Compression ratio sensitivity — effect of increasing clearance volume in I.C. engines If the clearance volume of an internal combustion engine is increased (with other factors constant), how is the compression ratio affected?

Introduction / Context:
Compression ratio strongly influences efficiency, power, and knock tendency. Understanding the geometric definition reveals how design changes alter this critical parameter.

Given Data / Assumptions:

• Swept volume Vs fixed.
• Clearance volume Vc is changed by head gasket thickness, piston crown shape, or combustion chamber design.
• Definition of compression ratio: r = (Vs + Vc) / Vc.

Concept / Approach:
From the definition, increasing Vc (denominator and part of numerator) reduces the ratio because Vc grows faster relative to the total volume at bottom dead center.

Step-by-Step Solution:
Let r = (Vs + Vc) / Vc.If Vc increases while Vs remains constant, the denominator increases.Therefore, r decreases.

Verification / Alternative check:
Numerical example: Vs = 500 cm^3, Vc = 50 cm^3 → r = (500 + 50)/50 = 11.Increase Vc to 60 cm^3 → r = 560/60 ≈ 9.33, which is lower.

Why Other Options Are Wrong:

• Increase or be doubled: contradicts the formula.
• Remain constant: impossible if Vc changes and Vs is fixed.

Common Pitfalls:
Confusing clearance volume with swept volume; only Vc change here affects the ratio inversely.

Final Answer:
decrease