"Fat Boy" 12/118 thrust engine

[Deleted]

Hi John

Wonderful always good when a change you have made is an improvement .... we all have I am sure, at some point changed something thinking its for the better, and its not been

Air impingement would soon get her up to speed...

All The Best
Andy

[Johansson]

Really good news John!

[CH3NO2]

Hi John,

How is a gas impingement starter generally designed?

Is it impinged on the compressor wheel or turbine wheel? Should it be impinged on the wheel near the beginning, middle or end of the volute?
@ 90 degrees tangent or some other angle? General orifice diameter sizing & mass flow rates?

Can CO2 be used for starting? (CO2 is attractive because it stores as a liquid with a relatively high density.)

Sorry for all the questions. This subject can be another field of study all by itself.

Thanks,
Tony

[racket]

Hi Tony

I haven't had a lot of experience with impingement compared to some of the other Members who use it regularly, hopefully they'll be able to enlighten us both :-)

The couple of times I have used it I impinged the comp wheel , though the turb wheel has been used by others , both methods have their pros and cons .

As I have an oxy set in my workshop, its simple enough to hook up the oxygen bottle using suitable plumbing , yeh I know , guys will say you should be using air not oxygen otherwise you'll end up oxy cutting parts inside , but considering the vast quantity of air going through the engine , the piddly bit of oxygen is hardly going to change the oxygen content by more than a percentage point or two .

CO2 is attractive , but ideally it needs "heating" on its way to the engine to help with the phase change and to increase the gas velocities once in the engine.

Yeh , another field of study :-(

Cheers
John

[pitciblackscotland]

Nov 30, 2017 9:17:12 GMT -5 CH3NO2 said:

Hi John,

How is a gas impingement starter generally designed?

Is it impinged on the compressor wheel or turbine wheel? Should it be impinged on the wheel near the beginning, middle or end of the volute?
@ 90 degrees tangent or some other angle? General orifice diameter sizing & mass flow rates?

Can CO2 be used for starting? (CO2 is attractive because it stores as a liquid with a relatively high density.)

Sorry for all the questions. This subject can be another field of study all by itself.

Thanks,
Tony

G'day Tony,
Have a look at these photos of the JFS i had, it uses air impingement start and electric start. I just use a cylinder of compress air could also can use a scuba tank as well. The three nozzles are just sitting behind the NGV.

www.youtube.com/watch?v=PmDDDzl3wGc

[Johansson]

Impingement is IMHO the easiest and cheapest way of starting a turbine if you have access to a scuba compressor, for JU-01 I use a single 3mm (I think) jet pointing at the turbine wheel tips through the NGV and you can see in my numerous videos just how easy it starts. I am thinking about fitting an impingement jet for JU-02 as well just in case I want to use it at some point.

But, this is probably a discussion best held in a separate thread so we don´t fill up Johns build thread.

[enginewhisperer]

hmmmm, tempting

www.ebay.com.au/itm/High-Pressure-30Mpa-Electric-Compressor-Pump-PCP-Air-Pump-110V-220V-Blue/322694335466

[Johansson]

Nov 30, 2017 19:22:46 GMT -5 enginewhisperer said:

hmmmm, tempting

www.ebay.com.au/itm/High-Pressure-30Mpa-Electric-Compressor-Pump-PCP-Air-Pump-110V-220V-Blue/322694335466

Wow! That is a great find, I´ve only seen scuba compressors for like 10x that cost. It would be interesting to know how much the air is heated when filling a fullsize scuba tank, if it runs too hot the 300bar soon drops when the newly filled tank cools down.

[racket]

Hi Guys

Conducted another test of the engine with the new IGVs in place and the "old" jetpipe installed so as to check any "changes" .

The usual start problems encountered , but eventually she was coaxed into life .

Not much has changed ,still a large temp difference between one side of the jet pipe and the other , starting off at ~100 C degrees at 0.5 and 1.0 Bar P2 , increasing to ~200 C degrees at 1.5 Bar

The IGVs have changed compressor efficiency a tad , dropping it to 72% at 0.5 Bar and 73% at 1.0 Bar from ~75% previously , rpm for each of those P2s is roughly the same as before at ~33,400 and 44,700 , but at 1.5 Bar P2 , efficiency climbed to 77.5% at 51,600 rpm , so maybe starting to come into its "sweet spot" , it should be capable of at least 80% effic .

