What is the principle of the engine?

Let's briefly talk about the principle of engine power: 1. Engine is an energy conversion mechanism, which converts heat energy generated by fuel combustion into mechanical energy. So, how does it complete this energy conversion process? That is to say, how does it convert thermal energy into mechanical energy? 2. To complete this energy conversion, the combustible mixture (or fresh air) must be introduced into the cylinder through the air inlet; Then the combustible mixture (or fresh air) entering the cylinder is compressed, and the combustible mixture is ignited when the compression is near the end point (or diesel oil is injected into the cylinder under high pressure to form combustible mixture and ignite); The combustible mixture is ignited and burned, and the expansion pushes the piston to do work downward; Finally, the burnt waste gas is discharged. That is, intake, compression, work and exhaust; 3. These four processes are called a working cycle of the engine. When the working cycle is repeated, the energy conversion is realized and the engine can run continuously. 4. After completing a working cycle, the crankshaft rotates twice (720) and the piston reciprocates up and down four times, which is called a four-stroke engine; 5. To complete a working cycle, the crankshaft rotates once (360) and the piston reciprocates up and down twice, which is called a two-stroke engine.