🔍 Key Concepts

• Ignition delay period in a diesel (compression ignition) engine • Effect of cetane number on ignition delay • How air temperature, compression ratio, and droplet size influence how quickly fuel ignites

💭 Think About

• Think about whether higher cetane number makes fuel easier or harder to ignite and how that affects the delay between injection and ignition. • Consider how air charge temperature and compression ratio affect the final temperature and pressure at the end of compression, and how that changes ignition delay. • Ask yourself whether smaller fuel droplets burn faster or slower than larger droplets, and what that does to the time before combustion really starts.

✅ Before You Answer

• Verify which factor tends to make the fuel ignite more quickly (this will shorten ignition delay, not increase it). • Identify which option will lead to a lower temperature at the end of compression, since that usually makes ignition slower (longer delay). • Confirm how cetane number is defined: is a higher cetane number associated with a shorter or longer ignition delay?