Four-stroke car engine
There is a four-stroke engine from the cylinders,which are mounted on the crankcase and are covered with a head from above. To the sump the bottom is fixed. In the cylinder head are installed valves - exhaust and inlet, injector for injection of fuel (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 onedead center to the other. The volume formed above it when it is detected in the TDC is a parameter of the combustion chamber. The engine displacement or working volume 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 an 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.
Four-stroke engine at the beginning of the intake strokeWhen working, it opens the intake valve, while the piston starts to move from the TDC. During the movement in the cylinder, a vacuum develops, 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 NMT, thanksrotation of the crankshaft, it starts to rise to 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 the 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 for the combustion of the fuel, the combustible mixture is ignited beforehand, before the piston reaches the TDC compression stroke. The mixture is ignited by an electric spark that jumps between the electrodes of a 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 significantthe number of energy-consuming gases that press 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 TDC direction, displacing the exhaust gases into the atmosphere. Then the cycle repeats in the same sequence.