Introduction: Turbojet Engine
This was a project I made in my high school engineering course. I Did a lot of research including other instructables, but due the nature of the process, there are many ways I had to improvise. So this is my story and recommendations on how to do it.
This is a fairly extensive build so make sure you are prepared to spend time and money to finish.
Step 1: Buying a Turbocharger and Planing the Build
The project started with me buying a Turbocharger from a local junkyard. I wanted the largest one I could find as that would provide the most Thrust, I was even offered a massive 150 lb turbo that came off an 18 wheel truck, but I settled for a more reasonable Garret turbo taken for a Volkswagen.
The Turbo, specifically the diameter of the air intake which was 1.5 inches, determined the sizing for the rest of the project. The diameter of the flame tube is supposed to be to be 2X this dimension (3 inches) and the length of the tube is 6X this dimension (9 inches).
Step 2: Fabricating the Combustion Chamber
I had difficulty finding thin steel tubing in the correct sizes, so I ended up using schedule 40 steel pipe. I used the dimensions calculated on the previous slide and cut the combustion chamber and flame tube to my desired lengths. I cut the combustion chamber about a half inch short to extend the flame tube and create an easier way to connect it to to the turbo.
The flame tube needs a series of holes drilled into it at specific sizes, so I used a program I found online to calculate how many and what sizes I needed. The first set of holes Take 30% of the Turbos intake Area, the second takes 20% and the third 50%. This was the ratio that all my research showed to be optimal. The 3 different groupings of holes have specific roles, the primary holes supply the air for fuel and air mixing, and this is where the burn process begins. The secondary holes supply the air to complete the combustion process. The tertiary or dilution holes provide the air for cooling of the gasses before they leave the combustor, so as to not overheat the turbine blades in the turbo. The combined area of all these holes must equal the area of the intake. The first set of holes should be smaller in diameter, and have 15-20 holes. the next two series should increase in size and decrease number 8-12 then 4-6.
To seal the whole combustion chamber, I plasma cut two end caps and using a hole saw bit I cut the inside of one to the outer diameter of my flame tube. I also fabricated a cone to reduce the size back to that of the turbo and welded a steel plate to the end of the cone that I can bolt to the turbo.
I used a hole saw bit to drill a hole into the combustion chamber, I put it slightly off-center in an effort to get a sort of swirling motion on the chamber. Then through a combination of pipe bending and angled cuts, I connected the combustion chamber to the intake side of the turbo. I then finalized all the welds and cleaned everything up.
Step 3: Fuel
To provide better mixing of the propane into the flame tube, I made a Fuel Injection tube to mix the propane and also ignite it in a safe and controlled manner. I used a barbecue spark generator as the ignition system. The hoop in the picture was made to ensure the flame tube is centered in the combustion chamber.
I used brass fittings and some tubing to connect the 1lb propane tank to my combustion chamber. Sealing everything with Teflon tape.
Step 4: Oil
To ensure that the turbo runs well I made an oil system. I fabricated a small oil tank that rests below the turbo and used a oil pump I bought online to supply the oil. its important to note that the oil is suposed to drip out by gravity, that is why I placed it below the turbo.
Step 5: Stand
This is important to keep it upright when being used. I basically just welded three legs to it. you can go about this however you want.