Turbo jet sucess

[mayviary]

My first post on any forum.

Ive been playing with turbo based jets for a while now and last Saturday had my first self sustain run , a few tweaks later it now starts well it only has approx. 6 PSI boost 450 C EGT, it  runs really smooth on butane, I'msure it has more to come with more fuel will probably move to propane. It runs OK down to about 2 PSI. Inductor is 54mm Dia combustor is 550mm long 100 Dia with 65mm flametube, holes as per jet specs, need to set up tacho for next run

I have a few questions;

Is hydraulic oil OK for lube ?its nice and runny and I was given 20 Ltr

Do you measure EGT at exit of combustor or turbine?

What are the approx. proportions for an after burner relative to the exhaust, I plan to use Kerosene for this.

Do I really need oil pressure greater than boost pressure, currently its about the same.

Where do you measure Exductor dia?

Is it OK to blow a bit of fuel into the compressor side , I would think it would be OK if you stay below the LEL.

Do you need bigger/ stronger sparks for afterburn ignition, I'm using a feable Chinese ignitor at present.

That will do for now

.

Jeff

[racket]

Hi Jeff

Could you do a build Thread in the DIY Section .

A few comments ............don't run the engine below ~5 psi P2 , below this pressure its very easy to run into hung start type problems if you try to accelerate the engine.

Hydraulic oil isn't the best oil to use as its generally far too thin and won't "control" the bearings behaviour once you start getting up to higher power settings , use engine oil of a type the turbo was designed for, or preferably a synthetic engine oil that can cope with more extreme temps . .

Measure TOT ( turbine outlet temperature) as it will be safer , no chance of the thermocouple pickup falling off and going through the turb wheel .

For a 54mm comp inducer , a 100mm afterburner diameter should be OK , but something 125-150mm would still be OK , length 600mmm plus , depends on diameter , bigger diameter = shorter length .

You need an oil pressure similar to the auto engine's pressure the turbo came off , don't skimp on lube supply or pressure , your turbos survival depends on it .

Exducer is the outlet diameter of each wheel , biggest dia on the comp , smallest on the turb .

Its preferable not to feed fuel into the comps inducer , you only want fuel to go to the primary zone of the flametube not to all of the flametube , besides , it'll make the comp less efficient as it soon gets dirty .

Spark for the A/B needs to be pretty good .

Cheers
John

[mayviary]

Racket
Thanks for the reply its really great to have a resourse like this. I will address the issues you raised on my current lubrication arrangements but for now they are the same as I will need a bigger pump, until then its only run for very short durations.
I have just tried again this time using propane inplace of Butane and with a higher pressure regulator (now 20 psi), the results were not much better than before, I can definatley get more fuel in. here's the problem,as the P approachs 12 psi it starts to sound rough and loses speed, could this be insuffiecient air? Looking at the flame tube the area between primary and secondary holes is a lot cooler , should I open them up a bit? I would be able to measure the temp at various positions any ideas what these might be?
What sort of delta T should there be across the turbine.
I now have most of the parts for the AB was going to postion parts as follows( as fraction of the total length from inlet );

                        Position
    Fuel                   1/8
    Flame holder        1/3
    Ignitor                1/2    



I did have a couple of thoughts.
Has anybody used car Lambda sensors to monitor O2? these might be useful in various positions of the flame tube or even the turbine exhaust this would give an idea of the dilution ratio.
What about using car HID Xenon ballsts as ignitors these have dual voltage output (superimposed ) a few Kv for the breakdown and a lower voltage once the arc is achieved. I have ordered one to have a play with.

[racket]

Hi Jeff

Don't use regulators , they invariably have restrictive flow passageways that will limit your fuel flow , simply use the cylinder valve for throttling the engine

Don't change your flametube hole pattern .

At 10 psi P2 you'll have maybe a 65 deg C rise in the compressor requiring a 57 deg C drop across the turbine stage , so T I T will be 57 deg C higher than T O T ..............the turb stage drop will increase as your P2 increases , there should be roughly an 85% of comp rise as a drop across the turb ,

You haven't mentioned your turbine wheels exducer( outlet) diameter , you did mentioned a 54mm comp inducer,but we need to know the turb exducer diameter to determine if it could be restricting flow through the engine .

Because we run very high A/F ratios of ~60:1 overall, I doubt the O2 sensor would be much use externally, whilst internally the gas temps will be so high any pickup would melt .

Can't comment on the electronic stuff , not my field :-(

As for A/B positioning of bits , we want everything as far "forward" as possible to maximise combustion length .

Cheers
John