bài giảng chi tiết động cơ đốt trong 1

CONSTRUCTION OF DIESEL ENGINES CHAPTER 1 OPERATIONAL PRINCIPLE OF A DIESEL ENGINE 1.1 THE HISTORY OF DEVELOPMENTS OF DIESEL ENGINES - In the 19th century and in the early 20th century, steam engines were widely used in the world as propulsion plans for steam ships as well as other industrial branches. The steam engines are known as external combustion engines. - In 1860, the first internal combustion engine in the world was invented by Lenuar, a French engineer. This is a 2-stroke engine, its operation based on burning amount of dynamite in the engine cylinder. However its efficiency was very low (about 3%), so it was not used in practice. - In 1876, German engineer Otto designed a 4-stroke engine. Fuel used for this engine is gasoline (benzine) that burned by electric spark, so it was called spark-ignition engine or gasoline engine. This kind of engine after has been widely used in industry and on means of transport.

BỘ GIAO THÔNG VẬN TẢI TRƯỜNG DẠI HỌC HANG HẢI KHOA MÁY TÀU

DÙNG CHO SINH VIÊN NGÀNH KHAI THÁC MÁY TÀU BIÉN

HẢI PHÒNG 2009 MỤC LỤC

CONSTRUCTION OF DIESEL ENGINES

1 Operational principle of diesel engines

2 Static parts construction of diessel engines

Hệ thông bôi tron

YÊU CẦU VÀ NÔI DUNG CHI TIÉT

Bộ môn phụ trách giảng dạv: Động lực tàu biển Khoa phụ trách: MTB

Điều kiện tiên quyết: Trước khi đăng ký học học phần này, sinh viên phải học

và thi đạt các học phần sau: Nguycn lý máy; Chi tiết máy; Nhiệt kỹ thuật

Mục tiêu của học phần: Cung cấp cho sinh viên kiến thức về kết cấu cơ bảnđộng cơ dicsel tàu thủy, các hệ thống phục vụ cho động cơ dicsel, kỹ năng khai thác

động cơ diescl cũng như các hệ thống phục vụ của nó

Nội dung chủ yếu:

- Nguyên lý hoạt động cùa động cơ diesel;

- Ket cấu của động cơ diesel;

- Cơ cấp phân phối khí;

- Các hệ thống phục vụ động cơ diesel và kỹ năng khai thác chúng

Nội dung chi tiết:

Lý thuyết Thực hành Bài ỉập lớn Tổng số

Chapter 2 Static parts construction of diessel engines 4.0 5.0 9.0

Chapter 3 Moving parts construction of diesel engines 5.0 5.0 10.0

Lý thuyết Thực hành Bài tập lơn Tống số

Nhiệm vụ của sinh viên:

như tại phòng thực hành, ghi chép nội dung bài giảng và đọc thêm các tài liệu tham khảo

của môn học;

-Hà Nội: Nhà xuất bản Giao thông vận tải, 1990

4 0OMHH FO H., Trần Hữu Nghị Chế độ làm việc của động cơ diesel tàu thuỷ.

-Hà Nội: Nhà xuất bản Giao thông vận tải, 1990

Prentice-Hall, Inc

6 Internal Combustion engines and its components No name, no source, no date.

7 0OMHH K).5I H Ap Cydoebie deueamejiu eHympeHHeao ceopaHUH — JL:

Cy^ocTpoeHHe, 1989.

9 raBpHJiOB B.C., KaMKHH C.B., LUMejieB B.n TexHUHecKLiH 3Kcwiyamaụnn

Hình thức và tiêu chuẩn đánh giá sinh viên: Thi viết, thời gian làm bài

60 phút Thang điểm: Thang điểm chữ A, B, c, D, E, F.

