🔍 Key Concepts

• Scavenging in a two-stroke engine starts when the scavenge ports are first uncovered by the piston and air begins to flow into the cylinder. • Note how the crank position changes from Fig. 1 through Fig. 6 and what that means for the piston’s vertical position. • Look closely at the arrows and labels that show air direction into and out of the cylinder (scavenge air vs. exhaust gas).

💭 Think About

• In which two consecutive figures do you first see fresh air being admitted through the scavenge ports into the cylinder while the piston has moved low enough to uncover those ports? • Compare the piston position at the bottom of the stroke through each figure: when is the piston just above the ports, when are they fully open, and when do they start to close again? • Which pair of figures shows the transition from no scavenging flow to the start of scavenging flow (not peak scavenging and not compression)?

✅ Before You Answer

• Identify exactly where the scavenge ports are drawn in the liner and watch when the piston crown passes them as the crank rotates. • Confirm in which figure you first see arrows indicating incoming scavenge air into the cylinder, not just exhaust flow out. • Make sure the chosen figures are consecutive (e.g., 2–3, 3–4, etc.) and represent the beginning of the scavenging period, not the middle or the end.