At the same time creates a negative pressure in the cylinder and through open inlet cylinder filled with fresh fuel-air charge sweep. At the bottom position of the piston to light the working mixture is impractical because the pressure of expanding gases can not be used. Flywheel continuing to rotate through the crankshaft and connecting rod moves the piston upwards, and the mixture is compressed, as the two openings in the cylinder is closed at this time valves. Compressed mixture ignites a working electric spark, and the processes will be consistently repeated. The piston, moving in a cylinder, then the upper reaches, the lower end positions. The extreme situation in which the piston changes its direction of motion, called respectively the upper and bottom dead center.
The distance that the piston comes between the dead point, called a stroke. For each stroke of the crankshaft rotates at turn or 180 . Process occurring inside the cylinder in one Stroke is called tact. When moving the piston from top dead center to bottom in the cylinder space is released, which is called a working volume of the cylinder. When the piston is at top dead center above it smallest space, called the volume of the combustion chamber. Cylinder and volume of the combustion chamber, taken together, constitute the entire volume of the cylinder. In multi-cylinder engines the amount of business volume of all cylinders expressed in liters and is called the displacement engine.
One of the important indicators of the engine is its compression ratio, determined by the ratio of the total volume of the cylinder to the volume of the combustion chamber. With increasing degree of compression engine increases its efficiency and power. Improved fuel economy is achieved by reducing heat loss, since the greater degree of compression decreases the surface of the combustion chamber, which contact gases. The increase in engine power is achieved by raising the average pressure on the piston. The average pressure on the piston increases with temperature and combustion rate of the working mixture at its greater compression. Of the described principle of the single-cylinder engine can be seen that for one clock cycle at which the combustion and expansion of the working mixture of gases, you must perform two preparatory cycles – intake and compression stroke and final – issue.