Afterburner trouble

[Johannes Hatle]

Hi

I am new to JATO, and this is my first post on any forum, ever.

I have built a pretty nice jetkart with twin turbojet at my school during the last two years.

Now I am having problems getting my afterburners to work proparly.



Does anybody have some suggestions for me?



Thank you





Jetkart photo album

[Johannes Hatle]

[Johannes Hatle]

[Johansson]

Hi Johannes and welcome to the forum!

A very cool looking cart indeed, I thought I had seen everything to see about DIY turbines on youtube but you proved me wrong.

What sort of fuel pump are you using to feed your afterburners? My first guess when watching the videos is that the pump isn´t capable of a high enough pressure so when the pressure in the AB increases it stops the fuel from flowing through the injectors.

I would suggest one Bosch fuel injection pump for each afterburner, that would keep them fed and happy.

Cheers!
/Anders

[racket]

Hi Johannes

Welcome :-)

Thats one mighty fine kart you guys are playing with, very professionally constructed and finished off .

Looking at the pics you've posted its obvious theres been a lot of thought go into to "balancing" the components flows etc .............do you have pressure readings from each turbo to compare ??

One A/B is looking good but that other one is certainly a bit sick , it is also appearing to produce a lot hotter jet nozzle , at shutdown its glowing whereas the "good one" isn't .

What sort of flameholder are you using in the afterburners ??

I notice you have a "dump" section where theres a sudden increase in diameter but its upstream of the fuel injection so won't be able "hold" any flame .

The A/B spray nozzles are fan types , do they spray "upstream" or "downstream" ..............could there be a difference in spray between the two A/Bs ??

As Anders said ......................a very cool looking cart :-)

Cheers
John

[racket]

Hi Anders

Heh heh, that machine really needs a couple of your gas producers on it , with A/Bs, it'd go like the wind :-)

Cheers
John

[Richard OConnell]

Very slick looking cart! I'm also curious to see your flameholders

[Deleted]

this is the layout of the afterburners most of us use in the uk, do you have one pump to each afterburner,

for dans mini, there is one pump teed off to both afterburners each with rated in line check valves

[Johannes Hatle]

Thank you all.



I have one fuel pump rated for max 8 bars, which delivers kerosene to both afterburners, distributed through a fuel "manifold". The combustion chamber runs on a separate fuel system. There are three spray nozzles in each A/B which spray downstream, and there is no obvious reason why they should not spray equally, and fairly in the same direction. I can tell that the fuel pump is capable to get the fuel into the A/Bs by all the unburnt fuel coming out the back, even at full throttle. But if it is enough overpressure to get an adequate atomization, I do not know.
I only have one pressure sensor in the back of the combustion chamber, which shows about 2 bars. I don't have one for each turbo, and I don't know what fuel pressure it is running on.
There is one sparkplug for each A/B which is located midways downstream the A/B.
Right after the diameter increase in the afterburner, I have placed some internal dampers which I can rotate/adjust from outside the afterburner, so that I can sort of manipulate the airstream after the turbo. I have not yet tried to experiment with these, but they have been installed.
The best afteburner results I've had was when we ran the combustion chamber on propane gas in addition to kerosene, but that I think, was because we got more RPM. Check this one to.

But now I am getting a feeling that I have missed something fundamental here, what is a flameholder ??

[Johannes Hatle]

[Deleted]

how are you lighting the afterburners..... you have an easy fix, extend the smaller tube into area where fuel injectors are , then replace with fuel ring, as drawing above, you need check valve in each fuel line ..... this is the results you can get

[Johannes Hatle]

I light them with sparkplugs.

Does a fuel ring work well with kerosene and no spray nozzles?
Why the smaller tube?
And why do I need a check valve in each fuel line?

[Deleted]

the smaller tube help cause a low pressure dump area to mix fuel and air, hold the flame front as well,

this afterburner based on drawing



the rated check valves need to be about 5 psi, they ensure fuel rate in to afterburner about the same, and that the pressure in the afterburner don't push fuel back to tank

[Deleted]

do you have any pictures of your flame tube

[racket]

Hi Johannes

You mentioned the A/B fuel is sprayed downstream , this will reduce vapourisation and mixing times for the fuel , have you considered orientating the fuel injectors so that the fuel is sprayed upstream towards the "step" in pipe diameters , there might then be a chance that the step will then act as a flameholder , we need some form of flameholder as the gas velocities within the afterburner is too fast for a flame to be held, it simply "blows out in the wind", the flameholder is an area of low velocity air/gases that will support a flame without blowing out , this "pilot light" then keeps the rest of the afterburner alight .

Flameholders can be either a "step" in tube diameters , often called a dump type afterburner , or you can have V gutters downstream of the fuel injection that a flame can "hide behind" , the point of the V is pointed towards the turbine wheel , the low velocity recirculation zone in the back of the V allows a flame to be "held" , hence the term "flameholder" .

The circular spray ring with a number of small holes drilled into the tube works OK , its not much different to full sized afterburners .

Theres some info on my efforts in this direction here jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart?page=9

Just some minor "technique" problem with your setup that needs correcting , Andy M will get you sorted, when it come to A/Bs , he's the man to listen to :-)

Cheers
John