Internal Combustion Engines (2)

1. Internal Combustion Engines(2) 2007-12-03

2. Confidence in yourself is the first step on the road to success. Don’t put off till tomorrow what should be done today.

3. REVIEW • C.E. /I.C.E/ E.C.E • Comparison of ICE and ECE • Three elements for operation • History –Otto cycle • Mechanism of converting reciprocation to rotation (power production)

4. 1.5 BASIC ENGINE STROKES Main topics: 1.summarization 2.four-cycle gasoline engine 3.four-cycle diesel engine 3.two-cycle gasoline engine 4.two-cycle diesel engine

5. Summarization 1.Stroke:Each movement of the piston from top to bottom or from bottom to top is called a stroke. 2. The piston takes two strokes (an upstroke and a downstroke) as the crankshaft makes one complete revolution. 3. When the piston is at the top of a stroke, it is said to be at top dead center (TDC). 4. When the piston is at the bottom of a stroke, it is said to be at bottom dead center (BDC).

6. 5. TDC-it refers to the point that the piston is furthest to the center of the crankshaft . 6. BDC-it refers to the point that the piston is nearest to the center of the crankshaft . 7. Basic part of ICE (mainly concerned) fuel supply system/lubricating system/cooling system/intake system/exhaust system/starting system(next term)

7. 8. Four-cycle and two-cycle engine • Four-cycle engine ----Four strokes of the piston in the cylinder are required to complete one full operating cycle. (two upstrokes and two downstrokes) Four-cycle gasoline engine Four-cycle diesel engine

8. Two-cycle engine ----Two strokes of the piston in the cylinder are required to complete one full operating cycle. (one upstroke and one downstroke) Two-cycle gasoline engine Two-cycle diesel engine

9. 1.5.1 Four-cycle gasoline engines 1.Basic components

11. Toothed timing belt 正时齿型带 • Camshaft 凸轮轴 • Exhaust port 排气口 • Distributor 分电器 • Air filter 空滤器 • Carburetor 化油器 • Ignition switch 点火开关 • Spark plug 火花塞 • Induction coil 感应线圈 • Cooled water 冷却水 • Intake valve and exhaust valve 进排气阀

12. Piston 活塞 • Connecting rod 连杆 • Crankshaft 曲轴 • Oil pan 油底壳 • Flywheel 飞轮 • Starter 启动机 • storage cell/storage battery 蓄电池 • Lubricating oil 润滑油

13. 2. Four-stroke cycle (1)intake stroke a.piston TDC----BDC b.intake valve is opened and exhaust valve is closed c. the mixture of air and fuel (suction) (2) Compression stroke a. piston BDC------TDC b. intake valve and exhaust valve are both closed c. compress the mixture in the cylinder

15. (3) Power stroke a. mixture is ignited by the electric spark b. intake valve and exhaust valve are both closed c. piston TDC------BDC (4) Exhaust stroke a. piston BDC------TDC b.only the exhaust valve is opened c. burned gases are forced out of cylinder

17. 1.5.2 Four-cycle diesel engines

18. Injector 喷油器 • Injection pump 喷射泵 • Fuel supply pump 输油泵 • Timing gear 正时齿轮

19. 2. Four-stroke cycle (1)intake stroke a.piston TDC------BDC b.intake valve is opened and exhaust valve is closed c.only the air

20. (2) Compression stroke a. piston BDC------TDC b. intake valve and exhaust valve are both closed c. compress the air in the cylinder

21. (3) Power stroke a. intake valve and exhaust valve are both closed b. fuel is injected into the cylinder and ignited by the high temperature of air c. piston TDC------BDC

22. (4) Exhaust stroke a. piston BDC------TDC b.only the exhaust valve is opened c. burned gases are forced out of cylinder

23. 1.5.3 Two-cycle gasoline engines

24. 1.Two-stroke cycle (1)Intake and compression stroke a. Piston moves upward. b.The exhaust ports, intake port and the transfer port are covered. c.Compression take place. d. The piston moves further upward, intake port opens,the mixture is drawn into the crankcase.

25. (2) Power and exhaust stroke a. Mixture is ignited by the electric spark b. Piston is forced down c. First the exhaust port is uncovered and then the transfer port is covered,spent gases flee out of the cylinder

26. d. As piston move further downward, the transfer port is uncovered,and the new mixture is forced into the cylinder e. A deflector on the top of the piston directs the fresh charge upward away from the spent gases leaving through the exhaust port.

27. 1.5.4 Two-cycle diesel engines

28. 2.Two-stroke cycle (1)Intake and compression stroke a. piston move upward, exhaust valve is still opened b.first the intake port is uncovered covered ,the blower forces the air into the cylinder

29. c.as the piston moves further upward, the intake port is covered and the exhaust valve is closed, the compression actually take place.

30. (2) Power and exhaust stroke a.The fuel is injected into the cylinder and is ignited by the high temperature b.piston moves downward

31. c.exhaust valve is opened, spent gases flow out of cylinder d. Further downward, the intake port is uncovered and the blower forces the air into the cylinder again for the next cycle.

32. 1.6 Comparison of Four-stroke and Two-stroke cycle Engines (1)Application Two-cycle: a. gasoline engine used in public utility,such as motorcycle, mower b. diesel engine used for locomotive, large trucks and ships. Four-cycle:used for automotive and industrial purposes

33. (2) Working process Two-cycle:one power stroke for every engine revolution Four-cycle:one power stroke for every two engine revolutions Note:Power of two cycle engines =2*power of four cycle engines (at the same size, operating at the same speed) ? Why??

34. 1. Some of the power is used to drive the blower . 2. The burned gases are not cleared from the cylinder . 3. Much shorter period the intake port is open , a smaller amount of fuel-air mixture is admitted. (3) Exhaust The 2-stroke engines have `dirty` exhaust and rather unpleasant sounding exhaust noise because of greater fuel consumption.

35. 1.7 The difference between compression Ignition and Spark Ignition 1) Intake stroke a. spark ignition: the mixture of air and fuel b. compression ignition: only the air 2) Power stroke a. spark ignition: ignited by the electric spark b.compression ignition: ignited by the compressed air of high temperature

36. 1.8 MULTIPLE-CYLINDER ENGINES • A single cylinder provides only one power impulse every two crankshaft revolutions in a four-cycle engine. • It delivers power only one-fourth of the time. • To provide for a more continuous flow of power, modern engines use four, six, eight, or more cylinders. • The same series of cycles take place in each cylinder.

37. 1.9 Timing • Valve timing refers to the exact times in the engine cycle that the valves trap the mixture and then allow the burned gases to escape. • The position of the valves is determined by the camshaft . • The position of the camshaft is determined by the crankshaft. • Correct valve timing is obtained by providing the proper relationship between the camshaft and the crankshaft.

38. Assignment 1. Could you list the strokes in a four-stroke cycle engine in their proper order? 2. Could you list the strokes needed in the two-stroke cycle engine? Could you explain the sequence of events during these strokes? 3. What are the basic differences between four-stroke cycle and two-stroke cycle engines? 4. What is the difference between the compression ignition engines and the spark ignition engines?