t18a96 turbo jet

[sub22b]

Hi john I wont change the size or length of my combustion chamber but I may make it out of thinner material. when I built it I figured a compressor tank would be perfect as it can handle a lot of air pressure and be fairly safe but it is fairly heavy. That's good to hear about the weight on the go-kart. I will still try and remove as much weight as possible to help out. what would be the limiting factor on the p2 psi? Do you think i will still get enough thrust from the engine at 30psi to push a go-kart?

cheers Nick

[racket]

Hi Nick

Yep , you should get sufficient thrust :-)

The good thing about thrust powered is that you don't need a lot of pressure in the jetpipe to produce reasonable velocities , theres a "square root" in the formula , so we need ever increasing amounts of pressure to get ever decreasing increases .

There is something that concerns me though , and that is the size of your turbine wheel and scroll A/R , could you supply some sizes and perhaps a pic .

The reason I'm concerned is if its similar in size to our TV94 turb wheels then you'll have trouble getting the potential flow from your comp wheel through the turb wheel , its OK when used as a turbo because its possible to have a higher exhaust manifold pressure than inlet manifold pressure , the higher exhaust density allows the quantity of gases to be processed , its the same "dilemma" that I'm having with my 12/118 engine where the turb stage flow potential is marginal .

Theres another alternative and that is to bleed off some of the comp discharge air and simply allow the "marginal" turbine stage to have full expansion through it to power the comp wheel, the exhaust gases from the scroll can be exhausted rearwards for some thrust , but the bleed air can be fed to a "high pressure" afterburner for main thrust production, with Mach diamonds ;-).

Download this Paper ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930082793.pdf and look at the BLEEDOFF analysis section from page 20 for ideas.

An extra benefit from this "cycle" is that your turbo combustor can be smaller as it will be processing only a percentage of the comps output , a fairly large percentage but you might find its well worth the effort involved especially if your turb stage restricts your comp flows.

I'll be happy to talk you through the mods :-)

Cheers
John

[sub22b]

Hi john I did wonder if having such a big exhaust housing would effect it. I have thought about the bleed off idea before on another engine i built it may be something worth trying.  I have checked the stamp on the housing and after wire brushing and cleaning it the numbers are still very hard to read but im in two minds about the stamp my mate thinks its 2.68 because 3.68 is massive so im really not sure now. what measurements would you like?

Cheers Nick

[racket]

Hi Nick

Yeh , 3.68 is a bit big , I looked on this Site www.turbomaster.info/catalogos/modelo.php?base=garrett&pagina=T18A and a 2.00 is about the biggest, a pic of the scroll will indicate whether its got "nozzling" normally associated with a normal smallish A/R of ~1.5 or its just a fat doughnut at over 2.0 .

Looking at the exploded view on the Site it appears there are comp diffuser vanes on the T18A96 does yours have them ?? , they will/could also have a bearing on flows

If you have a very large A/R then what will determine the flow will be the turb wheel exducer flow area choking , so what we need to look at is the exducer diameter and its tip angle as well as inducer diameter and tip height , then see how they compare with their respective comp wheel measurements.

Whereabouts is the "3.68" mark , it should be close to the rectangular "foot" .

Cheers
John

[sub22b]

Hi john i have made a massive stuff up with stuffed digital calipers pays to buy good tools i guess. the comp inducer is 4inch not 4.5 . I cant get to the exhaust wheel without pulling everything part so will have to check that this weekend. Now back to the air ratio i have scrapped the numbers off again and on close inspection it does read 2.00ar so my friend was correct. I will post a couple photos anyway as i know you guys like them.

cheers nick

[sub22b]

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[racket]

Hi Nick

Now a 4 inch inducer is a far better match , that 25% flow difference should do the job .

A 2.00 A/R is a BIG A/R , so the turbo was a low boost setup, just looking at the difference between comp and turb scrolls its obvious the turb scroll won't be the controlling influence with regards mass flow , you'll probably be choking the turb exducer.

Once you have the exact sizes of the wheels we'll have a better chance of understanding whats required in the way of flametube/combustor as well as potential thrust levels .

Cheers
John

[smithy1]

Nov 7, 2016 4:21:35 GMT -5 racket said:

Hi Nick

As you'll probably be limited to 30 psi P2 as a maximum , the outer can could be relatively thin , 1.6mm - 1/16" sheet will hold the pressure .

Your 530 mm length is OK .

Smithies GT6041 combustor is pretty heavy duty and along with the very heavy turbo its a sizeable weight hanging off the kart , but it survives .

Cheers
John

Yeah...the GT6041 is quite a heavy turbo.....I'm guessing ~45kg's+ for just the turbo itself....Big cast iron turbine housing/bearing section and very thick comp housing, she's definitely heavy duty. John has "triangulated" the loads nicely and it survives well....I've also added a goodly sized 5kg A/B pipe to it....still appears to be fine.

