🔍 Key Concepts

• Look closely at the cylinder liner to see if there are any scavenge ports in the cylinder wall (typical of many two-stroke diesels). • Study the valve positions (intake and exhaust) and the piston location relative to top dead center (TDC). • Notice the direction of gas flow through the turbocharger and ask yourself which stroke would produce that flow.

💭 Think About

• If the engine were a two-stroke, what additional openings or air passages would you expect to see besides the valves in the cylinder head? • At the instant shown, is the piston near TDC or BDC, and would you expect the valves to be open or closed at the end of compression versus the end of exhaust (think about valve overlap)? • Which stroke is associated with a strong flow of hot exhaust gas driving the turbine and fresh air entering from the compressor at almost the same time?

✅ Before You Answer

• Verify whether the cylinder wall shows scavenge or exhaust ports; their presence or absence helps decide between two-stroke and four-stroke. • Check exactly which valves are open (intake, exhaust, or both) and whether fuel injection appears to be occurring. • Confirm the piston is very close to top dead center (TDC) and match that with the correct stroke in a four-stroke cycle diagram.