Điểm đánh giá học phần: z = 0.3X + 0.7Y

Bài giảng này là tài liệu chính thức và thống nhất của Bộ môn Động lực tàu biên,

Khoa Máy tàu biến và được dùng đế giảng dạy cho sinh viên

Ngày phê duyệt:

- In the 19th century and in the early 20th century, steam engines were widely used

in the world as propulsion plans for steam ships as well as other industrial branches Thesteam engines are known as external combustion engines

- In 1860, the first internal combustion engine in the world was invented byLenuar, a French engineer This is a 2-stroke engine, its operation based on burningamount of dynamite in the engine cylinder However its efficiency was very low (about3%), so it was not used in practice

- In 1876, German engineer Otto designed a 4-stroke engine Fuel used for thisengine is gasoline (benzine) that burned by electric spark, so it was called spark-ignition

engine or gasoline engine This kind of engine after has been widely used in industry and

- In 1903, Russia launched the first motor ship that named Vandan, this was thefirst diesel engine ship in the world It was equipped three same diesel engines with output

of 88 kw, RPM 240, ship’s propeller was driven by electric driving mode

- From 1911 series of ship that used diesel engine with output of 450 kw islaunched

- Nowadays, diesel engines are widely used for the ships due to followingremarkable advantages:

High efficiency;

Low specific fuel consumption;

Small relative dimensions and weight;

High longevity;

Engine speed is appropriate for propeller revolution range

Figure 1.1 Energy transformation schematic in diesel engines

1.2 BASIC DEFINITIONS THAT USED FOR A DIESEL ENGINE

oDiesel engine

5 — Piston; 6 — Intake valve; 7 — Exhaust valve; 8 — Fuel injection valve;

9 - Intake manifold; 10 - Exhaust manifold; II - Cylinder cover.

For a diesel engine, they use the following basic definitions:

3 Four-stroke and two-stroke engines:

- Four-stroke engine: 4-stroke engine is that needs 4 strokes of the piston (correspond with 2revolutions of the crankshaft) to complete the working cycle

- Two-stroke engine: 2-stroke engine is that needs 2 strokes of the piston (correspond with onerevolution of the crankshaft) to complete the working cycle

8 Total volume V a :

Total volume (maximum volume) is the volume of the cylinder, when the piston located at the BDC.(Vmax = Va)

9 Working volume (stroke volume) V s

It is the volume of the cylinder that drawn by piston top, when piston moves between two deadcenters

V s = V ma x-V c = 7tD 2 S/4

10 Compression ratio 8:

It is ratio between the total volume of the cylinder and the clearance volume

6 = V max /v c = (V c + V s )/V c = 1 + v s /v c

1.3 OPERATIONAL PRINCIPLE OF 4-STROKE DIESEL ENGINES

1 - Suction stroke

The suction stroke is begun when the piston moves down from the TDC to the BDC, at that time theintake valve has been opened; the exhaust valve is being closed Fresh air from the air intake manifold ischarged into the cylinder due to difference of pressures between the intake port and the cylinder When thepiston reaches to the BDC, all of the cylinder volume is fully charged by fresh air, in which exists a littleamount of combustion gases in the cylinder from previous working cycle, these gases are called residuegases

The suction stroke finishes when the piston reaches to the BDC

2 - Compression stroke

The compression stroke takes place when the piston is moving up from the BDC to the TDC At thattime, both the intake and exhaust valves are being closed; the cylinder volume is decreased while thepressure of the working substance in the cylinder is gradually increased, because of this, the temperature ofthe working substance in the cylinder is gradually increased also

The compression stroke spends engine work (in the other word, compression work is negative), thework serves for the compression stroke is supplied from the engine flywheel

At the end of the compression stroke, when the piston goes up nearly the TDC, the fuel oil isinjected in the form of a fine mist into the cylinder by the fuel injection valve Due to the high pressure andswirling movement of airflow, the fuel oil when spraying into the cylinder is atomized and distributed overthe combustion chamber Because of high temperature of the compressed air in the combustion chamber, thefuel oil vapors and ignites itself

3 - Ignition-expansion stroke

The ignition-expansion stroke happens when the piston is moving down from the TDC to the BDC

At the beginning of the ignition stroke, the fuel oil is being still continuously injected into the cylinder Atthat time, the temperature of the combustion chamber is very high, because of this the injected fuel oil at thismoment rapidly vapors and ignites The

ignition process is divided into 2 phases: the former is the isochoric phase (equal volume phase) with 40% of the

supplied fuel oil; the latter is the isobaric phase.

