Jet Engines

Overview and Objectives:

The objective of this project is to build a low cost- high performance jet engine for drone and glider applications. Utilizing advanced manufacturing techniques to achieve these goals. I've based my design to achieve the following performance metrics:

Thrust = 400N
TSFC/SFC= 0.15 kg/Nhr
RPM: 100,000
Size: 150mm outer body diameter
Mass flow rate = 0.67 kg/s

With these performance specs in mind I have designed the jet engine. Which il be later designing the optimal Drone/Cruise missile around. Similar spec engines can be found in Anduril's barracuda cruise missiles. As well as the commercially available JetCatp400 whose performance I am aiming to beat at a fraction of the cost.

Turbomachinery has many intricate and interdependent design elements ranging from thermo-aerodynamic optimization and design of the turbines and heat management, dynamic vibration balancing of the compressor-turbine-shaft, Bearing lubrication, Compressor/Diffuser design and optimization in accordance to compressor maps and material limits. Sealing and prevention of gas leakage, flame stabilization and vaporization, and compressible flow optimization of nozzle as well as minimizing thrust losses due turbulence.

Given the complexity, it is important to not get stuck at the design optimization phase and go from idea to prototype as fast as possible. Therefore I split the project has 4 phases:

Phase 0) Building a pulse jet engine, before taking on the task of building a turbojet I had set out to build a simple jet engine that has no moving parts and working simply on the principle of acoustic resonance. A popular hobbyist jet engine that once terrorized england during WWII.

Phase 1) After gaining experience with welding and sheet metal fabrication I built a crude prototype of the jet engine I am to make, it was an important step as I will detail below. And saw great interest from investors and other hobbyists who were willing to invest and purchase the prototype on the spot.

Phase 2) Learning from my many mistakes and design flaws from the first prototype. I am changing the fuel system from propane gas to a liquid fuel, as well as adding an exhaust cone to prevent turbulence losses, bearing lubrication, optimized geometry angles, Ignition and starter system, Data acquisition elements like thermo-couples, pressure transducers as well as other electronic systems like ECU's and telemetry. As well as a MATLAB or python code to model the entire system and to help me make design changes on the fly.

Phase 3) I aim for this to be the equivalent RAPTOR 3 engine from SpaceX. I want to minimize as much as the complexity and part count as possible utilizing additive or investment casting techniques or forging. While pushing material limits utilizing film cooling channels. And to avoid the need of expensive metals like inconel as much as possible. It will be also possible at this stage to convert the existing model into a turboprop with added complexity of more turbine stages and a gearbox. Which would provide superior thrust and efficiency performances at lower cruising speeds. As proved by the famous MQ-9 reaper drone.

Phase 0: Pulse Jet

Being my first metal working project, I decided to gain expericence by building a pulse jet before jumping into an all out jet engine.

Although I had done acoustic resonance calculations as well as correction factors accounting for heat expansion and the change in the properties of the speed of sound. It apparently is still approximations and might need slight changes in the lengths post fabrication. Therefore it is often recommended to use ratios of dimensions of tried and tested designs. I have went with the "muffler shop special" which is the name given to this type of pulse jet by the community.

This type of pulse jet is often on the easier side to make and is therefore best for entry level hobbyists. As in terms of thrust it does not perform so well as the intake and exhausts are pointed in the opposite dirrections. Which if there were pointed in the same direction as in the lockwood's design (Most popular) the exhaust gas from the expansion cycle from the intake can be added to the outlet instead of being subtracted from it. Essentially adding a couple newtons of thrust.

I also made a second version of the same design but with a flared exhaust oulet, doubling the exhaust diameter, therefore quadrupling the area, therefore mass flow rate quadruples and thrust as well. 25N was expected for the standard design and 100N for the flared varient

Muffler Type Pulse Jet

Flared Exhaust Variant

Post Sheetmetal cutting

Labelled and dimentioned

Post-Rolling

Tacked and needs to be welded

Pre-welding

Arranged to be welded

Post Welding

Zinc-Coating

Turned out to be a mistake as zinc plating is not rated for high termperatures, this was later sanded off and coated with ceramic

Phase 1: Turbojet version 1

Gaining confidence from the pulse jet build, I had moved on to the design of the jet engine. The design was intended to be crude as possible to push prototyping as fast as possible as it is quit easy to get stuck in the optimisation phase for a project as complex as this, 3D printed prototypes altough work just as well for these purposes for checking fits and finding out flaws, I wanted to make a working prototype even if it were to give lower thrust performance.

Design features:

3D printed compressor and diffuser section - Given it was the cold part of the design. with temperatures expected to not go above the melting point of the plastic. Did not expect high RPM's due to material limits. Designed to give only 1/4th of the earlier thrust that was aimed for.
Lathe turned shaft for threads, left hands treads to create locking effect. Major design flaw, axial movement of the shaft-compressor-turbine section was no accounted for can be fixed with a stepped shaft
CNC machined shaft support - First turned by a lathe, then machined with a 3 axis cnc machine with two setups one for each side
Copper piping fuel manifold - Can be improved with liquid fuel to save fuel tank weight
Bellmouth intake shape - The bellmouth intake shape is to create a draft flow into the compressor section to increase mass flow rate. (Same principle used in dyson bladeless fans). The bellmouth is further extended back around to give the jet engine a streamlined aerodynamic shape.
Nozzle/combustion-chamber/Body/Turbine/Stator- Were all made out of laser cut mild steel. And then later rolled, welded, sanded and coated with ceramic coating.

3D Printed Impeller, Diffuser and shaft assembly

Rotor shaft

Turbine

Post Rolling and Tacking

Pre-Assembly

Ceramic Coating Applied

Post sanding of welds and body

Assembled Jet Engine

Phase 2: Turbojet version 2

I have made many many mistakes and learnings from phase 1 of the project. I am currently implementing those changes here

Meanline analyis code developed to quickly view velocity triangles, change blade angles, RPM. Without performing tedious hand calculations and simulations. This allows for quick resizing and tweaking of the design parameters which can be later validated with the aforementioned simulations
Optimizing fuel flow paths to perform lubrication of the bearings as well as utilize the combustion chamber's heat to vaporize the fuel before entering the combustion chamber.
Integrating electronics such as, ECU, Starter motor, Glow plugs, as well as data acquisition elements like pressure transducers and thermocouples.
Minor design flaw changes and other optimizations are being done

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