AS9120B, ISO 9001:2015, AND FAA AC 0056B ACCREDITED

How Does a Four-Stroke Piston Engine Work?

Commonly referred to as a reciprocating engine, piston engines are a common choice for powering small aircraft. Working to convert expanding gasses into mechanical energy, this is done by using pistons to push and pull on a crankshaft which drives the propeller. In addition, a piston engine is typically air-cooled, meaning it uses air flowing through the engine to keep it cool. This makes them well-suited for use in smaller aircraft with limited space for cooling systems.

Moreover, four-stroke piston engines are more common in today's vehicles and often consist of intake, compression, combustion, and exhaust stages/strokes. When in operation, the piston must first move downwards during what is known as the intake stroke to draw in fresh air. This air is then compressed during a subsequent compression stroke. Next, a spark plug ignites the fuel-air mixture to produce exhaust through combustion which is then pushed out of the combustion chamber by a piston to excrete exhaust gasses. Valves present in the system are closed during the compression stroke, and the piston moves upward, compressing the air/fuel mixture; this increases internal temperature and pressure inside the cylinder to ensure the expansion of gasses drives the piston downward, and the cycle repeats itself. This completes one cycle of engine operation, and below, we will briefly describe the function of engine intake, compression, power, and exhaust.

  1. Intake

At the start of an intake stroke, the piston reaches the top of the cylinder, and the intake valve opens. The piston then moves downward, drawing an air/fuel mixture into the cylinder.

  1. Compression

Operating based on the Otto cycle, which consists of four strokes, four-stroke piston engines execute four internal and reversible processes. Compression is essential to the proper operation of such engines because this action increases the internal temperature and pressure of the air/fuel mixture, making it easier for ignition to occur. However, too much compression can cause engine damage. Therefore, it is essential to maintain the proper compression ratio for your engine.

  1. Power

To generate power, a spark plug ignites the compressed fuel/air mixture inside a cylinder to generate combustion. The combustion causes a massive increase in pressure, causing the piston to return to its original downward motion. This is what generates the enormous torque required to turn the crankshaft.

  1. Exhaust

Finally, the exhaust stroke begins when the exhaust valve opens, and the piston pushes out any remaining exhaust gasses. However, this produces pollution, including carbon monoxide, nitrogen oxide, and particulate matter due to incomplete combustion. Reducing these emissions can be challenging, but it is essential for protecting air quality.


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