"Fat Boy" 12/118 thrust engine

[dieselguy86]

Hi John,

Inco is also EXPENSIVE as i know your aware of, figured stainless would be cheaper for testing. Id rather go through 5 stainless wheels to get 1 good inco wheel, than go broke after the second trashed inco wheel.

Perhaps ceramic coat the SS for a tad more insurance? Im probably wrong here but was my initial thoughts.

Dub her, "Big Bitch" or "Fuel Whore"

Joe

[racket]

Hi Joe

Started doing some " numbers" for the comp wheel and they aren't good , the inducer area to exducer area is getting close to a 3:1 ratio because of the rather small tip height of 8mm at the exducer

This isn't going to be an easy wheel to use , generally turbo comp wheels are somewhere in the 1.5-2 :1 ratio , that 130 mm unit has gotta be made for a specific purpose , and I suspect it a very high boost wheel for tractor pulling , at our lower pressures I feel there could be trouble :-(

I don't think I'd be even considering using it in a GT .

Cheers
John

[finiteparts]

Hi John,

Have you looked at the -C30 second stage turbine for the larger compressor wheels? The C30 was designed to flow 5.6 lbm/s and by using the second stage turbine wheel, you know that you have a wheel designed for 51,000 rpm as opposed to the 30650 rpm of the LP rotors.

As you can see, the C30 second stage wheel has fewer blades with a much larger throat area to pass the higher mass flow...this one here is marked with an effective area of 8.87 in^2....



Additionally, using a gasifier turbine wheel, you have a higher temperature capable material. The C30 turbine inlet temperature is around 1930F which is acceptable for life requirements using a MAR M246 material.

Now I haven't run the numbers to determine if the second stage C30 turbine could power the 180 mm compressor that you were chatting about, but just looking at the Allison Model-150 turbojet design, it would suggest that it is likely possible.  Seems ok for tip speeds...just over 1500 fps...



The 150 engine made 467 lbs thrust at sea level for a weight of 42 lbm! It flowed around 6 pps of air with a compressor ratio of 5.9:1. The compressor was based on the C30 design and the turbine was a modification to C30 casting to increase the flow area. With the C30 already handling 5.6 pps, adapting it to work with 4.5 pps should not be a problem.

Just for curiosity, I checked the throat area required to push 4.5 lbm/s of 1800F air with an upstream head of 30 psia and it comes out to be 7.745 in^2. So even if you had almost 15% blockage, you would just be at the edge of choked flow for the above turbine wheel.

The -C28 is a trimmed version of the -C30.  The compressor is the same compressor trimmed to the lower flow requirements, 4.4 pps, so it should be a viable option also...maybe more ideal?

Even better would be to get your hands on the single first stage rotors in the C24 or the C34...they handle turbine inlet temps of 1975/2040 F, respectively...and they are designed to achieve much heavier aerodynamic loading (thus only needing a single stage gasifier turbine)...but I have yet to see any of those on eBay.

Thought I would share some food for thought...

Enjoy,

Chris

[racket]

Hi Chris

Yep , I've looked at the C30 second stage as I've had both NGV and wheel for a number of years , the NGV has a marked flow area of 7.04 sq ins , probably OK for ~4 lbs/sec on my calcs if choked, I'm running ~7.7 sq ins NGV throat area in the 12/118

My C30 2nd stage turb wheel has 9.03 sq ins area , but the flow through it is even more limiting due to the fact that the actual gas velocity will need to be "restricted" otherwise the wheel will be turning out too much horsepower from the gas deflection, perhaps I need to redo the numbers in light of the higher pressure ratio potentials for the billet wheels , more pressure , greater density , more flow

When Andrew (in Melbourne) and I originally considered making an engine using the C30 bits we were looking at getting a comp wheel made that was a 1.3 times scale up of my FM-1 engines comp wheel , we were looking at a ~123mm inducer with a 183 mm exducer and a 11.5 mm tip height .

Because of the cost involved in a one off wheel, I actually purchased a used Garrett GTCP85 comp wheel to see if we could use it once the "backside" blading was removed as it was 116mm inducer with a 184 mm exducer, but after getting the wheel in my hand and thinking it over after doing some numbers the idea was shelved .

Now , some years latter, there are off the self billet wheels becoming available , but I still don't think I'd go with the C30 bits , they're just too rare compared to the C20 ones , break something during development and it might be impossible to replace.

My current thinking is to use the best/biggest readily available turbo turbine wheel , TV94 , GT6041 or HX82 , they're all about the same size , the TV94 and HX82 both have similar quill sizes which makes for more options with regards comp wheels , though the GT6041 turb wheel has a longer shaft which would increase flametube length considerably as a percentage ,and larger flow area into and out of the wheel which is of more modern design, but the shaft requires a screw on comp wheel which limits options.

The "performance" GT6041 turb wheel is different to the CAT "industrial" GT6041 turb wheels , the performance one has a 25 mm tip ht for the inducer with ~119 mm exducer whilst the CAT one is 21.6 mm ind tip ht and ~113 mm exducer .

KTS have a titanium comp wheel ( #6003) that would screw onto a GT6041 shaft , comp has 104 mm inducer , 151 mm exducer with extended tip to 161mm ,10 mm tip height , now this combo would make for an excellent high pressure engine, though more expensive than using the TV94 or HX82 turb wheel and a billet alloy X846 comp as Anders is doing for his JU-02 , which I feel is about as good a combo as can be had for our use.

