In-depth Analysis of the Working Principle of Aviation Piston Engines

The working principle of the aviation piston engine can be deeply analyzed as follows:

First, overview of the working principle

An aviation piston engine is a mechanical device that mixes gasoline (or other fuels) with air and then burns and expands to do work in a closed cylinder. This kind of engine must cooperate with the propeller and push the aircraft forward through the pushing (pulling) force generated by the propeller.

Second, the work cycle process

The working cycle of an aviation piston engine is usually four-stroke. Each piston moves back and forth in the cylinder for four strokes, successively completing the four processes of intake, compression, expansion and exhaust, forming a complete working cycle.

Intake stroke

The intake valve on the cylinder head is open and the exhaust valve is closed.

The piston slides downward from the top dead center to the bottom dead center. The volume in the cylinder gradually increases and the air pressure decreases.

A mixture of fresh gasoline and air is drawn into the cylinder through the open intake valve. The ratio of gasoline to air in a mixed gas is usually 1:15.

Compressed stroke

The crankshaft continues to rotate by inertia, pushing the piston upward from the bottom dead center.

Both the intake valve and the exhaust valve are tightly closed, and the volume inside the cylinder gradually decreases.

The mixed gas is strongly compressed by the piston, and the pressure and temperature gradually increase. When the piston moves to the top dead center, the mixed gas is compressed in a small space between the top dead center and the cylinder head. This small space is called the "combustion chamber".

Expansion stroke

Near the end of the compression stroke, the piston approaches the top dead center.

The spark plug on the cylinder head generates an electric spark through high-voltage electricity to ignite the mixed gas.

The combustion time is very short, but the speed is very fast. The gas expands violently, and the pressure and temperature rise sharply.

Under the powerful pressure of the gas, the piston moves rapidly towards the dead center, pushing the connecting rod to move downward as well. The connecting rod then drives the crankshaft to rotate. This stroke is the one that enables the engine to operate and gain power.

Exhaust stroke:

After the working stroke is completed, due to inertia, the crankshaft continues to rotate, causing the piston to move upward from the bottom dead center.

At this point, the intake valve remains closed while the exhaust valve is wide open, and the exhaust gas after combustion is discharged outward through the exhaust valve.

When the piston reaches the top dead center, the vast majority of the exhaust gas has been discharged. Then the exhaust valve closes, the intake valve opens, and the piston moves down from the top dead center again, starting a new cycle.

Third, the main components

An aviation piston engine is mainly composed of components such as cylinders, pistons, connecting rods, crankshafts, valve mechanisms, propeller reducers and casings.

Cylinder: The place where the mixture burns, and inside the cylinder, there is a piston that moves back and forth. The cylinder head is equipped with an electric spark plug (commonly known as an electric nozzle) for igniting the mixture, as well as intake and exhaust valves. When the engine is running, the temperature of the cylinder is very high, so there are many heat sinks on the outer wall of the cylinder to increase the heat dissipation area.

Piston: It bears the gas pressure, performs repeated movements in the cylinder, and converts this movement into the rotational activity of the crankshaft through the connecting rod.

Connecting rod: A component that links the piston and the crankshaft, converting the reciprocating motion of the piston into the rotational motion of the crankshaft.

Crankshaft: The component that outputs power in the engine, transmitting the power from the connecting rod to the propeller reducer.

Valve mechanism: It is used to control the intake valve and exhaust valve to open and close at regular intervals to ensure the normal operation of the engine.

Propeller reducer: Reduces the rotational speed of the output shaft to enable the propeller to rotate at an appropriate speed.

Casing: The outer shell of an engine, used to protect the internal components of the engine.

Fourth, Summary of working principle

The working principle of an aviation piston engine can be summarized as follows: High-temperature and high-pressure gas is generated through the combustion of the mixture in the cylinder, which drives the piston to move back and forth. The reciprocating motion of the piston is converted into the rotational motion of the crankshaft through the connecting rod and crankshaft, and then the propeller is driven to rotate through the propeller reducer, generating a pushing (pulling) force to push the aircraft forward.

Fifth, Characteristics and Applications

Aviation piston engines have the advantages of simple structure, high reliability and convenient maintenance, and are widely used in the aviation field. Especially on light low-speed aircraft, low-power piston aero engines remain an economical and practical power unit. However, with the continuous development of aviation technology, new power devices such as turbine aero engines have gradually taken the dominant position.