New Member With Turbojet Problems.

[astilwell611]

Hello all,

I've recently become interested in turbojets and decided to build one. I did a lot of research over the internet and used jet specs to design my
cc and flametube.My engine is running off of propane and uses a 1/8" hose barb as the injector. The hose barb is crushed at the end so that it will
hold pressure.I am having problems getting a consistent ignition. At first it would just blow gas into the cc for a while and blow out a fireball. I fixed
this by adding a "diffuser" over the hose barb to direct the propane towards the spark plug. This helped ignition but it still isn't very reliable. Sometimes
it will start right up and others it wont start at all. Any suggestions on how to make ignition more reliable? Maybe the injector is the problem, any
suggestions for a different injector design? I uploaded all the pictures of my setup that I have at this time to try to help you guys out. I also added a
video of it "running" using a shop vac, please excuse me I was excited lol. I'll try to answer any questions the best that I can.








vid1309.photobucket.com/albums/s625/astilwell611/2014-10-26_02-11-05_787_zpsuoo0zr0j.mp4

[racket]

Hi

Your propane injector needs to "spray" radially within the flametube , an "axial" injector will have problems .

The simplest method is to have a tube for the injector , seal the end of it and drill 6 small holes around the tube wall ( ~60 degrees apart) , this will spray the propane out over the flametube cross section .

Cheers
John

[astilwell611]

Hello John,

I assumed that the injector was the problem so what sized holes need to be drilled and can you elaborate on what
you mean by 60 degrees apart? Does that mean to stagger the holes? Do you know of any post on here that show a
good example?

My idea is to use one of these, cap the end and drill holes in it. What are you comments on length from the spark plug?
In theory closer is better right?


Thanks
Austin

[madpatty]

Hi Austin,
6 holes should be placed all around the injector tube....60 degrees apart means- 6 holes equally placed in a circle all around the circumference of the injector tube...

Ideally the injector openings should be at same axial distance as the primary holes(that is discharging just infront of the primary holes).

It appears you are using a brass fitting for the injector....i personally dont like anything except stainless steel in the hot combustion area...
For the injector i just used a 3/8" ID stainless tube with one end welded shut....i then drilled 3x 0.7 mm holes equally spaced around in that tube...

Cheers,
Patty

[racket]

Hi Austin

You could use that as your injector , but be very careful that things can't "unscrew" and go through the turbine wheel .

As long as the propane spray discharges into the vicinity of the spark plug it should ignite

You'll need 6 injection holes , make them as small as you can so that theres a decent injection velocity , 1/32"- 0.8mm diameter holes preferable , but if you need to go to 1/16" - 1.6mm , thats OK .

Patty ,........... remember you had problems with only 3 holes as the fuel spray didn't effectively cover the flametube's cross sectional area.

Cheers
John

[astilwell611]

Hello everyone

Thank you guys for you input. I went to lowes last night and picked up a brass cap that is six sided.
I plan to take advantage of the drill press at work today and drill a hole in each side. Patty, I havent
had any problems with the brass fittings with the few test runs I have got to work. So I'm not too worried
about them. John, I use thread sealant on all the fitting joints and make sure their tight. I have a good
amount of experience with turbos so I know how fragile the turbine blades are and such.

Austin

[Johansson]

Welcome Austin to the forum!

Thread sealant won´t survive the heat after shutdown, make sure to lock it by some mechanical means.

Cheers!
/Anders

[astilwell611]

Hello all,

Sorry for the slow updates but being in college I don't get a ton of free time to work on the gt engine. However, I did
manage to make it home this weekend to do some tinkering. I changed out my injector with better results but lighting the
actual flame still proved difficult. I decided the culprit was my bbq ignitor. So after a trip to the autoparts store I
built a hv circuit using an ignition coil, auto relay, and a capacitor. This lead to reliable ignition of the propane
with every attempt. So I decided to bolt the turbo on and give it a shot. The turbo deffinatly spools up much more than
last time. I still cannot get it to self sustain, after removing the shop vac the turbo slowly spools down. I do not have
any pressure or temp gauges yet but, plan to order some this week. Which should I look at measuring first? Should I look
more at the pressure inside the combustion chamber or boost pressure from the turbo? I will attach some videos and pics
of my most recent progress.

Thanks
Austin

My new injector is very similar to 8MadDog8's my spark plug is closer to the injector though.




Here is a video of the flame charactaristics with the new injector. Its less orange than the video makes it out
to be but there is still some orange to the flame.

vid1309.photobucket.com/albums/s625/astilwell611/photobucket-19821-1415597551110_zpsd1e435ef.mp4


This is a video of the spool down I was talking about. The fuel pressure stays steady at 80ish psi.

vid1309.photobucket.com/albums/s625/astilwell611/photobucket-14014-1415597506255_zpscfa54983.mp4


There was a nice bit of soot on the turbo when I removed it at the end of the day.

[enginewhisperer]

that turbo appears to have an integral recirculation (blow off) valve in the compressor cover. (the pressed metal cover with 3 bolts holding it onto the compressor housing)

You'll need to block it off or lock the valve closed (connecting the vacuum line port directly to the compressor outlet pressure should work)

[astilwell611]

enginewhisperer,

It just so happens that I have a block off plate for the turbo I wasn't sure if the recirc. valve would cause any
problems or not. Just out of curiosity why does it need to be blocked off? does it keep the turbo from reaching
maximum boost?

Austin

[enginewhisperer]

yep, as soon as you get any real positive pressure in the compressor outlet, the valve will open and circulate the air back into the inlet.

It's there so that on a car, when the throttle closes the air has somewhere to go, instead of stalling the compressor and putting a lot of extra load on the bearings.

[astilwell611]

Yeah I know what its purpose is I just wasn't sure what effect it would have on the engine. So do you think that
the valve was the reason it wouldn't self sustain?

Austin

[enginewhisperer]

hard to know, but if the valve was opening then it would definitely stop the engine from self sustaining.

[astilwell611]

Hello all,

Just a quick update, I blocked off the bypass valve with a block off plate. I also added a boost and egt gauge to the engine.
However, I just don't think that my shop vac moves enough air to let the turbo overcome itself. I took my gas powered leaf blower into
the shop to have it fixed, so hopefully next weekend I'll have enough juice to get it to selfsustain.

Austin

[mitch]

Using a leaf blower is a good idea, to start mine I have to use a large Stihl blower going nearly full throttle to bring it to idle!