1. Motive Power Types— Spark-Ignition (SI) Engines
CHAPTER 44
Motive Power Types— Spark-Ignition (SI) Engines

2. Introduction Internal combustion engine is irreplaceable.
Hauls food and water, delivers passengers, saves lives

3. Principles of Thermodynamic Internal Combustion Engines (1 of 3)
Science branch dealing with heat and energy
Used in internal combustion engine
Moves vehicle down road and provides power
Once powered all equipment
Steam engines

4. Principles of Thermodynamic Internal Combustion Engines (2 of 3)
External combustion engines A. Steam engine.
B. Stirling engine.

5. Principles of Thermodynamic Internal Combustion Engines (3 of 3)
<insert fig 44- 2>
Stirling engine
Internal replaced external combustion.
Gas and diesel engines
ICE classified in two ways
Piston engines are SI or CI engines.

6. Principles of Engine Repair (1 of 10)
Operate on physics and thermodynamics
Understanding will help diagnose.
Tightly packed molecules increase expansion pressure.
Burning black powder = fire.

7. Principles of Engine Repair (2 of 10)
Pressure and temperature
Directly related
Cylinder with moveable plunger
Diesel engines use same principle.
Heating increases molecule movement.

8. Principles of Engine Repair (3 of 10)
Pressure changes temperature.
Temperature changes pressure.

9. Principles of Engine Repair (4 of 10)
<insert fig 44- 6>
Temperature and energy
Measures energy
Latent heat in various fuels
Expressed in Btu

10. Principles of Engine Repair (5 of 10)
Pressure and volume
Inversely related

11. Principles of Engine Repair (6 of 10)
Force, work, and power
Force: effort to push or pull
Compressed spring/cable moves to create work.
Power: rate or speed at which work is performed

12. Principles of Engine Repair (7 of 10)
Power and torque
Torque: twisting force
Unit of measurement: ft-lb or newton meters
Amount of torque at crankshaft and speed of turning
1 hp = 33,000 ft-lb/min

13. Principles of Engine Repair (8 of 10)
Power and torque (cont’d)
Calculate twisting by adding distance moved and time.
Converting torque to work requires movement.

14. Principles of Engine Repair (9 of 10)
Torque vs. horsepower
Torque: twisting or turning force and horsepower
Naturally aspirated engines
Engine rpm rises faster as torque falls.

15. Principles of Engine Repair (10 of 10)
Engine load factor
Used in regard to diesel engines
Gives power as an average

16. Four-Stroke Spark-Ignition Engines (1 of 5)
SI engines operate on four-stroke principle.
Takes four strokes to complete one cycle
Can be simple or complicated

17. Four-Stroke Spark-Ignition Engines (2 of 5)
Basic four-stroke operation
One stroke out of the four delivers energy.
Compression stroke
Ignition occurs as piston reaches TDC.
Exhaust stroke: end of power stroke

18. Four-Stroke Spark-Ignition Engines (3 of 5)
Engine measurement—size
ICEs designated by volume pistons displace
Cylinder bore
Piston stroke
Piston displacement
Engine displacement
Compression ratio

19. Four-Stroke Spark-Ignition Engines (4 of 5)
Atkinson and Miller cycle engines
Variations on four-stroke engine
Use larger throttle opening for power
Efficient within range
Lower max operating rpm

20. Four-Stroke Spark-Ignition Engines (5 of 5)
Scavenging
Uses column of moving air
Engine displacement.

21. Components of Spark-Ignition Engines (1 of 9)
Widely used to power passenger vehicles
Main power plant
Gains in manufacture
Divided into two assemblies
The compression ratio of an engine is found by taking the volume of the cylinder at BDC and comparing it to the volume at TDC. In this example, a 9:1 compression ratio is found.

22. Components of Spark-Ignition Engines (2 of 9)
Short block and long block
Subassembly may be used.
The engine contains many parts that work together to power the vehicle.

