🔍 Key Concepts
• Compare the constant-pressure and constant-volume parts of each ideal cycle (Otto, Diesel, Gas Turbine/Brayton, Rankine) on a P–V diagram.
• Notice which segments of the diagram are curved (compression/expansion) and which are horizontal or vertical (heat addition/rejection).
• Think about where, in that cycle, point 1 would be if it is the start of compression, and what the next steps in that specific cycle look like.
💭 Think About
• From point 1 to point 2, are you looking at a compression that is mostly a smooth curve (isentropic) or a straight vertical line (constant volume)? Which cycles use which?
• Between points 2 and 3, the line is nearly horizontal (constant pressure). Which of the listed cycles has heat addition at constant pressure on its ideal P–V diagram?
• Does this cycle involve a phase change from liquid to vapor (as in Rankine), or is it a pure gas process throughout (as in Otto, Diesel, or Gas Turbine)?
✅ Before You Answer
• Verify which cycle has both compression and expansion as smooth, nearly adiabatic curves, with heat addition at constant pressure between 2 and 3.
• Eliminate any cycle whose ideal P–V diagram shows heat addition at constant volume (a vertical line) where your figure clearly shows a horizontal line.
• Make sure the cycle you choose is one that is used for a continuous-flow gas engine rather than a reciprocating piston engine with distinct intake and exhaust strokes, if that matches the diagram.