"Fat Boy" 12/118 thrust engine

[gidge348]

Hi John, I am no expert on this but if the evap tubes are not doing their thing, could it be that a finer spray nozzle may help evaporation rather than syringe needles? I have been making a water meth injection system for the Nimbus and am using leftover fuel nozzles from a J34. The original J34 nozzles are made by Eddington's and are 9/16 unef thread, 0.7mm dia, 80 degree fan and there a 2 rings in the engine 36 in the outer and 24 on the inner 60 total. These same nozzles are available in sizes 0.2mm to 1.5mm and spray angles of 30 degrees all the way to 90 degrees in stainless or brass and each one has a built in filter. www.directindustry.com/prod/delavan-france/product-18054-983145.html ....... www.aliexpress.com/item/9-16-oil-nozzle-for-burner-Oil-Nozzle-for-waste-oil-burner-brass-oil-mist-nozzle/32792459363.html I don't know the flow rate of these and know you are stuck for space in your engine and not sure if this has been discussed before, but just maybe an option?

Cheers
Ian...

[racket]

Hi Ian

They're a very good price :-)

Unfortunately not enough space available for "proper" spray nozzles, the bent tip syringe needles gave a nice fine fan spray but the air speed going into the evap tube was simply too powerful and it destroyed the spray pattern ...................we're thinking of using them though for Andy M's engine as it won't be having evap tubes , just the fine fan spray in a "rotary" directing in the head of the Primary Zone .

I've been reading up on my Combustion texts and the ~2 milliseconds of residence for the air within the flametube is stretching the combustion process unless I can get this vapourisation improved

Cheers
John

[lofi]

Hi John

If I remember correctly, you were struggling to get the fuel to fan out and hit the sides of the vaporiser tubes and were exploring ways the break up the boundary layer in the tube? What about increasing the turbulence of the air entering the vaporizers with some square projections at the entry points? If my understanding is correct, this should slow the flow down, prevent boundary conditions somewhat and aid mixing, which seems to fit with what you're trying to achieve.

The idea stems from research into steam loco exhausts, where proper function is achieved through maximising turbulent mixing in the boundary of the confined jet of exhaust steam into the combustion gases in the smokebox. The goal is to maximise turbulence at the boundary, minimise cylinder back pressure and keeping the jet velocity low.

An excellent PhD paper has been produced on the subject, and contains a lot of historical research into confined jets and turbulent mixing. A late development has been to make the steam exhaust exit square, with four small square projections on the flat sides pointing inwards. Practical tests by a Canadian gentleman testing on a large model suggest it has quite a profound effect. In the same vein, what about diffusing vaporiser tubes? A pain to make, but possibly another tool to slow things down in the vaporisers?

Just a thought that it may be of help to look outside into some different areas of fluid dynamics research. The paper has been published as a book titled The Fire Burns Much Better - its an excellent read.

Reading with interest as always. Apologies if I'm way off the mark!

Ian

[CH3NO2]

Hi John,

If inadequate vaporization is the cause, experimenting with 100% gasoline will help due to it's lower boiling point and higher vapor pressure.

Then I would put a spin on the incoming air going into the vaporizer tube. A spin will keep any liquid phase centrifuged against the wall forcing the clinging liquid to move more slowly while the vapor phase shoots quickly down the center.

I get the feeling Chris may have identified the root problem but if you could run it for a short period on propane it would make a good trouble shooting process to eliminate vaporization as a possible cause.

Tony

PS: Not that it would necessarily solve the problem in this situation, but there are various flame speed enhancing chemical additives that you could spike into your fuel.
Ethyl Hexyl Nitrate - A commercially available diesel fuel additive that increase cetane and burn rate by releasing reactive radicals early in the combustion process.
Ferrous Picrate - A commercially available diesel fuel additive that also increases cetane and burn rate by releasing reactive radicals early in the combustion process. And it releases iron ions that work as a very good combustion catalyst.
Anhydrous Ferric Chloride - ~0.05% w/w dissolved into the fuel will increase burn rate and combustion efficiency. Very cheap and easy to find. A powerful catalyst.
Diethyl Ether - ~10% w/w additive. High vapor pressure, low boiling point, very wide flammability limits, high flame speed and exceptionally low auto-ignition temperature. It'll start any other flammables burning much earlier than without it.

 gotta love energetic chemistry.

[racket]

Hi Ian

Before I fitted the "square springs" into the tubes I toyed with using some sort of inlet swirl arrangement , but because of the size/space limitations exacerbated by having to make 18 of them I felt there had to be another solution .

The positioning of the fuel manifold only a few millimeteres from the entrance to the tubes will probably mean theres some turbulence going into them .

The springs provide ~5 revolutions in 4 inches , and with airspeeds through the tubes of ~130 ft/sec , the "rifling" should produce a very high rate of RPM which should centrifuge the fuel to the wall .

Hopefully the actual spring will also produce some extra turbulence close to the inner wall as the air rushing through the centre of the tube spills over the springs as the springs attempt to get it spiraling.

Thanks for the Reference , I'll hunt it up and have a look , theres info out there , its just a case of finding it .

Cheers
John

[racket]

Hi Tony

I've been checking out the differences between Jet A and Jet B fuels , Jet A being kero whilst Jet B being a mix of ~30% kero and 70% gasoline/petrol .

