🔍 Key Concepts

• Diesel engines rely on highly compressed hot air and injected fuel, not a premixed fuel-air charge like gasoline engines • The shape of the piston crown strongly affects airflow motion (swirl/turbulence) in the combustion chamber • Good diesel combustion needs thorough mixing of fuel and air in a very short time

💭 Think About

• Think about what happens in the cylinder just before and during fuel injection—what motion of the air helps the fuel droplets spread and mix? • How would a concave (bowl-shaped) piston head change the path and speed of air moving in the cylinder compared with a flat piston? • Which options describe air motion and mixing, and which focus on afterburning—which is the primary design goal for piston crown shape?

✅ Before You Answer

• Identify which choices talk about air turbulence and fuel mixing versus afterburning effects • Consider whether diesel designers want to increase or decrease air motion near the fuel spray to improve combustion • Ask yourself: in a diesel, is rapid mixing of fuel and air desirable or something to be reduced?