23. Components of Spark-Ignition Engines (3 of 9)
Cylinder block, crankshaft, flywheel
Block is largest part of engine.
Oil pan completes crankcase.
Crankshaft is composed of cast iron or steel.
Crankshaft has main journals.

24. Components of Spark-Ignition Engines (4 of 9)
Connecting rod and piston
Connecting rod is made of cast iron, steel, aluminum, or titanium.
Rod causes piston movement.
Piston is composed of aluminum or synthetic materials.
Head is exposed to heat and pressure.

25. Components of Spark-Ignition Engines (5 of 9)
Ring lands
Areas between the ring grooves that support the rings as the piston moves.

26. Components of Spark-Ignition Engines (6 of 9)
The oil pan
Seals and holds oil
Houses oil pump

27. Components of Spark-Ignition Engines (7 of 9)
The cylinder head
Made of cast iron or aluminum

28. Components of Spark-Ignition Engines (8 of 9)
Engine cam and camshaft
ICE uses poppet valves.
Flathead engines had valves in block.
Camshaft is mounted on top of cylinder head.
Lobes open to hold and close valve.

29. Components of Spark-Ignition Engines (9 of 9)
Camshaft specifications
Base is rounded bottom part.
Duration is used when designing lobe.
High-performance engines have overlap.
Two listings for cam specs

30. Valves (1 of 15) Open or close cylinder heads
Intake controls flow of air/fuel in combustion chamber.
Valve head is disc shaped.

31. Valves (2 of 15)
Intake and exhaust valves
Control ICE

32. Valves (3 of 15)
Valve arrangement
One of two methods
L-head
I-head

33. Valves (4 of 15) Mechanical and hydraulic valve train
Combo of parts open and close engine valves.
Adjustments are made by lifter.

34. Valves (5 of 15) Roller rockers and lifters
Reduce friction and increase engine efficiency
Arms have fulcrum.
Arms increase lift into cam lobe.
Friction loss occurs.

35. Valves (6 of 15) Valve clearance
Amount of slack between rocker arm and valve stem

36. Valves (7 of 15) Valve timing Critical to proper ICE operation
Factory setting

37. Valves (8 of 15) Theoretical four-stroke cycle engine valve timing
Piston at TDC opens valve.
Valves open and close sooner than described.
Airflow creates velocity.
Cam allows valve spring to close.

38. Valves (9 of 15) Burning air/fuel expands air.
Some degree of overlap at TDC and BDC
Not much inertia
Large overlap at cranking speeds
Timing controlled by cam lobes
Advance or reduce power

39. Valves (10 of 15) Variable valve timing Benefit to engine performance
Valve timing managed by electronic modules
Vane-type phaser
Can be used on any arrangement

40. Valves (11 of 15) Variable valve timing (cont’d)
Inert gas does not react chemically
Variable cam timing is controlled by PCM

41. Valves (12 of 15) Valve train drives Driven by camshaft
Chains louder than belts
Freewheeling engine
Timing chain differs between cam-in-block and OHC.

42. Valves (13 of 15) Valve train drives (cont’d)
OHC requires longer timing chains.
Belts use toothed or cogged belt.

43. Valves (14 of 15) Intake manifold Part of air intake/induction
Many changes

44. Valves (15 of 15) Exhaust manifold
Output side of engine breathing apparatus

45. Two-Stroke Spark-Ignition Engines (1 of 4)
Produce large power to weight ratio
Every other stroke is power.

46. Two-Stroke Spark-Ignition Engines (2 of 4)
Basic two-stroke cycle engine principles
Differs from four-stroke SI engine
One revolution for every cycle in two-stroke
Piston movement creates suction.
Piston moves up to TDC.
Piston moves up, compression in cylinder.

