http://www.amazon.co.uk/Its-ONLY-Rocket-Science-Introduction/dp/product-description/038775377XA good introduction to the field.
Not exactly engine design, but here's my suggestion:"Fundamentals of Astrodynamics," by Bate, Mueller, and White. It's about orbital mechanics and planning spacecraft orbits. It's informative and structured as a textbook--lots of practice problems. Its use of imperial units is annoying in this day and age, but that's a surmountable issue.
Rocket Propulsion Elements - An Introduction To The Engineering of Rocketsby George P SuttonIt is *the* Bible of "rocket science" and is commonly referred to simply as "Sutton's".
"How to build your own spaceship" - the science of personal space travel by Piers Bizony. Published in 2009 by the Penguin Book group.Has a very good overview in about 200 pages, does not talk down to anyone - rather encourages you to look up.
I plan on taking courses in physics eventually, but it's not currently my highest priority. Any book recommendations?
Does any of these books have any engineering data about rocket engines or they are about just theory and physics?I'd love to look at P&ID diagramm of any real liquid rocket engine, but haven't found any. Is it classified/commercial secret?If not, maybe somebody knows where to find such information? I'ts just so interesting
If you want to to learn something about rocketry build your own model rockets up to the very large L1, L2,L3 class this will teach you the basics of rockets (solid Propulsion) and Fundamentals of Astrodynamics.