Four-stroke car engine

There is a four-stroke engine from the cylinders, which are mounted on the crankcase and are covered from above with a head. To the sump the bottom is fixed. In the cylinder head are installed valves - exhaust and inlet, injector for fuel injection (diesel engines) or spark plugs (gasoline). Inside the piston, connected through the piston pin with the upper connecting rod head, moves. The lower head of the connecting rod covers the crankshaft neck, in which the crank journals are mounted on the bearings. The piston in the cylinder is sealed by means of special rings. At the end of the crankshaft , the flywheel is fixed.

The dead top point is the position occupied by the piston at the end of its stroke up, the dead bottom point is the position occupied at the end of the stroke down.

Tact is the movement of the piston from one dead point to another. The volume formed above it when it is detected in the TDC is a parameter of the combustion chamber. The engine displacement or displacement is the amount released by the piston when moving from a dead center. The volume of the cylinder is the value of the common combustion chamber together with the working chamber.

The degree of compression 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. The modern single-cylinder engine has a compression ratio of about 10. A single-cylinder four-stroke engine has a higher compression ratio, at least 20.

The four-stroke engine at the beginning of the intake stroke during operation opens the intake valve, with the piston starting to move from the TDC. During the movement in the cylinder, a rarefaction occurs, and a four-stroke engine receives a mixture of air and fuel vapors, often called a fuel or fuel-air mixture.

After the piston passes through the BDC, thanks to the rotation of the crankshaft, it starts to rise toward the TDC, which is considered the beginning of the compression stroke. At the same time, the intake valve closes, and during the whole stroke both valves are closed. The combustible mixture that is in the cylinder, when the piston is displaced towards TDC, is compressed, its temperature and pressure increase. There is a maximum value of compression when the piston reaches the TDC. But since it takes some time to burn the fuel, the combustible mixture is ignited before the piston reaches the TDC compression stroke. The mixture is ignited by an electric spark, which slips between the electrodes of the candle. From the time of the appearance of the spark to TDC, the angle of rotation of the crankshaft is called the angle of the pre-ignition.

During the combustion of fuel, a significant number of energy-intensive gases pressurize the piston, which cause the four-stroke engine to make a working stroke at the next stroke, which occurs when the valves are closed, when the piston moves to the BDC from the TDC. The release cycle begins after the working stroke. At the same time, the exhaust valve opens, and the piston moves in the direction of TDC, displacing the exhaust gases into the atmosphere. Then, in the same sequence, the cycle repeats.