How the crankcase ventilation works

The internal combustion engine works on the principle of combustion of fuel-air mixture in the cylinders. After combustion of the fuel charge, the exhaust gases and other products of combustion of the mixture of air and fuel are mostly removed through the exhaust system to the outside., that is, released into the atmosphere.

However, given that, that high pressure is created in the combustion chamber, part of the gases, residues of unburned fuel and other products break through the piston rings and get into the crankcase. Carter is a closed cavity, in which there is a crankshaft and other details of the power unit.

There is always an oil mist in the crankcase, unburned fuel vapor, water particles and gases. These gases are called crankcase gases. Crankcase gases have a negative effect on engine oil. At the same time, excess crankcase gases can lead to an increase in crankcase pressure. As a result, the engine oil begins to be squeezed.

To reduce the amount of gases and reduce the pressure, PCV crankcase ventilation system is used in the design of modern internal combustion engines (Positive Crankcase Ventilation). In this article we will talk about the evolution and structure of this system, as well as address the issue of common faults.

The device and design features of the crankcase ventilation system

so, crankcase ventilation system allows you to remove excess crankcase gases, which increases the service life of engine oil, reduces the release of toxic substances into the atmosphere, reduces the pressure in the crankcase of the power unit. Systems can be:

• open type;
• closed type;

Let's note at once, that on different types of internal combustion engines the design of this system may differ, while the main functional elements on modern motors are:

• air branch pipes, on which gases circulate;
• crankcase ventilation valve, which regulates the pressure of crankcase gases when they are fed into the intake manifold;
• oil separator to prevent oil vapors from entering the combustion chamber to reduce soot formation;

In other words, today the closed type is actively used. The general principle of operation of such a crankcase ventilation system is based on vacuum, which is created in the intake manifold. Due to the liquefaction, the gases are removed from the crankcase. Next, these gases pass through the oil separator, which separates gases from oil. After cleaning the gases go through the air nozzles, then fall into the intake. Crankcase gases from the intake manifold, mixed with air, fed into the combustion chamber and burned.

Let's add, that in an outdated open system (ejection type) excess crankcase gases are simply released into the atmosphere. The method is very simple and cheap, however, there is increased pollution. Also, the efficiency of such a solution is not the highest, as at low speeds and in the XX mode similar ventilation does not work.

Even such a system does not perform its functions at high speeds. In parallel, there is a risk, that the crankcase will be sucked insufficiently cleaned outside air after cooling the internal combustion engine. Additionally, it should be highlighted, that in the presence of an open system on the engine increase in oil consumption is possible, also the oil can be thrown out together with gases outside, as a result, the engine surface is contaminated with oil stains.

Crankcase ventilation system closed, which is also called coercive, more complex in design. This solution allows to reduce the amount of harmful emissions into the atmosphere, taking into account environmental standards and reduce oil consumption.

The engine with such a system works stably, keeps the speed better in winter, as the cold outside air at the inlet is heated by crankcase gases, the risk of detonation is reduced. However, for all its advantages, this scheme is not without its drawbacks.

As a result of crankcase gases entering the intake there is increased contamination of air ducts and elements in the intake system of the engine. Experts also note, that the forced exhaust system can cause rapid oxidation of engine oil due to strong vacuum at high speeds.

Forced ventilation can also be implemented in different ways. At the same time, the basic principle remains that, that the gases must be "extracted" from the crankcase, and also there is their mixing as a result of giving in a crankcase of external air. After that, through a special valve, the mixture is fed into the engine cylinders.

On carburetor engines, units with mono-injection and injector engines can be found different types of crankcase gas supply. Previously, the design was quite common, when the system had two channels. One was removed in front of the throttle, and the second channel with the nozzle was output behind the throttle.

At idle, the gases were fed through a channel with a nozzle behind the valve. However, after the opening of the valve and the increase in the speed of the crankshaft discharge in the area behind the valve became less. The volume of gases, who broke into the crankcase, became more. The channel with the nozzle ceased to perform its function, but the output of gases through the channel in front of the throttle was connected. Further development of the ventilation system led to the emergence of valve solutions for regulating gas supply.

If simple, the valve is in the pipeline, through which the gases from the crankcase are lined up. Valves are also divided into spool and diaphragm. Let's add, that diaphragm valves better dose the amount of gases, however, the membrane itself often fails.

Why do you need an oil separator in the engine

As mentioned above, oil separator (oil catcher) is an element of the crankcase ventilation system. The main task of the oil separator is to prevent oil particles from entering the combustion chamber.

According to the method of separating oil from crankcase gases, labyrinthine and cyclic oil traps can be distinguished. Note, that on modern motors the oil separator of the combined type is used.

Labyrinth oil separator, which is also called a sedative, slows down the movement of gases. As a result, bulky particles of oil simply settle on the walls, then flow back into the crankcase.