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. When the piston moves from the top dead center downward, the pressure inside the crankbox changes from negative to positive, and the crankcase ventilation pipe exhausts gas to the outside. The following are the functions of the engine crankcase ventilation system: 1. Prevent lubricating oil from deteriorating and reduce corrosion of friction components. During engine operation, some combustible mixture and exhaust gas leak into the crankcase. The leaked gasoline vapor condenses, thinning the oil and degrading its performance, thereby reducing lubrication effectiveness. If the exhaust gas contains water vapor and sulfur gases, sulfuric acid can form, causing corrosion to the components. 2. Reduce pressure and temperature to prevent overheating. The gas leaking into the crankcase increases the pressure and temperature inside, causing oil leakage and deterioration from seals and gaskets. Ventilation helps cool the oil, reduce pressure, and prevent leakage. 3. Reduce atmospheric pollution and recover combustible gases, which improves fuel economy and reduces emission pollution.
I've been pondering the crankcase ventilation system for quite a while. When the engine is running, high-temperature and high-pressure gases enter the crankcase below the pistons, technically termed 'blow-by gases.' These dirty and humid exhaust gases must be promptly vented. If not, they'll dilute the engine oil, impairing lubrication, and cause excessive pressure in the oil pan, potentially blowing out oil seals. Modern vehicles come equipped with a ventilation tube—one end connected to the crankcase and the other to the intake pipe. Utilizing the engine's intake vacuum, this system draws crankcase gases back into the combustion chamber for reburning, making it both eco-friendly and fuel-efficient. However, high-end vehicles have refined this further by incorporating a PCV (Positive Crankcase Ventilation) valve to regulate flow. The valve opens wider during rapid acceleration to prevent pressure buildup and closes slightly at idle to avoid stalling. If this system malfunctions, oil may seep from the engine cover gaps, and blue smoke can emerge from the exhaust pipe.
