Skip to content

Easiest Way To Control Crankcase Fumes In IC Engines

the drawing of a four-stroke IC engine

Easiest Way To Control Crankcase Fumes In Internal Combustion Engines

Easiest Way To Control Crankcase Fumes In Internal Combustion Engines
Easiest Way To Control Crankcase Fumes In Internal Combustion Engines

Experience has shown that in some compression and firing strokes, some combustion gases inevitably escape past the pistons into the crankcase.

This is known as piston blowby. The fumes consist mostly of unburned fuel (hydrocarbons).

As an engine wears, piston blow-by increases. Because unburned hydrocarbons form an explosive mixture, dilute the sump oil, and form sludge, car makers ventilate the crankcase to let them out.

Easiest Way To Control Crankcase Fumes In Internal Combustion Engines
Easiest Way To Control Crankcase Fumes In Internal Combustion Engines

Until emission control regulations took effect the ‘road draught’ system was used, in which the forward motion of the car created a vacuum at the outer end of a ventilation tube from the crankcase.

Fresh air was drawn in usually through the oil filler to replace the vented crankcase fumes.

Easiest Way To Control Crankcase Fumes In Internal Combustion Engines
Easiest Way To Control Crankcase Fumes In Internal Combustion Engines

Unfortunately ‘road draught’ ventilation was ineffective below 25mph and oil contamination was high in engines used mostly in town traffic.

Positive crankcase ventilation was introduced to control emissions because unburned hydrocarbons are poisonous, it was also introduced to provide ventilation regardless of the road speed.

A positive crankcase uses the vacuum in the inlet manifold to suck fumes from the crankcase and pass them to the combustion chamber where they are burned.

The system contains a positive crankcase valve that acts as a fire precaution and adjusts the flow of fumes back-fire occurs in the manifold.

Easiest Way To Control Crankcase Fumes In Internal Combustion Engines
Easiest Way To Control Crankcase Fumes In Internal Combustion Engines

The back-flow pushes the valve down, blocking the route to the crankcase. When the manifold vacuum is high, at

Idling speed or small throttle openings, the valve lifts against spring pressure, inducing the flow of fumes into the manifold.

Conclusion

Please share your experience with us while executing this task for better updating of this post. Use the comment section for your feedback.

Leave a Reply

Your email address will not be published. Required fields are marked *

error: Content is protected !!