Looking back on the history of the generation and development of the engine, it has gone through two development stages of the external combustion engine and the internal combustion engine.
The so-called external combustion engine means that its fuel is burned outside the engine, and the engine converts the thermal energy generated by this combustion into kinetic energy. The steam engine invented by Watt is a typical external combustion engine. When it is heated into a large amount of water vapor, high pressure is generated, and then this high pressure pushes the mechanical work to complete the conversion of thermal energy to kinetic energy.
If you understand what an external combustion engine is, you also know what an internal combustion engine is. The biggest difference between this type of engine and an external combustion engine is that its fuel is burned inside it. There are many types of internal combustion engines. Our common gasoline engines and diesel engines are typical internal combustion engines. Our uncommon rocket engines and jet engines installed on airplanes also belong to internal combustion engines. However, due to the different ways of power output, there is a huge difference between the former two and the latter two. Generally, the former is mostly used on the ground, and the latter is mostly used in the air. Of course, some car manufacturers have used jet engines in their cars for the purpose of setting new world car speed records, but this is always a very special case and does not have the applicability of mass production.