A loop-scavenged engine utilizes the motion of its pistons and a turbocharger to provide scavenging air. Which of the listed mechanical designs prevents the air under the pistons from being pumped back through the scavenge ports during the piston power stroke?
• Loop scavenging in two-stroke diesels and how air flows around the piston and ports • What happens to the air trapped under the piston during the power stroke • Which component acts like a seal or barrier to stop reverse flow through scavenge ports
• Visualize the piston at bottom dead center: where is the scavenging air, and what path could it take back out when the piston moves up? • For each option, ask yourself: does this feature directly stop air below the piston from flowing back through the scavenge ports, or is it for a different purpose (timing, direction of flow, or supply pressure)? • Think about which component physically separates the crankcase air space from the scavenge ports as the piston travels upward on the power stroke.
• Identify which option actually creates a mechanical sealing effect between the crankcase and scavenge space during the stroke • Distinguish between features that shape/aim the flow (port masking, port angle) versus those that block reverse flow • Confirm which choice is located at the lower end of the cylinder/piston area where crankcase air could otherwise escape back through the ports
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