Question 156Motor Plants - 1st Asst/Chief

The correct answer is D) during the valve overlap period. Clearance volume scavenging in a turbocharged, four-stroke cycle diesel engine is accomplished during the valve overlap period, when both the intake and exhaust valves are open. This allows the fresh air charge from the turbocharger to flow through the cylinder, displacing the exhaust gases and improving the engine's volumetric efficiency. The other options are incorrect because: A) only the exhaust valve open would not allow for scavenging, B) scavenging occurs without cooling the cylinders or pistons, and C) scavenging occurs at a pressure above atmospheric due to the turbocharger.