Newbie with a VT50 Turbo

[maritimer95gt]

Now that I've got your attention... ;D

I'm starting a build with a VT50 turbocharger. This being my first build, I want to stay to the simpler side of things, but I also want to build something a little out of the ordinary. Any help, recommendations, or constructive criticism from those of you who surely know more about what you're doing than I do (pretty much everyone here ), would be greatly appreciated.

Here's a little bit of a rundown of what I want to do:

Warm up with propane
Sustain with diesel or kerosene
Then switch a preheated diesel/5w30 oil mix or just straight heated 5w30 for maximum BTU output
all while keeping everything portable on a 12/24v system

I'm sure it sounds like bad idea, but hear me out. I first got the idea when my friend's liquid propane turbojet had a bad oil seal on the turbo. When he got the turbo to full power on liquid propane and spun it all the way up, all the smoke that was just pouring out the exhaust before had all of a sudden ignited. The roar was deafening and I haven't seen anything like it anywhere on youtube after searching for days through all the turbojet videos. It acted as if it had an afterburner. A very powerful one at that. There was very little smoke at that point, just way more noise and power. Of course it's not usually a stable burn, but when the turbine is warmed up, it becomes more stable, fluctuating only a small amount. What once was easily held down with a few sand bags in front of the go-kart frame all of a sudden was tearing through the heavy plastic bags and quickly making its way to the back of the barn dragging everything with it.

So basically I want to recreate this effect in a more scientific and controllable manner, hence the diesel/5w30 mix. I could probably burn regular pre-heated 5w-30 as well, but I would just have to get it hotter. I plan on heating the heavier oil via heat sink on the hot side. The next problem would be figuring out the best way to inject it.

Thanks for the help!

[racket]

Hi Alex

There have been guys who've used "oil" as fuel , but unless you've got a supply of free oil it'll be cheaper to use diesel or kero

Did your friend have any exhaust temperature gauge on the engine to read TOT ( turbine outlet temperature ) ??

You won't be able to run the engine any hotter or have it produce any more power burning oil than you would using diesel or kero , power output is "fixed" by the turbine inlet temperature , and theres an upper limit of ~1200 deg F for the TOT measured in the jetpipe , the turbine wheel will fail if you run it any hotter whilst at max rpm , and max rpm is fixed by the compressor tip speed of 1450 ft/sec , exceed either the temp or tip speed and the engine will most likely malfunction ( die).

From what you've mentioned about your friends engine I'd conclude it suffered both an over temperature and and overspeed when the extra "fuel" was ignited , the ignition of the lube oil would have sent the T I Ts up and as a consequence the rpm would have increased substantially :-(

Hot lube oil can be sprayed into the combustor exactly the same as diesel or kero using an industrial oil burner spray nozzle at pressures of 100 psi or so .

Cheers
John .

[maritimer95gt]

Thanks for the insight John

We didn't have a pyrometer set up at the time. I have a laser temperature reader that I plan to use on the next run though. I will post numbers as soon as I can. I have noticed with other builds on youtube that when they usually run into a serious issue and get close to or actually cause turbine failure, there is usually a shower of fine sparks in the exhaust. This however wasn't the case. I will post a video if I can.

Cost isn't too much of an issue if I can filter and work with used engine oil, but if it HAS to be perfectly clean, then diesel or kerosene will probably be the way to go for me. Is there a certain style of combustor/flame tube I should use with running diesel compared to "oil"?

Thanks again for all the help!

[racket]

Hi Alex

A Jetspecs sized combustor should handle "oil" , the main thing is to get the viscosity of the oil down by preheating it to somewhere close to cold diesel viscosity and then atomise it using sufficient pressure to achieve acceptable droplet size for combustion within the restricted volume of the flametube primary zone .

Oil that has been through a standard oil filter should be "clean" enough to use without blocking the small passageways in the spraynozzle .

If you run into problems trying to get the oil to combust , the addition of some gasolene ( ~10-15% V/V) into the oil will help by providing some volatiles to get things burning .

Hopefully one of the guys who have used oil will provide more insights into its peculiarities :-)

Cheers
John

[maritimer95gt]

Last night I built a "buzz coil" for the ignition. It seems to work pretty well and tosses a powerful arc constantly for about an inch and a half. It easily ignites the propane combustor on my buddy's turbine. Now he wants one. ;D


I have seen quite a few different injection setups online for diesel or kerosene, but I have found very little on how fuel is regulated. What is the best way to feed a nozzle while still keeping a nice spray pattern across the entire throttle range? Will a "performance" fuel regulator for a gasoline engine possibly work?

[wolfdragon]

several different ways to "regulate" the flow

all have a key similarity, fuel pumped to the nozzle(s) is at "high" pressure and in a volume rate much higher than what the engine can ingest, thus there is a return of excess fuel to the tank

the simplest method is a needle valve in front of the nozzle and a relief valve to point excess fuel back to the tank, you could probably just use a T fitting if your pressure and volume were sufficient

you can also go the route of an automobile bypass style adjustable fuel regulator, this will directly let you vary pressure instead of flow with the previous example

just find something you like and fits your budget

[racket]

Hi Alex

Fuel control is simply on our turbines as theres only an ~4 :1 flow range between idle and full throttle , this can be covered by a simple spray nozzle .

Ideally an idling throttle fuel pressure of 50 psi to maintain reasonable atomisation , so lets assume you use a 3 GPH nozzle calibrated at 100psi , at 50 psi you'd be flowing ~2 GPH , with a 4:1 flow ratio that'll mean ~8 GPH at full throttle , this would need ~700 psi at full bore to get that flow through a 3GPH nozzle , flow changes as square root of pressure.
Theres lotsa info on fuel etc in the Files Section on the Sister Site at Yahoo DIY Gas Turbines tech.groups.yahoo.com/group/DIYGasTurbines/

A simply small needle valve controlling a "dump" back to the fuel tank is all you need for a stationary unit , the fuel from the pump goes to a Tee piece with the dump valve on one branch and the line to the spray nozzle on the other .

