Safe fuel mixes for flight and testing.

[Irvine.J]

Well gents...
Finally I have a nice running injector, with a neat little pump, all working on my RC TX unit.

The problem I am having is power production is low because of the kerosene that we have in australia is VERY low order stuff, and just doesn't burn without a huge amount of help. What I'm searching for is a fuel that has the inflammable properties of kerosene, with the power of petrol or diesel (or close to), maybe i'm talking like a mix that can be standardised but I just don't know. All I want to do before posting all the data is ask if anyone out there has experience with mixing fuels to provide power and that most important factor of saftey. I'd like yes and no's not "Maybes" as my life definitely depends on it. :-D
Can anyone help?
Regards all,
your flight systems are ready, lets just nail down the fuel.

Ps Larry your system is damn good one, everything a PJteer needs on a daily basis.

[larry cottrill]

Well, I hate to depart from the DIY spirit of this forum to make a crude and unsavory suggestion, but here goes:

Why don't you see if you can just buy some Jet Fuel (gasp!) from an airport or flying service? It's just purified kerosene, anyway. Is it restricted or something so that it's unobtainable to mere mortals? Should be cheaper than gasoline, right now.

L Cottrill

[Johansson]

I remember to have read somewhere that a mix of 25% petrol and 75% diesel makes a mix that has similar characteristics as flight kerosine, might be worth a try.

//Anders

[Dj Nafets]

Why are you making such a problem what fuel to use?

For a pulsejet engine is the rule: kerosine, petroleum and diesel have the same properties.

A strong, very inflameable mixture is:

50% Diesel
40% Gasoline
10% 2 Stroke Oil ( to sve the pump )

Thats it.

[Irvine.J]

Thanks for the tip guys.
I found that shellite (petrolium spirit) mixed with the kero makes for one hell of an aggressive burn in tiny amounts, I got some stuff to experiment with now to find good mixes with shellite and deisel etc.

Dj nafets 2 stroke oil may very well clog my injector buddy, so It will need to be left out of the mix. The reason things never go smoothly in this country is because our products especially kero, differ so much from most other western countries. Basically 99% of all the stuff we buy (EVEN THE BEER) is watered down and crap. So what might be true for most, over here theres only one word that can some up "For a pulsejet engine is the rule: kerosine, petroleum and diesel have the same properties.".... Apparently

I was looking for a mix that wouldn't explode and create a wild fireball on the ground if the aircraft comes down, I think anything with 40% gasoline would probably nuke a small area where the plane came down.

I've tried methylated spirits and shellite kerosene mixes, and now going to have play with deisel mixes.
Wont be long.
James.

[Dj Nafets]

Don´t be so naive´to think that Diesel or Kerosin won´t burn a huge area...

If a airplane come down with a several hundert km/h, there won´t be anything left of it....

[tufty]

Thanks for the tip guys.
I found that shellite (petrolium spirit) mixed with the kero makes for one hell of an aggressive burn in tiny amounts, I got some stuff to experiment with now to find good mixes with shellite and deisel etc.

Not sure "aggressive burn" is a particularly good measurement of whether it's a good fuel or not. What's important is more the calorific value of the fuel, I would have thought, and you can't really beat diesel for that one.

Basically 99% of all the stuff we buy (EVEN THE BEER) is watered down and crap.

Hey, at least Aussie beer has *some* alcoholic content, not like the stuff that gets sold in some other supposedly developed contries <duck, run, duck, run>

Speaking of Beer, has anyone heard from Bruno recently?

I was looking for a mix that wouldn't explode and create a wild fireball on the ground if the aircraft comes down, I think anything with 40% gasoline would probably nuke a small area where the plane came down.

You're about to put flammable fuel through your jet, you can't get around that. If there's a crash and it gets out, it's alost certainly gonna hit red-hot metal, and if that happens, it's gonna burn. I'd honestly worry more about containment rather than the fuel itself. That's not as easy as it sounds either, though, as if there's a fuel line rupture there is the possibility of the burn happening inside your containment vessel, at which point it runs a good chance of becoming a bomb.

There's two approaches, really, one is a bladder tank in a tough vessel, and pressurising it with something inert (and having some way of instantly depressurising in the case of catastrophe, preferably automatic and mechanical), or to have a fuel pump system, again with automatic switchoff, and somehow filling the space left in the (toughened) tank with, again, something inert.

