The document classifies internal combustion engines based on their method of ignition, type of fuel used, working cycle, thermodynamic cycle, cooling system, fuel supply system, cylinder arrangement, intended use, valve location, speed, governing method, cylinder action, lubrication, and starting method. Some of the main categories include spark ignition vs compression ignition engines, four stroke vs two stroke cycles, air cooled vs water cooled systems, carbureted vs injection fuel systems, and single cylinder vs multi-cylinder configurations.