The ignition of the fuel oil in the cylinder rapidly takes place and it is the same explosion Becausethe fuel oil bums in the small volume of the cylinder, pressure of the combustion gases highly increases.Then, the combustion gases expand and push the piston downward to turn the crankshaft This is the workproducible stroke of the engines

4 - Exhaust stroke

The exhaust stroke takes place when the piston is moving up from the BDC to the TDC At that timethe exhaust valve has been opened while the intake valve is being closed In the early of the exhaust stroke,the combustion gases escape from the combustion chamber due to difference of pressure between thecombustion chamber and the exhaust manifold After that, the combustion gases are discharged out bymovement of the piston When finishing the exhaust stroke, in the combustion chamber remain amount ofthe residue gases with the pressure Pr higher than the ambient pressure P0 Thus, the exhaust stroke is carriedout to scavenge the combustion chamber clean before continuing the new working circle

1.4 OPERATIONAL PRINCIPLE OF 2-STROKE DIESEL ENGINES

Figure 1.4 The working cycle of a non-supercharged 4-stroke diesel engine

1 Figure 1.6 The working cycle of a 2-stroke diesel engine

2- Second stroke

In the second stroke, the piston is moving down from the TDC to carry out the expansion process Atthe end of this process, when the piston opens the exhaust ports, the combustion gases escape from thecylinder because the pressure in the cylinder is higher than the pressure in the exhaust manifold This is freedischarge phase

The piston is continuing go down to the BDC, the pressure in the cylinder is quickly decreased.When the piston opens the scavenging ports (inlet or intake ports), supercharged air with the high pressure(higher than the environment pressure) from the intake manifold blows into the cylinder to force out theremaining combustion gases and to fill up the cylinder by fresh air This is called forced discharge phase.When the piston is in the BDC, the opening section of the scavenging and exhaust ports is maximal Andthen, the piston continues go up again to make a new working circle

Thus, in the 2-stroke diesel engines the fresh air has to compress to the pressure, which is higher thanthe environment pressure to carry out the gas exchange process

Figure 1.5 Principle diagram of a 2-stroke engine

1 —piston; 2 — Scavenging port; 3 — Intake manifold; 4 — Cylinder;

5 - Cylinder cover; 6 - Fuel injection valve; 7 - Exhaust manifold; 8 - Exhaust port

1.5 COMPARISON THE 2-STROKE WITH THE 4-STROKE ENGINES

1 - In comparison with the 4-stroke diesel engine, which have the same basic dimensions (diameter

of the cylinder D, stroke of the piston S, revolution speed of the crankshaft RPM), the 2-stroke engine has aoutput of about 1.6 ~ 1.8 times higher than the 4- stroke engine;

2 — Rotating moment of the 2-stroke engines is more even than the 4-stroke engines;

3 - Accelerating ability of the 2-stroke engines is better than the 4-stroke engines;

4 - Exhaust gases temperature of the 2-stroke engines is lower than the 4-stroke engines;

5 - The gas exchange process of the 2-stroke engines is less perfect than the 4-stroke engines;

6 - The supercharging for the 2-stroke engines is more difficult than the 4-stroke engines;

7 - The crankshaft angle that corresponds to the ignition-expansion process in the 2- stroke engines

is smaller than the 4-stroke engines;

8 - The selection and the adjustment of the valve timing in the 2-stroke engines is more difficultthan the 4-stroke engines;

1.6 TIMING DIAGRAM OF THE GAS EXCHANGE PHASES

1.6.1 The timing diagram of the gas exchange phases of the 4-stroke diesel engines

Figure 1.7 The timing diagram of a 4-stroke diesel engine

According to the figure 1.7:

N| : The opening moment of the intake valve;

N2: The closing moment of the intake valve;

Figure 1.8 The timing diagram of a return flow scavenging diesel engine

1

F i: The beginning of the fuel injection;

F?: The ending of the fuel injection;

Xj: The opening moment of the exhaust valve;

X2: The closing moment of the exhaust valve;

angle NiOC = oti: The early opening angle of the intake valve before the TDC (advanced opening angle);

angle N2OA = ay. The late closing angle of the intake valve after the BDC (delay closing angle);

angle FiOC = cps: The early fuel injection angle of the fuel injection pump be fore the

angle F2OC = cpkt: The ending angle of the fuel injection after the TDC; angle X]OA = Pi:The early opening angle of the exhaust valve before the BDC; angle X2OC = P2: The late closing angle of the exhaust valve after the TDC; angle N1OX2: The overlap angle of the intake and exhaust valves;

N| —> C-> A-» N2: The suction process;

Fi —» C —> E —> Xj: The ignition and expansion process;

X| —» A —» B —> X2: The exhaust process;

Some definitions'.

