1. The working principle of the engine is to convert internal energy into mechanical energy.

2. Engine is a machine that can convert other forms of energy into mechanical energy, including internal combustion engine (reciprocating piston engine), external combustion engine (Stirling engine, steam engine, etc.), jet engine, motor, etc. For example, internal combustion engines usually convert chemical energy into mechanical energy. The engine is applicable to the power generation device or the whole machine including the power device (such as gasoline engine and aeroengine). Engine * was born in Britain as early as, so the concept of engine also comes from English. Its original meaning refers to the kind of "mechanical device generating power".

3. The external combustion engine, that is, its fuel burns outside the engine. It was invented by R Stirling of Scotland in 1816, so it is also called Stirling engine. The engine converts the heat energy generated by this combustion into kinetic energy. Watt's improved steam engine is a typical external combustion engine. When a large amount of coal combustion generates heat energy to heat water into a large amount of steam, high pressure is generated, and then this high pressure drives the machinery to do work, thus completing the transformation from heat energy to kinetic energy.

4. If you understand what an external combustion engine is, you will know what an internal combustion engine is. The internal combustion engine is a reciprocating piston engine. This type of engine is very different from the external combustion engine in that its fuel is burned inside. There are many kinds of internal combustion engines. The common gasoline engine and diesel engine are typical internal combustion engines.