Engine geometry definitions: The ratio of the clearance volume to the swept (displacement) volume in a reciprocating engine cylinder is called the ________.

Introduction / Context:
Accurate use of cylinder volume ratios is fundamental to cycle analysis (Otto, Diesel, Dual) and to real-engine performance. Misnaming these ratios leads to errors in efficiency and pressure calculations.

Given Data / Assumptions:

• Clearance volume V_c: volume remaining when piston is at top dead centre (TDC).
• Swept volume V_s: volume displaced by the piston between TDC and BDC.
• Engine can be I.C. or steam; geometric definitions remain the same.

Concept / Approach:
The clearance ratio is defined as V_c / V_s. Compression ratio r (for I.C. engines) is (V_c + V_s) / V_c. Expansion ratio and cut-off ratio are distinct thermodynamic parameters used in cycle modeling and depend on specific states, not just fixed geometry.

Step-by-Step Solution:
Write the required ratio: clearance volume to swept volume = V_c / V_s.Match to terminology: “clearance ratio”.Exclude distractors: “compression ratio” involves total volume at BDC; “cut-off ratio” relates to Diesel heat-addition; “expansion ratio” relates to volumes during expansion.Conclude with correct term: clearance ratio.

Verification / Alternative check:
Check units: ratio is dimensionless as required for a pure geometry descriptor.

Why Other Options Are Wrong:
Cut-off ratio: uses volumes at cut-off and at start of constant-pressure heat addition, not V_c / V_s.

Expansion ratio: uses instantaneous volumes during expansion, not fixed geometry.

Compression ratio: equals (V_s + V_c)/V_c, the inverse-augmented form.

None of these: incorrect because “clearance ratio” exists and matches.

Common Pitfalls:
Confusing clearance and compression ratios; overlooking that only V_c / V_s uses purely geometric constants.

Final Answer:
clearance ratio