newbie, running but poorly!

[nickyracer39]

Hi all, first i wanna say this is my first post after reading many many great debates and discussions about all things jets for a long time!
After finding a diy jet video on youtube i was totally hooked and since then i made a great valveless PJ and thought it time to try a GT.

I have done much reading on desighns, specs blah blah and come up with what i have now, a kool looking, noisy, gas eater but not a jet! with my little experience with any of this stuff i have done the best i can to this point but cant get the engine to self sustaine.
I have bench tested the cc with good results( easy ignition, little flame exiting ft) but when its all together and spooling up it gets to a point where the compressor pressure comes up to 8-10-12 psi but is very noisy and shuddery.

I think it is surging but not shure....any help would b great. also how can i fix it? i was thinking about giving the dilution zone more flow (hole area) till it settles the pressure down. is ~10psi pressure too much, considering i am yet to get it to idle?

video is coming soon, just need 2 work out how to get it on here!

[metiz]

video is coming soon, just need 2 work out how to get it on here!

If you figure it out, press "post" once, not six times

[nickyracer39]

yeah, sorry about that people, damm thing froze up and i bommed myself....

[racketmotorman]

Hi Nicky

First off , congratulations on getting her fired up )

What sort of turbo are you using ??

Do you have a jet nozzle on it ??

What exhaust temperatures are you experiencing ?

How did you determine the flametubes hole pattern and hole sizes??

What fuel are you using ??

How is that fuel "injected" ??

A comp pressure of 10psi ( P2) is twice what you need as an idle P2 , normally ~3-5 psi should be sufficient .

To check for surge , securely position a bit of string at the comp inlet , just long enough so that it can't touch the comps inducer blading , when the engine surges you see the string bouncing in and out with the airflow , if it stays inwards in the streamlines without any reversals even if the engine is sounding rough , then its not surge .

Surge generally occurs when the turbine stage is too small for the compressor , the turbine wheels exducer diameter should be larger than the comps inducer diameter by several percentage points as a minimum , preferably >10%

The hole out needs to be bigger than the hole in )

Cheers
John

[nickyracer39]

hey thanks john,
thanks very much for taking the time to help me out.

What sort of turbo are you using ??

not shure about the turbo size, its a nissan turb thats all i can tell u atm.

Do you have a jet nozzle on it ??

yes i do but it is very short and i made shure the outlet is slightly bigger than the inlet as to not restrict the flow and increase the (tit?)

What exhaust temperatures are you experiencing ?

dont know about that yet but the setting up of a egt guage and photo tach is underway. although as u can see in the vid the turbine wheel slowly gets hotter and hotter as i increase the fuel.

How did you determine the flametubes hole pattern and hole sizes??

I just used the standard rules of thumb originally then when it kept flaming out i made more and bigger holes till i got better results. doesnt flame out now but wont idle.

What fuel are you using ??

using propane, through a tap then splits in2 4 and enters the cc evenly but only has a brass barb theaded through the cc wall with a cap on it and 5 small holes drilled in it.

Not shure how i can do the string infront of the comp test cos i can only get it to the surgeing stage with the blower pushing the air in, if i take it off it dies straight away. did i mention the p2 pressure, as it climbs it varies +/- 4psi surely this is not good coz any vids i have seen the pressure is pretty steady!


Thanks again 4 your help
Nick

[racketmotorman]

Hi Nick

I'd be removing the jet nozzle to start with , this will completely unload the turbine giving you full expansion thru it which should help to get the engine running due to lowered temperatures thru the turb stage .

Adding more/bigger holes indiscriminately generally only worsen the situation , if it has the correct distribution with regards hole area between the various zones of the FT , the engine should run .

Where can I find the video ??

Cheers
John

[nickyracer39]

ok, try this

http://www.youtube.com/watch?v=m_qTQqWIwzU

[Rossco]

WOW! Im not an expert at all on these beasts, but, i would say that is definitely in surge. No need for a piece of string for this one, look what its doing to your blower pipe.
All the same, very cool! (or hot if you ask your turbine stage, little too bright there i would say)
Well done for getting it up and going this far, there is so much work in these.

