A crankcase ventilation system removes gases and oil mist from the crankcase and maintains the vacuum inside the crankcase at the required negative pressure.
How does a crankcase ventilation system (CVS) work and what kind of systems are available?
When an internal combustion engine is operated, so-called blow-by gases are generated inside it. The combustion gases pass by the pistons and piston rings and enter the crankcase, where they mix with the oil mist that is generated as the crankshaft rotates in oil. The introduction of these combustion gases also increases the pressure in the crankcase. However, since the crankcase needs to be under slight vacuum, it is imperative to get rid of this mixture of blow-by gases and oil.
- Open systems
In older engines, these gases were simply discharged into the open air. This was known as an open system. As a result, oil spots of varying sizes were often visible on the ground underneath parked cars. This used to be considered completely normal. Car drivers, for example, were used to regularly checking the engine oil level and topping it up as necessary.
- Closed systems
As environmental protection laws became increasingly tighter, this was of course no longer possible. Instead, these gases were fed into the combustion air and burned along with it. This is referred to as a closed system and resulted in the development of crankcase ventilation systems (CVS).
Most of the early closed systems were simply fairly coarse separators, which were barely able to separate the oil droplets from the gas at all. However, the presence of this oil caused other problems, which quickly gave rise to the idea of filtering the gases before introducing them into the combustion air. Since then, the increasingly stringent emissions legislation has forced the industry to make continuous improvements.
Accordingly, modern crankcase breathers are used to remove oil droplets from the blow-by gases and to return the separated oil to the oil circuit. The more effective the CVS, the fewer tiny oil droplets will come into contact with the hot, fast-turning rotor inside the turbocharger. Without the CVS, the oil particles would form an oil crust on the hot turbocharger blades, altering their geometry. This would reduce both the efficiency of the turbocharger and the entire engine, resulting in more toxic exhaust gases, less engine power, and increased fuel consumption.
Advantages of crankcase ventilation systems (CVS)
When the engine is still new, the CVS has very little work to do. However, the older the engine gets, the harder the CVS is forced to work. Internal engine wear causes the gaps between components to expand, increasing the volume of blow-by gases. If the CVS filter is properly designed and contains a high-performance medium, it can reliably separate even the smallest and most widely distributed droplets. The CVS also includes a pressure-control valve that keeps the negative pressure inside the crankcase within the optimum range.
By means of flow-optimized geometry and a correspondingly designed CVS, the entry of oil droplets into the combustion process is reduced to a minimum by means of a suitable filter medium – thus ensuring that the statutory specifications and requirements are met safely and reliably.
By separating the oil internally, the CVS greatly reduces the rate of oil loss in the engine compared to open systems, which means the oil must be topped up less frequently. Therefore, a good CVS filter will not only ensure optimum engine performance and the adequate exhaust gas quality but will also lower the rate of oil consumption.
What is important when designing a crankcase ventilation system?
When it comes to designing a CVS, a high level of technical know-how and detailed knowledge of the engine concerned are mandatory, as is sufficient experience in adapting these systems. In many cases, careful testing and measurements are indispensable.
What are the signs of a defective crankcase ventilation system?
It is not usually possible to identify a malfunctioning CVS at a glance. This is because in most cases the required monitoring devices, such as a vacuum gauge, are not installed. In a modern passenger car, a faulty CVS can usually be detected during an emissions test. However, this will also depend on the vehicle’s age or mileage and thus the condition of the engine.
When should the filter element be replaced?
The replacement intervals for the filter element are determined by the engine – it should therefore be replaced at the intervals specified by the engine manufacturer. As a rule, it is changed at the same time as the air filter. For further details, refer to the operating instructions for the engine.
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