🔍 Key Concepts

• Review how a four-stroke diesel indicator (P–V) diagram is labeled: compression, combustion, expansion (power), and exhaust events. • Focus on what happens in the cylinder right when the exhaust valve first opens at the end of the power stroke. • On a P–V diagram, note what it means when the curve moves mostly vertically vs. mostly horizontally between two points.

💭 Think About

• From c to e, what stroke is taking place and is the piston moving up or down? Use that to identify the general part of the cycle at point e. • When the exhaust valve opens near the end of the power stroke, what happens to cylinder pressure and volume at that instant—does the piston move much, or does the gas escape first? • Look closely at the line segment between e and f: does pressure go up or down, and does volume change a lot or stay nearly the same?

✅ Before You Answer

• Confirm from the diagram whether the pressure between e and f is increasing or decreasing. • Check whether the horizontal axis (volume) changes significantly between e and f, or remains nearly constant. • Match that pressure/volume behavior to the correct named event in a four-stroke diesel cycle (intake, compression, exhaust blowdown, valve closing, etc.).