Saturday, May 28, 2011

The Begining of an Evaporative Fuel System

A liquid-fueled DIY gas turbine poses one fundamental challenge. Diesel fuel (this engine's fuel), Kerosene, Jet-A, etc. all need to take the form of an atomized vapor before being burned. In commercial aircraft, this atomization is achieved via high-pressure (~1000 psi) fuel injection system, and a special injector.
Unfortunately, a 1000 psi fuel pump would cost a pretty penny which I don't have, and gobble up lots of onboard power, which I won't have.
The solution to this conundrum lies in evaporation. The fuel will dribble out of a nozzle into a "tree" of 3 small stainless steel tubes, which are heated by the combustor. The diesel or kerosene fuel vaporizes quickly upon contact with the hot metal, and the resulting vapor burns easily in the combustor.
I plan to incorporate the "evap" system into the flame tube (the tube somewhat resembling Swiss-cheese inside the combustor which allows the fuel to burn with an even supply of air). For this, I will start with a 3.84" diameter, 3 inch tall "can" with a large hole in the side. This will mount to the end plate of the combustor, feed air to the evap "tree", and support the flame tube, which will fit snugly around it.
 With much cussing and a little blood, I milled two 3.84" stainless circles on my undersized rotary table, then drilled 6 holes to the front of which nuts will be welded. This is the "bottom" of the evap can, which will fit over the 2 fuel injectors (starting and main fuel).
 Here drilling corresponding holes in the combustor end plate.
The finished ring. I also milled a full circle of the same diameter, which will be used as the top of the can.
Heres the end plate installed back on the engine. Looking a little more complex :)
And last but not least, its my pleasure to welcome the newest member of the Feathers workbench, a harbor freight belt sander :). Should get some nice use out of this piece.

Check back soon!

Tuesday, May 3, 2011

Time-Lapse video of the build so far.

I've been making an effort to document this project as well as I can, and have been grabbing snippits of video here and there. While you look at this one, feel free to check out some of my other youtube videos.
Now lets see if I can imbed this for the life of me...

Stay thirsty my friends!

Monday, April 25, 2011

The Oil Cooler (or whats left after "Austin" happened to it)

The 15 row oil cooler I purchased for a thrifty $50 presented me with a problem. The fittings were, as expected, size 10 AN (Army-Navy) performance automotive fittings (they originated in the military, so they cost a pretty penny). Nearly worthless to me, because I'm using standard plumbing sizes and common 45* flared tubing connections instead of AN's weird sizes and awkward 37* flares (even though AN looks WAY cooler). Reason(s) being, AN fittings are ridiculously expensive, and you can't buy them at the hardware store.
As fate would have it, the inside diameters of these giant AN fittings were the perfect starting size for my 1/4" NPT (National Pipe Thread) tap. For the sake of space, I beheaded both the fittings, then tapped them out.
I then went ahead and plumbed an aluminum line from the oil filter to the forward side of the oil cooler. Not too bad.

Tune in next time.

The Re-birth of an Oil System...

I'm sick today, and had some time to get back to the engine. My first oil pump, a Fimco Gold series multi-diaphragm pump, was an agricultural pump, and simply wouldn't supply the viscous oil at any amount of pressure. I have a sneaking suspicion that this complete lack of oil pressure led to the death of my last attempt at building a gas turbine. As not to repeat the mistake, I've purchased a gear-type oil scavenging pump, meant to return oil from a low-mounted turbocharger, or to operate a separate oil system for the turbocharger. It's allegedly rated 2.5 GPM at 60 PSI for oil.
That is, of course, for a car. We'll see how it does.
Here's the engine with the new pump all mounted and plumbed up. I've replaced the pump feed line with silicone tubing which is larger than the original aluminum line. This is to avoid an effect called cavitation which would put air-bubbles in the line, depriving the turbocharger of a steady flow of oil.
 The pump will be a great fit with the engine. I have also installed an automotive ignition coil, which will be driven by a 555 timer circuit and amplifier.
Till next time, cheers!