Perhaps a performance GT6041 turb wheel and a KTS 122/151/161mm billet comp wheel ( #6004) with the inducer slightly reduced in diameter and the engine designed for higher pressure ratios of >4.5 :1 would be worth thinking about.

LOL.............lotsa food for thought

Cheers
John

[racket]

Hi Chris

Yep , once up ~4.5 :1 PR my numbers got better for the C30 bits and >4 lbs/sec , it would probably work with that 130 mm inducered wheel

But the GT6041 turb wheel would probably still be my choice of wheels to use due to availability , its in 713C and with ~16 sq inches of inlet annulus its got potential .

Cheers
John

[racket]

Hi Guys

A bit of an update.................its been too hot this summer for me to do much work on the engine , just trying to stay alive until the cooler weather arrives.

In the mean time I've been exploring the idea of incorporating an inducer bleed ( map width enhancement) to help get me over this mid range problems I'm having with the 12/118 once beyond a 2:1 PR, this is roughly where a lot of centrif. comp wheels have a sudden shift to the right in the surge line and which might be causing my flow to hit the surge line or be that close to it that theres "internal" problems .

I've spent a lotta time downloading various Papers on the subject and even longer hours sitting in the aircon digesting them , and I think I've got a fair understanding of whats involved and hopefully why its needed .

Theres also been a few Papers which include more modern transonic compressor wheels and their special requirements , the info might come in handy if Anders has any problems with getting the JU-02 engine up to full 5:1 PR.

I might give the engine a quick test firing with the current mods before attempting the casing treatment to determine if the new mods have made any difference , even if the engine does get up to full rpm I think I'll still fit the bleed slot simply to improve the surge margin for when more backpressure is put on the engine .

Current thinking is a 5 mm wide slot at or just marginally downstream of the inducer throat, a very small bevel on each edge seems to improve flow into the slot which will be ~6 mm deep radially , with 23 X 10 mm dia holes machined radially down to ~2mm from the shroud bore for venting the slot to atmosphere.

Now all I've gotta do is wait for some cooler weather, the heat and humidity has been oppressive this summer, too hot to even go fishing , the sweat was pouring out of me the other morning just after sunrise whilst wetting a line in the hope of catching lunch :-(

Cheers
John

[racket]

Hi Guys

Well I did it , the surge bleed slot is installed, its been cool the last couple of days , autumn is on its way at last , so got my arse into gear and pulled the engine from the test stand , disassembled it enough to remove the comp cover .

First job was to find where the throat of the inducer was located axially



A fiddly job but eventually found it was 9 mm rearwards of the leading edge of the main blades.




So popped the front comp cover in the lathe and cut a 5 mm wide groove 6 mm deep roughly straddling the throat position




Then came the job I was dreading , drilling 10 mm dia holes radially inwards to intersect the slot , the slot position put it in a position where I needed to machine some flats on the curved cast surface so the drill could enter cleanly



Cheers
John

[racket]

Hi Guys

Once the flats were machined it was time to get the holes drilled , I used a simple "indexing" contraption off the 26 outer can screw holes in the cover, to position the 26 holes around the cover snout


The holes were drilled to within a ~1.5 mm of the inducer shroud bore.

After a bit of a cleanup, things looked OK











Engine has been reassembled and is waiting to be fitted back into the test stand tomorrow.

LOL, I don't know why I was so worried about doing it , though it is a bit strange looking through the bleed holes and seeing compressor blades going past , it'll be interesting to see what difference it makes .

Cheers
John

[Johansson]

Hi John,

I can imagine you being a bit nervous about the job, many hours of work put into that comp cover that could be undone by a mistake now.

It will be very interesting to hear how the ports will affect the engine performance, put a piece of wool string near one of the holes so you can see when the air flow direction changes from blowing out to sucking in.

Cheers!
/Anders

[racket]

Hi Anders

Yep , it was a bit nerve wracking drilling those holes , I've had too many parts wrecked over the years when a drill bit decides to do something other than whats intended , I took it very slow and steady once the drill tip broke through into the slot , I was relieved to finish the last one.

A bit of sting tied to the oil inlet pipe and hanging down to the discharge holes should do the job.

Now I'd better go and get myself some fuel for a test run :-)

Cheers
John

[pitciblackscotland]

Hi John,
Interesting modification, let's see if this will work out Yes the weather been cool down here in Melbourne, our summer hasn't been the hot in Melbourne. Yep bring on autumn

Cheers,
Mark.

[Deleted]

Hi John

Looking good, glad its cooled off a little, hope for a few warmer days over here now so i can get the van finished

Looking forward to seeing test video

All Best
Andy

[enginewhisperer]

you could probably use one of those holes to mount an rpm sensor too

[smithy1]

Feb 20, 2017 17:27:40 GMT -5 enginewhisperer said:

you could probably use one of those holes to mount an rpm sensor too

Good call Andrew....I still have several proximity sensors I could shoot up to John....Bugger it...I 'll just send a couple up to him anyway...I'm not using them.

Cheers,
Smithy.

[racket]

Hi Guys

Yep , I'm looking forward to the new experiments ............the unknown is what gets me motivated.

Interesting thought about the proximity switch positioning ..........mmmmmmmmm, thanks Smithy ;-)

Cheers
John