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Post by racket on Nov 19, 2021 16:03:48 GMT -5
Hi Ralph
Thanks for the suggestions :-)
I've been having a good look inside the flametube and it looks like theres been "fluid" circulating around the corner between the front and outer wall .
The fuel sprays are producing significant rotary swirl within the primary zone .
I've also been experimenting with different injector designs to change the fan spray shape and fuel coverage in the spray , I've been able to make a narrower angled fan which may prevent fuel from impacting both the inner and outer walls .
I went with 9 injectors compared to the 18 injectors I normally use with my engines so as to increase fuel pressures and atomisation , but the consequences of this is a much longer and stronger spray , long enough and wide enough to allow fuel to "wet" the walls , especially the outer one , hence the lack of "colouring" of its Primary area .
I'm contemplating going to 18 injectors of smaller bore size so as to maintain pressures and atomisation , but unfortunately smaller bore mean more chance of blockage as well as them being more fragile .
I'm also thinking of reversing the direction of the sprays so that they are counterclockwise which should create more turbulence within the flametube as I have residual swirl from the diffuser channels around the outside of the flametube which then produce clockwise injection of air through the wall holes
I'll setup some spray testing of the current manifold today to verify whats actually happening before making any mods .
I've been checking out the results of Andy's engine build using injectors and noticed he used longer injectors which placed the sprays further from the front wall which when combined with using 18 injectors vs my 9 injectors probably accounts for why his build worked and mine is having issues .
All food for thought :-)
Cheers John
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Post by racket on Nov 19, 2021 23:41:31 GMT -5
Hi Guys Was doing some flow tests of the injectors and found there was fuel pressure fluctuations :-( So decided to run a test where the engine supply valve was left shut and the dump valve operated to put backpressure on the pump . The fuel pressure gauge wasn't very steady youtu.be/DdhmINyhndk and you can hear the pump making strange noises , especially at the higher fuel pressures . This might be some of my P2 P4t gauge vibrations, erratic fuel delivery Cheers John
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monty
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Currently being spanked by mother nature.......
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Posts: 400
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Post by monty on Nov 20, 2021 0:29:19 GMT -5
Hi Guys Was doing some flow tests of the injectors and found there was fuel pressure fluctuations :-( So decided to run a test where the engine supply valve was left shut and the dump valve operated to put backpressure on the pump . The fuel pressure gauge wasn't very steady youtu.be/DdhmINyhndk and you can hear the pump making strange noises , especially at the higher fuel pressures . This might be some of my P2 P4t gauge vibrations, erratic fuel delivery Cheers John John,
Sounds like cavitation! What kind of pump are you using?
Monty
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Post by racket on Nov 20, 2021 1:34:50 GMT -5
Hi Monty
LOL.....an "inexpensive" 044 pump .
Yep it does sound like cavitation , but its not so bad when the pressure is lower and the flow is higher .
I'll investigate further tomorrow , might need a high flow low pressure pump at the fuel tank to prime the EFI pump .
Cheers John
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Post by finiteparts on Nov 21, 2021 22:27:30 GMT -5
Hi John,
It is interesting how "calm" the gauges were on your other runs from what I can see in your older videos (other engines), so it was making me wonder what was different on this engine?
I agree with Monty about the potential for the gauge coupling with a system resonance...and on that theory I looked at your old videos to see if there was a difference in how the gauge was connected. It looks as though in the past, the P4 gauge was a touch closer to the pressure tap...is that true? It looks like in the past, the gauge was on the side of the engine nearest you, while your current setup has it on the side farthest from you on the panel, which maybe added a bit of length to the pressure sensing line.
I know that Bourdon tube style pressure gauges are not really good at handling high frequency pressure oscillations, but I had no idea how high a frequency was too high. So I did a search and the only information that I could find was here:
If you jump to page 6, we get a hint of the resonant frequency of similar gauges, 100 to 400 Hz. If we assume that the average temperature of the gas in the total pressure sensing line between the probe and the gauge is much lower that the gas flow that it is sensing, say for the sake of argument, 180 deg F. Then, if the distance between the sensing port and the gauge is varied, we can see how the natural frequency of the sensing line changes. For several lengths, here are the natural frequencies:
Length(ft) Natural Frequency (Hz) 1 ft 307.5 Hz 1.5 ft 204.7 Hz 2.0 ft 153.5 Hz 3.05 ft 100.7 Hz
So, we can see that the system response and the gauge could be on similar order of magnitude and the potential for acoustic coupling is definitely a possibility.
The nice thing about this theory is that it is easy to test by just shortening the sensing tube length and see if the needle vibrations are reduced.
As Monty said, if you add a restriction in the sensing lines, you can reduce the effective length of the resonant cavity (the sensing line) because of the impedance change imposed by the sudden area change. If you look at the NASA or other literature out their on pressure pickups, the general guidance is to have a very small orifice that opens up to the larger diameter in the sensing line, which helps to reduce the transmittance of the acoustic waves into the sensing line. So if the pressure inlet on the probe is the same diameter as the i.d of the tubing, it might also help to weld over the end and drill it with a very small port.
Just a few ideas that I thought I would share....Good luck!
Chris
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monty
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Currently being spanked by mother nature.......
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Post by monty on Nov 22, 2021 0:05:54 GMT -5
John,
Another thought: If the pump is that close to cavitation, any pressure fluctuations would tend to exacerbate the issue. As the pressure rises, the cavitation worsens until the negative return wave allows fuel delivery to resume. Rinse and repeat. Combustion instability which feeds back into the pump causing fuel delivery instability.....a vicious cycle. If there are any secondary resonances with the volume of the engine case/exhaust tube length it will only be worse. All of this could also cause problems with the gauges of course. I've worked on systems where all kinds of things that should never have stacked up did...unintentionally. It can be quite a chore to separate it all out. A lift pump and nice clean flow into the main fuel pump are a good place to start. I have no doubt you'll get it sorted.
