Holset HX50 Supermoto Jetbike

[htevo80]

Jun 3, 2020 4:08:56 GMT -5 racket said:

Hi Scott

If you can get a reading that produces an efficiency of 72-75% you'll be OK .

Yep , gotta have reliable TOTs

All the best with the next testrun :-)

Cheers
John

How does one derive efficiency numbers for our jets
Thank you
Gavin

[racket]

Hi Gavin

Do you mean compressor stage efficiencies ??

postimg.cc/sB6jk9vC

Cheers
John

[slittlewing]

Thanks John, I had a much more successful second run this weekend, with all panels and seat fitted. I first did a 35second full throttle (no AB). The T2 got to 173 deg, but then I had a small fire at the front of the engine and had to back off to idle to extinguish it. so (273+15) /(273 + 173) = 288/446 = 65% efficiency? However, with subsequent full throttles (and afterburn) the T2 reduces as shown:




Video:



I am unsure whether to push the PR higher than 3:1 (to 3.5:1) but from all the info so far, it seems I am probably close to the limit on the compressor map and I don't want to hit the "choke line". For the effort of an extra 0.5bar P2 vs risk of turbo failure (along with needing to remap the new injector flow vs PWM in the software) I might keep it as it is, with the 13.5GPH injector? Especially whilst I haven't verified true "max" TOT readings. At the back of my mind is also the existing "tip damage" on a couple of the turbine blades.

The AB ran very nicely with my old gain. I installed a brand new 6mm K Type (inside the thermowell) before fireup. There were some problems with it immediately after starting engine. In fact both thermocouples (oil temp aswell) stopped reading, so after 5 minutes running the oil had warmed and dropped in viscosity. I programmed the Arduino to push the oil pump harder as the oil gets hotter to compensate for this, but without the temp reading the oil pressure dropped and eventually dropped below P2, where I got an oil pressure kill from my Arduino code (at the end of the video). On a later start however, it all worked nicely and TOT showed 387degC at idle (0.4bar P2). On that run, stupidly I didn't throttle it up as I did a "smoke test" and thought I had tested the neighbours patience enough for one day. I think its still an EMC issue, so I am going to turn off the thermocouple reader PCB's during startup (when there is spark on). 

I am hoping the next time I run the bike, it will be to ride it!!

Many thanks for all the support,

Scott

[racket]

Hi Scott

T2 of 173 on a 15 C day gives us a temp rise of 158 C degrees , a 3:1 PR at 100% effic on a 15 C day would result in a rise of 106.32 C degrees, 106.32/158 = 67.3% effic , thats not too good , I'd say you were well into the choke side of the map where your RPM could be quite a bit higher than the 3:1 PR would normally indicate , I think I'd be calling it quits at 3:1 until you get some accurate RPM numbers .

The drop in T2 with the afterburner is understandable as flow could have been restricted back to a better efficiency , but you'd probably find your turb temps may have increased and/or P2 dropped a tad with the afterburner activation which would have dropped T2 even though still flowing into the choke region, we'd need to see all parameters together to determine exactly what was happening

The afterburner is sounding sweet and the "right" colour ;-).................I think Andy M would sign off on it .

Time to ride her :-)

Cheers
John

[pitciblackscotland]

Awesome work mate As John said time to ride Good luck.

Cheers,
Mark.

[jetric]

    Its good to see my afterburner design still works nicely,

   Richard S.

Jun 8, 2020 20:47:38 GMT -5 racket said:

Hi Scott

T2 of 173 on a 15 C day gives us a temp rise of 158 C degrees , a 3:1 PR at 100% effic on a 15 C day would result in a rise of 106.32 C degrees, 106.32/158 = 67.3% effic , thats not too good , I'd say you were well into the choke side of the map where your RPM could be quite a bit higher than the 3:1 PR would normally indicate , I think I'd be calling it quits at 3:1 until you get some accurate RPM numbers .

The drop in T2 with the afterburner is understandable as flow could have been restricted back to a better efficiency , but you'd probably find your turb temps may have increased and/or P2 dropped a tad with the afterburner activation which would have dropped T2 even though still flowing into the choke region, we'd need to see all parameters together to determine exactly what was happening

The afterburner is sounding sweet and the "right" colour ;-).................I think Andy M would sign off on it .

Time to ride her :-)

Cheers
John

[slittlewing]

Thanks for the feedback all! The numbers are a good enough reason for me to leave it as it is!! I do now have the tachometer but haven't had a chance to use it without a "helper". Getting my hand into the bellmouth to fit a reflective tape also looks tricky haha.

