Back again..!... The GT6041 powered "Green Beast"..!

[pitciblackscotland]

Good one Brett, looks like she very easy to start???

Cheers,
Mark.

[racket]

Hi Smithy

Plenty of excess fuel there now , good white smoke.

25,000 and 4.5psi is well within the ballpark..............nice low idle TOT at 460 C .

Yep , low rpm A/B combustion will need some fine tuning of the fuel flow , not much pressure in there or sufficient temperature (460 c) for "self ignition" , easy to exceed the combustion limits on such a "skinny" A/B ..................heh heh , she was made for full bore running.

All in all , a very acceptable first test of the new system , excellent hot streak ignition ...........I'd be more than happy with those results :-)

Cheers
John

[smithy1]

Hi John,
Yeah plenty of fuel happening . I'm still not totally happy with the hot-streak though...will need to think about it a bit more, will pop the combustion can off during the week and check to make sure all is as it should be. Andrew came along today and helped me out taking some rpm readings etc...Did three engine runs today with no dramas at all...easy light-offs for all of them.

I spun the old 6041 up to the max limit of 34-35psig on the P2 gauge, Andrew and I were quite surprised to see 73,000+ rpm , I was really expecting to see ~66-67,000, not sure about this so I might get the P2 gauge checked and also see if the rpm sensor is reading correctly. I'll take them both to work and check them against our calibrated workshop equipment. Apart from that the engine is running nicely with good temps and oil pressure dropping to ~55psi when warm....all good.

I think Andrew has some video of one of today's runs.

Cheers,
Smithy.

[racket]

Hi Smithy

OH .........something is certainly amiss with the data , at 35 psi P2 and 73K it'd have to be flowing well into the choke region with ~185 lbs/min , but the turbine map won't allow it to flow that much at the temps and pressures going in ............heh heh , I wonder which instrument is faulty , detective work required :-)

Good to hear the runs went well , will be looking forward to Andrews video .

Cheers
John

[enginewhisperer]

Yep, nice run yesterday

I have some good video, including instruments - just need to edit and upload but I haven't had time yet.


The rpm pickup seemed to be pretty consistent, but there's definitely a chance it was picking up a consistent error

[enginewhisperer]

video: youtu.be/qHt6vE3k3GY

[racket]

Hi Andrew

Thanks for the video , I'll go have a few viewings :-)

Yep , probably easier to check the P2 gauge than the tach which can get "strange" readings from "reflections".

Cheers
John

[enginewhisperer]

I'll have to dig up my optical tacho and try that as well next time

[smithy1]

Hey Guy's,
Just a small update....I've done a few minor "modifications" to the "beast", (it seems all we do is modifications to our engines...!! :....with the engine itself running very sweetly I don't want to mess with it unless absolutely necessary...so I've done just small items like adding a little more to the flame holder and fitting an infinitely adjustable flow restriction to the A/B line downstream of the pumps, it's adjustable from full closed to full open, this should allow me to fine tune the A/B fuel to suit the conditions etc...The addition of some more flame holders should also disturb the airflow somewhat at the flame holder more than it is now. I may have to make up a second pipe assembly of a larger diameter, ~8" or so to help sustain the flame at most throttle settings. The current pipe is 6" dia and was specifically made by John to work at higher rpm settings, which is does..!

John, I've fitted some 0.015" stainless lock-wire into the holes of the spray ring to restrict it a tad, this may help atomize the fuel somewhat, I believe the holes may be a tad large, I have made it reversible so if it doesn't help or improve things I can revert back to the original easily.  

I found the hot-streak injector line had indeed melted due to the nozzle entering the flame front in the primary zone, although it did work fine for a short time until it melted .... so to help eliminate the possibility of this happening again I've now got it entering the CC from the top wall/face of the combustion chamber with only a few mm of it protruding into the CC.......this should hopefully work, time will tell.

I might be able to get the Beast out on Wednesday to give her a bit of an engine test run to see if it needs any more alterations prior to me taking it down south to Pambula, on the far south coast of NSW, ~6-7 hours drive from Sydney, for a car show on the 27th-28th next weekend.

Cheers,
Smithy.

[racket]

Hi Smithy

You have been busy , I love hearing about "modifications", thats the interesting part of this hobby , makes up for the boring "standing at lathe time" :-)

Yep , an 8 inch pipe with a "dump step" from the 6" dia would increase the combustion "flexibility", just cut the 6 incher a tad downstream of the current flameholder , weld on a 6 to 8 inch ring and a length of 8 inch pipe with suitable nozzle.

LOL , I was only talking to Andy M about this a couple of days ago after he'd viewed the recent video and in his very experienced A/B opinion the 6 incher wasn't up to the job of giving both a good flame show as well as performance, and that an 8 inch pipe with dump would be the solution, just as the guys in the UK are doing with their very large Holsets , some have fitted extra fuelling at the jet nozzle.

Heh heh , I was a bit skimpy with the flameholders , didn't want to have any more pressure loss than necessary .

One reason I used the size fuel holes I did in the spray ring was that I was a bit worried that any higher "pressure" might squirt the fuel onto the thermocouples..........you know me , always over cautious .

