Four Stroke SI and CI engines

Four Stroke SI and CI engines

1. I.C. Engines 4 Stroke Petrol & Diesel Engines 1 Dr. S. VIJAYA BHASKAR Professor in Mechanical Engineering Sreenidhi Institute of Science & Technology, Hyderabad

2. Working Principle of IC Engines NOT TALKING ABOUT 2 OR 4 STROKE OR PETROL OR DIESEL ENGINE JUST WORKING OF ANY IC ENGINE TWO stroke engine rotates only 360  or ONE revolution of crank shaft rotation FOUR stroke cycle completed through 720  of crank rotation or TWO revolution of crank shaft rotation

3. Working Principle of IC Engines All IC Engine must have the following FOUR EVENTS in the same order Suction Compression Expansion / Power and Exhaust

4. Spark plug Inlet valve/Port Exhaust valve/ Port Cylinder Piston Fuel Injector

5. Inlet valve/Port opens SUCTION STROKE Exhaust valve/Port Closed

6. Piston down INTAKE STROKE Inlet valve/Port opens Exhaust valve/Port Closed

7. Inlet valve / Port open Piston down INDUCTION STROKE Air/Fuel Mixture In Air ONLY In Exhaust valve/Port Closed

8. Inlet valve/Port closes COMPRESSION STROKE Piston up Exhaust valve/Port Closed

9. Inlet valve/Port closed COMPRESSION STROKE Piston up Exhaust valve/Port Closed

10. POWER STROKE FIRING Inlet valve/Port closed Exhaust valve/Port Closed

11. POWER STROKE Piston down powerfully Inlet valve/Port closed

12. Inlet valve/Port closed POWER STROKE Piston down powerfully

13. Inlet valve/Port closed POWER STROKE Exhaust valve/Port Closed

14. Inlet valve/Port closed EXHAUST STROKE Exhaust valve/Port opens

15. EXHAUST STROKE Exhaust valve/Port opens Piston up Exhaust gases out Inlet valve/Port closed

16. EXHAUST STROKE Exhaust valve/Port opens Piston up Exhaust gases out Inlet valve/Port closed

17. Inlet valve/Port opens INDUCTION STROKE Exhaust valve/Port Closed

18. 4-Stroke Spark Ignition (SI) Engine 18

19. Inlet valve opens S UCTION STROKE Four-stroke SI Engine

20. Inlet valve open Piston down SUCTION STROKE Four-stroke SI Engine

21. Inlet valve open Piston down INDUCTION STROKE Four-stroke SI Engine Air/Fuel Mixture In

22. Inlet valve closes COMPRESSION STROKE Four-stroke SI Engine Piston up

23. Inlet valve closed COMPRESSION STROKE Four-stroke SI Engine Piston up

24. Inlet valve closed POWER STROKE Four-stroke SI Engine Combustion

25. Inlet valve closed POWER STROKE Four-stroke SI Engine Piston down powerfully

26. Inlet valve closed POWER STROKE Four-stroke SI Engine Piston down powerfully

27. Inlet valve closed POWER STROKE F our-stroke engine

28. Inlet valve closed EXHAUST STROKE F our-stroke engine Exhaust valve open

29. Inlet valve closed EXHAUST STROKE Four-stroke SI Engine Exhaust valve open Piston up Exhaust gases out

30. Inlet valve closed EXHAUST STROKE Four-stroke SI Engine Exhaust valve open Piston up Exhaust gases out

31. Inlet valve opens INDUCTION STROKE Four-stroke SI Engine Exhaust valve closed

32. Operation of 4-Stroke Petrol Engine 34 INLET   EXHAUST

33. 4-Stroke Petrol Engine 35

34. 4-stroke petrol engine

35. 4-S Petrol Engine 37 Works on Otto Cycle

36. Power Cycle : Ott o cyc l e The air standard Otto Cycle is an ideal cycle that approximates a spark- ig nitio n internal co m bustio n engine. I t as s ume s t h at t h e heat add i tion occurs instantaneous l y while t h e pisto n is a t T D C.

37. Process ( 1 - 2 ) Is ent r opi c Comp r ession Compressio n fr o m ν 1 to v 2 ↓ B DC( β = 1 8 º ) ↓ TDC ( θ= º ) ( 2 - 3 ) Constan t V olum e H ea t Addition : Q H • While a t TDC • Ignition o f fuel (che m ica l reaction take s place) ( 3 - 4 ) Isen t ropic E x pansion • Power i s del i ver e d wh i l e s = cons t . ( 4 - 1 ) Constan t v olum e H ea t R e j ec tio n pro c ess Otto Cycle

38. Otto Cycle

39. Process 1–2 is an isentropic compression of the air as the piston moves from bottom dead center to top dead center. Process 2–3 is a constant-volume heat transfer to the air from an external source while the piston is at top dead center. This process is intended to represent the ignition of the fuel–air mixture and the subsequent rapid burning. Process 3–4 is an isentropic expansion (power stroke). Process 4–1 completes the cycle by a constant-volume process in which heat is rejected from the air while the piston is at bottom dead center.

