What is a single-cylinder engine and a two-cylinder engine? What's the difference?

Single cylinder and double cylinder refer to single cylinder and double cylinder engines. Generally speaking, low power, light weight requires one cylinder, and high power requires multiple cylinders. The number of cylinders is small and simple, and the cost is low. Motorcycles generally have one cylinder, medium-pole cars have four cylinders, advanced cars have six cylinders, and marine engines have more than 24 cylinders. In the1938+0940s, the aero-engine had 39 cylinders.