Internal combustion engines are classified according to a variety of criteria, including:
* Fuel type: Gasoline, diesel, natural gas, propane, etc.
* Engine type: Reciprocating (piston), rotary (Wankel), or jet (gas turbine).
* Number of strokes: Two-stroke or four-stroke.
* Number of cylinders: Single-cylinder, two-cylinder, four-cylinder, six-cylinder, eight-cylinder, etc.
* Arrangement of cylinders: Inline, V-type, or radial.
* Cooling system: Air-cooled or liquid-cooled.
IC engines are widely used in a variety of applications, including:
* Automotive: Cars, trucks, buses, motorcycles, etc.
* Industrial: Generators, pumps, compressors, etc.
* Marine: Ships, boats, etc.
* Aerospace: Aircraft, rockets, etc.
IC engines are a major source of pollution, including greenhouse gases, nitrogen oxides, and particulate matter. However, significant progress has been made in reducing emissions from IC engines in recent years, and further improvements are expected in the future.