PrintJet - the 3D printable pulsejet engine

thingiverse

Scaled down to the size for 5 lbs of thrust, these pieces would be printed and glued / bolted together. Parts would be printed in the orientation shown in the disassembled snapshot, with no supports. Two tailpipe pieces would glue onto the combustion chamber. The petal valves would bolt through the valve plate into the intake cone by self-tapping an M3 screw into the hole. These parts would then bolt onto the combustion chamber using M3 screws, and a short piece of rubber hose would be used for clamping a small carburetor to the intake, such as from a moped or other small engine. It is suggested to print the petal valves from a semi-flexible material such as TPU or Ninjatek Cheetah or Armadillo filament. For starting the engine, with the carburetor ready to flow fuel you would apply a vacuum cleaner to the tailpipe of the engine to draw the air/fuel mix through. For ignition, it might need to be something like a pair of sewing pins heated and pushed through into the combustion chamber until they nearly touch, and then on the outside hook wires from those to an electric grill ignition button. Note that there is a non-zero chance that your vacuum cleaner may explode if it draws too much air/fuel mix in and any of that sees a spark from the vacuum's motor. Always make sure to follow safety rules regarding playing with fire, have an extinguisher ready, and most important of all whatever you do, make sure to film it! It is only expected that this engine would run for a few seconds before melting apart at the tailpipe, but if it can run self-sustaining for even a moment that would be a success. If a person were to print this with sparse fill from a water-tight filament, it might be possible to increase engine life by pouring water in and letting it freeze so that it has an ice jacket inside of the printed engine parts. But again, the point is just to see if the dimensions are correct to make it possible to get the sustained pulse jet combustion cycle to occur. I will try to get one printed and tested soon, and will update with results. Update 30DEC2017: Uploaded new .stl files in mm to avoid loss of quality in model when having to scale in slicer program from English to Metric. ChamberXL added which will only need a single tailpipe extension as it is taller, since my Rostock Max V3 can handle it. Attempting to print from PETG tonight. Update 02JAN2018: After wiring up an ignition system and adding a carburetor and fuel system, we performed a few tests trying to start the engine. We used a vacuum on the tailpipe to prime the motor, drawing air/fuel through the carburetor to then be ignited electrically inside the engine. We did get one double-bang which I believe was the engine just barely trying to run, otherwise most were single bang's or a sustained flame only while the vacuum was on the tailpipe. Eventually everything melted apart before I could get the carburetor tuned and/or the vacuum method applied correct to get it to actually start running. But it definitely motivates us to move forward with the bigger project (see my other design for a 50lb thrust version made from welded sheet metal).