Richard, I had a question for you - do you know the reason why the AB will only light at idle/low throttle? I was wondering if it might be due to spark plug location being too lean once the fuel spray gets pushed further down the tube after the "expansion void"?

I am making plans to ride it, in the meantime I have a joblist to try and make it a bit more "reliable" or at least less prone to the small fires I have had. The main one being a small boost leak between turbine housing and combustor, which I think is leaking a small amount of very hot air and was the cause of the fire in the previous vid. I should have made my combustor top thicker, it has bevelled slightly and gapped a tiny amount from the turbo, so I have a new gasket on the way and some "extreme heat" sealing paste.
There also appears to be a bit of oil weeping from the silicone "flexi" between the compressor outlet and combustor, I think a little oil coming past the compressor seal. There are a stack of 20 or so other little "finishing" jobs, so a busy few weeks ahead but hopefully a reward at the end, not a burnt bottom!!!

Many thanks,

Scott

[racket]

Hi Scott

Yep , gotta have thick flanges where theres heat , 3/8" minimum .

LOL, no burnt bottom , maybe some fireproof undies ;-)

Cheers
John

[racket]

Hi Scott

Most of our DIY afterburners are based on the AiResearch ramjet dump combustor used on their 1030 Low Cost Turbojet , I think this might be the Link apps.dtic.mil/dtic/tr/fulltext/u2/a067277.pdf.

Getting exactly the right combination of fuel injection and plug position does get complicated when taken in conjunction with mass flow rates and dump step/afterburner diameter .

Lotsa data in the Paper :-)

Cheers
John

[slittlewing]

Many thanks for the link John, very interesting (and I imagine impossible to find on the internet)! So I can now see where our 7 degree AB "cone angle" and 8x1mm holes come from!!

I am intending to ride the Jetbike in about 2 weeks time on a UK Dragstrip, weather dependent. My main concern about having another fire half way down the strip and kissing goodbye to the bike, means I have started on my leak fixing exercise - which has involved dropping the combustor down. Unfortunately as everything is so packed in (or maybe because I "designed" it without considering serviceability!!) this has meant stripping almost the entire bike down and removing all the pumps.
The combustor is now out and having looked inside it with a torch, the flame tube looks in good condition. The turbine blades on the turbo also look the familiar dry "white" colour.







The AB tube mounts to turbo on bolted flange, I didn't have a new stainless gasket so re-used the old one in conjunction with JB Weld "Extreme Heat" Metallic Paste. I intend to use the same on the combustor joint (with new SS gasket). I will also be routing the oil tank breather into the compressor entry to avoid all the oil mist. I am aiming for the bike to have no leaks at all and no smoke or vapour around the engine, also making any problem easier to spot during startup etc!!

Cheers

Scott

[pitciblackscotland]

Not a good idea to have oil tank breather into the compressor entry, will gum up the compressor with oil deposits. I did that on my first turbojet engine and the compressor wheel was coated with oil.

Cheers,
Mark.

[turboron]

Scott, on the aircraft gas turbines I worked on we routed the oil fumes to the turbine exhaust.

Thanks, Ron

[slittlewing]

Thanks for the replies on this, was there any negative to the oil on the compressor wheel (ie did it go black or harden on it)? I’m thinking routing it to the exhaust could be difficult due to the high temp and also AB pressure!

Cheers,

Scott

[pitciblackscotland]

Jun 18, 2020 13:40:41 GMT -5 slittlewing said:

Thanks for the replies on this, was there any negative to the oil on the compressor wheel (ie did it go black or harden on it)? I’m thinking routing it to the exhaust could be difficult due to the high temp and also AB pressure!

Cheers,

Scott

As the comp wheel gets coated with oil deposits, dust, dirt will stick to the wheel and put it out of balance. You could run a steel tube along side of the AB pipe, similar to mightyfinejonboy done on his jet kart www.youtube.com/watch?v=GDIq_ujgVP0


Cheers,
Mark.

[racket]

Hi Scott

Yep , fires aren't a good thing when we sit on top of them :-(

Early on with the TV84 bike testing I had a fire near the freepower and had to lay the bike on its side and let it burn itself out , it was just some oil leaking onto a hot surface , but a tad scary at the time as fires can very quickly get out of control .

Looking forward to hearing how the testrun goes , all the best :-)

Cheers
John