Many innovations of the 20th century owe their success to the internal combustion engine, such as the automobile, aircraft, and small engine products such as lawnmowers.
The basic principle of the internal combustion engine is using the rapidly expanding gas from combusted fuel to drive a piston. The piston then turns a crankshaft, which provides rotational motion. Engines are generally classified by their volumetric displacement capacity, provided in units of cubic centimeters.
Types of Internal Combustion Engines
There are two categories of internal combustion engines: four-stroke and two-stroke.
- Four-stroke engines are found in most cars, trucks, and other large engines. A four-stroke cycle actually consists of two complete piston cycles. Wankel engines, which use a rotary, piston-less approach, are still categorized as four-stroke engines.
- Two-stroke engines are found in systems such as motorcycles and lawnmowers. A two-stroke cycle consists of one complete piston cycle.
Several other engines are technically considered internal combustion engines, although they are radically different than the traditional automobile engine. Jet engines, such as those in aircraft, are internal combustion engines, although different parts of the engine are used for each phase of the engine operation, rather than all phases occurring in one cylinder. Gas turbines also use this approach.
Internal Combustion Engine Operation
There are four phases that exist in any internal combustion engine:
- Intake – A fuel/air mixture is drawn into the cylinder through a valve as the piston strokes downward
- Compression – The returning piston stroke compresses the fuel/air mixture
- Combustion and Expansion – The fuel combusts, and the gas expands, pushing the piston down. In a gasoline engine, a spark plug is used to ignite the compressed gasoline/air mixture. In a diesel engine, the combustion is caused by the heat and compression within the cylinder, and a spark is not required.
- Exhaust – The combusted gas is expelled from the cylinder through a valve as the piston strokes up
In a four-stroke engine, the first two phases occur during the first complete cycle of the piston, while the third and fourth phases occur during the second complete cycle of the piston. The phases continue to alternate through every other cycle. The opening and closing of the intake and exhaust valves are generally controlled by a camshaft.
In a two-stroke engine, the process is simplified so that all four phases occur during one complete cycle of the piston. Because of this, two-cycle engines are generally less efficient than four-cycle engines. Two-cycle engines generally do not use valve systems, but rather include intake and exhaust vents into the cylinder design.
Internal combustion engines simplify human existence and ease many tasks that were previously relegated to manual or animal labor, from transportation to farming. To learn more about different types of engine designs and their applications, please read Internal Combustion Engine Designs.
