Mortise - Rocket Engine
I am the lead designer of Mortise, a 453 LBF gaseous methane-gaseous oxygen heat sink rocket engine, which will be used as a test bed for a DMLS, 3D-printed engine that I am also developing. I am personally responsible for the injector design, thermal analysis, propellant feed system, structural design, test campaign, and share responsibility for the chamber geometry.
Quick Specs
Testbed for 3D printed flight version of Dovetail
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Injector
For the injector, I decided to go with 6 coaxial injector elements. Since the combustion of gaseous propellants happens on the contact plane between the two props, having 6 injector elements doubles the surface area of combustion, leading to higher efficiency. The injectors follow the curvature of the spherical chamber. This causes them to be scarfed in towards the center axis directing propellants to the center of the chamber. This reduces wall temperature and allows for mixing between injector elements, increasing efficiency and allowing for higher chamber pressures.
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Chamber
A spherical chamber was decided for a couple of reasons. First it reduces wall surface area needed to be cooled. It also decreases the length of the engine while keeping the same chamber volume which is important for the next iteration that will be 3D printed. I wrote MATLAB code for thermal analysis, incorporating elements of legacy code, to calculate the temperature at any point in the thickness of the wall, at any axial point in the engine, and at any point in time during a hot fire. The code calculates one-dimensional slab series solution for the heat transfer, and I rewrote it to optimize the wall thickness of the engine such that the internal wall would never hit a temperature where the tensile strength was below 50% nominal and the outside wall only hit 400 K for a 5 second burn at a chamber pressure of 400 psi and an OF of 2. I designed the test campaign and the fluids system for this engine (I go into the fluids system more in Citadel). This engine is made up of 4 parts. I designed the seals between the parts. They are a combination of standard polymer o-rings, and also metal U-rings for connecting the two chamber pieces as they will see elevated temperatures.
Manufacturing
I am currently manufacturing the 3 piece injector in Boston Universities Machine shop. I am using CNC machines for the complex geometry and mixing in hand tools where necessary for efficiency. I did the engineering drawings for these three pieces using GD&T in order to better control the final product to the specs needed for functionality. I am using GibbsCam for the CNC tool paths.
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