The GT6041 will easily run ~42psi P2 max as well....I wouldn't be doing that with your lowish pressure turbo Nick....it probably wouldn't end well.

Cheers,
Smithy.

[sub22b]

Hi guys I would say my turbo weighs in at about the same as the gt6041 there not light that's for sure. I guess I wont push it past 30psi that's if it will get to 30psi and im also going to put a tachometer on the comp wheel this weekend and run it. what would the max rpm be for a turbo this size or is it more p2 pressure that is the more important factor?

cheers guys your help is awesome and im learning a lot about these engines. there totally different to the ww2 piston aircraft engines im used to playing with. so its great to have guys with lots of know how

cheers Nick

[racket]

Hi Nick

For an old turbo of unknown heritage a max rpm at ~1450 -1500 ft/sec tip speed for the largest wheel , assuming its your 5" comp , then ~68,000 , but if as I suspect your turb wheel could be ~129 mm dia like our TV94 ones then ~67,000 , so lets round it down a tad to 65,000 to give a bit more safety so early in its development, we can always squeeze a few more thousand at a latter date .

If your comp wheel is bigger than 5" exducer dia then you'll need to reduce rpm a tad more.

With such a large turb scroll A/R you might find that flow from the comp is more to the choke side of its map , in which case the P2 being developed will seem a bit low for the rpm , but don't be tempted to increase rpm to get the "30 psi" .

Your TOT will need to be kept fairly modest as well as we don't know the makeup of the turbine wheel material , if the turbo was for a diesel engine then it could have been made from GMR235 which is only good for ~850 C whilst if it was for a petrol engine then maybe in Inco 713C which has another 200 C degree limit , as long as your temps exiting the turb stage are in the 650 C range or lower then even at your max rpm you should be safe .

Do you know what the turbo was off ??

LOL , yep lotsa differences to piston engines , though those big centrif blowers on those WW2 engines and the B1 turbochargers at least look familiar :-)

Cheers
John

[sub22b]

Hi john im not going to push it that's for sure. I will see what rpm it is doing at around 20psi first before I push it any harder I really don't want a blown up turbo. I cant believe the noise it makes from the comp inducer at 20psi. without ear protection on it would cause serious hearing problems. I cant imagine what it will sound like at a higher p2 psi that's why I want to check the rpm because I have a bad feeling it may already be near its max rpm just from the noise it makes.  I have stood next to the bac strike master with a Rolls-Royce Viper Mk 535 turbojet in it and the Rolls-Royce is not much louder. Im going to use a handheld tachometer will that be accurate enough on the comp wheel? if not I may have to design a better tachometer. I am also getting a egt gauge and probe to keep a close eye on the exhaust temp. I will keep you posted with my results of how much rpm and how hot she gets.    

problem is i now cant decide if I like the smell and noise better from a turbojet or big radial.

Cheers Nick

[racket]

Hi Nick

I use a hand held laser tach on my 12/118 engine , I cut a thin crescent shaped piece of the reflective tape that came with the tach , and stuck it on the comp snout radial flat area just outboard of the nut, the snout and nut are also painted half black and half white with the reflective tape on the white hemisphere postimg.cc/image/nv05okd6j/ .

At 20 psi P2 you'll probably be indicating 55,000 plus rpm

At the relatively low rpm we run at with our bigger units the tape seems to stay stuck :-)

LOL, maybe big radial for sound , turbojet for smell

Cheers
John

[sub22b]

youtu.be/ebkAaF_s1IQ a video of me running it a few days ago.




The cook idle and full on the panel is from a turbojet powerd bbq i made so dont mind that writing. But i will show you a picture. And yes the steak did float.

img upload



cheers Nick

[racket]

Hi Nick

She sounds sweet :-)

May I suggest you fit a bellmouth to the inlet , turbos normally have an airfilter and plumbing which provides the turbo with an axial air delivery , but without the plumbing air will be drawn in from all around and this can produce a vena contracta en.wikipedia.org/wiki/Vena_contracta with reduced airflow to the comp and often producing high temps .

Cheers
John

[smithy1]

Nov 8, 2016 22:11:15 GMT -5 sub22b said:

I cant believe the noise it makes from the comp inducer at 20psi. without ear protection on it would cause serious hearing problems. I cant imagine what it will sound like at a higher p2 psi that's why I want to check the rpm because I have a bad feeling it may already be near its max rpm just from the noise it makes.

Cheers Nick

LOL... If you think that's loud....you should hear my GT6041 powered go-kart at 42psi P2 ....plus full afterburn.. .....it does it's best to rearrange your internal organs....nothing better than the thundering sound of a open exhaust turbojet making some serious power... I hear it nearly weekly these days and I still get a silly grin on my head....Thundering vibrations come to mind..!

LOL...John and I have seen grown men run away because of it...

Cheers,
Smithy.