so your design hole area is now relatively oversized, adding more holes will potentially make the situation worse .
I've had another look at your flametube and really can't see any problems .
Is there any indications of where combustion is occurring ??
Generally the stainless will provide some "colour" variations that can provide clues .
The TV81 is an old design like my TV84 was but even when I was running an undersized turb stage in the very early days , it didn't surge until I fitted the jet nozzle and increased temps .
My undersized turb wheel was 97/86 mm with 15 mm inducer tip height , , I tried 1.08 and 1.39 A/R scrolls , the 1.08 was too small , but the 1.39 was OK without the nozzle .
|
|
|
Post by racket on Apr 7, 2024 20:39:39 GMT -5
If surge is intermittent and at all rpm I don't see it being the turbo configuration , the TV81 map is a bit skinny at higher PRs but at say 2:1 PR it goes from ~37 lbs/min Corrected flow to 85 lbs/min which is quite acceptable .
What fuel are you using ??
Is your combustor drain valve open??
Is there fuel exiting the drain ?
I'm trying to determine if theres fuel possibly puddling and suddenly flashing off and causing a momentary thermal choking of the turbine , ..........its got me puzzled :-(.
|
|
|
Post by racket on Apr 7, 2024 16:49:16 GMT -5
Well , thats the strangest thing :-(
With such low temperatures you shouldn't get surge unless theres a restriction somewhere .
LOL................I once left a rag inside my TV84s delivery air tube that had me scratching my head for quite a while trying to workout why the engine wouldn't work , this is just as perplexing :-(
Could you collect some data on when the string bounces , its a bit hard seeing the numbers on the video .
|
|
|
Post by racket on Apr 7, 2024 1:50:38 GMT -5
|
|
|
Post by racket on Apr 6, 2024 17:24:05 GMT -5
A 29mm turbo has severe limitations with component efficiencies in a turbo thats produced as cheaply as possible, there are "scale effects", wheel clearances have a huge effect, bearing drag from the "brass" is a greater proportion of losses .
Personally I wouldn't use anything less than a 50 mm inducered turbo to make a DIY engine from .
Radial turbines are better than axial ones at small sizes if we can control the clearances and use similar stators rather than a scroll with its large surface areas and losses compared to an axial NGV .
LOL.............you were successful in getting that small turbo to run , thats an achievement in itself , don't feel bad about the lack of thrust , or compare it to the HP output of the engine it came off.
When I was developing my TV84 engine and it only produced 110 lbs of thrust whilst burning huge amounts of fuel I couldn't understand why when the turbo came off a 460 HP diesel engine , but once you do the maths , things become clearer , I spent 2 years going around in circles trying to get more thrust before finally doing the maths , ...........felt a bit of an idiot afterwards for wasting so much time :-(
But the piston engine burns all the oxygen , and runs a higher compression ( expansion) ratio than our DIY engine so is able to extract more energy from those expanding gases .
LOL...............don't blame Jetspecs , its trying to cover all sizes of turbos , all levels of build sophistication or lack thereof , all levels of component efficiencies etc etc etc :-)
Cheers John
|
|
|
Post by racket on Apr 5, 2024 23:36:26 GMT -5
Hi Turbo based jets AREN'T poor in this area , its simply a case of mass flow and thrust per pound of flow ...............plus the RC aero engines tend to fiddle the numbers a bit ;-) A turbo based engine can produce both good thrust and good shaft horsepower , my TV84 turbo bike jetandturbineowners.proboards.com/thread/1366/tv84-turbine-bike with a 3.5"inducer and ~1.8 lbs/sec flow produced ~110 lbs of thrust at a rate of 61 lbs of thrust per pound of mass flow , this is vastly better than the rate of the early fighter jets that used centrif compressored jet engines , when it was converted into a freepower machine the bike produced 115 RWH on the dyno after all the losses through the transmission etc etc , it was a very crude build . Anders bike used a TV94 turbo rotor in his 306 kph bike , even though the engine was not a turbo based one , if a TV94 turbo or HX82 size turbo had been used for the gas producer it would have performed nearly as well , any shortcomings would have been from the slightly lower efficiencies of the comp/turb stages using scrolls . Checkout the numbers here www.amtjets.com/pdf/Titan_specifications.pdf 88 lbs of thrust from 1.46 lbs./sec = 60 lbs/lb I did better 25 years ago with an old secondhand turbo ..............our engines aren't toys . Cheers John
|
|
|
Post by racket on Apr 5, 2024 23:16:16 GMT -5
Hi Richard
I use two 330 CCA 12V batteries in series for starting and the fuel pump , for the rest of the bits theres other batteries including a deep cycle one .
The 044 fuel pump draws ~15 Amps on 12V so not much on 24V , the coupla car batteries should cope with 5 minutes worth of run time
Hopefully all will be well , it looks like the terminal fittings simply "relaxed" over time and I never noticed it :-(
Cheers John
|
|
|
Post by racket on Apr 5, 2024 16:22:05 GMT -5
Hi Richard
A couple of 12V car batteries , they're only a few years old and I keep them fully charged .
I found it "interesting" that the hot fitting bolt wasn't all that tight, things might have "settled" over time , don't know , but hopefully a fix and things work OK now .
I've got the power for the fuel pump taken off at the starter solenoid input , with very heavy cabling from batteries to solenoid, so I can't do much more to power the pump .
Cheers John
|
|
|
Post by racket on Apr 4, 2024 23:43:10 GMT -5
Hi Guys
Bit of an update on the starter .
RPM of motor with 70 psi cold oil ~22 deg C and fully charged batteries was 9,500 rpm , ~15% N1 which should be enough to get a successful spoolup with some fuel burning .
Without the jetnozzle and with recharged batteries and same oil , 9,950 rpm , not a lot of difference , maybe ~10% of starter power being used at the jet nozzle constriction.
Pulled starter apart and it looked OK inside so didn't machine anything , a bit of fresh grease in the gearbox and back together .
I did find a couple of "hot" fitting on the battery pack after testing , so cleaned them up and retightened them as they were a tad loose .
On viewing the gauge video of the failed testrun I noticed my fuel pump pressure dropped to virtually zero whilst the starter was activated , the pump is running off the 24 volt battery pack .
So maybe it was a combination of poor conduction through the fitting and the starter sucking all available power leaving the pump doing nuthin'
Hopefully next testrun will be successful :-)
Cheers John
|
|