Today is April 6th 1996, in Murphy Oregon, USA. Yesterday the word "duh" was added to Webster's dictionary I hear. Duh is a cool word like yeah & Huh? Ok, now, on to my creation. It's a story of a father-son project that ended about two years ago. I'm the son. I want to tell this story with the hope it will inspire other father-son projects. And also I want to put something about my dad on-line, something that might actually be interesting enough that maybe someone might actually want to read it. Who on earth would want to read what Larry has to say about his dad? Duh. But how to make a jet engine for $25, now thats worth reading. Unless you ask my girlfirend who will tell you I'm crazy making these things and no one could possible be interested.
This page is about the second engine we made becuase the
first one was a total failure -
except that it led to this version. Below you can click on "Background" and
read all about how we got from nothing to version 2.
The photo here, taken with my super cool CASIO QV-10 pocket digital camera (List price $999 but only $689 at Office Depot - um, update 8 years later: QV-10's on eBay $24), shows the top of the "combustion" chamber, which I like to call the HB (Heater Box), even though it is round. On the lower left you can see the compressor housing out of which comes a 1.5" (38mm) pipe feeding the compressed air to the HB. The chrome pipe is from a bathroom sink drain and the brass couplings are for 1.5" fire hose. Hey, it works! The HB is a steel pipe with an aluminum top which can be removed easy (I also made a top out of 3/8" (9mm) Plexiglas and watched the flame burn inside! Propane (LPG ?) burns blue, diesel is bright white, and Vodka + Whiskey burns invisible with wispy yellow/blue/white shadows). The shiny tube on the right with a pocket clip is a tire pressure gauge. It records the highest HB pressure for a run has a digital read out, requires no power, is easy to reset, and costs $1.49 (1GBP) at the local department store.
If you have some free time, check here for the
Background - my first jet engine...
Onward
Here is the test gurney. Not a good idea to run in a closed building like my shop, DUH, (I tried it), ... "then there are some of us that never learn". On the left is an old acetylene gas regulator which just happens to fit the 5 gallon propane gas tank in our barbecue perfect! After a year of swapping the tank between the jet and the barbecue, my girlfriend made me get a second tank just for the jet. The blue box in front of the tank is a frequency counter which I use to measure the shaft RPM (actually RPS (revolutions per second)). In the center is a power supply and below is a motor and pump to supply oil to the turbo-charger's hydrodynamic bearings, which need lots of oil or they don't work. At 120dbA ... it really screams!
<-- The hole midway in the HB is for the spark plug. I use an electronic starter from an old barbecue, powered by one AA cell. It sparks my spark plug about twice per second. Once a flame gets going the spark is turned off. On the table is a fish scale attached on the left to the carriage which has 4 bearing "wheels" which ride on the table so the overall thrust can be measured.
On the right -- see the CCCCL (Coffee Can Combustion Chamber Liner), or 4CL, AKA flame holder, which was the breakthrough for me that made it work. My 4CL is made from a 12 ounce (340g) Mountain Grown Folgers Coffee can (Aroma Roasted). "Cold", pressurized, fast moving air is being pumped into the HB about where my thumb is. We need to heat the air with fire, not blow out the flame, and do it fast! That means high heat! But we don't want to melt the turbine blades. The design of this liner (I call it "the can", get it?) is what helps all this happen. The large hole is for the spark plug to reach in.
In a real jet, only about 25 percent of the air that enters is used to burn the fuel. The rest is mixed with it which cools things down in a way as it heats up. Also, the real "can" has holes designed to mix the air and distribute it just right for maximum heating efficiency. It runs on hot air! The heat energy re-expands the compressed air in the HB. It keeps the pressure up but not higher than the pressure at the diffuser so the compressed, released, moving, and re-expanded (hot) air pushes the "hot wheel" (just like moving water turns a water wheel) which in turn drives the compressor.
hmmmm, looks like I have a balance problem here.
