🔍 Key Concepts

• Cetane number and what it indicates about diesel fuel ignition quality • Effect of a longer ignition delay on how much fuel accumulates before combustion starts • How ignition delay influences pressure and temperature during the power stroke

💭 Think About

• Think about what happens inside the cylinder if fuel keeps being injected but does not ignite immediately. When it finally ignites, what is different compared to normal timing? • Would a longer delay tend to increase or decrease the amount of fuel present at the moment of ignition? How would that affect pressure? • Consider which options would logically follow from a larger, quicker release of heat energy versus a slower, more gradual burn.

✅ Before You Answer

• Verify what low cetane means in terms of ignition delay (shorter vs. longer). • Decide whether more or less fuel is present in the cylinder at the instant of ignition when the delay is longer. • Consider which option is most consistent with a rapid pressure rise versus a gentler, prolonged combustion.