Propulsion Cold Flow Update - Injector/Engine

Written on11/7/2020

Propulsion Cold Flow Update - Injector and Engine

Hey readers!

Last post we discussed the plumbing system for our ethanol cold flow test. For this week, we’ll go over the injector and engine design. 

Following the plumbing, the next major piece of cold flow tests (although not included in our ethanol cold flow test) is the engine. The engine consists of the injector, the chamber, and the nozzle. The fuel and oxidizer coming out of both towers are fed into the injector, which sprays them together in the combustion chamber, where they combust. This high pressure and fiery gas is then forced out of the engine through the nozzle, which compresses and accelerates the gas.

The injector is one of the more difficult pieces of the engine to design due to its relative complexity and higher risk if it fails. Because of this, the propulsion team has been working on the injector design for the past 5-6 months. The injector we are using resembles a showerhead, but with the orifices (holes) pointed towards each other. This way, the propellants spraying out of these holes will hit each other and create a bunch of tiny droplets in a process called atomization. In our injector design, we are doing a like-on-like doublet design, which basically means that fuel orifices are pointed towards each other and oxidizer orifices are pointed towards each other in groups of two. Since our Aphlex 1b rocket will be relatively small, we don’t have too many pairings (8 oxidizer pairs and 4 fuel pairs) and designed a simple orifice pattern.

One of the main constraints on design of the engine is manufacturing, which heavily dictated our nozzle design process. The problem is that a while ago, we thought the only way we’d be able to machine our engine was with a manual lathe, which makes cutting a curved nozzle shape out of an aluminum rod extremely difficult. However, we eventually found a way to access a CNC machine, which will cut out our engine non-manually through machine operation. Because of this, we decided on doing a de Laval (parabolic) nozzle shape since we now have the resources to cut it accurately and precisely. We now have a full engine design including o-ring selection, so all we need to do now is buy a thick aluminum rod and cut it into the injector, combustion chamber, and nozzle. Below is an image of our fully cadded, assembled engine cross section.

Next post we’ll go over how these parts fit together on the test stand. See you then!

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