VT-50 Jr. Dragster (kindof)

[racket]

Hi Feathers

With a 3" inducer you probably need a minimum flametube ID of ~5.2 inches -130mm to get a 3 times inducer area , at present you don't even have a 2 times area ..........................you'll have nothing but problems with such a small crossection ...................there isn't any way of "fixing" the problem by hole manipulation ...................it will end up being an engine that disappoints :-(

If you use a 1" trunk , say7/8" ID evap entry that'll leave ~1.5 sq ins for the primary holes , say 8 X 5/16" and 8 X 3/8", try and get the first line of holes to blow across the vapourised fuel exiting the evap , a half inch "above" the outlets.

Secondary holes , maybe 9 X 7/16"

Tertiary 12 X 5/8"dia .

Cheers
John

[Feathers]

Well we'll see about the "dissapointment", but RCdon (if you havn't already figured out that I'm modeling my engine largely after the one he built) used the same combustor diameters, and had an even shorter combustor, and his engine runs fairly well.

I'll give it a try.

Feathers

[racket]

Hi Feathers

LOL.......suit yourself , but don't come crying when you run into combustion problems ;-)

Don does beautiful construction work but his engines aren't run to their full potential , and unless you have exactly the same turbine stage scroll A/R and wheel to control mass flow rates you could run into problems following his design

Cheers
John

[Feathers]

Please don't be surprised at my slight offense taken to your comments above:

I very much trust that you have a great deal of experience with these engines, and greatly admire your patience, attention to detail, and craftsmanship.

And while I value your input, a person such as myself posts on this forum looking for advice and constructive criticism, not fortune-telling.

I've put almost 100 hours into this project (which you guys do frequently, but this is my first time taking on such a thing), and it began at a time when I wasn't so wise as I am now . I'd made a mistake in my design, but it is too late to make such radical changes, and I need to proceed with what I have.

Thanks for the input!!!

Feathers

[stoffe64]

Itcould endup With serious engine problems,hot starts...flames out thrue the turbine wheel With risk of destroying the turbine wheel,that 4" flame is too small so flames Will travel all way down and out the turbine melting it in worst case.

[wolfdragon]

Don't be afraid to all out scrap something. If there is a significant design flaw, it's usually the cheaper way to go (says the engineer that is making stuff out of stainless...) (50usd in material scrapped thus far)

A leafblower check of the combustor alone should help reveal/dismiss any issues with your design. Blast it hot and hard as that engine will only suck more air than your leafblower us likely to deliver.

[stoffe64]

Yes,à combustor test is essential i have learned,every flaw in the combustor design Will show up,higly recommended to do.

[Johansson]

I don´t know if I agree 100% with that, the problem is that a leaf blower can only simulate low idle conditions so you still don´t know how it will behave at higher air flows.

Another thing is that a leaf blower can only produce flow and not pressure so I wouldn´t put much weight to the results from such a test.

Still, if you decide to try make sure to measure the temp at the outlet and try to regulate fuel flow so you won´t exceed the TIT you are planning to run at (800°C or so). It is very easy to become disappointed when a 50cm flame comes out of the combustor exit and assume that the combustor is badly designed when in fact you are giving it much more fuel than the air blown into it can handle.

[stoffe64]

Hi Anders
I fully agree that à leafblower doesnt give enough airflow
To simulate the compressors airflow,what i meant was that
You should have à very good fan With ducting connected
To the combustors air inlet,very good photos of such installation
Can be found on the Yahoo DIY gas turbine forum at photos
Look for Mike earlys photos,he builder such combustor fan unit
And ofcourse you must take into count that you have to have less fuel amount
For that lesser amount of air from the fan unit.

[racket]

Hi Feathers

I gave you advice ...............if you don't wish to use it, thats fine with me :-)

As for fortune telling .........nah , not my thing , I just tell it as it is , ...........over the past several years whilst contributing on the DIY Site I've had to help too many guys running skinny flametubes , that why I wrote up the RoTs for DIY and with Jesse we made Jetspecs , advising more generously proportioned flametubes to "guarantee" problem free combustors for first time builders .

My first flametube ( for the turbine bike) was started back in the early 1990s , it has a crossectional area ~2.5 times the comp inducer area , I use 3 times inducer for my "micro" engines ....................it took me several months of research before cutting metal , ...................it was never atmospherically tested , neither has any of my subsequent flametubes , all seem to provide a workable combustor because I've followed well proven design principals and haven't tried to increase combustion intensity beyond reasonable limits , your current flametube may very well "work??" , but combustors with very high combustion intensity are often very fussy about fuel presentation and power ramp up speeds , not an ideal scenario for a first time builder to have to cope with , ...............I have enough trouble coaxing a new engine into life and getting it sorted even after a lot of DIY turb experience , it'll be doubly hard for a first timer even with a forgivingly generous flametube , with a marginal flametube it could prove a daunting task, I hope it won't be , but at least you are forewarned of the possibility .

Cheers
John

[Richard OConnell]

Well, the way I look at it is this:
If you want to keep your design scheme, thats great for more than one reason.
If you get it right, fantastic, you have an engine that runs well.
If you get it wrong, you may be disappointed or even heartbroken, but I would hope you would at least contribute your findings either way. I will be interested to see how it goes.
Best of luck with your project
-Richard

[Feathers]

I understand John, I mean absolutely no disrespect, but I think I'll proceede and see what happens! Hopefully It'll run!

[racket]

Hi Feathers

I hope it'll run as well , I've know the disappointment of an engine that doesn't .

As Richard said , please let us know what does eventuate :-)

Cheers
John

[Feathers]

Sure will! Considering my last engine, anything that doesn't burn up after 3 minutes of runtime will be great news! My standards aren't quite as high as they might be for you guys and your engines.

I've built a tesla coil, and anyone who's done that before knows much excitement, dissapointment, and has learned alot about radio electronics It didn't teach me a whole lot about gas turbines, but it taught me how to be patient and that not everything works the first time around (it took about 4 times around with the tesla coil ).

I'll give it a shot and keep everyone updated as I go.

About to swiss cheese the combustor and finish the evap system!

First light will be on propane I think, but diesel will folow shortly thereafter.

Hopefully I can come up with a leafblower to turn this beast over with warm oil in the bearings at 40 PSI...

[stoffe64]

Goodluck feathers With your engine build
Im also hoping for the best results With your
Design,please keep us informed here how it
Performs and about the outcome if it survived
Or not so we all can learn something from it,
After all,it is trial and error that makes us to
Learn what work and dont work.
Good luck Feathers!