ScottsCrazyBuilds Jet Kart

[andym]

Why have a speed control on the A/B pump, you going to need all and may be more, that pump can give... and why have a more complex system than pushing a button ? that way you can fire the A/B off what ver P2 is . When you tested the oil system, did you warm the oil. Cold and engine not running 5 Bar oil pressure, some oil could of got past, and be sitting in the can

[slittlewing]

Andy, the pump being in current control is effectively fixed pressure of 5 bar regardless of flow because current = torque = pressure.
Of course the aim is to use the one button but I need to know what the AB pump PWM is at different P2 to map it in the first place! Hence the pot on the top.

So today I fired up the kart, it took a few attempts and some head scratching but found the issue being that my AB ecu was backfeeding the 18.5V (more like 20v fully charged) to the engine fuel pump which should run at 12v, and so overfuelling at “idle setting” so it was too rich to start. Once I changed the AB ecu to a different source (direct from battery, separate from engine fuel pump), this was fixed and it fired up.

I’ll let the video explain the rest!



I have partially stripped it already and think I just need to add clearance to the NGV back plate. I don’t yet know how much wall thickness there is though. I may fit new bearings whilst it’s apart and I’m not sure if I need to rebalance the rotor afterwards.

Cheers

Scott

[andym]

What a mess...... erm, fire in engine, not one isuue when i ran the engine, you got the start up all wrong and not how i told you, rubbing like that would not stall the engine, and it did not rub when i had it, may be welding has pulled some thing, oh and you made changes to system you did not fully understand. As for oil system... i set vesc as advised by some one that knows them better than me, and it should of been on current, you said you reset it ? 

As for engine stalling, does the fuel pump still run, you put 20 volts in to the system the wrong way, perhaps the drop down has brown out ?

So after looking at the video again, you can clearly hear the engine spool down with no rubbing, would be a lot more noise.....Have also noticed the engine drain dont seem to be connected ? so fuel and oil from bad starts could not drain out

Also noticed the NGV back plate is black, did not see that on or after any of the test runs i did 

[racket]

Hi Scott

All part of the learning process .

The spooldown appears to have been caused by the fuel being "cut off" , normally a rub sufficient to cause such a dramatic reduction in RPM would have resulted in your TOTs going to extremes as the overal fuel/air ratio increased as the air flow reduced whilst fuel flow remained constant, your flametube would have become an "afterburner" and potentially melted your turb wheel tips off

The flames and smoke are more what would be expected from the usual seal leakage and oil fire when the P2 pressure is removed .

The "rub" sounds more like individual blades "tinging" when touching an "object" , maybe a "scab" on the shroud, maybe see if it stops with oil pressure on the shaft as it will "lift" the shaft a tad , .... not enough "grind" for a rub , will be interesting to see what you find .

I've had a number of "scabs" during initial testing, often caused by assymetric expansion of parts during failed start attempts , simply gring off the scab and away you go , some turbine engines can't be restarted until the engine has cooled considerably due to assymetric expansion of internal rotating bits , the "longer hot bits" at the top of the engine will bind with the cold stationary bits at the bottom

One very good lesson learned.............always point a jet aircraft "into wind" before starting ................LOL, I had flames like that with my PJ experiments , nearly got scorched a few times before learning that lesson.

What sort of "numbers" did you collect ??

Cheers
John

[slittlewing]

Andy,

Cut the BS please, “not one issue when I ran the engine” apart from several engine “fail videos” you have posted on here and youtube.
The vesc was previously in speed control not current control.
The fuel pump is completely fine, it had 20v back fed to it (still the correct polarity), from the supply you were using for the ab pump because you run that one at 20v which is an identical 044. We all know they can run at 24v.
Quite obviously I am making changes to systems that I don’t fully understand, because I didn’t build them and am reverse engineering as i go.
The start sequence was not incorrect at all.
The drain was connected after any of the previous failed starts.
The engine is black and sooty because of the fire at the end.

As for the “it did not rub when I had it”, In your build thread you mention the turbine wheel rubbed when the engine was first assembled and had to be rectified.
After the engine had run, you had some failed fireup attempts and then stripped it:

jetandturbineowners.proboards.com/post/26410/thread

After zooming in, i can clearly see turbine wheel rubbing marks.
ibb.co/wgQLG2P


John,

I’m afraid to say the spool down was definitely not due to fuel being cut off. I was watching the gauges with confusion as the engine spooled down with stable fuel and oil pressure. Eventually it got to the point of “below sustain” and started smoking so i hit the kill switch, which killed both pumps and the rotor came to an immediate stop, the extra fuel that had been injected during the unsustained running which was presumably alight was then able to flare back out of the engine inlet due to the lack of airflow.

