For Earendel, we are using liquid oxygen and isopropyl alcohol in a pressure fed engine at a relatively low pressure of 180 psi. These conditions make using impinging jet injectors a good first place to start. Since the flow rate is relatively small and our orifice size is relatively large due to fabrication constraints, this means we will have a small number of elements and they should be unlike jets to promote mixing with the large orifice sizes. In addition, we will have film cooling protecting the chamber wall so using unlike jets as the main element is fine. After running through some sizing, we end up with unlike impinging doublets as a functional design and the simplest of the impinging jet designs. You can see the injector manifold design below.
In addition to a unlike impinging jet, we are also going to experiment with a pintle design. This design will be simpler to manifold and potentially lighter and, thus, cheaper to 3D print. Given the relatively large unknowns in specifically sizing the pintle injector, we expect a few bad performers, either low performance or burning up walls, before we can get something to work.