I don’t want to make a spam post because I have no affiliation with this book other than I’m reading it. I found it at a used book store. It’s called the Aicraft Engine Operating Guide" by Kas Thomas It was written in 81 so for those flying the newer stuff some info might or might not apply.
It discusses the engine itself, but also how the engine instruments work. It also goes into detail about each phase of flight.
It’s a good read for those who fly light airplanes and have not gone into more advanced flying, or have a background in aviation mechanics.
It looks like it is a book that a few libraries carry. The price on a used copy is pretty steep like 50$ at Amazon. I found mine by chance in MN for 2$.