🔍 Key Concepts

• Diesel combustion timing relative to piston position (before, at, and after top dead center) • Difference between injection period and combustion period • What happens during the expansion (power) stroke after top dead center

💭 Think About

• Think about where most useful work is produced in the cycle: is it before or after top dead center, and what does that imply about how long combustion should last? • Is fuel still burning after the injectors stop spraying? How does that relate to the power developed on the piston? • If combustion continued all the way to bottom dead center, what effect would that have on efficiency, exhaust temperature, and engine stress?

✅ Before You Answer

• Clarify the difference between end of fuel injection and end of combustion—they are not the same moment • Recall that peak cylinder pressure should occur slightly after top dead center, not exactly at TDC • Consider whether a brief, controlled period of burning after top dead center is normal and desirable in diesel operation