Fuel flow is still "high" at ~1,000 cc/min at 0.5 Bar , 1,300 cc/min at 1.0 Bar , but then it gets "silly" at 1.5 Bar with ~2,500 cc/min which combined with the 200 C degree difference in the two thermocouple reading in the jetpipe sorta indicates a combustion problem , temps were 791 and 984 C , getting a tad hot, but did have 4.5 psi of total pressure in the jetpipe .

I'll remove and disassemble the engine so as to fit impingement start onto the comp wheel and maybe make some changes to improve combustion , possibly too much liquid fuel dribbling down the front face of the flametube and burning in the lower half

Cheers
John

[turboron]

John, hard to troubleshoot if its not running. I am impressed that the IGV with rotation made a difference.

Thanks, Ron

[racket]

Hi Ron

Yep , still early days , but nothing "bad" from fitting the IGV other than that slight drop in efficiency at lower P2s .

The rpm didn't change much for a given P2 so maybe the engine needs more mass flow to get the swirl "activated", at lowish P2 flows the air might just be going straight through the gap between vanes , I'll refit the piece of "surge" string to the inlet to check just how much deflection I'm getting .

I really need a bigger fuel tank , the 10 liter one is emptied before I have a chance to do much fiddling .

Cheers
John

[racket]

Hi Guys

Bit of an update ...............Christmas and New Year have come and gone , life is returning to normal , and with a "chilly" 17 deg C this morning , it was time to do some shed work.

Back in December I'd started to remove bits off the engine in preparation to removal/disassembly , but didn't want bits everywhere and gathering dust over the Holiday Season so left final removal until now .

A couple of hours work had her apart and the rotor removed , fuel and propane manifolds tested OK , no blocked injectors ...........flametube looked OK other than the covering of soot from post shutdown "smokin'" and rotor OK other than a bit of extra heat colouring on the blades .

So time to do some more modifications , first job is to machine down the comp exducer and remove the extended tip , the Precision Turbo's PT118
www.precisionturbo.net/Street-and-Race/ss/2-000--HP/details/Street-and-Race-Turbocharger---GEN2-PT118-CEA--174-/633 has a similar comp wheel inducer at 117.98 mm vs my 117.5 mm , but their exducer is only 149.71mm vs my 151 mm with extended tip out to 163.11mm , I'll machine mine back to 150 mm straight across , this will then require probably 5% more rpm to achieve the same Pressure Ratio as before , which for me is a good thing as it effectively makes the turb stage's job a tad easier, which combined with the comps IGV stator will hopefully make me run another 5 or 6,000 rpm to get my 3.5:1 PR .

Whilst the engine is apart I'll fit high pressure air impingement start so as to compliment or replace the electric starter.

Before doing anything on the engine though, I want to do some testing of the flametube's vapourisers , I'll make up a test rig that will feed low pressure air at ~0.75 psi thru the evaporator to simulate the ~5% pressure drop across them , whilst at the same time I'll inject water from a standard injector position as currently , I need to check whats exiting the tube and at what sort of speeds etc, hopefully I'll find a reason for the widely differing TOTs between opposing sides of the jetpipe...............I might even replace the evaps with a different design .

Cheers
John

[enginewhisperer]

It's a shame to have to machine such a shiny compressor wheel!

It makes sense though. Will it end up running closer to surge the the reduced exducer?

[racket]

Hi Andrew

Yeh, I don't like having to do it , but I don't think the turbine wheel has the grunt to spin that bit extra bit of tip compared to the PT118 , theres a reason why they are running a 62 Trim for the comp wheel with a turb wheel the same size as mine.

I can't see why there'd be much difference in flow once the extended tip is removed other than a modest reduction in PR for a given rpm , I've got no problems spinning it faster as I was only looking at ~60,000 rpm previously , another 5-6,000 won't stress the turb wheel either , but it will give the turb wheel a bit more of a "gearing" advantage , instead of lugging along in overdrive , its now in top gear .

They advertise that the billet wheel is good for 70 psi of boost , I'm only wanting half that , so a small reduction in exducer diameter even with a modest rpm increase shouldn't be a concern , I'm only going to "restore" the tip speed required to produce my 3.5:1 PR , a bit more load at the inducer end , but hopefully the IGV will help out there.

LOL, lotsa unknowns , so I can experiment with a clear conscience ;-)

Cheers
John

[enginewhisperer]

yep, definitely uncharted territory!