Main Engine Turbocharger: Function, Cooling, and Lubrication
(a) Function of a Main Engine Turbocharger:
A turbocharger is a device used in internal combustion engines to increase power output and efficiency. It utilizes the exhaust gas flow from the engine to drive a turbine which, in turn, drives a compressor. Here’s a breakdown of its operation:
- Exhaust Gas Drives Turbine: Hot exhaust gases from the engine cylinders flow through the turbine housing, pushing the turbine blades and causing the turbine shaft to spin.
- Compressor Boosts Intake Air: Connected to the same shaft as the turbine, the compressor wheel draws in fresh air from the engine’s intake system. As the compressor wheel spins, it compresses this air, increasing its pressure.
- Denser Air for More Power: The compressed, denser air from the compressor is then delivered (often after being cooled by a charge air cooler) to the engine’s intake manifold. This denser air allows for a larger and more efficient fuel burn, resulting in increased engine power output.
(b) Turbocharger Cooling:
Turbochargers operate at high temperatures due to the hot exhaust gas flowing through the turbine section. To prevent overheating and ensure proper operation, turbochargers require efficient cooling:
- Oil Cooling: The primary cooling method for most turbochargers involves engine oil. Engine oil continuously circulates through passages within the turbocharger housing, absorbing heat from the turbine housing and bearing areas. The hot oil then returns to the engine’s lubrication system where it’s cooled by the engine oil cooler.
- Indirect Air Cooling: In some cases, especially for larger turbochargers, additional cooling fins might be present on the turbine housing to promote some heat dissipation directly to the surrounding air. However, oil circulation remains the primary cooling method.
(c) Turbocharger Lubrication:
The high-speed rotation of the turbocharger shaft requires proper lubrication to minimize friction and wear. Here’s how lubrication is achieved:
- Engine Oil Supply: The same engine oil used for cooling also provides lubrication. The pressurized oil from the engine’s lubrication system reaches the turbocharger through dedicated channels.
- Bearing Lubrication: Oil passages within the turbocharger housing deliver oil to the bearings that support the turbine shaft and compressor shaft. This ensures smooth and efficient rotation of the shaft.
- Oil Return: Used oil from the turbocharger bearings drains back to the engine’s crankcase through a return line, where it re-enters the lubrication system for filtration and further cooling.
Maintaining a healthy engine oil system with clean oil and proper oil pressure is crucial for optimal turbocharger lubrication and cooling.