🔍 Key Concepts

• diesel combustion timing and how it affects pressure and temperature • relationship between late fuel injection and incomplete combustion (smoke color and quality) • what typically causes mechanical knock in a diesel cylinder

💭 Think About

• Think about what happens to cylinder pressure and temperature if the fuel injection occurs later than it should in the power stroke. • Which of the listed choices would most directly result from fuel burning later and more slowly, producing black or gray smoke? • Ask yourself: is mechanical knock more often associated with fuel igniting too early (advanced timing) or too late (retarded timing)?

✅ Before You Answer

• Identify whether late injection tends to raise or lower peak firing pressure. • Decide if exhaust temperature would logically be higher or lower when combustion is delayed and incomplete. • Match the symptom of black/gray smoke to the condition that best indicates incomplete combustion rather than low compression only.