What I do
As RED and Saguaro have a shared injector, there are a lot of similar properties between both. I typically work on seeing how the injector system will be integrated with Red, the idea is to have a slip on slip off system so it will be pretty modular to assemble. I also do some analysis on the expected heat transfer rates through the injector This is done through making semi-infinite body calculations for the injector and breaking that into smaller bits as areas such as LOX and fuel cooling can be considered, eventually a full model will be developed to simulate all forces on the injector.
A big concern here is making sure that the injector face plate stays cool enough during combustion, especially for RED as the JetA fuel would already be in the 550-700 k range while the combustion chamber has temperatures of 2490 k.