A combustion engine, often referred to as an internal combustion engine (ICE), is a type of heat engine where the combustion of fuel occurs within a confined space called a combustion chamber. This process converts chemical energy from the fuel into mechanical energy, propelling vehicles and powering various machinery. The most common fuels used are gasoline, diesel, and natural gas. In an internal combustion engine, fuel mixes with air, and a spark or compression ignites this mixture, causing an explosion. This explosion generates high-pressure gases that move pistons within cylinders, creating a rotational force on the crankshaft. This rotational motion is then used to drive the wheels of a vehicle or operate other machinery. Combustion engines are classified mainly into two types: spark-ignition engines, which use a spark plug to ignite the fuel-air mixture (common in gasoline engines), and compression-ignition engines, where air is compressed to a high temperature before fuel is injected (common in diesel engines). This book unfolds the innovative aspects of an internal combustion engine which will be crucial for the holistic understanding of the subject matter. The topics included in this book on combustion engines are of utmost significance and bound to provide incredible insights to readers. This book is a complete source of knowledge of this important field.