47. Two-Stroke Spark-Ignition Engines (3 of 4)
Two-stroke intake system
Piston port
Reed valve
No rotary valve

48. Two-Stroke Spark-Ignition Engines (4 of 4)
Four- and two-stroke engine differences
Lube from mixing oil with gas
Benefits
Downfalls

49. Rotary Combustion Spark-Ignition Engines (1 of 5)
Fewer parts used
Increased power and smaller engine
Rotary combustion in many applications

50. Rotary Combustion Spark-Ignition Engines (2 of 5)
Basic principles
Not as common
No reciprocating piston
Smooth and vibration free
Basic principles as rotary engine
Intake cycle

51. Rotary Combustion Spark-Ignition Engines (3 of 5)
Basic components of rotary engine
Mounted in oval-shaped housing
Two spark plugs
Rotor has three apexes.
Combustion chamber is formed by hollows in rotor flanks.
Teeth of rotor walk around stationary gear.

52. Rotary Combustion Spark-Ignition Engines (4 of 5)
Engine power pulses
Three power pulses per rotation

53. Rotary Combustion Spark-Ignition Engines (5 of 5)
Renesis rotary engine
Same as conventional
Primary, secondary, auxiliary ducts
Three intake ports
Two fuel injectors/rotor

54. Summary (1 of 11) Internal combustion engines are common.
Combustion engines are piston or rotary.
Piston engines are spark or compression ignition.
Pressure and temperature are directly related.
Internal combustion engines heat a gas.
Pressure and volume are inversely related.

55. Summary (2 of 11) Force causes movement.
Work = distance moved × force applied.
Power = distance × force/time in minutes.
Engine power is measured in torque.
Torque is called engine output.
Horsepower is the speed of torque.

56. Summary (3 of 11)
Load factor = time a vehicle can operate at max speed and power.
Piston stroke = distance traveled from TDC to BDC.
Internal engines are two- or four-stroke.
Five events must occur in a four-stroke engine.
Compression ratio is based on cylinder volume.

57. Summary (4 of 11)
Piston displacement: bore squared × 3.14 × stroke ÷ 4.
Engine displacement: piston displacement × number of engine cylinders.
Miller and Atkinson are variations of the four-stroke engine.
Miller has engine-driven compressor.
Atkinson has lower power output and torque.

58. Summary (5 of 11)
Valve overlap: time intake and exhaust valves are open.
There are 11 major components of an internal combustion engine.
Cylinder block includes additional parts.
Crankshaft: converts piston’s reciprocating motion into rotary motion.
Flywheel stores energy from piston.

59. Summary (6 of 11) Connecting rod connects piston to crankshaft.
There are 7 components of the piston.
Gases can leak past piston rings.
Intake manifolds deliver air to cylinder head.
Oil is stored in the oil pan.
Camshaft opens valves.

60. Summary (7 of 11) There are 4 parts to a camshaft.
Engineers must consider several issues when designing camshaft lobes.
There are 4 parts of an intake valve.
Intake valve is large and runs cool.
Exhaust valves are small and run hot.

61. Summary (8 of 11) Modern engines are arranged in I-head.
Valve lifter is hydraulic or mechanical.
Roller rocker arms act as levers.
Valve clearance must be accurate.
Timing of valves is critical.
Valve timing can be modified.

62. Summary (9 of 11) Variable valve timing is available.
Cam actuators can be twisted.
ECM controls variable cam timing.
Pulse width modulation signals regulate solenoids.
Engines are freewheeling or interference.
Two-stroke engines use piston to open and close exhaust ports.

63. Summary (10 of 11)
Internal combustion engine events are controlled by a piston.
Two-stroke engines use reed or rotary valve.
Two-stroke engines don’t use camshaft or valve train.
Four-stroke engines are more environmentally friendly.

64. Summary (11 of 11)
Rotary and Wankel engines use a rotor in place of a piston.
Rotary engines have two spark plugs.
Rotary engines have four phases.
Faces of the rotor have a combustion chamber.
Renesis rotary engine is fuel efficient.
Renesis engine can be low output.

65. Credits
Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.