Exam Question
(a) Why exhaust outlet of marine diesel engine turbocharger is lower than inlet temperature? (6)
(b) Why do we need an air cooler and why is the scavenge air temperature maintained at 40°C? (10)
Class 4 (4th Engineer)
MEKM
📅 Jul 2025
Reference Answer
### Part (a): Turbocharger Exhaust Temperature Drop (6 Marks)
The reduction in temperature of the exhaust gas between the turbocharger turbine inlet and its outlet is a direct consequence of the fundamental principles of thermodynamics and energy conversion. The turbine's primary function is to extract energy from the engine's exhaust gas stream and convert it into mechanical work to drive the compressor.
1. **Energy Source**: The exhaust gas from the engine cylinders possesses high thermal and pressure energy, collectively known as high enthalpy. This high-energy gas is directed to the turbine inlet.
2. **Expansion Process**: The gas passes through a nozzle ring within the turbine casing. This causes the gas to accelerate to a high velocity and expand, resulting in a significant drop in both its pressure and temperature. This conversion of pressure and thermal energy into kinetic energy is a key step.
The reduction in temperature of the exhaust gas between the turbocharger turbine inlet and its outlet is a direct consequence of the fundamental principles of thermodynamics and energy conversion. The turbine's primary function is to extract energy from the engine's exhaust gas stream and convert it into mechanical work to drive the compressor.
1. **Energy Source**: The exhaust gas from the engine cylinders possesses high thermal and pressure energy, collectively known as high enthalpy. This high-energy gas is directed to the turbine inlet.
2. **Expansion Process**: The gas passes through a nozzle ring within the turbine casing. This causes the gas to accelerate to a high velocity and expand, resulting in a significant drop in both its pressure and temperature. This conversion of pressure and thermal energy into kinetic energy is a key step.
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