A relatively short but complete book I'd recommend would be Ferguson & Kirkpatrick's "Internal Combustion Engine". It was used in an undergrad engines course I

A relatively short but complete book I'd recommend would be Ferguson & Kirkpatrick's "Internal Combustion Engine". It was used in an undergrad engines course I did. The classic, big textbook, AFAIK, is John Heywood's (MIT Prof) Internal Combustion Engine Fundamentals. These books give you a general understanding of the functioning of ICEs. For practical design considerations, I've found "Internal Combustion Engine in Theory and Practice" by Charles F. Taylor interesting. There's a lot of other books on specific aspects of design, look for example at books published by the SAE. I'm not sure exactly how much one would get from going through a book like Ferguson without basic notions in physics (basic thermodynamics, dynamics, fluid mechanics, materials). I think a motivated individual could certainly supplement as he goes using wikipedia as a starter for things he does not understand. No advanced knowledge of these topics is needed, as I said, just the basics.