2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42
The four-stroke engine consists of cylinders that are mounted on the crankcase and are closed with a head on top. A pallet is attached to the bottom of the crankcase. Valves are installed in the cylinder head - exhaust and intake, a fuel injection nozzle (diesel) or spark plugs (gasoline). A piston moves inside, connected through a piston pin to the upper head of the connecting rod. The lower head of the connecting rod covers the neck of the crankshaft, in which the main journals are mounted on bearings. The piston in the cylinder is sealed by special rings. A flywheel is attached to the end of the crankshaft.
The top dead point is the position occupied by the piston at the end of its upward stroke, the bottom dead point is the position occupied at the end of its downward stroke.
Tact is the movement of the piston from one dead center to another. The volume formed above it when it is detected at TDC is a parameter of the combustion chamber. Displacementengine or displacement is the amount released by the piston when moving away from the dead center. The volume of the cylinder is the size of the total combustion chamber, together with the working one.
Compression ratio is the most important aspect, which is defined as the ratio of the total volume of the cylinder to the total volume of the combustion chamber. A modern single-cylinder engine has a compression ratio of approximately 10. A single-cylinder four-stroke engine has a higher compression ratio of at least 20.
A four-stroke engine at the beginning of the intake stroke during operation opens the intake valve, while the piston begins to move from TDC. In the process of moving, a vacuum is created in the cylinder, and a mixture of air and fuel vapors, often called a combustible or fuel-air mixture, enters the four-stroke engine.
After the piston passes BDC, due to the rotation of the crankshaft, it begins to rise to TDC, which is considered the beginning of the compression stroke. This closes the intake valve, and during the entire stroke, both valves are closed. The combustible mixture that is in the cylinder, when the piston moves to TDC, is compressed, its temperature and pressure increase. The maximum compression value occurs when the piston reaches TDC. But since the combustion process takes some time, the combustible mixture is ignited in advance, before the piston reaches TDC on the compression stroke. The mixture is ignited by an electric spark, whichslips between the spark plug electrodes. From the time of spark to TDC, the angle of rotation of the crankshaft is called the preignition angle.
During the combustion of fuel, a significant amount of energy-intensive gases are released, pressing on the piston, which cause the four-stroke engine to work on the next stroke, occurring with the valves closed, on the piston stroke to BDC from TDC. The exhaust stroke starts after the power stroke. At the same time, the exhaust valve opens, and the piston moves towards TDC, displacing exhaust gases into the atmosphere. Then the cycle repeats in the same sequence.
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