When I then (hot) tried to turn the rotor with the slightest sideways load it was rubbing enough to pretty much lock solid. As the engine cooled it rubbed a lot less.

After partially stripping the engine, I can see the comp section is all fine and there is evidence of turb blade rubbing the NGV back plate.
At the moment it seems that there is next to no clearance to the turb wheel when cold. My best guess is that as the aluminium shaft tunnel grows, the NGV back plate is then contacting?





The engine wasn’t running for long enough to get any real numbers but the TOT was oddly high and I assumed there to be a problem with the thermocouple, but maybe your explanation shows that’s not the case. I saw a it sitting around 700 which is way higher than expected for idle condition.

Cheers

Scott

[andym]

No BS..... everything worked fine.... one failed start.... nothing to do with any rubs... As both John and I have said... the fail was not dew to a rub.... the drain pipe clearly not connect on the start in video

The start was not done how I explained it needed doing

The oil system worked fine, in all but one video.... and the engine was tested again after the failed run, you can see video for that at bottom of page

This is the test done after the engine was rebuilt, after failed start, and thanks for linking that video, it has pictures of strip down, flame tube looking a little differant from my picture. If as you said... you cut fuel when the engine stalled... or something, clearly something was burning in the can, in your video you can hear the engine ideal pick up more from the start, then sortly after the engine start to spool down, and even after that the rota is still moving air




And another running engine up to full power twice, with no issue




Then this one, when low oil pressure shut engine down



All with know issues.... and i share all me testing video, the good and bad, failed starts, engine running hot etc

No BS.... but what ever Scott, am done, all i know every thing worked fine when it left me, had been run a few times no issue, so whats changed 

Last test after fail, with low oil pressure cut off

[slittlewing]

You prove my point exactly... you had plenty of issues and problems that needed sorting. It’s expected and part of the hobby hence you saying “not one issue when I ran the engine” is simply not true.

The start routine was perfect. Oil pump on first, wait a few secs for oil pressure, add impingement air then a couple of seconds later fuel and spark.

[andym]

Apr 25, 2021 3:56:10 GMT -5 slittlewing said:

You prove my point... you had plenty of issues that needed sorting. It’s expected and part of the hobby hence you saying “not one issue when I ran the engine” is simply not true.

The start routine was perfect. Oil pump on first, wait a few secs for oil pressure, add impingement air then a couple of seconds later fuel and spark.

Proven what, had two issues, and neither caused any problem, one...... low oil pressure switch working as it should, i had made changes to oil system, which was the cause of that, the other.... i changed ideal fuel pressure, and tried a fuel mix, which then egine did not like, and dont think the spray nozzle worked so well at lower pressure...... nothing mechanical.

As for start..... it shoiuld be prime oil sysytem..... air..... then oil and fuel together.... oil pressure builds as engine spools on air, and when oil pressure switch come in, the fuel turns on, and the ignition fire

[slittlewing]

I don’t see any need to start it like that, all that’s doing is using the oil pressure build time as a delay before fuel is added, which is the same as starting it on full oil pressure and waiting 3 or 4 seconds.
Additionally there was no issue with the start. The engine started.

The issue is that it has interference on the turbine after thermal expansion and 10 or so seconds idling.

[andym]

Apr 25, 2021 4:16:57 GMT -5 slittlewing said:

I don’t see any need to start it like that, all that’s doing is using the oil pressure build time as a delay before fuel is added, which is the same as starting it on full oil pressure and waiting 3 or 4 seconds.
Additionally there was no issue with the start. The engine started.

The issue is that it has interference on the turbine after thermal expansion and 10 or so seconds idling.

That you don't see why it should be done the way I explained... that you think you no better.... there is a reason to do it the way I explained... but not going to waist my time any more.... you clearly know better than the person that designed and built the engine

Also, I have been at this some time, the ngv back plate so called rub... was not the reason for the fail... would see much more damage... and there would be noise heard in the test

[racket]

Hi Scott

Thanks for the idling high TOT and other info , that will put a different complection on my viewing of the video , I'll have a few more looks .

Having a turbine to NGV rub like you have has happened to me on a couple of occassions as parts "settle" , simply fixed by skimming another 0.020" off the wall , remember the wheel is a casting with inbuilt stresses which might be relieving themselves a tad, same with the NGV as it finds its "shape" , one of the reasons why turbos have to run larger than desired clearances on everything at the hot end , plus the front side of the wheel's blades aren't ground square to the shaft , something that has caught me out at times , there can be considerable "wobble" with high and low blades , we need to check all blades when determining axial clearance ...............maybe a better idea would be to "face" the wheel before getting it balanced .

