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i c engines efficiencies


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in this presentation , the different engine inefficiencies has been discussed including all sort of friction losses which affects the brake power of the engine. It includes volumetric efficiency, thermal efficiency, IMEP, BMEP, brake power etc.

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i c engines efficiencies

  1. 1. ENGINE EFFICIENCIES Prof. (Dr.) M P Poonia Director NITTTR, Chandigarh
  2. 2. Revision
  3. 3. 1. Indicated and Brake Mean Effective Pressure 2. Indicated Power, IP 3. Brake Power, BP 4. Mechanical Efficiency 5. Friction Power 6. Indicated Thermal Efficiency 7 Brake Thermal Efficiency Performance Parameters
  4. 4. 8. Specific Fuel Consumption 9. 10 Heat Balance 11. Fuel Air-Ratio 12. Equivalence Ratio Performance Parameters Volumetric Efficiency
  5. 5. IDEAL P-V Diagram Average IMEP 4-12 bar
  6. 6. Actual P-V Diagram PMEP = IMEP (g) AREA 1 AREA2 IMEP (n)= AREA1-AREA2 BMEP= IMEP (n)-FMEP
  7. 7. Metric Horse Power 1 hp= 735.5 W
  8. 8. The indicated power is the power actually developed by the engine cylinder. INDICATED POWER (IP)
  9. 9. The indicated power is the power actually developed by the engine cylinder. IP= 𝑷 𝒎 ×𝑳×𝑨×𝑵 𝟏𝟐𝟎 Where IP= Indicated Power, W Pm= Mean Effective Pressure N/m2 L = Stroke Length , m A = Piston Top Area , m2 N = Engine RPM
  10. 10. BRAKE POWER : The brake power is the power available at the crankshaft of the engine. Indicated Power BP
  11. 11. BRAKE POWER (BP) ɳm= 𝑩𝑷 𝑰𝑷 BP= ɳm× IP = ɳm×𝑷 𝒎 ×𝑳×𝑨×𝑵 𝟏𝟐𝟎 = BMEP×𝑳×𝑨×𝑵 𝟏𝟐𝟎 BP= 𝟐𝝿𝑵𝑻 𝟔𝟎 Where: T=Torque in N-m N= Rotational Speed in Minutes BP=Brake Power in watt
  12. 12. BRAKE POWER (BP)
  13. 13. Mechanical Efficiency
  14. 14. Mechanical Efficiency (i)
  15. 15. Mechanical Efficiency
  16. 16. Friction Losses 1.Crank Shaft Bearing
  17. 17. Friction Losses 2. Connecting Rod Bearing
  18. 18. Friction Losses 3. Cylinder Piston Assembly
  19. 19. Friction Losses 4. Piston Rings
  20. 20. Friction Losses 5. Valve Train
  21. 21. Friction Losses 5. Oil Pump
  22. 22. Friction Losses 6. Water Pump
  23. 23. Friction Losses 7. Generator and Starter Motor
  24. 24. S I Engine Friction
  25. 25. Friction Power
  26. 26. Thermal Efficiency
  27. 27. Typically Gasoline Engines will have an sfc of about 0.3kg/kW-h Specific Fuel Consumption(SFC)
  28. 28. Volumetric Efficiency • Volumetric efficiency is a comparison of the actual volume of air–fuel mixture drawn into an engine to the theoretical maximum volume that could be drawn in. • Volumetric efficiency is expressed as a percentage
  29. 29. Volumetric Efficiency
  30. 30. Heat Balance
  31. 31. Heat Balance
  32. 32. Air Fuel Ratio
  33. 33. Air Fuel Ratio
  34. 34. Air Fuel Ratio Rich mixture - more fuel than necessary (AF) mixture < (AF)stoich Lean mixture - more air than necessary (AF) mixture > (AF)stoich
  35. 35. Air Fuel Ratio
  36. 36. It shows the deviation of an actual mixture from stoichiometric conditions. Equivalence Ratio (ɸ) actual stoich stoich actual AF AF FA FA )( )( )( )( 
  37. 37. The ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston is called a) mechanical efficiency b) overall efficiency c) relative efficiency d) volumetric efficiency Answer: d FAQ
  38. 38. FAQ Explanation: Volumetric efficiency is the ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston while mechanical efficiency is the ratio of the brake power to the indicated power and relative efficiency is the ratio of the indicated thermal efficiency to the air standard efficiency whereas overall efficiency is the ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time.
  39. 39. Which one of the following event would reduce volumetric efficiency of an engine? a) Inlet valve closing after bdc b) inlet valve closing before bdc c) inlet valve opening before tdc d) exhaust valve closing after tdc Answer: b Explanation: Volumetric efficiency of an engine is reduced by closing inlet valve before bdc. FAQ
  40. 40. Thanks