40. 4-S Petrol Engine- Otto Cycle 42

41. THEORETICAL VALVE TIMING DIAGRAM FOR FOUR STROKE ENGINE 43

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44. Typical Theoretical P-V an d Valv e Timing Diagram s of a Four-Stroke Spark Ignition Engine 46 Observations:  P-V diagram show s shar p edges i.e., valves open/close instant a neously a t dead centres

45. Actual Case: Inlet Valve (IV) an d Exhaust Valve ( EV ) open/close before an d afte r dead centres Mechanical Factor Dynami c Facto r o f Ga s Flow Valve s are opened an d close d by cam mecha n ism Valve s wil l bounc e o n its sea t i f close d abruptly Opening/closing of valves spread over a certain cran k angle Every Corner in the P-V diagram is ROUNDED 47

46. Suction or Intake Stroke Suction stroke starts when piston is at top dead center and about to move downwards. The inlet valve is open at this time and the exhaust valve is closed. Due to the suction created by the motion of the piston towards the bottom dead center, the charge consisting of fuel air mixture is drawn into the cylinder. When the piston reaches the bottom dead center the suction stroke ends and the inlet valve closes. 4-Stroke Spark Ignition (SI) Engine Detailed Notes

47. Compression Stroke The charge taken into the cylinder during the suction stroke is compressed by the return stroke of the piston. During this stroke both inlet and exhaust valves are in closed position. The mixture which fills the entire cylinder volume is now compressed into the clearance volume. At the end of the compression stroke the mixture is ignited with the help of a spark plug located on the cylinder head. During the burning process the chemical energy of the fuel is converted into heat energy. The pressure at the end of the combustion process is considerably increased due to heat from the fuel.

48. Expansion or Power Stroke The high pressure of the burnt gases forces the piston towards the BDC, both the valves are in closed position. Of the four strokes only during this stroke power is produced. Both pressure and temperature decrease during expansion.

49. Exhaust Stroke At the end of the expansion stroke the exhaust valve opens and the inlet valve remains closed. The pressure falls to atmospheric level a part of the burnt gases escape. The piston starts moving from the bottom dead center to top dead center and sweeps the burnt gases out from the cylinder almost at atmospheric pressure. The exhaust valve closes when the piston reaches TDC.

50. Four Stroke Diesel / CI Engine Diesel Engine was invented by Rudolph Diesel . It is ignited by compression of charge, so it’s also called as compression ignition (CI) engine. It is similar to four stroke petrol engine but operates at a much higher compression ratio. The compression ratio of an SI engine is between 6 and 10:1 while for a CI engine it is from 16 to 20:1 . A high pressure fuel injector is used to inject the fuel into the combustion chamber.

51. Suction / Intake Stroke Suction stroke starts when piston is at top dead center and about to move downwards. The inlet valve is open at this time and the exhaust valve is closed. Due to the suction created by the motion of the piston towards the BDC, Air alone is inducted during the suction stroke.

52. Compression Stroke Air inducted during the suction stroke is compressed into the clearance volume due to return stroke of piston. Both valves remain closed during this stroke. The air in the combustion chamber is at high temperature and high pressure with a decrease in volume. Both Valves Closed

53. Expansion Stroke or Power Stroke At the end of compression stroke, the fuel is injected into the cylinder in the form of fine spray through the nozzle and is ignited by the temperature of hot compressed air in the chamber. So that combustion process is started at the end of compression stroke . The combustion of gases expands inside the cylinder so that piston start to move towards BDC. Both the valves remain closed during this stroke Both Valves Closed

54. Piston Crown 56

55. Exhaust Stroke The piston traveling from BDC to TDC pushes out the product of combustion. The exhaust valve is open and the intake valve is closed during this stroke.

56. 4-Stroke Diesel Engine 58

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58. S No Four Stroke Engine Two Stroke Engine 1. The thermodynamic cycle is completed in four strokes of the piston or in two revolutions of crank shaft or 720 ° of crank angle. The thermodynamic cycle is completed in two strokes of the piston or in one revolution of the crank shaft or 360 of crank angle 2. One power stroke is obtained in every two revolution of crank shaft / 4- strokes of the Piston. One power stroke is obtained in each revolution of crank shaft. 3. Because of above, turning moment is not so uniform and hence a heavier flywheel is needed. Because of above, turning moment is more uniform and hence a lighter flywheel can be used. 4. Power produced for same size of engine is less. In order to produce same power the engine is heavier and bulkier. Power produced for same size of engine is twice, or for same power the engine is lighter and more compact .

59. S.No Four Stroke Engine Two Stroke Engine 5. Lesser cooling and lubrication requirements. Lower rate of wear and tear. Greater cooling and lubrication requirements. Higher rate of wear and tear. 6. It has valves and valve actuating mechanisms for opening and closing of the intake and exhaust valves. It has no valves but only ports 7. Because of comparatively higher weight and complicated valve mechanism, the initial cost of the engine is more. Because of light weight and simplicity due to the absence of valve actuating mechanism, initial cost of the engine is less. 8. Volumetric efficiency is more due to more time for induction . Volumetric efficiency is low due to lesser time for induction. 9. Thermal efficiency is higher, part load efficiency is better. Thermal efficiency is lower, part load efficiency is poor. 10. Application : Cars, Buses, Trucks, Tractors, Aero planes and Power generation etc., Application : Mopeds, Scooters, Motorcycles, Hand sprayers etc.,