Definition in I.C. engines: scavenging In reciprocating internal combustion engines, what is the process called by which the burnt gases are removed from the cylinder at the end of the power stroke and during the exhaust stroke?

Introduction / Context:
Exhaust gas displacement is essential for the next fresh charge to enter and for maintaining volumetric efficiency. The term used for actively clearing residual combustion products from the cylinder is standard in both two-stroke and four-stroke engine discussions.

Given Data / Assumptions:

• Cylinder has just completed the power stroke.
• Exhaust valve opens (four-stroke) or ports uncover (two-stroke).
• Fresh charge may assist in displacing residuals (especially in two-stroke).

Concept / Approach:

Scavenging denotes the organized removal of spent gases from the cylinder so that the incoming mixture or air can occupy the cylinder for the next cycle. Effective scavenging reduces residual fraction, improves combustion stability, and enhances performance. In two-stroke engines, dedicated scavenging flows (cross-flow, loop, or uniflow) are designed. In four-stroke engines, exhaust blowdown plus piston-driven displacement and valve overlap accomplish the task.

Step-by-Step Solution:

Verification / Alternative check:

Textbook valve-timing diagrams include overlap specifically to aid scavenging by using pressure differentials to draw in fresh charge and push out residuals.

Why Other Options Are Wrong:

Detonation is abnormal combustion; supercharging increases intake pressure; polymerisation is a chemical process unrelated to cycle gas exchange; after-treatment refers to exhaust emission control devices outside the cylinder.

Common Pitfalls:

Equating scavenging only with two-stroke engines; while more critical there, four-stroke engines also benefit from effective scavenging via valve overlap and exhaust tuning.

Final Answer:

scavenging