Steam Engine Geometry — Definition of Cut-Off Ratio What is the name given to the ratio of the cylinder volume at cut-off to the swept (stroke) volume?

Introduction / Context:
Indicator-diagram analysis uses several geometric ratios. Two important ones are the cut-off ratio and the expansion ratio; confusing them leads to errors in work calculations and valve-gear design assessments.

Given Data / Assumptions:

• Volume at cut-off (when admission ends) is known.
• Swept volume equals piston displacement per stroke.
• Clearance volume is present but handled separately.

Concept / Approach:
The cut-off ratio is defined as V_cutoff / V_swept. The expansion ratio is typically the ratio of the volume at release (or end of expansion) to the volume at cut-off, while the clearance ratio is V_clearance / V_swept. Precise definitions help derive mean effective pressure via idealized cycle relations.

Step-by-Step Solution:
Identify the instant of cut-off → admission valve closes.Compute ratio: r_c = V_cutoff / V_swept.Distinguish from expansion and clearance ratios to avoid mix-ups.

Verification / Alternative check:
Cross-check with indicator diagram annotations; textbooks label r_c accordingly.

Why Other Options Are Wrong:
expansion ratio: relates end-of-expansion to cut-off, not to swept volume directly.clearance ratio: ratio of clearance volume to swept volume.none of these: incorrect because “cut-off ratio” is the established term.

Common Pitfalls:
Using absolute volumes instead of ratios; always normalize to swept volume or to cut-off as defined.

Final Answer:
cut-off ratio