Lubrication 19 - Oil Mist Separation
Why, in the last few years, is so much attention being paid to the subject of the crankcase ventilation? There have been, e.g., at VW, some small disasters involving engine damage etc. In addition, more and more
components, some of them with valves and rotary mechanics are appearing on the market, briefly, it's becoming more and more complicated. But why?
If you consider only, that the share of engines with turbo-chargers has increased in leaps and bounds, then you must realize, that not only under extensive driving operations, the pressures involved have become
perceptibly higher. Indeed, the direct injection with increased torque has also contributed to this situation.
Now, what is the result of noticeably higher mid-range pressure? The pressure in the oil-sump also increases and, on the way to the intake system, it drags along more oil, which, as much as possible, must be
removed, since the oil consumption of our engines has also been reduced, we won't even mention the environmental laws.
A higher engine-oil content in the intake air also damages the engine itself. It was always possible that the oil could carbon-up the intake valves and be baked onto the compressor wheel of the turbo-charger, whose
surface has been carefully shaped to avoid any possible turbulences.
In the meantime, a distinction is made between active and passive systems. For the former, the above shown model is a good example. The so-called 'blow-by gas' from the crankcase enters at the bottom in the
center and the separated oil flows back on the bottom left hand side. That which is led upwards (in green), is hopefully, well purified gas on it's way to the intake section.
Please follow the path of the blow-by gases, in the center upwards and then, at the top they are diverted to the left and to the right. Shortly afterwards, because of their mass inertia, the droplets can't repeat the trip
downwards and thus land, through a sort of filtering, on or in the fleece, from which they then drain off and are allocated to the opening at the bottom left.
Do me a favour, let's not go into the layout of the openings and the fleece. Neither will we deal with the question of whether there is a throughflow or just an incident-flow, that, and the
function of the funnel at the top will not, at this point, be conclusively explained. An important point perhaps, is that this fleece does not have to be exchanged.
Of further interest, is the spring-loaded disc-valve. This has to do with the degree of efficiency, a question which the engineers have repeatedly asked themselves. Without the disc-valve, the bottom opening would
have to be so much bigger, to cope with the high throughflow, which would limit the degree of separation. With the disc-valve, at the bottom this is consistently quite good, because the excess amount can flow off
towards the top.
The engineers are also constantly thinking about the number of modifications necessary for the various engine sizes. They can almost all be covered by using a one-size component, whereby the disc-valve
compensates for the greater amount of throughflow. Apparently, its pre-tension can be varied according to the desired application. The in- and out-flow pipes are big enough anyway.
The experts speak of less than 1 g/h, which escapes from this system. At this point, please allow a rough calculation. 10.000 kilometers, at an average speed of 50 km/h means 200 hours of operation. Even if oil had
a specific gravity of 1 g/cm³ (which it doesn't have), it would still mean an oil consumption of less than 0,2 liters.
This doesn't mean that you should only check your oil every 10.000 kilometers. As you already know, even though the engine-seals may be completely intact, a certain amount of oil is carried out together with the
exhaust gas. This information was more than likely given out without taking the cold-running phase into consideration. Nonetheless, the calculation is definitely proof of the effectivity of modern oil separation.
To return to the above mentioned problems, e.g., at VW: Oil may contain small quantities of water which can freeze, thus blocking passages at important points, before the engine has had time to warm up. Recently,
e.g., the French manufacturers have started installing electric heating here, indeed, the malfunctioning is confusing everthing. They are designed for particularly cold regions and, for use in our latitudes, can easily put
out of commission by means of the fuse. 01/14