I'm trying to do some research on this but very much struggling to work it all out. I'm looking for a cutaway diagram of said rocket engine (ideally one used on a first-stage), but I can't for the life of me work out what rocket uses what engine. Can anyone help?
In terms of "widely used", I'm looking for either (or perhaps both) the engine used on the most number of launches per year, or the engine used on the most varied number of rockets (e.g. is there an engine used on many different rockets?).