"Fat Boy" 12/118 thrust engine

[racket]

There shouldn't be too much of a problem cobbling something together , most very large turbos would have sufficient flow at 3:1 PR to cope with the IC engines appetite , you'd need some sort of fuel control to keep the P2 steady, more fuel being required as the IC engine consumed more air reducing the "balance" between comp/turb flow .

A GT6041 will flow between 80 and 185 lbs/min at a 3:1 PR , 100 lbs/min is good for 1,000 HP

[rolandsean]

Jun 24, 2020 17:20:49 GMT -5 racket said:

Hi Ron

I think 200 SHP is realistic , I found with my TV84 engine that its 110 lbs of thrust as a pure jet converted to 115 HP on the bike dyno test , so my current 190 lbs of thrust should give 200 SHP.

The current design of the 12/118 was for a thrust engine using a turbine wheel that had been heavily clipped back to increase mass flow , and relying more on impulse energy from a choke NGV , but now I find myself with a NGV thats grossly oversized and feeding a choked wheel exducer thats powering the comp from reaction energy .

I'll run some more numbers today to better understand the "Corrected Flow" across the turb stage to see if anything can be "massaged" to improve the situation .

The current 61 Trim for the comp wheel isn't ideal for a shaft horsepower engine as its undoubtedly compromising things at higher P2 pressures , unlike Anders engine with its 48Trim which will probably be able to produce the same amount of thrust but from a higher P2 and P4t and is ideal for the 2 stages of expansion through the freepower.

LOL, I'm caught with a combination of parts that aren't the best match , but the positive is , its forced me to find ways around problems that shouldn't have been there in the first place .

Andy M's 110 mm inducered comp is probably a better match for our 129/112 mm turbine wheels , the lower mass flow should mean flowing in higher efficiency islands of the map , the NGV can be produced with a "lower" angle giving more impulse energy to the turb wheel, whilst the exducer throat area should still be capable of flowing his 3 lbs/sec design flow.

Without any turbine map for the TV94 wheel its been a bit of a trial and error approach to figure out where its max flow is , at present the oversized NGV will be providing fairly modest gas velocities feeding into the turb wheel at less than ideal angles , the wheel's inducer tips are probably having to "accelerate" the gases "circumfrentially" as they go in , this is sucking power from the wheel leaving less for the comp and requiring me to substitute heat energy in the form of higher temps to compensate ................its a bit of a "dogs breakfast" , not very tidy , but its working :-)

Cheers
John

John, 

So thrust is roughly equal to shaft HP you can extract? What are the advantages to using shaft power then instead of thrust to power a vehicle? The ability to use a transmission and gear reduction? 

Appreciate it,
Sean

[racket]

Hi Sean

As a very rough guide only , there can be "variables" .

Theres no comparison between thrust and shaft horsepower with the ability to accelerate a vehicle , shaft horsepower will win every time .

Using my 12/118 as an example , with ~200 lbs of thrust as a pure jet , but when fed through a freepower produced ~70 ft lbs at the stalled turbine shaft .

That 70 ft lbs is fed through a ~4.36:1 gearbox , so 305 ft lbs out when stalled with a 7,000 rpm capability .

Assuming we'd use an ~3:1 chain reduction to the "axle" , that 305 ft lbs becomes 915 ft lbs , so assuming a tyre of 2 foot diameter ( 1 foot radius) then there will be a "thrust " of 915 lbs between tyre and road .

So our 200 lbs of pure jet thrust can become 900 lbs of SHP "thrust", ...............a 4 to 5 time "increase" wouldn't be unreasonable with most setups.

My 2 shaft kart jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build even with dumping ~40% of the TV84 exhaust flow effectively reducing its 110 lbs of pure jet thrust to ~65 lbs , when fed through a very rudementary freepower stage with limited "gearing" produced 160 lbs of drawbar "thrust" .

Cheers
John

[finiteparts]

Oct 11, 2020 23:07:13 GMT -5 rolandsean said:

Chris, the first link you sent (jetandturbineowners.proboards.com/post/29728) just sends me to one of my posts. Is this the correct link? I am curious to see how a turbo compound setup might be superior in a GT setup. The automotive world uses turbo compounding to help with spooling a larger turbo quicker, same with split channel turbine housings; I would think that this benefit would have much less importance for the GT world. I also have a few Variable Geometry (Variable Nozzle) turbos I have toyed with the idea of seeing how they react but just like turbo compounding, VGT's shine in their uses for emission control more than outright flow. Now a turbine section of a VGT/VNT repurposed for a power take off might have benefits.