- The early opening angle of the intake valve:

- The late closing angle of the intake valve:

- The early opening angle of the exhaust valve:

- The late closing angle of the exhaust valve:

- The early injection angle:

Purpose of early opening and ¡ate closing the valves, as well early injection of fuel

1.6.2 The timing diagram of the gas exchange phases of the 2-stroke diesel engines

TDC

BDC

According to the figure 1.8:

b: The opening moment of the exhaust ports;

d: The opening moment of the scavenging ports (inlet ports);

d’: The closing moment of the scavenging ports;

b’: The closing moment of the exhaust ports;

Fi —>• c —» F2 —» b: The ignition and expansion process; b

—» d: The free discharge phase;

d —> d’: The scavenging (forced discharge) and air charge phases; d’ —> b’:

The loss phase of the fresh air

1.7 CLASSIFICATION OF THE INTERNAL COMBUSTION ENGINES

1 - Classify by operational principle:

+ 4-stroke engines +

2-stroke engines

2 - Classify by kinds of using fuel oil:

+ Engines with gaseous fuel + Engines with light liquid

fuel (Petrol, kerosene)

+ Engines with diesel oil (DO)

+ Engines with heavy fuel oil (FO or HFO)

+ Engines with mixing fuel oil (Gas and liquid fuel or DO and FO)

3 - Classify by kinds of combustion chambers:

+ Engines with direct injection chamber

+ Engines with pre-combustion chamber

+ Engines with swirl combustion chamber (vortex combustion chamber)

+ Engines with the combustion chamber in the piston crown

4 - Classify by the working circle:

+ Engines with isochoric circle (Gasoline engines, gas engines, in which the fuel is burned by electric spark)

+ Engines with isobaric circle (Engines, in which the fuel oil is supplied by compressed air This kind of engines nowadays is rarely used)

+ Engines with combining circle (Diesel engines)

5 - Classify by methods of air charge:

+ Non-supercharged engines (Engines, in which the pressure at the intake port is equal to the environment pressure, P0)

+ Supercharged engines (the pressure at the intake port Ps is higher than the pressure of the

environment P 0 )

6 - Classify by the numbers of the cylinders:

+ Engines with only one cylinder +

Engines with many cylinders

7 - Classify by the arrangement of the cylinders:

+ Engines with the cylinders in the vertical line + Engines with the

cylinders in the horizontal line + Engines with two lines of the cylinders

in the V-shape + Engines with many (5) lines of the cylinders in the

star-shape + Engines with the opposed pistons (figure 1.9)

-Injection Exh»u*t Scavenging

Compression (d)

Figure 1.9 Principle diagram of a opposed pistons engine

8 - Classify by the reversibility of the crankshaft:

+ Reversible engines + Irreversible

(non-reversible) engines

9 - Classify by the action of the piston:

+ Single action engines +

Double action engines

10- Classify by the speed (n - revolution perminute) of the engines:

+ Low speed engines: n < 240 rpm (rev/min)

+ Medium speed engines: 240 < n < 750 rpm (rev/min)

+ High speed engines: n > 750 rpm (rev/min)

11- Classify by the construction of the crank-connecting rod mechanism:

+ Trunk piston engines: (in which the connecting rod is connected directly with the piston through the piston pin)

+ Crosshead piston engines (or crosshead engines, in which the connecting rod and the piston rod

IE

Upper /piston t L

.Exhaust port Fuel

12 - Classify by the stroke length of the piston:

+ Short stroke engines: ratio S/D is about 1,0 ~ 1.5 +

Long stroke engines: ratio S/D = 2.5 ~ 3.0 + Super long

stroke engines: ratio S/D >3.0

Review questions

1 State the basic definitions that used for a diesel engine: working process; working circle; 4-stroke and 2-stroke engines; stroke circle; TDC and BDC; piston stroke; clearance volume; total volume; working volume; compression ratio.

2 State operational principle of 4-stroke and 2-stroke diese! engines.

3 Compare 4-stroke with 2-stroke diesel engine types.

4 Explain the working circle of 4-stroke diesel and 2-stroke engine on the timing diagram.

5 Represent classification of internal combustion engines.

CHAPTER 2 STATIC PARTS CONSTRUCTION OF DIESEL ENGINES

2.1 BEDPLATE

2.1.1 General construction

- Bedplate is subjected to the entire weight of the engine, receives the combustion gases pressureand action forces of the moving parts of the engine Therefore, the bedplate must be constructed with thesufficient strength and rigidity to resist the bending in the longitudinal direction

Figure 1.10 Principle diagram of a crosshead engine

engine is made either of a single forging, or of separate construction and then is welded to the lower side ofthe bedplate.

