Chapter 9

1. Chapter 9 Automotive Engine Designs and Diagnosis

2. Introduction to Engines • All gas and diesel engines are internal combustion engines • Largest part is the cylinder block • The cylinder head sits on top of the block • Engines are constructed from iron, aluminum, magnesium, and plastics

5. Engine Classifications • Operational cycles • Number of cylinders • Cylinder arrangement • Ignition type • Cooling system • Fuel type • Valve train type – OHV, OHC, DOHC

6. Overhead Valve

7. Overhead Cam OHC Valvetrain DOHC Valvetrain

8. Four-Stroke Cycles • Intake Stroke • The piston moves down and the intake valve opens to draw air and fuel into the cylinder • Compression Stroke • The piston moves up with both valves closed to compress the mixture

9. Four-Stroke Cycles (Cont.) • Power Stroke • With both valves still closed, the mixture is ignited, and the expansion pushes the piston back down • Exhaust Stroke • The piston moves up and pushes the spent gasses out the open exhaust valve

10. Firing Order • The sequence in which the cylinders are ignited • Also indicates position of the pistons when a cylinder is firing • For a four-cylinder firing order of 1342 • #1 is at TDC compression • #3 is at BDC intake • #4 is at TDC exhaust • #2 is at BDC power

11. Firing Order Examples

12. Knowledge Check • Explain what takes place during the four strokes of a gasoline engine.

13. Two-Stroke Gasoline Engines • Produce power every two strokes instead of every four • Not as fuel efficient as four-cycle • Emits more pollution than a four-cycle • Oil for lubrication is mixed with the fuel

14. Engine Rotation • Rotation standard set by SAE • Most engines rotate counterclockwise as seen from the rear or flywheel side

15. Combustion • Many factors affect combustion • Incomplete combustion causes the engine to run poorly • Starts at the spark plug gap • Should move steadily across the air/fuel mixture • The rapidly expanding gases force the piston down

16. Engine Configurations • Inline • V-type • Slant • Boxer or opposed

17. Engine Measurementand Performance • Bore and stroke • Displacement • Compression ratio • Engine efficiency • Torque vs. Horsepower

18. Bore and Stroke

19. Displacement

20. Compression Ratio

21. Knowledge Check • How does compression ratio affect an engine’s performance?

22. Engine Volumetric Efficiency

23. Engine Thermal Efficiency

24. Engine Mechanical Efficiency

25. Torque vs. Horsepower

26. Hybrid Vehicle Engines • Many hybrid electric vehicles (HEVs) use specially modified gasoline engines for improved fuel economy • Atkinson cycle engines • Miller cycle engine

27. Atkinson Cycle • Holds the intake valve open longer - during the time compression is taking place • The open intake valve allows some of the mixture to escape back into the intake manifold • This reduces the effective displacement and compression ratio

28. Atkinson Cycle (Cont.)

29. Miller Cycle • An Atkinson cycle engine with forced induction (supercharger) • The decrease in intake air and lower power is compensated for by the supercharger

30. Diesel Engines • Main power source for heavy-duty applications • Operates similar to a gasoline engine • Use high compression pressure to ignite fuel • Larger than comparable gas engine • Produce large amount of torque • Run at low speeds

31. HCCI Engines • Homogeneous charge compression ignition (HCCI) engines have the torque and efficiency of a diesel and the low emissions and power of a gas engine

32. Other Powerplants • Hybrid vehicles have at least two types of power or propulsion systems – usually an ICE and electric motors • Hybrids do not require plugging in to charge • EVs do require plugging in

33. Toyota Prius MG2

34. Other Powerplants (Cont.) • Battery operated electric vehicles (EVs) – operate solely on battery powered electric motors

35. Other Powerplants (Cont.) • Fuel cell electric vehicles – use hydrogen to generate electricity to power electric motors

36. Other Powerplants (Cont.) • Rotary engines – another type of four-cycle ICE • Rotary engines use a rotating triangular rotor, no reciprocating engine parts

37. Other Powerplants (Cont.) • Variable compression ratio engines can maximize power when needed and minimize fuel consumption when power is not needed

38. Knowledge Check • How do hybrid vehicle powertrains differ from non-hybrid vehicles?

39. Engine Identification

40. Engine Identification (Cont.)

41. Engine Diagnostics • Compression Test • Checks the compression of each cylinder • Cylinder Leakage Test • Helps determine where compression is leaking • Power Balance Test • Checks to see if all cylinders are producing the same power • Vacuum Test • Helps to determine the engine’s efficiency by measuring manifold vacuum

42. Compression Testing • Relative compression • Measures starter current flow when cranking • Cranking compression • Dry and wet tests • Wet test checks for rings sealing • Running compression • Used to determine valvetrain problems

43. Relative Compression Test

44. Cranking Compression Test

45. Running Compression - Good

46. Running Compression - Bad

47. Knowledge Check • A four-cylinder engine has the following compression readings, what could be the cause? 1) 150 psi 2) 150 psi 3) 80 psi 4) 80 psi

48. Cylinder Leakage Test • Pressurizes the cylinder • Used to determine cause of leakage • Cracked head or leaking head gasket • Leaking rings • Burnt valves

49. Power Balance Testing • Checks for each cylinder’s contribution • Can be done manually • Typically a scan tool test

50. Knowledge Check • While discussing power balance testing, Technician A says each cylinder should drop the same rpm. Technician B says a cylinder that does not drop rpm is a good cylinder. Who is correct?