Hi Sean,

I never said it would be superior, I just stated that I wanted to see how they would work as a GT.

So your partially correct in your statement that compound turbos are a means to reduce turbo lag on what would normally require a large turbo. But if you read the literature from Caterpillar and others, the primary reason they use them is the need to fit a turbocharger into a given volume.  Using two turbos to break up the work, you can use smaller, lower pressure ratio designs to achieve the larger pressure ratio required.  They also state that there is also the advantage that you can usually use exist production turbos as opposed to using a new, larger, high pressure ratio turbo.

Using two lower pressure ratio compressors also leads to a wider operational range because it is easier to achieve wider peak efficiency islands at lower pressure ratios than it is to do at high pressure ratios.  Higher pressure ratios with high efficiency are more challenging due to the higher internal impeller flow speeds and discharge Mach numbers.  Higher Mach number flows entering the diffuser are also more challenging and usually hurt the overall system efficiency, especially if there are shock losses.

Additionally, using two compressor stages allows the use of intercooling between stages and this offers the potential to increase the overall system efficiency or even to keep the compressor discharge temperature below some specified limit.

Now, why would I like to use one?  Because I am interested in the system behavior and interaction between the two rotors.  I have a numerical model that predicts the work split between the two rotors and I am pretty sure that it is fairly correct.  But, watching the data stream off an instrumented, running engine is more exciting.

I also have a bunch of VNT turbos that are on the list.  I have the build started on one with the combustor in process and I think the interesting thing that will come out of testing it, is to illustrate the behavior of the system as a function of the turbine nozzle throat area.  As you can see, most of my turbine design is focused on testing system behavior and using them more as testbed engines to collect data...not for other purposes.  Now, that being said, I still have the dream of building a turboprop engine for my ultralight aircraft...one day.

- Chris

[azwood]

I’ve looked into this a bit what I believe is a compressor needs to first overcome 14.7 atmospheres before producing positive pressure then we have our compressor map that’s rated for a given pressure rating cfm/ps1 rpm and efficiency etc when you feed that compressor with say 20psi positive pressure it acts as if that’s 14.7 atmospheres.by doing this the second compressor /the biggest one/still has its entire map to build up to but thinking 20psi is atmosphere it will now add said 20psi on top of what if was capable before.well that’s what I’ve been led to believe it makes sense but I’m not sure how the big compressor dragging air through the smaller one at higher pressure rates wouldn’t get restrictions.but in saying that it seems to work

[turboron]

azwood, the clearest way to think about this issue is using volume. The first compressor sucks a given amount of volume ( cubic feet per minute )based on the design and rpm of the impeller. This volume sets the amount of mass flow ( pounds per minute ) which does not change after it is set. As the impeller raises the pressure the volume is reduced. The reduced volume sizes the second compressor.

Thanks, Ron

[azwood]

Yeah that’s the part I struggle to understand. How they seem to work well a priority breather valve(reed valve)might help on the big turbo like I’ve used on my bikes to let the engine breathe before boost

[racket]

Hi Aaron

We need to always work in absolute pressures , eg we have 100 CFM of ambient air at 14.7 psiA to start with , that a 1:1 PR , when we have a 2:1 PR across the comp we end up with 29.4 psiA and 50 CFM ( neglecting the temp change effects on density) , that 50 CFM at 29.4 psiA goes into the smaller HP compressor ,with half the inducer area, which has a 2:1 PR that then bumps up the pressure to , 2 X 29.4 = 58.8 psiA ( 44.1 psi of gauge boost) and only 25 CFM going into the engine

As Ron suggested , think in volumes rather than lbs/sec

Why did you need a "priority valve" ??

Cheers
John

[azwood]

I used a reed valve in my plenum chamber on the triumph to make sure the turbo didn’t restrict the engine down low it’s didn’t do the much to be honest lol

[bigkwaka]

Dec 2, 2015 19:31:20 GMT -5 racket said:

Hi Smithy

A coupla pics of the mounted motor






LOL, being a cheap arse the starter only costs me $75, second hand 1987-1989 Toyota Camry SV-21 starter , simply cut off the gearbox and solenoid , throw away the gears but retain the solenoid to fire up the starter.

Just need to make the actual connection piece that fits onto the starter gear and goes to the comp nut , I'll have to have the rotor in the engine to get distances , so thats a job for another day .

Cheers
John