I'd go for an armoured bladder tank in either case, the only questions that remain are what to make the bladder from (preferably something fireproof) and how to fill the space left by removing fuel, and how to stop your fuel spurting out in the case of a crash. Stopping a fuel pump dead in the case of a crash is probably best done with an accelerometer that turns off a relay through a flipflop. Sudden deceleration == no more fuel.

Some thoughts, may be helpful, may not.

Simon

[Irvine.J]

Tufty thanks for the tips.
A while back in a thread I mentioned the pump setup etc I'm using.
I've already got-
A fuel pump that automatically stops flow... (At off position on controller or when battery disconnects) In the event of a crash breaking an electrical circut is far easier then some kind of accellerometer though the idea definitely works. The pump will not allow any more fuel to be sucked from the fuel line. (i'm not sure if its a tight impellor or a small valve in the pump.
Bladder bags are a must with this kind of pump setup though no pressure will be required (as you know its all pump driven), I have plastic tee junctions and fittings for all your tanks if you wish to use more then 1. The pump however will draw from all tanks equally, which isn't such a bad thing.
The fuel system works, now i'm just playing with fuel :)

Dj nafets : I've seen lots of jets on youtube crash at high speed and not fireball, some do, some don't, so I'm sure its simply part design issue part fuel used.
If it does fireball well it happens, though I'm trying to make it "As safe as possible without neglecting power".

Yes, I'm completely aware its a calorific value issue. However, diesel does not atomise as readily as many other fuels and for want of a better term "Break down" as fast in the induction pipe as other fuels for instance alcohol or kerosene in small engines. I proved some small theories today by using different fuels without moving the injector at all.

Kerosene would not fog in the its position and gave good throttle range (But not much power as our kero here is poor.)
By simply switch to diesel, It foged a massive amount, but was amazing loud and you could "feel the power" :-D.
Simply, its flashpoint is higher, so for getting the most out of it, I think it should be thinned out to a little more volatile mix, without destroying its inflammable properties.

Some of the experiments I completed.
Straight kero.
Match will not light kero, after 10 seconds (approx) a very small vapour trail though no flame what so ever.

Kero / methlyated spirits.
Takes 24 hours to break down and mix properly.
Ratio 25:1 Instantly volatile. Spirits burn which causes kerosene to heat rapidly and burn.
Spirit/kero mix = Not good. Not enough control over flashpoint. Too easy ignition

Kero / Shellite Mix. (Shellite = white gas / petroleum ether)
Ratio 50:1
Mixes instantly. HIGHLY VOLATILE.
Aggressive reaction, kerosene bubbles and spits tiny balls of fire about 5 to 10 cm. Interesting, but not good in a crash.

Diesel. (High calorific value) 44,800
Will not light with match.
Fogs very easily in small engine.

50:1 Diesel / Shellite
Match wouldn't light it. Interesting... not run in engine yet.

25:1 Diesel/ Shellite
Match still wont light it. Will need more experimentation, shellite has a high calorific value also, so we shouldn't be loosing too much by thining it out like this if we can keep it relatively inflammable.

More to follow.

[larry cottrill]

Note to James -

I know what you mean, but in most of the English speaking world, inflammable does not mean "not flammable" - it's just another way of saying "flammable" (which is actually a shortened form of the older word). For "not flammable", we would use "nonflammable" or preferably, "non-flammable". (Everything I've just said must be utterly baffling to those whose first language is not English.)

Maybe Oz is just "different" ... no, that couldn't be it, could it? ;-)

L Cottrill

[loco]

I made enquiries at my local airport fuel suppliers and they're happy to provide fuel. They only requested that I provide them with a steel jerry can (plastic woldn't do...). Works out a fair bit cheaper than regular unleaded petrol. It's the fuel I plan to use when I go over to liquids.

Phone your airport!

[tufty]

A fuel pump that automatically stops flow... (At off position on controller or when battery disconnects) In the event of a crash breaking an electrical circut is far easier then some kind of accellerometer though the idea definitely works.

Possibly, yes. I was working on the assumption that a crash wouldn't necessarily "hit" the point you want it to.

