This document discusses different types of vehicle engines, including internal combustion engines, jet engines, and rocket engines. It provides details on how internal combustion engines, jet engines, and solid rocket motors work using a four-stroke cycle of induction, compression, ignition, and exhaust. The key difference between jet engines and rocket engines is that rocket engines carry their own oxygen, which is important for space travel where oxygen is not readily available. The document also briefly mentions future ion thrusters and external combustion engines.