What is the working principle of an automotive engine

The automotive engine is the engine that powers the car and is the heart of the car. The working cycle of an automotive engine includes four-piston processes, namely intake stroke, compression stroke, expansion stroke (power stroke), and exhaust stroke.

Here is the content:

Intake process

Compression process

Work process

Exhaust process

Intake process

The carburetor gasoline engine mixes air and fuel in the carburetor outside the cylinder before being sucked into the cylinder. During the intake stroke of the automotive engine, the intake valve opens and the exhaust valve closes. As the piston moves from top dead center to bottom dead center, the volume of the cylinder above the piston increases, so that the pressure in the cylinder drops below the atmospheric pressure, that is, vacuum suction is created in the cylinder. In this way, the combustible mixture is sucked into the cylinder through the intake pipe and the intake valve.

Compression process

The larger the compression ratio, the higher the pressure and temperature of the mixture at the end of compression, and the faster the combustion speed. Therefore, the greater the power generated by the automotive engine, the better the economy. However, when the compression ratio is too large, not only the combustion situation cannot be further improved, but abnormal combustion phenomena such as deflagration and surface ignition will occur. At the same time, it will also cause a series of undesirable consequences such as automotive engine overheating, power drop, and fuel consumption increase. When the surface ignition occurs, there is also a strong knocking sound (duller), and the high pressure generated will increase the load of the engine parts and reduce the service life.

Work process

During this trip, the intake and exhaust valves are still closed. When the piston approaches the top dead center, the spark plug installed on the cylinder head emits an electric spark to ignite the compressed combustible mixture. After the combustible mixture in the automotive engine is burned, it releases a large amount of heat energy. Therefore, the pressure and temperature of the gas increase rapidly. The high-temperature and high-pressure gas push the piston to move from the top dead center to the bottom dead center. The connecting rod rotates the crankshaft and outputs mechanical energy. In addition to maintaining the engine itself, the rest is used for external work.

Exhaust process

The exhaust gas generated after the combustion of the combustible mixture must be removed from the cylinder for the next intake stroke. When the expansion is close to the end, the exhaust valve opens, and free exhaust is carried out by the pressure of the exhaust gas. When the piston reaches the bottom dead center and then moves to the top dead center, the exhaust gas will continue to be forced into the atmosphere. When the piston reaches near the top dead center, the exhaust stroke ends. In the exhaust stroke, the pressure in the cylinder of the automotive engine is slightly higher than the atmospheric pressure. Since the combustion chamber of an automotive engine occupies a certain volume, it is impossible to exhaust the exhaust gas at the end of the exhaust, and this part of the exhaust gas left is called the residual exhaust gas.

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