Liquid rocket engine injectors can be extremely expensive to manufacture and hard to iterate to achieve high performance. Internal sealing points can also be the source of reliability issues. The technology disclosed here covers the application of a 3D additive manufacturing (AM) process to produce a functional aluminum injector for liquid propellant rocket engines, along with injector and overall engine design features that optimize the application of such processes to improve performance, reliability, and affordability relative to components produced using standard machining processes and designs. Aluminum was used for the injector instead of higher- temperature metals like stainless steel because its thermal conductance properties provide more opportunity to leverage the cooling potential of liquid oxygen and other cryogenic propellants.
The function of a liquid rocket engine injector is to condition the two propellant flows to achieve the full combustion of the liquid propellants. To do this, injectors form a multitude of fluid streams/jets to mix and atomize the liquid flows. Due to the high pressure and high heat within the injector, this needs to be done uniformly and while avoiding excessive heat flows into the injector or the chamber walls. An ideal flow solution is often severely restrained by the fluid routing of the propellants to the individual jets (cost and physical manufacturing constraints).
The application of additive manufacturing to produce a liquid rocket injector allows for intricate and formerly impossible internal flow paths whose geometry cannot easily be replicated with traditional manufacturing techniques. AM with aluminum allows for the creation of one intricate part for which the as-printed material properties are on the level of a T6 tempered alloy, and consequently do not require any additional tempering that can often cause thermal warp. AM also enables integration of previously separate components, thereby eliminating potential failure modes associated with sealing devices and improving reliability. To fully exploit the benefits of AM, the injector design is tailored with respect to internal passages, channels, manifolds, and orifices, as well as external interfaces.
This application of AM technology has the potential to improve the performance, reliability, and affordability of liquid propellant rocket engines for small launcher vehicles and spacecraft. Current AM print size is more suited to smaller engines such as those for nanosatellite launch vehicles (NLVs) and in-orbit propulsion.