Electric Jet engine Compressor Mk4

This is the most thrust-optimized electric compressor to date, being a compromise between boost pressure and flow rate. Designed to push the limits of printed plastic, this compressor is optimized to use an extremely powerful motor that can draw up to 4.2kW of power. The second significant achievement of this design is its ability to run continuously without catastrophic heat buildup. The oversized motor and high surface area compressor shroud make this design outperform even the best of the old designs in terms of reliability. This being said, even optimized hybrid jet engines are not entirely practical because the thrust to weight ratio of the power system rarely exceeds one.

THIS IS A DANGEROUS PROJECT THAT SHOOTS FIRE WHEN IT WORKS - AND EVEN MORE FIRE WHEN IT DOESN'T

Thrust/Power performance:

• 69.5A at 42.4V for full power - 2932W Continuous
• ≈2.5 CFM of propane gas with full afterburner, only 0.5 CFM to sustain combustion
• 20.3N observed at full power with combustion, 8.1N observed running with compressor alone.

Power system:
I used a Surpass Hobby Rocket RC 4092 brushless motor with a speed of 920kv (rpm/volt) and a peak power rating of 4200 watts.
for cooling, I ran cold propane gas through the water cooling jacket to keep the motor cold before piping it into the combustion chamber.
To control the motor, A 150A HV ESC was used with an Arduino-based controller to regulate motor speed and fuel flow by using a servo valve in the fuel line.
The entire system was powered by a 12s 5200mAh lipo pack and would run at full throttle for about 4 minutes or so before a battery swap.

Printing:
Make sure to print all parts in a high-strength and temperature resistant filament such as PETG, CF Nylon, or PC
For spinning parts such as the impeller, print at high infill and slow speed to maximize your x/y tensile strength. This is important in preventing your impeller from exploding when it spins at over 40k rpm. Good print quality and a radially symmetric part is important for avoiding vibration, and post balancing is still recommended.
For pressurized parts such as the housing, shroud, and adapters, Prioritize Z-layer adhesion and use solid infill whenever possible. From the 4 PSI boost this compressor makes at full power, that means over 50lbs of force are trying to pull the layers apart along the walls of the compressor housing. Use higher nozzle temps, reduce cooling, and use plenty of support for external geometries.
print the motor plate at low infill for reference only to be used as a drilling guide for aluminum plate (DXF is included for laser cutting).
carefully post-process all printed parts prior to assembly.

Assembly:
To assemble this engine, Print all parts as described and purchase the parts listed:
15x #8 x 1in thread forming screws
4x M3 x 10mm machine screws (or whatever fits your motor)
20x #8 x 1/2 in thread forming screws
6x #8 x3/4 in sheet metal screws
1x 3-5mm aluminum plate (at least 150mm x 150mm)
1x 5mm shaft collet prop adapter
1x 4092 - 920kv motor with cooling jacket
1x 100A+ HV ESC
2x 5200mAh 6s lipo batteries
1x conical double walled stainless water bottle (varies greatly)
other power system wiring equipment (varies greatly)
200mm+ length of 5mm copper tube (fuel line)
other fuel system components (varies greatly)
Use the printed motor plate guide to cut out and drill a motor plate in the 3-5mm aluminum or get it laser cut. Attach the motor to the aluminum plate with the 4x M3 machine screws. Then use the collet prop adapter to attach the impeller to the motor so the bottom of the impeller sits 5-6mm above the motor plate. Insert the impeller shroud and attach the motor assembly to the housing with the 15x #8 x 1 in thread forming screws, making sure to screw all the way into the shroud at the front. Make sure the impeller spins freely in the housing - if scraping occurs, use sandpaper and/or adjust collet positioning until it rotates smoothly. Then, use 8 of the 20x #8 x 1/2 in thread forming screws to attach the intermediate adapter to the compressor housing, and the remaining 12 screws to attach the bottle adapter to the opposite side. Select a bottle for your chamber that fits into the bottle adapter, ideally without any paint or coating. Remove the bottom cap on the bottle and use a grinder in a well ventilated area to grind the top and bottom surfaces until the layers separate. Remove the inner layer and drill a uniform hole pattern starting with small holes at the original "bottom" end and large holes at the nozzle end. Put an extra ring of small holes just before the nozzle for film cooling. Bend your fuel hose into a circle with the same diameter as the inner bottle and put several small holes in the tube to distribute the gas. Insert the tube into the inner chamber and slide the whole assembly into the outer chamber to be fixed in place by 3x sheet metal screws. Run the spark wire through a small hole in the front end of the inner chamber before using the last 3 sheet metal screws to fasten the chamber onto the compressor. Now your engine should be ready for testing!

Final notes:
This is an extremely dangerous propulsive device that is essentially a mini flamethrower. DO NOT stand too close to the "flamey end" and make sure you have a clear test area with fire suppression on hand. DO NOT Build if you have no idea what you are doing because a mechanical, electrical or fuel failure could have LETHAL results.
Test at your own risk and make sure to approach the building process of this engine with the caution it deserves.