Compression in the engine provides an increase in useful energy from the combustion of the fuel mixture. The concept itself comes from the Latin word compressio. Compression is the compression of gas under the influence of forces from outside. This leads to a decrease in its volume. An external effect may be elevated temperature or pressure. In ICE (internal combustion engine), engine compression also takes place. In this case, the fuel mixture is compressed.
In many designs of modern cars, four-stroke ICEs are installed. Engine compression is detected primarily in the combustion chamber, in the area between the walls of the chamber, the compression ring and the piston bottom. It occurs at a time when the pressure reaches a maximum, when the piston has almost reached the mark of top dead center, before ignition of the combustible mixture.
Engine compression, excluding deformation and forcing the engine, is considered a relative indicator for the state of the cylinder-piston engine system and a number of other nodes. Piston, rings, valves (exhaust and inlet), gaskets in the head of the engine block and a number of other details ensure the quality of compression.
A load arises in the chamber, which can reach fifteen atmospheres in a gasoline engine. Compression of a diesel engine is formed at a pressure reaching thirty atmospheres. In this regard, all the details involved in the process must be able to withstand such a load constantly.
When the piston moves from the generated pressure, gases penetrate into the gap between the groove and the ring. Gases as a result are pressed against the surface of the cylinder of the ring.
The constant load on the cylinder-piston system, the gas distribution mechanism, due to the constant high pressure, adversely affects the condition of the parts. This, in turn, degrades the power and efficiency of the motor. It should be noted that engine compression (of the same) can be completely different. This is due to different measurement conditions: temperature, crankshaft speed, the amount of incoming air into the cylinder.
So, for example, oil, having a greater density, viscosity, enhances compression, accumulating on the cylinder walls, sealing gaps in the mating parts. Excessive fuel that enters the cylinder rinses off this oil film, resulting in reduced compression.
When measuring compression ratios in cylinders, it becomes possible to determine the causes of a decrease in motor power or a “poor" start. So, for example, in cars with a range of more than one hundred and fifty thousand kilometers, high compression can be caused by the formation of a significant layer of soot on the walls of the combustion chamber. This, in turn, reduces the volume of the cavity. Because of this, the compression increases accordingly.
The compression level can be measured in many ways.
With the throttle open, the maximum possible intake of air in the motor. The results may be affected by leakage from the air cylinders during wear of the rings, in the presence of burnouts, cracks, scratches on the walls of the piston and cylinder, valve freezes, etc.
With the throttle closed, fairly accurate indicators of the compression level can be obtained. In this case, a small amount of air flows. At the same time, it is possible to calculate the leaks arising from the deformation of the shaft or the wear of the valve seat.
When the motor is difficult to start, it is recommended to measure on a cooled engine. In this case, the compression is less than when measured on a hot engine. As a rule, measurement with a hot engine should be carried out at a temperature of about 80-90 degrees. This is due to a decrease in the viscosity of the oil and a decrease in the gaps between the movable elements.