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THERMODYNAMICS - CASE STUDY

    Introduction


Presentation

 

During Max's presentation of his senior capstone design project, someone asks him about comparisons between spark-ignition (SI) engine and compression-ignition) CI engine.

What is known:

  • The displacement volume of each cylinder is 1.0 L.
  • The crankshaft rotates at 2600 RPM.
  • The clearance volume is 15% of the volume when the piston is at the bottom dead center (BDC).
  • The pressure and temperature of the gas-fuel mixture just before compression are:
    P = 100 kPa and T = 15oC
  • The maximum temperature the engine cylinder can tolerate is T = 1800oC.
     
    Question


 
  • Determine the thermal efficiency and compression ratio using the ideal Otto-cycle model.
  • For the same temperature limits and equal amounts of heat input, which air-standard cycle has a higher thermal efficiency, Otto or Diesel? Which one has the higher compression ratio?
     
    Approach


 

Model the cycle of this engine as an air-standard Otto-cycle and Diesel-cycle, respectively. Calculate their thermal efficiencies and compression ratios.