Intro: Homemade Turbojet Engine
Attached is a documented process with instructions allowing reproduction of a turbo jet engine; primary construction materials include junkyard parts and scrap steel. From beginning to end this includes all of our steps and processes, with as much critical information as we can provide, so that you might be able to design and construct your own turbo jet engine.
Step 1: Acquiring the Turbocharger.
The first and most important piece of the homemade jet engine is the turbocharger. This is an automobile part, normally attached to an exhaust manifold to reclaim power for the engine. This is not entirely important for our purposes, what is important, however, is that it has a fan and a compressor, which make up the heart of a jet engine. The turbo needs to be obtained first, as its dimensions serve as the basis for the other parts of the system, such as the combustion chamber, and the flame tube. This is the part that the system is made around as it has a turbine in the back end, which the heat from the flame tube feeds directly into and a compressor which keeps air flowing into the chamber, and going through the holes of the flame tube, so as to keep the ratio of air to fuel proper for combustion. Above is a diagram of the airflow through the jet engine.
Step 2: Combustion Chamber, Flame Tube and Math
The step that follows acquiring a turbo is to determine how the combustion chamber will be built. The combustion chamber consists, in essence, of three parts: the outer housing, the flame tube, and the end piece that allows the part to be bolted to the turbo. The flame tube needs to have a diameter of twice the turbo intake. This can be found by measuring across the turbine on the intake side of the turbo. In general the intake side is the half of the turbo with a more metallic shine and is less corroded. The flame tube needs sets of holes to distribute the fuel into the combustion chamber.
The overall area of these holes must add up to percentages of the area of the turbo intake. These percentages, for three sets of holes, are 30% for the first set, 20% for the second set and 50% for the third set. For our turbo the diameter of the intake is 1.5 in. and therefore the area is 1.76 in^2. 30% of that is 0.53 in^2. This first set of holes should have the most holes, for even fuel distribution, so somewhere between 10-30 depending on the size of the turbo. A larger turbo intake would allow for more holes, as the area that is used to determine the size would be larger. For ours we are using 10 holes, at 1/8 in each. This was found with 0.53 / 10 = 0.053. 0.053 = pi R^2 = 0.129 in = R. This number is not exactly practical to use so we are going to go with a close approximation of 1/8 in, as that is .125 only 4 thousandths difference. For the second set of flame tube holes 20% of the area of the intake is 1.76 /100 X 20 which is .35. We are using 4 holes at 11/64 each. This is done with the same math as before, .35 / 5 =0.0875 0.0875 = pi R^2 = 0.166 which would be about 4/25th. This is again not a standard drill bit size, so instead we would be using an 11/64th which is about 0.17. The last set of holes is at 50% of the turbo intake area, and these are drilled out to fewer and larger holes, so as to allow a large flow of fuel into the chamber. Same math as the previous two sets 50% of 1.76 which is 0.88. for the last section we are using 5 holes at 1/4. 0.88 / 5 = 0.176. 0.176 = pi R^2 = 0.246 rounded up to .25 which is 1/4.
Step 3: Building the Combustion Chamber
With the flame tube completed, the next step is to attach the flame tube inside the housing. The house is just a steel tube 1 or 2 inches larger in diameter than the flame tube. The two tubes are connected by a flat steel ring on the side that goes into the turbo. The other side of the combustion chamber is closed off with an end cap, a flat steel circle, that closes off both the flame tube and outer cylinder. To connect the combustion chamber to the turbo a steel reducer needs to be fabricated. This goes on the part that would normally be attached to the manifold of the car. The way we did this was by first cutting the piece that attaches to the turbo out of 1/8 inch steel, and drilling holes for the the threaded bolts coming out of the turbo to go through. we also cut a hole in the center that lines up with the hole in the turbo, naturally, as it allows necessary air flow. With this piece completed. The reduction part can be added, we made this by cutting four equal pieces of 1/8 inch steel with a 3.5 inch bottom length and a 1.5 inch top length. By welding these pieces into a pyramid, and attaching the recently created flat mounting piece, a reducer that is made to attach to the turbo can be created. This reducer can now be welded to the opening of the combustion chamber, and the project is ready to move into the final assembly step.
Step 4: Assembly of Parts
The fully completed combustion chamber can now be attached to the turbo, via the reducer that was previously fabricated. The plate on the reducer should fit over the threaded rods coming from the turbo, and nuts can be threaded on over them to tighten it in place.
The last part of the assembly is to connect the outlet of the compressor end of the turbo to outer casing of the combustion chamber. This functions to force air into the flame tube holes, and enables combustion in the flame tube, which is forced into the turbine of the turbo. The spinning of the turbine also spins the intake fan, and allows the system to continue running. We used plumbing black pipe for this, as it was readily available at home improvement stores, and can be purchased in threaded sections. The parts that connected to the outlet of the turbo, and the inlet of the chamber were welded on. The pipe piece that connected into the chamber needed to be ground into a shape that would fit flush against the side of the combustion chamber outer tube.
Step 5: Fuel System
With the combustion chamber completed, the fuel and ignition system can be added to back end, in the center into the flame tube. The fuel for our engine is propane as it is a gas and under pressure, therefore it does not require a fuel pump. Liquid fuel can be used, but it needs to be pumped, and vaporized into the flame tube. The fuel will go into the back end of the combustion chamber, via a valve located in the center, inline with the flame tube. The Ignition system is a small spark plug, from either from a small gas engine, or automobile.
A battery to power the spark plug is needed, and if a liquid fuel with a pump is used, then a power supply for the fuel pump is also necessary. For our system we used a 12 volt battery, and a simple push button to spark the system into combustion.
A ball valve with a level allows easy control of fuel flow, and this is what controls the rate at which the propane goes into the combustion chamber.