🔍 Key Concepts

• On a diesel engine indicator diagram, ignition delay is the crank angle between the start of fuel injection and the point where rapid pressure rise/combustion actually begins. • Look for where the actual pressure curve first departs sharply from the normal compression line – that marks the start of combustion. • The labeled horizontal distances (H, K, G, J) each represent different phases such as compression, injection period, ignition delay, and combustion period.

💭 Think About

• Which lettered distance covers only the short interval from the first injection line to the point where the cylinder pressure starts to rise much more steeply? • Which labeled span does not extend through the entire combustion or expansion process, but is confined to that brief lag just before the big pressure spike? • Compare the lettered intervals that begin near the start-of-injection vertical line and see which one stops right where the pressure curve breaks away from the smooth compression shape.

✅ Before You Answer

• Identify on the diagram which vertical line is the start of fuel injection. • Identify exactly where the pressure trace leaves the smooth compression curve and begins its sharp rise – that’s the start of combustion. • Choose the option whose horizontal arrow begins at start of injection and ends at start of rapid pressure rise, and does not include the full combustion or expansion period.