Another issue to consider is failure due to fuel lines coming loose or failing, that's going to result in fuel potentially spraying over the motor. Not sure how you'd deal with that, to be honest. A pressure switch on the fuel feed maybe. A standard automotive oil pressure sensor might do the trick for that.

Assuming you have a contained bladder tank, you need to deal with the issue of what you refill the containment vessel with; this absolutely cannot be oxygen-rich. Either that, or have the tank itself made from something flame-and-puncture-proof, bladder and containment in one. Kevlar or Nomex spring to mind as good "outer shell" materials. With a rigid containment vessel, you could backfill from the cc, in the same way as a "pressurised" setup works, but with a bleed valve; basically make sure what's in there is atmospheric pressure exhaust, not normal air. With this one, you'd have to worry about combustion byproducts demolishing your bladder.

I'd consider a little bit of electrickery, and I think the accelerometer approach is probably inherently less liable to failure modes than "breaking the circuit", and could be paired with a pressure tap to deal with fuel line failures too. The whole thing could be done with a PIC or other microcontroller, and needn't cost more than a couple of bucks. If it's a one-off, you could probably get all the parts needed as samples. Total weight would be less than a couple of grams, I would think. These things are small.

To avoid electronics, one could mount the battery in such a way that deceleration of, say, more than one G, breaks contact to the pump, this could be a purely mechanical setup with the battery "sliding" doing all the work. The worry with something like this would be it failing to slide, or sticking, of course.

Simon

[larry cottrill]

I agree with Simon - a battery would make an excellent mass for crash sensing. Hold it in place with strip balsa rails or very small wood dowels. These would be selected experimentally to handle normal maneuvering G loads, but break away under the G-loaded inertia of the weight in a crash situation. You could rig these not just for thrust/anti-thrust loading, but for vertical and lateral sensing, too. Breakaway could be sensed by lightweight music wire 'trackers' that would trigger fuel cutoff (or whatever is deemed an appropriate response).

On my proposed U-control propane-powered monster, I was going to use a spring type mousetrap (with most of the wood trimmed away) as the servo to shut off the fuel valve. It would be set in the normal "mousetrap" fashion before opening the cylinder valve for engine startup. On crash, a small weight would break a single balsa shear pin and a dowel "firing pin" would trigger the trap. This was in the forward direction only, for "powered crash" scenarios. I could have rigged it for additional directions, though. Note the total absence of electrics - there is no reason this scheme couldn't be virtually 100 percent foolproof, even if the whole plane is demolished in the next split second after it triggers. The hard part would have been making sure it never "false triggered" from in-flight vibration or whatever, but a little experimental work would have taken care of that.

Remember, the early bird gets the worm - but it's the second mouse that gets the cheese.

L Cottrill

[Rossco]

Hey! go easy on our Beer James! You know it is my favorite pass time!
Ive drunk a lot of the other stuff, and ours is goooood! Some are maybe a little on the light side although at least it still tasts like beer! Ha, just wait till you tast my new brew, definitely not waterd down!... mmmmm, beeer.

Larry, you baffle me with your words a lot of the time! Aussie different! ha, we try.
Im by no means an expert although i would say, actual meaning asside, that any aussie would take inflamible to mean mostly or nearly non flamible.
A little like [shock or similar] resistant and proof, one is not the other, but its close enough.

One option you havnt brought up James, Dump and Burn! This may be going in the face of what you are trying to achieve, although that is a way the big boys get around it! They dump excess fuel before landing too dont they?
Fight fire with fire! well, a beter term, make lots of fire while you can!
I suppose you could dump it without burning, but, you know.

Rossco

[larry cottrill]

Larry, you baffle me with your words a lot of the time!

Me too.

I would say, actual meaning asside, that any aussie would take inflamible to mean mostly or nearly non flamible.

N'worries, mate - I'm with you now that you really tied it down for me ;-)

Rossco, I really thought you'd at least have a comment on that second mouse ...

L Cottrill

[Irvine.J]

MUahahahhahahahah I love it. <Grins>
http://youtube.com/watch?v=HYHtWpdUzRQ
Damn thats fast :D

Rosco I haven't tried your beer yet, but I'm sure it will fit in the catagory of
"Good tasting rocket fuel" :-D