🔍 Key Concepts

• Diesel combustion timing and what happens when fuel is injected too late • Relationship between firing pressure, combustion completeness, and exhaust appearance • Typical causes of smoke color and engine knock in diesel engines

💭 Think About

• When fuel is injected late, does the combustion event finish earlier or later in the power stroke, and how does that affect peak (firing) pressure? • Think about what incomplete combustion looks like at the exhaust and whether it tends to raise or lower exhaust temperature. • Which of the options is a classic symptom of unburned or partially burned fuel leaving the cylinder?

✅ Before You Answer

• Identify which choice is most strongly associated with incomplete combustion of diesel fuel. • Consider whether mechanical knock usually goes with very early or very late injection timing. • Match the exhaust condition in the options with late, slow-burning fuel that continues burning as it exits the cylinder.