Views: 8 Author: Site Editor Publish Time: 2019-07-31 Origin: Site
When the engine is working, the high-pressure combustible mixture and the burned gas of the combustion chamber will more or less leak into the crankcase through the gap between the piston group and the cylinder, causing helium. The components of helium are unburned fuel gas, water vapor and exhaust gas, which will dilute the oil, reduce the performance of the oil, and accelerate the oxidation and deterioration of the oil. When water vapor condenses in the oil, it will form sludge and block the oil circuit; the acid gas in the exhaust gas will be mixed into the lubrication system, which will cause corrosion and accelerated wear of the engine parts; the helium gas will also cause the pressure of the crankcase to be too high and destroy the crankcase. Sealed to make oil leaks.
To prevent excessive crankcase pressure, extend oil life, reduce parts wear and corrosion, and prevent engine oil leakage, crankcase ventilation must be implemented. In addition, in order to meet increasingly stringent emission requirements and improve economics, crankcase ventilation system design must also be carried out in the design of automotive engines.
Crankcase ventilation includes natural ventilation and forced ventilation. Modern gasoline engines often use forced crankcase ventilation, also known as PCV systems.
1) Natural ventilation
Natural ventilation means that a ventilation pipe is arranged on the crankcase, and an air filter is arranged on the pipe. When the pressure in the crankcase increases, the gas leaking into the crankcase is discharged through the vent pipe.
2) Mandatory ventilation
The forced ventilation method guides the mixture in the crankcase to the appropriate position of the intake pipe through the connecting pipe, and returns to the cylinder to re-burn, which can reduce the exhaust pollution and improve the economy of the engine. Manned gasoline engines use mandatory ventilation, and automotive diesel engines also use mandatory ventilation. Mandatory ventilation can be divided into open and closed.
The open forced crankcase ventilation device generates a large amount of cross-talk when the engine is at full load and low speed, but the opening of the flow control valve is reduced, and the excess blow-by gas is dissipated into the atmosphere through the open ventilation cover, and the purifying is performed. The rate is only about 75%.
The closed forced crankcase ventilation device can completely control the discharge of the crankcase, achieve complete ventilation of the crankcase, prevent the accumulation of sludge and other harmful substances, and reduce engine failure and wear. Closed forced crankcase ventilation is a necessary design for gasoline engines to meet emission regulations.