• Turbocharger Boost Characteristics at Engine Idle:
• Operating Principle: A turbocharger compressor is driven exclusively by the enthalpy and mass flow rate of engine exhaust gases passing across the exhaust turbine wheel.
• Ineffectiveness at Idle:
• At engine idling conditions, fuel delivery is minimal, resulting in very low exhaust gas mass flow rate, pressure, and temperature.
• Consequently, the turbine cannot generate sufficient power to spool up the compressor wheel above its threshold speed, producing zero boost pressure.
• As engine speed and load increase, exhaust enthalpy rises sharply, enabling the turbocharger to deliver positive boost.
• Conclusion: Idling (Option 4).

Correct option: (4) Idling