Monty
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Post by racket on Nov 22, 2021 3:23:53 GMT -5
Hi Monty
I've been doing more testing today with the engine supply valve closed and all fuel exiting via the dump valve , and the pump flows 4500ml/min at nil pressure, other than the restrictions through the dump valve, this is close to what an 044 pump does .
At 60 psi it drops to 3400ml/min , 80psi 3,000 ml/min and 2800ml/min at 90 psi .
The greatest noise and bouncy needle is at ~60 psi .
I've tried lifting the fuel tank to level with the pump to reduce any lift effects , but no difference .
Then I removed the suction tube in the tank and only had the 10mm ID rubber hose , still the same :-(
So have now removed the inline filter and will fit some "ovesized" suction line between tank and pump to erradicate all restrictions .
But , I got thinking and realised that "direct injection" is different to using vapourising tubes , direct injection is instantanious whereas vapouriser are "softer" in that the flow of fuel down the tubes tends to smooth out any peaks or troughs .
Any pressure blip at the pump is hydraulicaly transmitted to the injector with a change in flow which will change the rate of heat release and expansion that the P2 gauge will sense .
An accumulator in the supply line would "soften" things , I added an accumulator into my bikes TV84 fuel system to erradicate the pulsing caused by the fuel pump being gear driven by a 2 stroke engine that couldn't supply a steady amount of fuel .
I'll see how my mods tomorrow go and report back :-)
Went to the sheet metal guys today , they'll roll up the remaining A/B body and nozzle and weld them to my bits that connect to the engine, hopefully A/B testing early in the new year .
Cheers John
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Post by finiteparts on Nov 22, 2021 8:18:32 GMT -5
Did you use that pump on previous engines or is it new for this one?
- Chris
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monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 400
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Post by monty on Nov 22, 2021 17:44:37 GMT -5
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Post by racket on Nov 23, 2021 3:25:20 GMT -5
Hi Chris
Yep , the pump was used on the previous engine, I had to replace my original test stand pump as it simply couldn't supply enough fuel .
Today I fitted a 16mm ID suction line between pump inlet and fuel tank to remove all restrictions ...................the pump now "sings" continuosly :-)
Theres some "wandering" of output pressure , a couple of psi , but smoothly/slowly not jumping ..............it looks like theres been cavitation for some time , probably since I installed the larger 044 pump and left the rest of the suction line as previously, it never entered my mind that there could be a problem :-(
Tomorrow I'll do some flow checks at various output pressures and compare to the data from the other days testing to see how much flow was being lost to cavitation .
LOL.......I guess I've been fixated with the engine's behaviour to not take much notice of fuel pressure stability , thinking the bouncing P2/P4t gauges were being caused by surge rather than fuel delivery , it'll be interesting to see what the gauges do on the next test :-)
Cheers John
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Post by wannabebuilderuk on Nov 23, 2021 3:52:29 GMT -5
I had no idea the big 044 style pumps actually used metal parts let alone a rotary vane style pump... The pumping element is very compact and I wonder if it could be modified to become an oil pump with a lower rpm motor hmmm...
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jetric
Veteran Member
Joined: December 2014
Posts: 141
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Post by jetric on Nov 23, 2021 11:40:07 GMT -5
I had no idea the big 044 style pumps actually used metal parts let alone a rotary vane style pump... The pumping element is very compact and I wonder if it could be modified to become an oil pump with a lower rpm motor hmmm... I have used one of these EFI fuel pumps as a oil pump on my first DIY engine back in 1999, It did work quite well and it was handy having the internal pressure relief valve, The only issue I had was the carbon brushes on the comutator as this brush material acted as EDM on the comutator and soon ate away at the copper comutator because of the oil film creating a poor contact, the only way I solved the issue was to replace the carbon brushes with copper brushes that I made to the same shape as the originals, this totally solved the erosion. My next development on this idea was to try to fit a brushless RC car motor inside in the place of the original motor. Richard S.
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Post by enginewhisperer on Nov 23, 2021 19:22:13 GMT -5
Today I fitted a 16mm ID suction line between pump inlet and fuel tank to remove all restrictions ...................the pump now "sings" continuosly :-) The 044 was apparently designed to be fed from a low pressure "lift pump", so they are pretty sensitive to any restrictions on the inlet side. Hopefully it does the job with the bigger pipe
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Post by racket on Nov 24, 2021 3:10:37 GMT -5
Hi Andrew
Thanks for that , kinda help explain things :-)
Today I did more test at varying pressures and found I was getting ~10% extra flow at each pressure than previously with the cavitation.
I've ordered a twin 044 setup and will modify my fuel valving to better represent the extra flows.
Along with fitting smaller injectors and doubling the number from 9 to 18 , the finer atomisation should produce better combustion ...............I wanna see 3 Bar of P2 on the next test run :-)
Cheers John
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Post by racket on Nov 26, 2021 0:53:59 GMT -5
Hi Guys
A quick update ..................18 X 21G injectors fitted to the fuel manifold , orientated to spray in the opposite direction to previously , hopefully to promote more mixing of fuel/air as there is some residual swirl in the air going through the outer wall holes .
Adjustments made to the main can O'ring groove so that the silicone o'ring doesn't jam when it swells after coming in contact with fuel , also the turb end o'ring groove needed similar treatment , the comp end was modified at the last disassembly and is now working as it should .
Time to think about putting her back together :-)
Cheers John
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