Working of Crankcase Ventillation System

Introduction: The Crankcase Ventilation System helps move Blow-by gases to the intake of an engine. This further helps in better fuel efficiency and performance. Crankcase Ventilation System further reduces environmental pollution. In this article, we will discuss the necessity, history, and benefits of the Crankcase Ventilation System.

Why is Crankcase Ventilation Needed?

Between the piston rings and the cylinder wall of an engine, there is a small gap that allows combustion gasses into the crankcase. This causes pressure build-up in the crankcase. These gases cause lower fuel efficiency, dilute engine oil, and have bad impacts on the environment. So, the removal of blow-by gases is necessary and this is done by a Crankcase Ventilation System.

There are two basic types of Crankcase Ventilation System:

1. Open Crankcase Ventillation(OCV).
2. Closed Crankcase Ventillation(CCV).

Open Crankcase Ventilation also called OCV allows crankcase gases into the atmosphere. This system is simply low efficient and consumes more fuel.

Closed Crankcase Ventilation or CCV is a system that allows crankcase gasses back to the intake manifold which improves the engine's efficiency, and performance and is simply better for the environment.

History of Crankcase Ventilation

Early engines released these gases into the atmosphere by providing separate passages to the atmosphere. The First Specific Crankcase ventilation used was a road draft tube. This was a pre-emission device for removing crankcase gasses from the atmosphere this was used in vehicles before 1960. During years like 1963 need for emission standards arose due to some environmental-related problems like smog in Los Angeles, USA. Furthermore, during the early 1970s, different countries like Australia, Canada, and other European countries set emission standards.

This gave rise to different technologies. One of these technologies was Closed Crankcase ventilation or Positive Crankcase ventilation. This system sends crankcase gasses back to the combustion chamber. PCV was developed in California, USA in 1961. This system was among the first devices developed for emission controls.

Blow-By Gasses

These gases are unburnt air/fuel that enter the crankcase by a small gap between piston rings and cylinder walls. This gap is also called the ring gap which is so small that for a piston of 90mm dia, this gap is 0.09mm. This ring gap is necessary because rings expand during combustion due to thermal expansion. Moreover, a ring gap is necessary to avoid binding or sticking of the piston. But this gap also causes a problem of leading blow-by gases to the engine's crankcase.

These Blow-by gases have carbon monoxide(CO), carbon dioxide(CO2), nitrogen oxides(NOx), and different hydrocarbons. These are bad for our environment and causes an increase in harmful emission if these lead to the atmosphere. Another problem these gases can cause is wear and tear of engine parts due to high pressure. Moreover, these gases can dilute engine oil which can further lead to many problems.

Main Components of Positive Crankcase Ventilation

PCV system has 3 main components:

1. PCV valve.
2. PCV valve line from the crankcase to the intake
3. Breather Line

PCV Valve

The PCV valve is the main and most important component of the PCV system. PCV valve consists of a rubber diaphragm that is further attached to a spring and housing. On one of its sides, there is a supply of vacuum and on the other side, there is pressure of blow-by gasses from the oil chamber. So, when a vacuum from the upper side and pressure from the lower side are applied it opens and causes the flow to blow by gases to the intake manifold.

PCV Valve Line

One side of the PCV valve is connected to the intake while the other is to the crankcase. This line provides a vacuum from one side and blow-by gas pressure on the other side which opens or closes the PCV valve.

PCV Breather Line

This line allows fresh air from intake to the crankcase. This is necessary for better ventilation.

Working

Now, it would be easy to understand how this system works.

First of all, when the engine sucks air from the intake manifold this creates a vacuum inside the air intake. PCV valve takes that vacuum and gets opened. Moreover, it is provided by the pressure of the crankcase from the other side which also helps it to open. For better ventilation and evacuation of these blow-by gases breather line provides fresh air from the air intake to the crankcase.

Remember: The PCV valve is a non-return valve which means it would not allow intake gases to crankcase. As can be seen in the above diagram if intake gases enter the PCV valve it will close the valve by pressing the rubber diaphragm downward(according to the diagram).