Engine Classifications

1. Application. 
• Automobile.
• Truck.
• Locomotive.
• Light aircraft.
• Marine.
• Portable power system.
• Power generation.
2. Basic engine design.
• Reciprocating engine (arrangement of cylinders : eg. in-line, V, radial, opposed)
• Rotary engines (Wankel and other geometries).
3. Working cycle.
• Four stroke cycle (Naturally aspirated, supercharged, turbocharged)
• Two stroke cycle (cranked chaft scavenged, supercharged and turbocharged)
4. Valve or port design and location.
• Overhead
• Underhead
• Rotary
• Cross-scavenged
• Loop-scavenged
• Through or uniflow-scavenged
5. Fuel.
• Gasoline (or petrol)
• Fuel oil (or diesel)
• Natural gas
• Liquid petroleum gas
• Alcohols (methanol, ethanol)
• Hydrogen
• Duel fuel
6. Method of mixture preparation.
• Carburetion
• Fuel injection into intake ports or intake manifold
• Fuel injection into the cylinder
7. Method of ignition.
• Spark Ignition (SI)
• Compression Ignition (CI)
8. Combustion chmaber design.
• Open chmaber (disc, wedge, hemisphere, bowl-in-piston)
• Divided chamber (small and large auxiliary chambers, many design; eg swirl chambers, prechamvers)
9. Method of load control.
• Throttling of fuel and air
• Control of fuel flow alone
• A combination of both
10. Method of cooling.
• Water cooled
• Air cooled
• Uncooled (by natural convection and radiation)

Internel Combustion Engine Fundamentals, John B. Heywood, Page 7.