🔍 Key Concepts

• diesel combustion at cold start (ignition delay, incomplete combustion) • effects of fuel injection timing and pressure on knocking • difference between abnormal knock from defects and sounds that change as the engine warms up

💭 Think About

• Think about what physically changes as the engine warms up from cold to normal operating temperature and how that affects combustion noise. • Ask yourself whether a mechanical defect in a single cylinder would typically disappear just because the engine warmed up, or if it would persist. • Consider how retarded vs. advanced injection timing and high injection pressure usually affect when and how the fuel burns in relation to top dead center and noise produced.

✅ Before You Answer

• Verify whether cold diesel engines commonly sound different (louder/knockier) at low speed right after start compared to when warmed up. • Check if a true mechanical defect in one cylinder would usually remain present at all temperatures and speeds. • Consider whether changes in fuel injection characteristics alone would stop the knock only as the engine reaches normal operating temperature, or if this behavior is expected under normal conditions.