What is the Principle of Crankcase Ventilation?
2 Answers
The principle of crankcase ventilation is: when the engine piston moves upward, the gas pressure inside the crankcase is negative, and the ventilation pipe draws air from the outside inward; when the piston moves downward from the top dead center, the pressure inside the crankcase changes from negative to positive, and the crankcase ventilation pipe then exhausts gas to the outside. The functions of the engine crankcase ventilation system are: 1. Preventing lubricating oil from deteriorating and reducing corrosion on friction components. During engine operation, some combustible mixture and exhaust gases leak into the crankcase. The leaked gasoline vapor condenses and dilutes the engine oil, degrading its performance and reducing lubrication effectiveness. If the exhaust gases contain water vapor and sulfur, they can form sulfuric acid, which corrodes the components. 2. Reducing pressure, lowering temperature, and preventing overheating. The gases leaking into the crankcase increase the pressure and temperature inside, causing oil to leak from seals and gaskets and deteriorate. Ventilation helps cool the oil, reduce pressure, and prevent leaks. 3. Reducing atmospheric pollution and recovering combustible gases, which improves fuel economy and reduces emission pollution.
The crankcase ventilation system is essentially designed to address the issue of exhaust gas emissions inside the engine. I often encounter customers asking about this during repairs, but the principle is actually quite simple: during engine operation, a small amount of gas leaks into the crankcase and mixes with oil vapor. The ventilation system uses hoses to connect the crankcase to the intake manifold, utilizing intake vacuum to draw out these exhaust gases for secondary combustion. The key component is the PCV valve, which acts like a smart switch—opening at idle to allow exhaust gas flow and automatically closing during rapid acceleration to prevent oil backflow. Regular inspection of the rubber hoses is crucial. Last week, I replaced a cracked hose on an old Tiguan—air leaks can accelerate engine carbon buildup and cause a noticeable increase in fuel consumption.
