During the valve overlap period, the exhaust pressure of a turbo-charged, four-stroke cycle diesel engine must be less than the intake manifold pressure to ensure __________.
• Valve overlap in a four-stroke diesel (what is happening with both intake and exhaust valves at that moment) • Relationship between intake manifold pressure, exhaust back pressure, and air flow direction • Purpose of a turbo-charger regarding scavenging and cylinder cooling
• During valve overlap, which way do you WANT the fresh air to move, and what pressure condition will cause that to happen? • Which answer choice directly describes what happens inside the cylinder when fresh air pushes out burned gases during overlap? • Which options talk about the turbo‑charger’s pressure behavior in general, and which talk about what happens INSIDE the cylinder at overlap?
• Identify which choice mentions cylinder scavenging (removal of exhaust gases) and cooling inside the cylinder, not just turbo‑charger behavior • Check which options incorrectly focus on constant pressure in the turbo‑charger instead of gas flow through the cylinder during overlap • Confirm that the correct condition (exhaust pressure lower or higher than intake?) will cause fresh air to flow INTO the cylinder and help push exhaust gases OUT
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