What are the two major categories of internal combustion engines?

[DiCamila]

Internal combustion engines can be classified by cooling method into air-cooled and water-cooled types; by the number of cylinders, they can be divided into single-cylinder and multi-cylinder engines, among others. Broadly speaking, they are categorized into free-piston internal combustion engines, reciprocating piston internal combustion engines, and rotary piston internal combustion engines, which also include jet engines and rotary turbine gas engines. Based on the type of fuel used, internal combustion engines can be classified into gasoline engines, diesel engines, and gas-fueled engines. Engines that use gasoline as fuel are called gasoline engines; those that use diesel are called diesel engines, while gas fuels mainly include natural gas, liquefied petroleum gas, and others.