🔍 Key Concepts

• Study the crank angle coverage of the diagram (from TDC back to TDC) and decide whether it represents one revolution (360°) or two revolutions (720°) for a full operating cycle. • Look at the arcs showing intake and exhaust valve open periods and focus on whether there is valve overlap around TDC and how long the valves stay open. • Consider how turbocharged diesel engines typically use longer valve overlap and scavenging compared to naturally aspirated engines, and how that would appear on a timing diagram.

💭 Think About

• From the diagram, how many distinct strokes (intake, compression, power, exhaust) can you identify between one TDC and the next? What does that tell you about 2‑stroke vs 4‑stroke? • Compare the size and position of the intake and exhaust arcs: do they suggest forced scavenging with overlap, or shorter, more separated events more typical of naturally aspirated engines? • Look closely at where fuel injection begins relative to TDC—does this pattern better match common 2‑stroke marine diesels or 4‑stroke high‑speed OSV propulsion diesels?

✅ Before You Answer

• Confirm whether the full cycle in the diagram is completed in 360° or 720° of crankshaft rotation—this is the key to distinguishing 2‑stroke vs 4‑stroke. • Check for significant valve overlap around TDC; extended overlap is a strong indicator of turbocharged rather than naturally aspirated operation. • Verify which colored arc represents fuel injection and ensure its timing (start and duration) is consistent with the stroke type you’ve decided on.