With a T2 of ~150 deg C at the 2.75 PR where I'm having troubles , Jet A hasn't even reached its boiling point of ~163 C , whilst Jet B has already boiled off nearly 50% of its mass ( 50% at 159 deg C ) ...............so we can be pretty confident just from the airs T2 that I'll have nearly 50% evaporated by the time the fuel exits the evap tube whereas nil would have been previously , then with contribution from the wall heat transfer it should be an even higher percentage.

90% evaporated by 193 C for Jet B but Jet A needs 232 C , so not such a big difference at the top end where both fuels are starting to get into similar constituents , but still some difference at 100% with 235 C vs 259 C for Jet A .................its gotta make a difference to combustion , one way or the other , it'll be obvious :-)

I'll try my 50/50 mix and see what happens , gather some more numbers , compare with current ones and hopefully find a trend :-)

Cheers
John

[CH3NO2]

Hi John,

You mentioned in other threads about gasoline not burning as stable compared to Kero or Jet fuel. What was it you noticed when gasoline was burned?

Tony

[racket]

Hi Tony

I've never used "high concentrations" of gasoline , only 10-15% levels which probably didn't make enough difference to be obvious .

Over the years I've tried to steer guys away from using gasoline because of the volatility and consequent less safe operational conditions especially for first time builders who often have unsafe construction even for kero , kero on a red hot turbo turbine scroll is bad enough without the added dangers of gasoline fumes .

The Literature indicates kero is a "better" fuel for us guys to use , even though I've known for >25 years that a large number of aircraft flew on "turbine gasoline" , and even straight gas in an emergencies despite it doing damage to fuel pumps.

High altitude cold restarts needed the volatility of gasoline in the fuel , not a problem for us at sea level .

I'd use straight kero if I could , LOL......80 years of aircraft gas turbine use hasn't come up with anything better.

Cheers
John

[ripp]

Hi John,

I would like to reconsider your construction again.

A wedge diffuser saves a lot of space. The combustion chamber can be extended

Anders ju 2 has been designed very klever. also includes an air divider (I would attach the divider ring on the compressor diffuser so

the combustion chamber can expand).

the Tertiary holes must end 10mm before the NGV, and are located opposite each other, and ...


I really wish this part will be running soon!

Cheers
Ralph

translate.google.com

[racket]

Hi Ralph

I don't know where I can change anything to be able to make the flametube longer , I've used every last millimetre , unfortunately all my Build Thread pics are no longer available, so I can't show you .

Yep , my air divider is mounted to the back of the diffuser and has radial vane supports to negate any swirl between flametube and diffuser .

My Tertiary holes are opposite each other , 18 X 12.7 mm dia in the outer wall and 18 X 9.5 mm inner wall ....................LOL, my flametube design should be very similar to Anders as they came from the same designer ;-)

You're not the only one wishing it would run ,.............its slowly getting there though


Cheers
John

[CH3NO2]

Hi John,

Could it help to hook up a bleed air valve?

Tony

[racket]

Hi Tony

Just at the moment I don't feel a bleed valve will solve my excess fuel injection problem , but it might exacerbate my excess temperature problems as the turb wheel struggles to supply power to the comp when theres less mass flow through the turb relative to the comp .

Things have been a bit busy on the home front this last week but I'm hopefully of a quieter one next week so should be able to get a test run in to see what the new fuel mix does, I'll post the results, good or bad :-)

Cheers
John

[racket]

Hi Guys

Another failure.

From the video of the gauges it appears as though my starter is sucking so much power from the 24V system that the fuel pump , also hooked up to 24V for the PWM , is lowering the preset fuel pressure to such a degree that I ended up with a hung start despite having the starter engaged until there was 30,500 rpm on its tach , thats ~50% N1 .

The drops in both fuel pressure and oil pressure during subsequent spoolup attempts was erratic with oil pressure dropping below the safety cutout for the fuel pump , in the end the starter was too hot to handle , the batteries were empty , so I came home defeated :-(

It looks like I'll need dedicated batteries for the starter only , with the rest of the systems running on their own set of 24V batteries , bugger , more weight to haul around , I'll do some more static testing to check what happened.

Cheers
John

[smithy1]

Hmmm, she should be up to self sustain by 30k or 50% John, agree a poor/low fuel supply pressure wouldn't help.

I have separate power supplies for my fuel & oil systems now, mainly due to my 750psi+ fuel pressure requirements. Need a nice big 10ah 6cell lipo (22+v) for my fuel pump drive and a normal 12v motorcycle battery is sufficient for all other systems...although I'm using a blower to start, so that eliminates that as a power supply issue.

Ignition also uses a separate 6cell lipo battery for my C20 igniter system, so I have three separate batteries on the kart now.....and none of them are used for starting duties.

Cheers,
Smithy.

[racket]

Hi Smithy

OK it looks like another battery needed .

I did find a semi loose connection at the starter solenoid , it didn't show any signs of distress so mightn't have been a problem , but am fitting another fuel pressure gauge on the supply line near the final filter so as to know exactly whats getting to the engine during spoolup , the other fuel pressure gauge is out of the pump prior to the dump valve etc .

Cheers
John