Lecture Notes on Turbocharged Car Engine Operation

Summary

This lecture covers the working principles of a turbocharged car engine. It explains the mechanisms that allow a turbocharger to increase the power output of an engine by using exhaust gases to compress the air intake, including the components involved in the process like the turbine wheel, compressor wheel, and intercooler.

Detailed Points

Basics of Engine Air Intake

• Normal Aspiration: Air enters the engine under atmospheric pressure when pistons move to increase chamber volume.
• Turbocharging: Utilizes a compressor to force more air, and consequently more oxygen, into the engine leading to increased power output.

Turbocharging Components

1. Compressor: Houses an impeller (compressor wheel) that, when rotated, compresses incoming air and directs it into the engine.
   • Air particles are forced to the perimeter of the impeller and exit through the volute into the engine.
2. Rotation Transfer:
   • Mechanical Drive: Uses belt drive connecting engine shaft and compressor shaft.
   • Turbocharging: Uses exhaust gases to turn a turbine wheel connected to the compressor.

Turbine Operation

• Positioned in the exhaust flow, the turbine utilizes exhaust gas velocity to rotate.
• The turbine wheel rotation is transferred to the compressor wheel, thereby compressing the intake air.

Full Turbocharged Engine Cycle

1. Cylinder fills with a mixture of fuel and air.
2. Mixture ignites at high compression, moves the piston, which rotates the crankshaft.
3. Exhausted gases exit the cylinder, pass through the turbine, causing it to spin.
4. Spinning turbine powers the compressor wheel which compresses and feeds air back into the engine’s cylinders.

Thermal Dynamics and Efficiency

• Exhaust gases and compressed air generate significant heat.
• Intercooler: A critical component utilized as a heat exchanger to cool down the compressed air before it enters the engine.
  • Types: Air-to-air and air-to-water.

Economic and Environmental Impact

• Manufacturing and operation of turbochargers are initially costly.
• Increased backpressure in exhaust lines could be a downside.
• Despite costs, the power efficiency gains make turbochargers beneficial, particularly for high-power engines. Recently, they are also used in low-power engines to enhance economy and environmental friendliness.

This detailed overview reveals how turbocharged engines optimize power and efficiency through advanced engineering principles, balancing benefits against increased complexity and costs.