PURPOSE AND FUNCTION

1. PURPOSE AND FUNCTION Internal combustion engine is either gasoline or diesel design. They are different because of the method used for burning the fuel. The mechanical operation of each style of engine is nearly identical. In an engine, fuel is burned to create mechanical motion.

2. The major components of the internal combustion engine include: • Cylinder block assembly • Exhaust system • Valve train • Lubrication system • Intake system • Cooling system

3. THE COMBUSTION PROCESS Combustion is the process of igniting a mixture of air and fuel at the correct time. In the combustion process a mixture of air and fuel is drawn into a cylinder. The compressed mixture is ignited to create energy for vehicle motion.

4. The air/fuel ratio is the amount of air compared to the amount of fuel. • The ideal air/fuel ratio when using gasoline is 14.7 to 1. • This means there are 14.7 parts of air to one part of fuel.

5. Stoichiometric Ratio

6. The ratio will fluctuate between 12 to 1 as a rich mixture • and 18 to 1 which is a lean mixture. • A rich mixture means there is more fuel in the combustion chamber. • A lean mixture means there is less fuel

7. Question Time 1. What two designs can a internal combustion engine be? Gasoline and Diesel 2. Summarize 4 major components of the engine? Lubrication system, Valve train, Exhaust system, Engine block, Intake system, Cooling system 3. Combustion is the process of igniting a mixture of --------- and ------------ . Air and Fuel 4. 12:1 Air /Fuel ratio is an example of a ----------mixture Rich mixture 5. Why do you think we burn fuel in a engine? To create energy motion to move the vehicle

8. Fuel Properties • Internal combustion engines can be powered by different fuels. Gasoline is the fuel designed for spark-ignition. • All of the necessary gasoline additives are added during the manufacturing process; • no additional aftermarket additives are necessary • The result is a carefully blended fuel that is adjusted seasonally.

9. Combustion • the fuel system Is designed to break the liquid fuel into a vapor and mix them with air.

10. CREATING MECHANICAL MOTION • When combustion occurs, the high pressure pushes the piston down in the cylinder. • The piston is connected to a connecting rod, which is connected to the crankshaft. • The connecting rod and crankshaft convert the up and down motion of the piston into rotary motion.

12. Power Pulses As combustion occurs in each cylinder, pulses of energy are transferred from the pistons to the crankshaft. The flywheel, which is a heavy round metal plate attached to one end of the crankshaft.

14. Question Time? 1 How would you summarize the fuel system? 2 What would result if we used fuel additives in the fuel system ? 3 Explain what pushes the piston down in the cylinder? 4 How would you explain the part, that converts up and down motion to rotary motion?

15. Piston Stroke It is the distance the piston slides up or down from TDC to BDC This takes half a turn of the crankshaft, 180 degrees for one stroke TDC - Top Dead Centre BDC - Bottom Dead Centre

16. Four Stroke Cycle Requires 4 piston strokes to complete one cycle or (series of event) For every four strokes the engine produces one power stroke (useful energy) Almost all automobiles use the four stroke cycle engine

17. Intake Stroke The intake valve is open and the exhaust valve is closed The piston slides down and forms a low-pressure area or vacuum in the cylinder Outside Air pressure pushes the fuel and air into the engine combustion chamber.

18. Compression Stroke Squeezes the air-fuel mixture to prepare it for combustion (controlled burning) The mixture is more combustible when pressurized During this stroke the piston slides up the cylinder while both of the valves are closed in the combustion chamber

19. Power Stroke The spark plug ignites and burns the air/fuel charge driving the piston downward with tremendous force. Since both valves are closed, pressure forms on the top of the piston This is the only stroke that does not consume energy

20. Exhaust Stroke Removes the burnt gases from the engine and readies the cylinder for a fresh charge of air/fuel mixture During this stroke the piston moves up the cylinder, the intake valve is closed the exhaust valve is open The burnt gases are pushed out the exhaust port into the exhaust pipes

21. The engine must rotate two complete revolutions to complete the four stroke cycle, the crankshaft rotates 720 degrees.

22. Exercise

23. Engine Bottom End Bottom end refers to the block, crankshaft, connecting rods, pistons and related parts. Another name for this is the Short Block. It is an assembled block without cylinder heads and manifolds.

