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This document outlines our research on injector design during the Fall 2020 semester.
Our main topic is Unlike Doublet Impinging Injector Design.
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Injector Basics
What is an injector?
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The injector serves many purposes, and a few very important ones are outlined below.
To optimize the flow of the propellants into the combustion chamber
The geometry of the injector is designed to optimize the flow of the fuel and oxidizer into the combustion chamber, where they will collide, mix, and combust. In this document, we look at one specific injector design: the Unlike Doublet Impinging, where there are pairs of fuel and oxidizer orifices which are angled to collide with each other. The Helios injector is also of this design. There are several other designs that may be considered depending on the needs of the mission, but we will not discuss them in this document. We will also look at other stream parameters which are dependent on the injector, like droplet size and mixture ratio.
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Fig. 2: Unlike doublet impinging injector design.
To ensure the sustainability of the combustion chamber
The positioning and orientation of the injector orifices is important to ensure that the resulting combustion flames and exhaust do not melt or deteriorate the chamber walls. This also has to do with other parameters of the engine design, like the mixture ratio of the propellants, the mass flow rates, etc. Without the injector, or with a poorly designed injector, we risk destroying the combustion chamber. Here, it is vital that our resultant stream is angled either parallel to the chamber wall, or slightly towards the central axis.
Another consideration is that cryogenic propellants (like the very common LOX) may provide minor film cooling for the chamber walls. This can be done by positioning the oxidizer orifices on the inner manifold angled towards the chamber walls.
To ensure combustion stability
This ties into the second point 2, but is different. The injector is designed so that the flow of the propellant streams is manageable and combusts in a way we are prepared for (with the design of the rest of the rocket). An unstable combustion would result in an unstable rocket which is typically not something you want.
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