The Yengine

1. Simple is often best: although our system functioned as designed, there were many opportunities for improvement across all the subteams (propulsion, fluids supply, avionics, and structures).

2. We used the difficulties we encountered during the water flow test as a valuable learning opportunity; we took everything we learned across the entire system and applied the knowledge to the design of our new engine (see here) with the goal of static firing this engine and attaching it to a full-fledge rocket. 

Side view of a single injector element

Yale Project Liquid is a student organization under the Yale Undergraduate Aerospace Association, and we are working towards building and testing Yale's first liquid-fueled rocket engine. I joined Project Liquid's Propulsion team in Fall 2022, and since the design work for the engine had been completed, I had a chance to work on the manufacture and assembly of the engine (nicknamed the Yengine).

Design: We used a coaxial shear injector: a system that injected oxidizer (nitrous oxide) and fuel (isopropyl alcohol) through concentric cylinders into the combustion chamber. This design was chosen because it was relatively easy to manufacture and it was easy to manifold the propellant inlet lines. The chamber itself and the nozzle were commercial-off-the-shelf (COTS) parts. The chamber used an ablative cooling system; the inner walls were lined with a phenolic ablative liner that would burn away and take most of the combustion heat with it. The soot and char left behind would further insulate the chamber wall. The nozzle was made of the same phenolic material to ensure ablation and cooling. The injector and chamber designs were completed before I joined Project Liquid, so I did not contribute to these developments. Instead, I led the manufacture and assembly of the injector plate and thrust chamber (see below).

Manufacture: The stacked plates were machined out of stock aluminum rods using a bandsaw and a mill. The propellant orifices were drilled out using a CNC mill. The hypodermic needles were cut into one-inch pieces from a single, long stock needle.

Assembly: The hypodermic needles were connected to the mid-plate using epoxy, and the entire stacked plate design was brought together with four corner screws. Rubber o-rings were placed on the outside of the assembly to provide a pressure-tight seal and to secure the plates to the screw-on mount. Finally, the plates were screwed into the mount and the mount was screwed onto the thrust chamber.

Testing: The injector assembly underwent a water flow test in April of 2023. The tanks were filled with water and pressurized with nitrogen gas before the valves were opened to allow water to flow through the system. The assembly initially experienced some leaks, but upon tightening the screws on the injector face, the assembly performed perfectly. Below is a video of the water flow test, produced and edited by a member of the team (skip to 2:46 to watch the actual test).

Fully assembled coaxial shear injector