I am often asked questions about crankcase gases in a gasoline engine. Namely, what is it? Where do they come from? They ask questions about the valve (of this system), the ventilation system and so on. Everything in this article will not work, because it's just a huge material, but here we will try to start with what it is, where it comes from, what is the danger, and whether it can be released into the environment.
At first, I would like to note that these gases are absolutely normal condition of any gasoline engine, they are on both working and defective aggregates (they just appear a little differently).
What are crankcase gases?
Crankcase gases are gases that have formed during compression and ignition of the fuel-air mixture and through compression rings (at the compression and ignition cycle) have passed into the crankcase of the engine. Moreover, some part of the engine, even with a new engine, always gets into the crankcase (usually from 5 to 7%), with worn-out units this percentage is much higher.
System design
Now I suggest we talk about this in more detail, starting with the device.
So, everybody knows that any internal combustion engine has only 4 basic bars:
- Inlet - the inlet valves open, the piston goes down, the atmosphere is discharged (discharged in the inlet manifold), the air-fuel mixture is sucked in.
- Compression - the piston goes up, compressing the mixture.
- Ignition - the most compressed mixture in the VMT (upper dead spot), ignited by the spark plug, a "flame front" is formed, which pushes the piston down.
- Exhaust outlet - the exhaust valve opens and the exhaust gas mixture is discharged (pushed by the piston into the silencer).
4 engine cycles
For many, there is nothing new here, it's a conventional 4-stroke engine (or rather, its operation scheme).
However, it should be noted that in order for the engine to work, the pistons have so-called rings, usually, they are divided into two types:
Compression rings. Those that hold the compression (usually two) do not allow the gases to pass by the piston
Oil removable. Remove excess oil from the walls (often one, standing at the bottom of the piston) to prevent grease from rupturing into the combustion chamber.
However, the compression rings cannot 100% exclude the passage of gases into the crankcase. Part of it still penetrates, for example, through the ring locks, through the loose fit to the walls, at a slight deformation (walking) of the rings during the piston operation.
Rings
And as I wrote from above, the crankcase contains about 5-7% of the gas from the combustion chamber. There is also an air-fuel mixture on the cycle of compression + exhaust gases after the fuel ignition (because the ignition pressure is enormous). But if the piston is very worn out, then the passage may increase by several times.
Crankcase gas recirculation system
Where do the bursting gas mixtures go? As a rule, they are lifted up through various channels (e.g. where the chain runs) into the valve cover (can be lifted upwards by hoses directly from the crankcase). And here begins the most interesting thing, namely, the device recirculating crankcase gases, they can be separated from the conditionally "old" to progressively "new".
The old device. Here everything was simply "as a drum", from an engine crankcase there was a special "tube" (hose) sometimes even was simply a box on blocks which simply connected to atmosphere, yes - yes, they simply left in atmosphere. At that time, everyone was absolutely "sideways" to the environment, there were no environmental systems in the cars (such as catalysts, etc.). There were special "oil separators" (sometimes just a labyrinth of small channels, sometimes a metal mesh), which delayed the oil mist and returned it back to the engine in the form of oil.
Oil trap
It is worth noting the contamination of crankcase gases - in fact, it is an unburned air-fuel mixture + "exhaust", which escaped directly from the combustion chamber, mixed with the "oil mist" which is in the crankcase of the combustion engine. And all this rattlesnake (very dirty) mixture, before (without any filters) went simply into the underhood space, and then the atmosphere. By the way, both the driver and passengers could breathe all this too, because nothing prevented these gases from entering the cabin.
The first recirculation systems. But then the people thought that this is not right and we need to filter it (at least minimally). That's why on the first carburetor ones, for example, crankcase gases went up the hose and came out to the air filter of the carburetor. Drivers of that era remember the round air filter, which did not allow dust and dirt to pass in the carburetor, all this was closed in a round metal case and covered with a cover.
To be continued in next part https://zen.yandex.ru/media/id/5d934fbd8d5b5f00b14d5a38/carter-gases-what-is-it-in-the-engine-part-2-5d95a3c834808200b112f741