Emissions and Crankcase Ventilation What is the primary function of the positive crankcase ventilation (PCV) system on a road vehicle?

Introduction / Context:
Blow-by gases are combustion products that leak past piston rings into the crankcase. If not managed, they contaminate oil, increase pressure, and pollute the atmosphere. The positive crankcase ventilation (PCV) system is a core emissions and engine health feature in modern vehicles.

Given Data / Assumptions:

• Spark-ignition engine with a closed PCV system.
• Intake manifold vacuum available at idle and part load.
• PCV valve or metering orifice controls flow.

Concept / Approach:
The PCV system routes crankcase vapours (unburned hydrocarbons, moisture, blow-by gases) back to the intake stream to be re-burned in the cylinders. This reduces emissions, prevents sludge formation, and maintains crankcase pressure near ambient or slightly negative, improving seal life. A PCV valve meters flow and prevents backfire from igniting vapours in the crankcase.

Step-by-Step Solution:
Identify problem: blow-by accumulates in crankcase.Required action: remove and reburn these gases safely.Mechanism: PCV routes gases to intake under vacuum control.Conclusion: option describing return to intake is correct.

Verification / Alternative check:
Emission regulations require closed crankcase ventilation; service manuals show PCV plumbing from rocker cover to intake.

Why Other Options Are Wrong:
Mixing fuel with air or inducing swirl is the carburetor/throttle-body/port design’s role, not PCV.Routing to exhaust manifold is unsafe and nonstandard.Pressurizing the crankcase is harmful; slight vacuum is preferred.

Common Pitfalls:
Blocked PCV valves cause oil leaks, sludge, and increased emissions.

Final Answer:
returns blow-by gases from the crankcase to the intake system