The significance of the crankcase ventilation technical system has greatly increased over the past few years, caused by the increases in specific engine power. Approx. 0.5 to 1% of the cylinder load is dissipated via the piston rings, the valve guides and the turbocharger circuit in the crankcase.
The blow-by mainly consists of exhaust gas, combustion air and fuel, and is saturated with engine oil vapour and oil droplets. Ventilation into the atmosphere is not possible for environmental protection reasons. For this reason, most modern engines are equipped with an enclosed crankcase ventilation system.
On engines with external mixture generation such as gas or petrol engines, the blow-by contains a substantial quantity of uncombusted fuel. The return of this fuel thus increases the efficiency of the engine.
On turbocharged engines with charge air intercoolers, it is also especially important to separate the oil mist as much as possible from the blow-by gas in order to avoid contamination of the intake passage and the turbocharger assembly and the related adverse effects on engine operation. The higher the useful mean pressure under full load, the higher are the requirements on the separation rate to be achieved.
In case of high-performance engines in continuous operation, a long maintenance-free operation period for the filter is, in addition to the separation rate, of great importance, in addition to other criteria such as
- Minor drops in pressure
- Low space requirements; can easily be integrated into the engine construction
- Sufficient vibration resistance
- High levels of operating safety
- Cost efficiency during procurement and in operation.
Specifically the requirements for a high separation rate, a high filter lifetime, small space requirements and low costs are hard to fulfil all at the same time. Accordingly, engine manufacturers and users currently require innovative technical solutions.
The objectives for the development of IFT blow-by filters are:
- Separation rates for the oil mist from the blow-by gas > 99.98 %
- Maintenance-free filter lifetime > 30,000 full-load operating hours
- Maximum filter housing size < 0.025 l/kW engine power
- Maximum adaptability to different market requirements and operating conditions
- Low manufacturing costs
The oil mist in the blow-by gas consists of a mixture of oil droplets in different sizes.
The droplet fraction at the bottom end of the diameter spectrum is of a dimension established outside the measuring range of most particle measuring devices and is therefore very hard to record in measurements (<0.1 μm) Although the distribution of the size differs from engine to engine, it basically corresponds with the curve presented below.
Frequency distribution of the particle size in oil mist for a typical blow-by gas.