Naughty boy , burning off hot streak lines ;-)

I'll be looking forward to news later in the week, hopefully all will be well for the trip south .

Thanks for the update .

Cheers
John

[smithy1]

Hi John,
Agree totally with the 6"-8" step-up on the pipe....I'll set about getting it done as soon as funds allow. Do you have any sources for some 8" 304 or possibly 316 pipe..?
With the spay ring...hopefully the wind going past will stop the fuel from actually getting to the thermocouples and a finer spray with the similar pressures will maybe help with atomizing...hopefully..!

Extra fueling near the exit nozzle certainly gives a nice flame show, works very well on my little dragster, I'll look into that down the track a bit.

Cheers,
Smithy.

[racket]

Hi Smithy

Midway Metals is the biggest stainless supplier , www.midwaymetals.com.au/contact-us/australia/ , I use to get all my little bits and pieces from them but then they started going more into the wholesale supply , so they palmed me off onto more retail outlets , but contact Midway about supply or they may be able to give you a contact , ...............my rather old catalogue gives the round welded 8" tube( 203.2mm) as 2mm wall thickness in 316 grade , either mill finish or buff polished , the 8 to 4 inch concentric reducers for the jet nozzle can also be supplied by them.

The 2 mm thick 8" tubing might be a tad thick/heavy , there could be 1.6mm available somewhere , or even get a section rolled by a sheetmetal shop , I think the current jetnozzle is fairly thick .

When I made the spray ring I think theres a bias of flow to the "centre" with less going to the outside as I wanted to keep the wall a bit cooler , but with a dump style A/B the extra turbulence near the wall will negate that possibility so it might be worth thinking about a bit more fuel to the outer side of the spray ring ,........ no point wasting that oxygen :-)

Cheers
John

[finiteparts]

Hey Smithy,


I like the video!  You get quite a crowd...you need to sell hot dogs and let people roast them behind the engine...if they like the taste of kerosene that is!  ha!!!

Just a quick question...when you stated:

"I spun the old 6041 up to the max limit of 34-35psig on the P2 gauge, Andrew and I were quite surprised to see 73,000+ rpm , I was really expecting to see ~66-67,000..."

are you basing that on the printed map values or are you correcting them for ambient temp and density.

Just an FYI for those out there that might have missed this step, the values printed on the compressor maps are corrected (normalized) to some set of standard conditions (many times STP-standard temp and pressure at sea level, check with the manufacturer) and you have to calculate the actual operating conditions from the map values and ambient conditions. The flow rates are usually functions of temperature and pressure...some manufacturers like Holset include the "corrected to" conditions, which for example the HX40 is at 85*F and 14.425 psi. The equation given by Garrett is (Holset's is similar):

Corrected Flow = Actual Flow * SQRT([Air Temp+460]/545) / (Baro/13.95)


The speed lines are also corrected based on temperature, which again for example on the HX40 is 85*F.

Ncorrected = N / (Temp/Reference Temp)

I haven't check the numbers to see how far off your ambient conditions have to be to make a noticeable change, but a quick eyeball of the equations makes me think that you wouldn't have to be too far off in temp to make the corrected speed move by about 9%. Ok...I couldn't resist. So if you were at 92*F, your actual rotational speed would be 73000rpm. Interesting too that it appears that Garrett uses 13.95 psia as the corrected condition...maybe they are at 1450 ft altitude?! hehee!

~ Chris




Correction:  

John spotted that I forgot to include the square root term on the temp ratio in the corrected speed line, so just to make sure it is clear, here is the equation again and fixed to include the SQRT term

Ncorrected = N / SQRT(Temp/Reference Temp)

with this in mind, the 9% increase in actual rotor speed of 73,000 rpm from the corrected speed of 67,000 rpm would require the ambient temp to be increased to right around 100*F.  

Sorry for the mistake...the dangers of doing things right before bed!  But hopefully the point is still valid, that the map values have to be corrected to the actual ambient conditions and not just pulled from the map.
 

[racket]

Hi Chris

Rpm correction needs the temp division square rooted , assuming it was 20 deg C - 68 F - 528 R on the day , about right for this time of year here in Oz at Smithys latitude , so square root of 528/545 = 0.9842, therefore a corrected 73,000 rpm = 74,166 rpm on the map , this makes the differences even worse :-( ............the P2 should have been even higher in the "colder" air .

Cheers
John

[smithy1]

Hi Chris,

Thanks for your input, I can certainly use the numbers, however, I believe John is quite correct...in fact it was very close to 20-21c at the time I ran the engine...so at a glance the error in rpm recorded vs P2 is rather strange.....as John suggests...the P2 should have been significantly higher than the ~35 psig recorded for the rpm to be anywhere near 73,000rpm...the altitude where we were is not too far above sea level and an ambient temp of ~20-21c, even allowing for some slight differences, the rpm still a fair way away from what I would expect at the P2 we were seeing.

I'm hoping to do a couple of test runs tomorrow, I'll try to take some more readings if I get a chance. I suspect we may have a P2 gauge calibration error rather than an rpm sensor issue...which was just too consistent to be reading incorrectly, if it was a "reflection" error, I suspect it would be a little more inconsistent...Andrew got good smooth readings every time.


Cheers,
Smithy.