"Fat Boy" 12/118 thrust engine

[racket]

Hi Guys

Removed the engine and the outer can came off and no surprises inside .......yet .

But did notice a segment of the outer wall right at the back end hadn't been coloured as far back as the rest of the flametube and that segment corresponded to the lower temp side of the jetpipe , so it looks like I'm going to have to do some testing of the fuel manifold to find out why I've got 200 C degrees difference in the temps , it appears as though theres fuel being burnt in that "cool" segment , but just not the same rates as the other side.

The outer wall is seeing more "temperature" than the old wall it replaced and theres heat colour right up to the front wall , so combustion is starting early giving me a bit more dwell time for its completion , fuel pressures for the various P2 pressures are a little less than previously so maybe more complete combustion .

The turb wheel is seeing only the medium temp of ~650-700 C so getting an easy time of it .

At the 3.85:1 PR the fuel pump max'ed out at 82 psi , comp efficiency seems to be ~78-79%

Cheers
John

[racket]

Hi Andy

Yep , she's purring nicely according to my long suffering offsider ;-)

Cheers
John

[turboron]

John, your achievement is very encouraging to the rest of us that are struggling to find solutions. Your innovations to improve combustion are very innovative.

Thanks, Ron

[madpatty]

Racket.

As Ron said your achievement is really encouraging for all of us here, especially the new techniques you have used in your combustion design and in Andy's engine, very few people have done that in "Homemade" engine category. I am sure combustion is no more a "black art" for you anymore!
Hopefully you have patented the fuel injection techniques used in yours and Andy's engine.

Cheers.

[racket]

Hi Guys

I've opened up the flametube and alls OK inside , no holes

The combustion is starting right at the front wall with blue'ing of it between thimbles where the opposing air jets from neighbouring thimbles collide and provide sufficient turbulence , its hot enough to blue the 2 mm stainless and certainly hot enough to evaporate any stray droplets of fuel that might land on any surface , the thimble tops are still "silver"



The outer wall is nicely coloured from front to back



The "hot" side is heating the wall past the last row of small holes



Whereas the "cool" side isn't as "active"



Cheers
John

[racket]

Hi Guys

Well I've checking out the fuel system and there doesn't appear to be any problems , the new fuel pump is capable of >3 LPM at 90 psi , ~ 4 LPM at more normal fuel pressures , so no starvation at full power , only losing ~10 psi max from "plumbing" up to the engine .

Then progressed to checking the fuel manifold using water supply and final filter , at 20 psi delivery pressure all injectors were flowing ~120 ml/min , give or take ~10 ml/min because of my rough technique and lotsa overspray from adjoining injectors with their bent tips providing plenty of water mist over everything including me ..............so I can discount any blocked injectors for my >200 C degree variation in the jetpipe thermos .

When the fuel manifold was mounted onto the flametube endwall with the evap tubes , the water sprays from the injectors produced varying amounts of spray exiting the inlet to the tubes.

I'll replace all the current 21 gauge bent tip injectors , don't need the bent tip and spray fan now that I have the tube internal spring to spread the flow over the ID .

I have enough 19 gauge syringe needles to replace the 21 gauge ones and will leave them as just tubes , no bent tips ,..........their larger bore will flow ~50% greater so I can dial back the supply pressure and hopefully get more even/consistent quantities entering the tubes.

Once the new injectors are installed in the manifold and the manifold fitted to the flametube rear wall, I'll do another water test to check flows etc ...............if alls OK, I'll reassemble the engine for a test run .

Cheers
John

[monty]

John,

I've been enjoying this combustion stuff.....soon enough I'll be the next victim! Not really looking forward to it. I'm comfortable with machining and making parts.....keeping all that fire contained and behaved....not so much!

Monty

[racket]

Hi Monty

LOL............I'm glad someone is getting some enjoyment from my suffering ;-)

I think I might have found the problem , ..........after removing the old 21 gauge injectors I drilled out their mounting holes in the manifold to 1.1 mm dia for the 19 gauge syringes , even though I used compressed air fed into the manifold to expell any bits of metal as I drilled , I thought I'd better just give the manifold a bit of a shake and see what came out of the supply line .

To my surprise , huge chunks of rusty looking material fell out .............bugger I thought , better give it a bit more rough treatment and see if anymore comes out , which it did, so the process was repeated a few more times ..............methinks its time to make a new manifold and cut the old one apart to see whats going on , its made out of steel Bundy brake line so shouldn't be rust prone , might need to make the next one out of stainless .

Cheers
John

[turboron]

John, my first attempt at starting my DIY gas turbine a few years ago was a disaster. Very high fuel pressures were required to get to idle. After spending a lot of time troubleshooting and consulting with the late great Mike Early I discovered the fuel nozzle was full of machining swarf I had not cleaned out. A water flow test showed some fuel nozzle ports plugged. Others squirted to one side, etc. The cleaned nozzle had a uniform radial pattern.
Thanks, Ron

[racket]

Hi Ron

I slit the current fuel manifold in half and found a couple of spots where there was considerable rust pitting of the bore, it appears that this brake line didn't have any surface treatment of the bore,it was just plain old steel:-(

I'll go looking for something more suitable tomorrow.

A jetnozzle has now been fitted to the jetpipe ..............I cut off a section of one of my diffuser exhausts and simply turned it around and welded it on , easy :-) ........at ~106-107 mm it should be about right .

Cheers
John

[racket]

Hi Guys

The new fuel manifold has been constructed with 18 X 19 gauge syringe injectors to replace the smaller 18 X 21 gauge bent tip ones .

I also purchased a high quality 4" dia, 2.5 Bar pressure gauge to do the flow checks with, the larger diameter makes for easier use at lower pressure changes .


With the fuel manifold mounted to the flametube rear wall with its evap tubes, the whole assembly was fitted into a large container and testing at various pressure drops conducted , I only need an ~11 psi pressure drop to flow ~2700ml/min , add on 40 psi P2 , and the fuel pump need not go much past 50 psi .

To test uniformity of flows I fitted small plastic "shot glass' " under each evap tube outlet



With throttle set at a supply pressure drop of ~ 6.5 psi or 2,000 ml/min , a mid range throttle setting , I flowed a tad over 400 ml into the 18 containers , ~23 ml/container , with fuel levels all within close specs to each other





The bores of the syringe needles do vary a tad , taking that into account , the results are encouraging

Cheers
John

[Deleted]

Hi

Sounds like time for a new test soon

[racket]

Hi Guys

Took the engine out for a test run this morning , things went rather well so I taught Fat Boy to dance ;-)

youtu.be/U_Ltkxa-Ddk

Cheers
John

[racket]

and a spoolup
youtu.be/Ri5TRvpG1lo

[racket]

And some "numbers" .

youtu.be/2Gtn5SEyc_s

I've got a bit of autopsy work to do today , but things are looking good , a bit too much start fuel from the bigger 19G injectors vs the old 21 G ones which lengthened the spoolup in conjunction with the addition of the jetnozzle , but the temp differences between the 2 jetpipe thermocouples appear to be fixed .

She's making some serious thrust now,............. development finished :-)

Cheers
John