🔍 Key Concepts

• four-stroke diesel cycle: intake, compression, power, exhaust • purpose of scavenging in diesel engines (removing exhaust, filling with fresh air) • when valve overlap occurs between exhaust and intake valves

💭 Think About

• First, list the four strokes in order and briefly note what happens in each one. At which point would it make sense to be pushing out burned gases while bringing in fresh air? • Think about valve timing: during which parts of the cycle are both the intake and exhaust valves slightly open at the same time? • Ask yourself: does scavenging happen only during one stroke, or during a brief period that bridges two strokes?

✅ Before You Answer

• Be clear on the definitions of intake, compression, power, exhaust strokes in a four-stroke engine. • Verify that scavenging involves both clearing exhaust gases and admitting fresh charge, not fuel injection. • Check which option describes an interval that spans the overlap between exhaust and intake events.