Trying to determine a happy compromise is problematic , we don't want too much clearance as efficiency suffers , but too little and we might get a rub , then theres other unknowns that can creep in over time , but thats RandD

What sort of idle P2 were you experiencing so I'll have an idea of fuel burn rates ??

As for shaft tunnel expansion ............its less than 4 inches long and even if 200 C degrees hotter than the shaft it'd only account for ~0.015", but with all that oil running through it I doubt it'd be even 50 degrees hotter with only a few thou difference , I think stress relief might be more likely . .............we'll wait and see whats exposed inside :-)

If the comp stage is still OK , and the rest of the insides are as well , then a skim on the NGV wall is just a minor hiccup .................LOL, its given you a chance to look inside :-)

Please post more pics as you delve deeper as they're all informative and educational to me .

Cheers
John

[andym]

Scott.... thinking about where you work... the engines have a start up procedure ?

[slittlewing]

Thankyou as always John for the informative and helpful reply 🙂

Sounds exactly like the problem and solution this needs.

I have removed the rear of the turbine housing this morning and now visible is the rubbing area on the NGV back plate, near the end of the turbine tips.
The contact/fretting has made some sizeable lumps. The rotor turns more or less freely now it’s all cooled down but these must be what was causing the rotor to jam if I apply side load to the shaft.








Idle P2 was around 1bar. As you can see in the video by the time I had picked up my notebook to write down all the readings, the engine had started to spool/be dragged down in speed!

The welds on the studs, presumably for anti rotation, have also cracked on most of the studs but I think that’s unrelated.

One area of concern is that the rear of the outer casing is flat rather than domed, thereby making it a 10” pressure vessel with a flat end. Do you think there’s a danger that even with a 0.5mm skim and refaced rear turbine blades, under high P2 the casing “bulge” could drag the NGV toward the turbine, as all are bolted together? If that was the case I am not sure if it would be worth adding a bit extra clearance.

Also, the turb wheel is obviously very hard material. Do you think it’s possible to skim it using a lathe or would this have to be done using a grinding operation?

Obviously this engine has already demonstrated 3bar P2 previously, I think it may be good for even more once this is sorted 😈

Cheers

Scott

[andym]

Looks like it's had some failed hot starts... any chance sharing your video of failed starts...the welds had not cracked before.. lots of burnt soot and oil on the back plate... Anders engine has flat back plate.. and done more than 3 Bar

[finiteparts]

Scott,

I might suggest checking your fuel injectors. If you have one flowing high, you might be getting a hot streak and just like I posted in another thread on this site, you could have suffered a local deflection of the aft plate. But, since this engine has the NGV assembly directly in contact with the combustor discharge, if one or tow of the fuel injectors were flow higher, the local heating might cause the NGV plate to bow locally into the rotor aft cavity.

Since Andy ran the engine in the past without this issue, I would say that the idea of the thermal growth of the shaft tunnel is very unlikely. In that same line of thinking, the pressure load of the back casing is also probably not a real concern.

The tack welds look to have cracked due to the stress concentration created at the edge of the stud and the NGV hole. It was not a full penetration weld and thus there was a built in crack which just opened up over time due to the cycling. Since they are not structural welds, I would just retack and keep an eye on them. To get a full penetration weld at that location, it would probably be more damaging than helpful (thermal distortion, part rework, etc).

Finally, the rubs that you are showing in the pictures, appear to have quite bit of material transfer. Due to the large amount of transfer damage, I would highly suggest checking the turbine for cracks. In the aerospace industry, that turbine would be scrapped because the material properties of regions involved with the rub are most certainly no longer the same as what was processed into the original turbine wheel. Now, we all know that turbocharger parts are not that same quality of aerospace components, but I feel confident that Holset heat treats the cast turbine wheels to get the proper grain structure after they friction weld the shafts on. Inconel 713/LC is not a very weldable material due to its propensity for shrinkage and microcracking and this is why I am suggesting that you inspect the rotor for small cracks. During the rub, metal was transferred because the frictional heating essentially liquified the metal. This means that on the rotor side, locally, the metal went to melting or very near melting temps. Some of the metal was pulled to the NGV plate, thus less material was left at that location on the turbine wheel and would have cooled into a very high tensile stress state due to the shrinkage due to cooling. Since 713 is prone to microcracking, there will likely be cracking damage. The concern is that the cracking could weaken the turbine or worse, let go at high rpm.

Additionally, the damage if significant, will need to be "blended" out and thus rebalancing the rotor will be mandated. Without blending, the damage could produce stress concentrations that could also produce fatigue crack initiation or worse, weaken the blade so that under the high centrifugal loads experienced at high rpms, cause the blade to let go.

Ideally you would inspect it with fluorescent penetrant (FPI) such as MagnaFlux Zyglo, because the cracks may be extremely difficult to see.

Good luck!

Chris