Rossco

[racketmotorman]

Hi Rossco, Nick

Certainly looks like surge from that start air tubing gyrations , but it could be caused by the very high temps being run , this can cause "thermal choking" of the turbine stage reducing mass flow to the point where the comp complains , this is why I suggested removing the jet nozzle so as to lower temperatures .

If the flametube holes have been "modified" from the standard 30- 20- 50% division of area , the fire might not be commencing until too late in the process exacerbating the thermal choking .

Looking at the flames exiting the jetpipe towards the end of the vid , their orange colour suggests too much fuel especially as LPG is being used , it should be producing that nice blue flame .

I think theres a combustion problem which may or may not be causing the surge as its flame front bounces back and forth up the flametube ( FT) .

The combustor is more than large enough for the turbo , but I'd like to know what size the FT is compared to the comp inducer dia ??

Also how much gap between FT and combustor wall and how the "round" FT is matched up to the scroll inlet , as there could be a problem there .

The fuel injector might be a culprit , could you give me a bit more info on it please , things like hole diameters , spacing , orientation etc etc .

But first things first , remove the jet nozzle and get the temps down a bit )

Cheers
John

[nickyracer39]

hey all,

Ok first off i have removed the jet nozzle for now till i get it sorted.

the FT is ~100mm dia, just under double inducer dia (depending where u measure from, the dia of the inlet casting is 55mm but tapers into about 49mm at the blades) The FT holes were originally 30,20,50% but when it wouldnt even get close to running i just added holes willy-nilly, it did stop the flame out but now it surges! I probably have stuffed the FT and might make a new one and set out the holes according to the jetspecs program.
The gap around the FT is ~14mm/.55 inch seems like everyone says thats ok.

Also added this difuser thingy 2 stop the gas going straight through the ft and give it time to mix (probably a bad idea)

these are the only marks on the turbo accept for on the hot snail its got "D" and "16V" in the casting.

chow

[racketmotorman]

Hi Nick

Yep, too many holes with too much hole area, may I suggest you use the following ...............
..........primary zone holes surrounding the fuel injector , 8 X 6mm and 8X8mm dia holes

..........secondary half way along the tube , 8X8mm dia

..........tertiary at 3/4 distance down the tube 9 X 12 mm dia

with all holes bellmouthed/countersunk to cleanup the entry for better flow

With your fuel "baffle ", its best removed , there shouldn't be any requirement for it and it could fail and go thru the turbine wheel .

Fuel injectors must have radial holes only , no axial holes , the injector can be a short length of tube fitted thru the end cap of the combustor with its inside end crimped shut and with 6 or more small radial holes along its wall , preferably a dozen 1.6mm dia holes in a bit of 3/8 pipe , with the gaseous fuel squirting out directly towards the primary holes , the incoming air thru the primary holes will mix quickly with the fuel for a fast burn .

Could you give me the size of your turbine wheels exducer please , it should be > 55mm dia , if only 49mm the same as the comp inducer blades , this is getting too marginal for a gas turbine unless running low temps ( no jetnozzle)

Hope this helps

Cheers
John

[nickyracer39]

Hey thanks very much guys for the advice, I have alredy started pulling it all appart to remake a few things and tidy the whole unit up a little.

I will let yous know how it goes and will post a vid if it actually runs this time....

I got plenty to do so till then, Chow

[nickyracer39]

Well i have remade my FT according to the specs u gave me john, came up nice i think but it seems very few holes.... ahh well i guess we will see.

[racketmotorman]

Hi Nick

Have faith my friend )

Cheers
John

[nickyracer39]

Hi all,

OK, did a bench test of new cc and ft and fuel inlet 2day, all went ok, little hard 2 light ( had to play with air and gas a bit) but once it was going seemed to burn really nice, I could throttle it down really low and at wide open there was very little to no flame exiting the cc.

After pulling her down i can now see the different heat areas on the ft coz this time i used stainless.

2 q's i want to ask, 1- is the bronze colored areas the hottest? compared to the blue and purple areas.
if so is this where i should drill some little holes to cool it a little?

Q2- is it normal for the closed end of the cc ( where the fuel comes in) to get very hot?
I noticed after a few mins on bout 1/2 throttle the metal at the end inside the perimeter of where the ft meets it it was glowing dull red hot.
Do i need a slightly longer fuel inlet to get flame away a little or do i just need a few small holes right there to cool it?

will post a few pics soon.

chow Nick