11/127 manned flight engine.

[racket]

Hi Guys

That was an easy fix :-)

Just needed to adjust the bent tip injectors from ~70 degree bend back to ~35 degrees , this projected the spray a little further in and at a shallower angle where it impacts the bore of the evap tube , nothing coming out even when the wall was vertical , hopefully more even turb temps in future :-)

Cheers
John

[racket]

Hi Guys

Nice sunny day , the winds have dropped , time for a test run this arvo :-)

Cheers
John

[racket]

Hi Guys

Well that was a waste of time and fuel ..............as I accelerate from 3 Bar P2 towards 4 Bar the engine started cutting out , then cut back in as the rpm dropped ,the whole test stand bouncing back and forth , with fuel pressure needle bouncing all over the place as if the P2 over pressure switch was cutting in and out , but it wasn't touched from previous tests , guess I'll need to check it tomorrow.

Thrust was up marginally but temps were also up , so a bit of thinking required on the next step to take .

Cheers
John

[racket]

Bit of vid youtu.be/B1dFgzNEURc

[racket]

P2 overpressure switch checked out OK :-(

Something weird going on ...............LOL, might have been the full moon :-)

[finiteparts]

That looks like it is going into a moderate surge condition.

[racket]

Hi Chris

Yep , had me baffled , still does , all I did was provide more flow area when I had it apart , so surge shouldn't be the issue .

I've still got ~35% of my fuel drums fuel left so it shouldn't have been sucking air either, I really don't have the faintest idea why it started behaving the way it did :-(

I'll keep looking :-)

Cheers
John

[praendy2203]

Hi John,

At 03:12 min in the vid:

3,5 Bar P2, the fuel pressure gauge shows 95 psi and the engine starts to go crazy.

The next time the fuel pressure shows 70 psi and the engine starts to shake.

Its a kind of fuel or combustion problem.

Could it be a flame stall?
Cavitation?

Andy

[racket]

Hi Andy

I don't know what has caused it , the only changes I made were a slight mod to the fuel injectors and increased turb exducer clearance by 3mm to provide more flow area so as to increase pressure drop across the NGV, which there was as the NGV exit static pressure reading was lower , 1.5 Bar vs 1.8 previously at 3 Bar P2 , and provide greater impulse energy to the turb wheel to compensate for the exducer clearance , the positives of a radial wheel is the inducer and exducer are two separate entities .

I noticed that the green manometer readings weren't much different than the previous test with the red manometer indicating a bit less dumping of air this test.

Fuel pressures were a lot higher this test, 80 psi vs 65 psi at 3 Bar P2 which would account for the higher turb temps and 15% thrust increase at 3 Bar , even though P4t was lower.

Theres got to be a solution to these variables , just need to figure out what it is :-)

Another test run with a full tank of fuel and some new data collection points maybe ..............I've been also looking at my oil pump pressures which appear to suggest that the pumps power supply is fading a bit too fast, hopefully its not another battery dying :-(

Cheers
John

[finiteparts]

The increased clearance should provide more flow assuming similar entry temperatures, but at the cost of turbine efficiency. The increased fuel flow to achieve the same PR suggests that in fact the turbine efficiency has been reduced. You need to turn the wick up to get the power required to achieve the target PR. If you did get more mass flow via the area increase, it may be diminished due to the need to increase the firing temperature. How do the PRs vs RPM look? That may help you understand how the operating point moved in the compressor map space.

[jetric]

Hi John,
Your problem with your engine is the pressure relief valve is opening in the Bosch fuel pump, this is causing the fluctuations in your engine rpm, as you have said you have had to turn the fuel pressure up, you are now hitting the limit of the fuel pump.

Richard S.

Jul 23, 2024 4:13:34 GMT -5 racket said:

Hi Andy

I don't know what has caused it , the only changes I made were a slight mod to the fuel injectors and increased turb exducer clearance by 3mm to provide more flow area so as to increase pressure drop across the NGV, which there was as the NGV exit static pressure reading was lower , 1.5 Bar vs 1.8 previously at 3 Bar P2 , and provide greater impulse energy to the turb wheel to compensate for the exducer clearance , the positives of a radial wheel is the inducer and exducer are two separate entities .

I noticed that the green manometer readings weren't much different than the previous test with the red manometer indicating a bit less dumping of air this test.

Fuel pressures were a lot higher this test, 80 psi vs 65 psi at 3 Bar P2 which would account for the higher turb temps and 15% thrust increase at 3 Bar , even though P4t was lower.

Theres got to be a solution to these variables , just need to figure out what it is :-)

Another test run with a full tank of fuel and some new data collection points maybe ..............I've been also looking at my oil pump pressures which appear to suggest that the pumps power supply is fading a bit too fast, hopefully its not another battery dying :-(

Cheers
John

[finiteparts]

Hopefully you find something else, but that sort of instability really looks like a classic surge condition. Since you did change the operating point, it could have somehow lost surge margin.

It seems like the increase in area, increases flow and that is supported by the slight increase in thrust. If the turbine efficiency goes down, then the PR point for a given speeding should go to a lower PR, higher mass flow point...i.e. away from the surge line.

Maybe when you juice it to get it to accelerate, the transient firing temperature increase pushes you over the surge line. Could maybe test that theory with a very slow accel.

Good luck!

[racket]

Hi Richard

Thanks for the suggestion , so just went and checked the fuel pump and all is normal , took it up to 120 psi without problems , its a 12V pump running on 24V so plenty of grunt , I think I can tick that off as a potential reason.

Bummer , gunna have to keep searching :-(

Cheers
John

[racket]

Hi Chris

RPM vs P2 pressures were within a couple of hundred rpm of previous test , well within variables.

The higher jetpipe temps at 3 Bar , ~120 C degrees averaged increase , coupled with the lower P4t ,0.4 vs 0.45 Bar, meant only ~30 ft/sec difference in gas velocity, ~2% , so the 15% thrust increase was mainly from greater mass flow, this would also tie in with the lower NGV exit static pressure as the extra mass flow and higher temps would have needed more pressure drop to get through the throats .

More testing required :-)

Cheers
John

[finiteparts]

John,

Just a quick estimation of the loss in efficiency due to the increase in the radial clearance based on the data reported here:

ntrs.nasa.gov/citations/19700008458

Using the last plot on page 19, I took a SWAG at estimating the impact of the 3mm increase.   Based on an image of your turbine exit, I estimated the exducer blade span as roughly 40 mm.   

So the original 1mm diametral clearance (128 -127 mm) was roughly 1.25% of span, while going to the 7mm diametral clearance (134 -127 mm) increases this to roughly 8.75% of span.

As plotted below, this data set would estimate somewhere near an 8% loss in turbine total to total efficiency.



Just some food for thought.

- Chris