Holset HX50 Supermoto Jetbike

[racket]

Hi Scott

I'd still try the 60 degree hollow cone nozzle before doing any mods .

Remember your current FT cross sectional area is less than 3 times inducer area so is going to be prone to "problems" , thats why I suggested leaving holes as they were so as to provide more "energy" in the air injection to promote turbulence

Cheers
John

[slittlewing]

Hi John,

Thanks for the advice and reminder about the air injection and smaller diameter FT than ideal!

I now have a nozzle on order but there’s no Uk stock so it may take some weeks to arrive I will probably look to at least add washers to reinstate the 8mm topcap cooling holes which were drilled to 9.5 whilst testing on Saturday.

Cheers

Scott

[racket]

Hi Scott

Yep , put her back to original specs , better to have a running engine with a hot cap than one that has problems.

A quick spoolup with things put back to original specs will soon indicate if another problem has arisen or if it was just those tubes causing the problems , which I still feel is unlikely unless the flametube is "marginal" and thats all it took to throw it out............interesting .

Cheers
John

[slittlewing]

Yes indeed!! I hope I can get it back together for this weekend and do an idle test and see whether or not it really is this sensitive

I did some calcs regarding the possibility of opening up the last set of tiny holes in my FT primary zone to improve the possible delayed combustion >2 bar P2. If I opened them from 3mm to 7mm, it would give quite alot more primary hole area but still remain well under the effective area of the comp (in terms of utilising air injection "energy")!



Cheers

Scott

[slittlewing]

So after welding washers over the enlarged cooling cap holes, I did a "quick spool up" test again today to check the engine idle.

However... after welding up the holes, I found something that I think is likely to be the actual cause of the issues last weekend (John you were right of course!). The Monarch nozzles have an internal threaded "banjo" style grub screw with a hex cut inside it, which pushes on some kind of vortex generating disc that sits behind the nozzle orifice. This little grub screw had come pretty loose, and I guess the disc under the orifice was able to move around. Undoubtedly this would have lead to a different spray pattern or maybe atomisation issues. Frustratingly I found it after welding the holes up, and I have seen this issue before on an old 13.5GPH injector.






I think that even when re-tightened, there is an ability for this little "grub screw" to loosen as during running the nozzle must be getting very hot and expanding, releasing any pressure on the threads.

Anyway... With the cooling holes back to original spec and this grub tightened, I was able to get the engine to idle down to 0.4bar at a PWM of ~12%. Below this the engine switched off as I must have been getting poor atomisation or not enough fuel pressure to get past the pump non return valve.

Going forwards, I am very tempted to try and make a new lower flame tube, which I could easily bolt in. I am currently missing a swirler which I know promotes mixing and adds a stationary flow zone in the centre of the fuel spray cone. With the addition of a swirler like below, I would also have a cool burner nozzle and cool top cap. The design below has 30% PZ area in the swirler which is of a radial design (concept shown to me a long time ago by Jetric, thankyou Richard). The two rows of primary holes would intersect the fuel spray at injector spray angles of 80 and 60 deg.
Do you think its worth giving this a go?






Cheers

Scott

[finiteparts]

Scott,

That sounds like a really likely theory on why you had such difference in the testing.  That is the problem with "armchair mechanics" or in this case, "armchair engineers"...ha!  With the spin disk lifted off the the nozzle surface, it would have been nearly impossible to impart the needed tangential velocity to the fuel for proper atomization. Additionally, the slots in the spin disk are the "controlling" area for the fuel flow, so you would have been flowing fuel at a much higher rate for a given pressure, but with poor atomization.

I had been thinking about John's comment about the fuel injector and I was concerned that with your fuel injector mounted to the glowing hot headend, that it might experience some coaking issues....but from your photos, that doesn't seem to be an issue. Now, the heating of the fuel nozzle could have aided in the loosening of the retaining screw. Also, I think that most fuel nozzles have an included filter that helps to keep the retainer screw from walking out.

