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One of the projects that I am currently working on with other mechanical engineering students in YUAA is Project Liquid. We are designing and building a liquid engine that will use IPA (isopropyl alcohol) and nitrous oxide (N₂O) as propellants and will eventually be put on one of the rockets that our Yale rocketry team will send to IREC. I worked on designing and CAD modeling the thrust chamber assembly including the injector, which has 29 individual coaxial-shear elements to direct the propellants for ignition.
Thrust Chamber assembly
Thrust Chamber assembly
The outer shell of the thrust chamber consists of the Aerotech casing as well as the forward and aft closures. The nozzle at the bottom is a converging/diverging nozzle for optimized performance. Both the nozzle and the liner (shown in brown) are made of ablative material that absorbs heat and disintegrates to cool the engine during firing.
Coaxial-shear injector
Coaxial-shear injector
Our injector design is based off the concept of a coaxial-shear injector, which uses a thin needle to separately deliver the 2 propellants to the exit orifice, where they expand and combine. There are 29 of these coaxial-shear elements in the injector arranged in two concentric rings in order to uniformly "spray" the propellants in the thrust chamber before ignition.
Propellant flow
Propellant flow
The main 1/4" pipe in the injector directs the IPA propellant down to the lower chamber where it then flows around the walls of the hypodermic needles and combines with the N₂O propellant at exit orifice. The N₂O is fed through space around the 1/4" pipe, entering the hypodermic needles through the upper chamber. The pressure transducer is connected to the pipe that leads to a port machined in the injector, exposing it to the pressure in the chamber while protecting the sensor from the extreme temperatures.
The forward closure from Aerotech will be modified with some additional machining in order to accommodate our feed system design.
Stacked plates design
Stacked plates design
In order to machine the cavities necessary for the injector's function, a stacked-plate design was adopted, where each plate is machined separately and fastened together to form a cohesive manifold. The injector stack is then inserted into the cavity in the forward closure, with high-pressure O-rings being used to seal the injector and isolate the chambers from each other.
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