🔍 Key Concepts

• ignition lag in diesel engines (time between start of injection and start of combustion) • how fuel accumulation in the cylinder affects rate of pressure rise and knocking • difference between short vs long ignition delay and their effect on smoothness vs knocking

💭 Think About

• Think about what happens if fuel is injected but does not ignite immediately—what builds up in the cylinder, and what happens when it finally does ignite? • Which option(s) describe a condition where a large amount of fuel is ready to burn all at once, causing a rapid pressure rise? • How would shortening the ignition delay vs lengthening it change the violence (or smoothness) of combustion?

✅ Before You Answer

• Make sure you understand that ignition lag/ignition delay is a time interval, not a fuel quantity. • Check which choice(s) increase the amount of fuel present before combustion actually starts—this strongly relates to knocking. • Verify that reduced ignition lag would tend to make combustion more immediate and controlled, not delayed and explosive.