Cheers
John

[maritimer95gt]

Alright, so I purchased some parts for my fuel system. I went to McMaster-Carr and ordered a fogging nozzle that should do a better job at atomization than a normal spray nozzle. It flows 12.9ga at 100psi. It was only 25 bucks so I can always order another type if need be. I have a 1.4 GPM Shurflo pump that WILL RELIABLY reach and hold 300 psi for brief periods if I bridge the factory electronic regulator and control flow only with a needle valve after the bypass on my automotive style fuel regulator.

The reason why I went with the fogging nozzle is that I wanted to avoid building an evaporator assembly if at all possible. Instead I want to preheat the diesel fuel by running a coil further down the flame tube to act basically as a heat exchanger, thus heating the fuel. The fuel line will come through the flange at the top of the combustor, go about 2/3 down the flame tube, go around with a few coils so as to block the air flow as little as possible, then back up through the flame tube and out of the combustor flange, and then finally back into the combustor, this time through the center. The nozzle will be placed 6" from the flange. Hopefully, by that point, as soon as the diesel exits the nozzle, it will instantly boil before it even reaches the walls of the flame tube due to the severe drop in pressure at such a high heat. This is only theory though...

Next question though...

Will it make any difference in output power if I lengthen my my combustor? I have a 6" SS pipe for the outside of the combustor and a 4" SS pipe for a flame tube. I have 36" of length to work with. I wanted to ask for some opinions before I started making cuts at least. I figured that I have 36" to play with so I can always shorten it from there. I have 3" tubing leading from the cold side to the combustor.

Next issue is that when I took my VT50 apart to clean it thoroughly, I found that all the seals had been scavenged, even the heat packing on the hot side is gone. I have no idea where to find any of the rebuild parts and Cummins has yet to get back to me on a rebuild kit. Yay....

[racket]

Hi Alex

Flametube extra length won't increase power , power is "fixed" by the turbine inlet temperature (T I T ) , and thats fixed by the overall air/fuel ratio .

What size is your compressor inducer diameter ??

A 4" flametube is probably going to be small a diameter to allow liquid fuel to hold a flame , combustion will be very unstable , if it works at all . .....................extra length WON"T cure a skinny flametube , axial air/gas velocities will be too high

Cheers
John

[maritimer95gt]

The inducer diameter is 75mm wall to wall. The reason why I chose to go 4" is because it was proven to work on the GR-7 engine built by RCDon.

www.rcdon.com/html/gr-7_turbojet_engine_project.html

I may be wrong though... What size do you recommend?

Again, I really appreciate the help!

[racket]

Hi Alex

RC Don's Site is invaluable for construction technique, but the theory is suspect , his engine never achieved its full potential , and his evaporators overheated badly due to restricted airflow .

The overheated evaporators meant he had very hot gasious fuel exiting them that allowed an undersized flametube to work up to a point , a case of two wrongs making a "right" , those overheated evaporators could have failed and a piece go thru the turbine wheel with disasterous results .

You need a flametube of at least 5 inch diameter to be on the safe side if you wish to safely burn sprayed liquid fuel .

Use the Jetspecs program to design your flametube and you should have a running engine first time .

Cheers
John

[maritimer95gt]

Well crap...

Either way, it sounds like I will have to post ideas of mine here before I do anything. It can't hurt to have expert input

Will a 5" flame tube leave enough clearance within a 6" id combustor? 1/2" really doesn't seem like a lot of room...

I was already planning on porting the holes in the flame tube at an oblique angle so that there would be as little resistance for the air to enter the flame tube as possible. It would give the holes almost a "knife edge" that would allow air in more easily almost like some sort of cheese grater effect. the goal of this was to create less turbulence within the flame tube itself. Of course the holes wouldn't be perfectly circular either, but more oblong, with their greatest length lined up with the direction of air circulation.

I was also planning on having the 3" pipe lead in to the combustor at an oblique angle as well to further facilitate smooth, circular flow.

I was hoping to achieve something like this...

www.diyturbinejet.com/vortex.html

Is this something that I should do?

Thanks for the helpful insight!

[racket]

Hi Alex

There'll be less problems from the smaller clearance between a 5" FT and the outer can than there will be from using a 4" FT .

Be careful about building in too much swirl in the combustor , it can cause problems , a delivery tube at right angles to the combustor works OK , the addition of swirl producing primary zone holes is OK , but theres no need for any of the other holes to produce swirl , a nice bellmouthed edge on the holes will produce the best flow , sharp edged holes only flow ~2/3rd the air as a bellmouthed one of the same throat diammeter .

Cheers
John

[maritimer95gt]

A 5" flame tube will actually make things easier for me.

I'm exactly not sure I get what you mean by "bellmouthed". Is there any way you could clarify, just to make sure I'm on the same page?

[racket]

Hi Alex

When we bellmouth or "plunge" our flametube holes we drill a slightly smaller diameter hole than is required, then by forcing a suitable mandril into it, the hole is opened up to the correct size and a bellmouth shape is made in the sheet metal , have a look at the large dilution holes in my 10/98 engine flametube
jetandturbineowners.proboards.com/index.cgi?action=downloadattachmentpage&board=diygeneral&thread=19&post=84

A vena contracta en.wikipedia.org/wiki/Vena_contracta severely reduces the airflow rate when a plain hole is used , its not always possible to make a bellmouth in a flametube wall if the material is thick unless we use a larger drill and just make a bit of a countersink at the inlet to the hole .

Cheers
John