I think that the effort to remake you combustor liner will be very beneficial. When I worked at a previous job, we would make gas fuel nozzles with drilled swirl hole like that and they were very effective. We also used milled slots that were closed off when bolted together and those had the benefit that we could shape the air passage to converge toward the inner lip. I will look for some open source information on how to design them to achieve a target "Swirl number".

Good luck,

Chris

[racket]

Hi Scott

Yep , that'd be the problem .

As Chris mentioned, the filter works as a kind of "lock nut" to prevent the swirler producer from unscrewing .

My TV84 flametube had the fuel nozzle mounted into the FT mounting stub, in such a way that it couldn't fall into the FT, and the "hole" surrounding the fuel nozzle allowed air to pass over the nozzle and "centralise" the spray

imgbb.com/hXLJgpM

The fuel nozzle pocket was fed air through 4 holes in the side of the stub , LOL, I just copied the description of how they should be constructed in one of my texts.

ibb.co/zNcnSHh

Cheers
John

[slittlewing]

So during the last month I have been slowly progressing this new FT. I ordered material to make the boss but it took 3 weeks to come! I also got a SS dome of the right diameter from China.

The 60 degree hollowcone nozzle has had to come from the USA and should arrive soon.

The turned parts are now manufactured thanks to a friend who kindly machined them for me during one of his evenings.






I have completed the new FT design and will send it for laser cutting along with a new thicker end cap (6mm va 3mm before). It should not see any radiant heat thus should also not be weakened and bevel as much as the last one did anyway.



Cheers

Scott

[slittlewing]

Minor update, the 17.5 Hollow cone nozzle arrived from America. 36x small holes drilled into the dome, awaiting FT from laser cutting 👍





Cheers
Scott

[racket]

Hi Scott

Nice dome :-)

What was it ??

Cheers
John

[slittlewing]

Cheers, it was from China (AliExpress) sold as a SS304 tube cap, you can get them in multitudes of sizes. I might buy another to use as a concave end cap for kart engine! I bought some Kilner funnels off amazon first but they were too thin for my welding (about 0.5mm).

I got my laser cut parts today, the new end cap (now 6mm instead of 3mm) and FT. Rolled it up and welded up tonight. I purged it but didn’t get much penetration, was too scared to hang around heating the thin metal with the torch but hopefully it’ll be ok.

I have also made a gasket from 1.5mm high temp gasket material (300degC) as the copper one didn’t seal very well. My previous attempts with gasket material didn’t like the high temps from the glowing end cap but hopefully that is now resolved!











image hosting for forums

I removed the retaining grub screw from an old monarch injector and loctited against the standard grub in the new 17.5 hollowcone one, to also try and prevent it backing out again, which it no longer should considering the injector is now heavily air cooled by the swirler.

Fingers crossed this all works!

Cheers

Scott

[racket]

Hi Scott

Its looking nice and solid :-)

Looking forward to seeing how things perform .

I'll checkout Alibaba , thanks for that

Cheers
John

[slittlewing]

Thanks John, I’m keeping my fingers crossed!

Try this link

￡1.87 | Industrial Use 114 133 159 168 180 200 219 250 273 300 325 350 377 400mm End Cap 304 Stainless Steel Pipe Fitting
a.aliexpress.com/_mPIQnih

Cheers
Scott

[slittlewing]

Well I got the new FT in and fired it up, not too great for a first off though.

It started fine but smoked plenty at idle. I waited to see if it would “burn off” but it didn’t. Under throttle it was much worse so I shut it down before it attracted unwanted attention from neighbours!!



I wonder if the hollowcone spray is either hitting the FT walls or is too dense for the air to penetrate. I think the first (easiest) thing to try is refitting my semi solid 80deg PLP I was using before. If that’s no good, some hole blocking maybe required.

Cheers

Scott 

[wannabebuilderuk]

"before it attracted unwanted attention from neighbours" I think the noise would get them first lol, hope you find the issue.

Also I've just noticed the wonky hole and it stands out like a sore thumb now 😂