🔍 Key Concepts

• Two-stroke diesel cycle timing – when the exhaust valve opens vs when the scavenging ports are uncovered. • How a polar timing diagram usually assigns different concentric circles to different parts (fuel valve, exhaust valve, scavenging ports). • Difference between exhaust blowdown (pressure loss) and supercharging (pressure boost from scavenging air) in the cylinder pressure curve.

💭 Think About

• Look at the crank angle where section III occurs: is it before or after the scavenging ports (IV) are uncovered? Would a pressure boost or a pressure drop be more likely at that point in the cycle? • On a uniflow two-stroke, which happens first after the power stroke: the exhaust valve opening or the scavenging ports opening? Match that sequence to II and IV on the diagram. • Compare the radial position of II and IV: which ring would more logically represent the exhaust valve in the cylinder head, and which would represent the scavenge ports in the liner near BDC?

✅ Before You Answer

• Verify which event (exhaust valve opening or scavenge port uncovering) starts earlier in crank angle after the power stroke – that must match the segment that begins first on the diagram. • Confirm whether III is drawn during the initial part of exhaust opening before scavenging begins, or during the period when scavenge air is flowing – that tells you whether it is a pressure loss or a supercharging effect. • Make sure your final choice has the sequence: exhaust opening → blowdown or pressure change → scavenge ports opening, in the correct order shown on the diagram.