🔍 Key Concepts

• On a pressure-volume (P‑V) diagram, the horizontal axis represents cylinder volume, not time or crank angle. • The compression ratio of a reciprocating engine is the ratio of the total cylinder volume at bottom dead center to the clearance volume at top dead center. • Think about whether the numbers 0–16 on the volume axis must be actual cubic inches/PSI/degrees, or could instead be dimensionless units showing a ratio.

💭 Think About

• First, decide what each axis of this P‑V diagram represents and whether crankshaft degrees or pressure would normally appear on the horizontal or vertical axis. • Ask yourself: if the volume scale runs from 0 to 16 units, what does the point of minimum volume (near A) represent compared to the point of maximum volume (near B)? • Consider which choice depends on an exact numeric value (like cubic inches, PSI, or degrees) and which choice can be shown using a simple, unitless scale from 1 to 16.

✅ Before You Answer

• Verify that on standard P‑V diagrams, pressure is plotted on the vertical axis and volume on the horizontal axis. • Check whether a compression ratio needs specific units (like cubic inches) or is expressed as a pure number (for example, X to 1). • Confirm that crankshaft motion in degrees is normally shown on an indicator diagram of pressure vs. crank angle, not on a pure P‑V diagram.