24. Engine Block It forms the main body of the engine. Other parts bolt to or fit inside the block Cylinder are large round holes machined through the block from the top to bottom

25. Features of the Engine Block The deck Is the top of the block surrounding the cylinders It is machined perfectly flat The cylinder head bolts to the deck Water Jackets Are coolant passages through the block. They allow a solution of water and antifreeze to cool the cylinders

26. Core Plugs Are round metal plugs on the outside of the block. They seal holes left in the block after casting (manufacturing) They prevent coolant from leaking out the water jackets

27. Main Bore Main Bearing Bores are holes machined in the bottom end to hold the crankshaft Main Caps Bolt to the bottom of the block and hold the crank shaft in place

28. Crankshaft Harness the tremendous force produced by the downward thrust of the pistons. It changes up and down motion of the piston into rotating motion The crank fits into the engine block journals

29. Crankshaft Continued Counterweights are formed on the crankshaft to prevent vibration they counter act the weight of the rods and pistons Crank snout sticks through the front of the block it provides a mounting point for the chain, damper and fan pulley Crankshaft Flange holds the flywheel the flywheel bolts to the flange *The journals are arranged so 1 cylinder is always on the power stroke

30. Questions • What is the 4 strokes of the engine? • What is the short block? • What is the deck? • What is the purpose of the core plugs ? • What does the crankshaft do?

31. Plain engine bearing/Friction bearing Are removable inserts that fit between the block main bore and the crankshaft main journals The other half fits into the block main caps Oil holes on the upper bearing line up with holes on the block

32. Main Thrust Bearing Limits how far the crankshaft can slide forward or rearward in the block This limits the crankshaft endplay Normally one of the main bearing serves as a thrust bearing

33. Bearing Construction Steel is normally used for the bearing body or backing which is in contact with the stationary part of the engine Softer alloys are bonded over the backing to form the bearing surface (plating) They use Babbitt- lead tin alloy copper or aluminum

34. Bearing Characteristics Bearings operate under tremendous loads, severe temperature variations and abrasive conditions Bearing load strength : bearings ability to withstand the pounding and crushing during engine operation this can be several tons of force Bearing conformability: is the bearings ability to adjust to imperfections in the journal surface

35. Bearing Characteristics Bearing embedability: the bearings ability to absorb dirt, metal or other hard particles they should be able to sink into the bearing material Bearing Corrosion resistance: the bearings ability to withstand being acted on by acids, water and other contaminates in the oil

36. Bearing Crush The bearing is made slightly larger in diameter than the bearing bore This helps prevent the bearing from spinning inside the bore

37. Bearing Sizes Standard Bearing Undersize Bearing Has the original dimensions specified by the manufacturer For a new, unworn, or unmachined crankshaft Designed to be used on crankshafts that have been machined to a smaller diameter A machine shop can grind down the journals if they have been damaged

38. Spun Bearing

39. Main Bearing Clearance It is the space between the crankshaft main journal and the main bearing insert The clearance allows lubricating oil to enter and separate the journal and bearing

40. Questions ? • What material can be used on the bearing surface? • What are the two types of crank bearings? • What is bearing crush? • What are the sizes of a bearing? (hint if we have the crankshaft machined)

41. Connecting Rods It fastens the piston to the crankshaft It transfers piston movement and combustion pressure to the crankshaft rod journals.

42. Connecting Rod Construction I Beam is the centre section of the rod The shape provides very high strength to weight ratio The rod cap bolts to the bottom of the rod body The rod has a Lower end, and a Top end

43. Piston It transfers pressure of the combustion (expending gases) to the connecting rod Piston Head must be shaped to match and work with the shape of the combustion chamber

44. Piston Ring grooves Are slots machined in the piston for the rings The upper two grooves hold the compression rings The lower piston groove holds the oil rings

45. Piston Construction Piston ring lands: is the area between and above the ring grooves Piston Skirt: is the side of the piston below the last ring, it keeps the piston from tipping in the cylinder

46. Piston Pin or (Wrist Pin) It allows the piston to swing on the connecting rod The pin fits into the small end of the connecting rod

47. Piston Compression Rings They seal the clearance between the outer side of the piston and the cylinder wall They must keep combustion pressure from entering the crankcase

48. How Compression RingsWork Combustion pressure pushes the compression rings down in their grooves and out against the cylinder wall This produces an almost leak proof seal

49. Oil Rings They prevent engine oil from entering the combustion chamber They scrap excess oil off the cylinder wall If too much oil entered the combustion chamber blue smoke would appear in the exhaust

50. Questions • What gives the connecting rod it’s strength? • What are ring grooves? • What is the piston skirt? • What are the two different rings used on the piston? • What function does the wrist pin perform?