Oh well, it is my first home made animation (9/96).
The flow begins at the compressor, through the HB,
past the hot-wheel and out the exhaust pipe
because that is the path of least resistance!
The highest pressure point is at the "diffuser"
(which is just a place located near the tips of the
compressor blades.) It must be, by definition,
because air moves from high pressure to low
pressure. Air has mass. (It is not space,
it has weight. An average bedroom has about
135 pounds (60kg) or air in it! Grab 135 pounds (60kg) of
anything, accelerate it to 700 mph (1100kh)
in a short time in one direction and what you
get is Newton's third law. The air and fuel
are the mass, and the compressor and turbine
make it flow. So what we have is mass flow! Duh?
The intake of the compressor. On the right is my home made tachometer sensor made of 2 tubes, one with a light, the other with a photo-transistor. The diameter of the blades (at this point) is 2.3 inches (58.4mm). So that makes the circumference = ( 2.3 x pi ) = 7.2" (183mm) The speed of sound (mach 1) is about 750 MPH = 1100 ft/sec. = 792,000 in/min. (1200kh = speed of sound = 20,000 m/min or 183mm x 110,000 rpm) So at 110,000 RPM the tips of the blades go supersonic?
At the very top center you can see part of the brass fitting that feeds oil to the hydrodynamic bearings. The next closer tube goes directly into the hot-wheel housing at a steep angle to help start the engine. I pump shop air in at about 60 psi (4 bar) and it gets the wheels spinning. The last tube on the left in the exhaust pipe is a failed experiment. To the right is a thermal couple sensor I found at a surplus shop for $2. (1.25GBP). It works great with my cool Atkins #39658-k digital Thermometer.
That's about it. I sure know more about jet engines now than when I started. It is hard to imagine I was even dumber then than I am now. I have ideas for GT#3. I want to try an afterburner, a second hot wheel for power take-off, use the HB pressure to pump the oil and other things, air-bearings, make the smallest GTJE, ... Applications, ?, ?, ... make noise, annoy the neighbors, melt snow, drive a large wheel hooked to a generator, a turbo charged burn barrel (use trash as fuel), .....
Update: 8/13/96... several have asked ... how much thrust did I get? Almost 7 pounds! I guess I forgot to say, sorry. My first successful test run was 5pm on Sunday February 6th, 1994. There was no measurable thrust but it ran unassisted and made a lot of noise. We were very happy because it took months of trying and it met all of our requirements to declare total success! So I did! And Dad was there! Just me and Dad. It was our success. Dad, age 75, me 45, was the real reason I did the project now because it was something that we did together and he enjoyed it and came over every day to work on it, even though he couldn't help much due to a stroke 10 years before, he had lots of wisdom and a sense of what works. After months of trying and disappointment, we finally had our very first, very successful run (5:05pm that cold Sunday evening, February 6th, 1994 ), we did the "high five", Dad said "I'm cold, see you later", he drove home in his John Deere 5 wheel ATV ("The best thing I ever bought!" ... he would say. ), sat down in his arm chair in front of his TV, lit a Winston filter cigarette, turned on his TV, and died. Seven months later I ran the engine again and had my best ever test run with 6.5 pounds thrust as measured with my $5 fish scale. The "head" pressure was over 25 psi (1.75 bar), and the rpm was over 140,000 (too high), the exhaust temp was about 1200 F (650 C). Dail DeV... (genius, inventor, entrepreneur) of California was here to see it. The nut came loose, the cold wheel spinning at 100 thousand RPM hit the side of the housing and made one heck of a noise as it came to a stop. The engine has not run good since, even with new parts and new balancing. On 9/20/94 with home made aluminum bearings I got 4.5 lbs.(2kg) ... hearing it spool up, and up, and then up more, and faster, then more faster,.... is an awesome experience. It will never be again like it was. I have not run it since,... I miss it.
IPO: 6OCT98