🔍 Key Concepts

• Four-stroke diesel engine cycle (intake, compression, power, exhaust) • Relationship between air compression and temperature rise in a diesel engine • How diesel ignition differs from gasoline (spark-ignition) engines

💭 Think About

• First, mentally walk through the four strokes of a typical diesel engine and identify what is happening in the cylinder during each stroke. • Ask yourself: at which point do we need very hot, highly compressed air for the fuel to ignite without a spark? • Consider whether fuel should be present while the air is being compressed, or only after the air reaches a very high temperature.

✅ Before You Answer

• Make sure you know which stroke is the compression stroke and what the piston is doing during it. • Confirm that in a diesel engine, fuel is not used to compress the air; only air is compressed first. • Verify that auto‑ignition (self‑ignition) of diesel fuel depends on spraying fuel into already hot, compressed air.