The bottom of the crankcase is usually slopewise arranged to the flywheel side or the middle of theengine (it is convenient for flowing of the lubricating oil) When the engine is working the big end of theconnecting rod must not be reached to the lubricating oil surface

- The bedplate is secured to the ship’s structure by bolts

2.1.2 The bedplate of low-speed large engines

- The bedplate of the large engines is normally made of welding steel plates It allows to reduce theweight and to increase rigidity of the bedplate

- Basically, the bedplate consists of longitudinal girders, transverse girders (crossgirders) andstrengthening bars

The transverse girders strengthen the rigidity of the bedplate in transversal direction The center ofthe girders is formed the saddle to support the main bearings of the engine

These transverse girders, together with partitions divide the bedplate into spaces corresponding to thenumber of the cylinder The lower part of the partitions is made a hole to circulate the lubricating oil in thecrankcase

Figure 2.1 is an illustration of the bedplate construction of large engines

Figure 2.2 shows the transverse partition of the large engines

Figure 2.2 Construction of the transverse partition

- In multi-cylinder diesel engines with long axial dimension, the bedplate is normally built up ofseparate sections, which are secured to each other by bolts

2.1.3 The bedplate of high and medium-speed engines

For high and medium-speed, small engines the bedplate is generally made of cast iron or cast steel(Figure 2.3)

2.2 MAIN BEARINGS

The main bearings are placed on the transverse girders of the bedplate Each main bearing consist

of a bearing cap and two bearing shells (bearing liners)

1 - Crankshaft; 2 - Transverse girders of the bedplate;

3 — Bearing shell; 4 — Bearing cap; 5- Bolt

2.2.1 Main bearing shells

- The bearing shell has a form of a cylindrical half Inside of the bearing shells is covered by a thinanti-corrosion layer (white metal or copper-lead alloy, figure 2.5)

Figure 2.3 Bedplate of high and medium-speed, small engines

Figure 2.4 Main bearing

1 — Upper shell; 2— Lower shell

- The upper shell is drilled one or some holes, these holes connect to the annular groove inside the shell for purpose of distribution the lubricating oil on the shell surface

Figure 2.5 Main bearing shell

a convex claw on the back that fits in the hollow of the bedplate or the bearing cap.

- There are two kinds of bearing shell: thin wall and thick wall type

+ Thin wall bearing shells has a thickness of 3 ~ 5 mm This type of bearing shells are made

of steel, interior is anti-friction metal, next layers are nickel and zinc, outside surface is covered by athin anti-corrosion layer (figure 2.6)

Thin wall bearing shells are normally used for high-speed engines

+ Thick wall bearing shells has a thickness of 7 ~ 15 mm They are made of cast iron, thesurface is cast white metal or other soft metal On the assembling surfaces between the two bearingshells are placed thin shims to adjust the oil clearance when necessary

Thick wall bearing shells are generally used for low-speed engines However, in recentyears the type of thin wall bearing shell is commonly used for all of the engines

2.2.2 Main bearing caps

- Bearing caps are used for pressing bearing shells on the bedplate and to ensure the contact withoutclearance between the two bearing shell in all working condition of the engine

- To secure the main bearing caps on the bedplate, they can use bolts (figure 2.7a) or jacks, in thiscase, two ends of the jack press on the bearing cap and engine frame (figure 2.7b)

Figure 2.6 Construction of thin wall bearing shell

Anti-corrosion layer (2jim) Galvanised layer (20- 60nm)

Nickel barrier (2-4nm) Bearing metal (0.3-1.2mm) Steel backing shell

a) b)

Figure 2.7 Fastening between bearing caps and bedplate by bolts (a) and jack (b)

- The main bearing caps are normally made of cast iron, their cross section has a form of rectangle orletter I The main bearing caps are drilled the centripetal groove to fed the lubricating oil to the bearing shellsand journals (figure 2.8)

Figure 2.8 Oil groove for lubricating journal and bearing shell

For high-speed, small engines without bedplate, the underslung main bearings construction is used Inthis case, the main bearing caps are fastened to the engine frame (framework) by bolts, below the engine isarranged a light oil tray to collect the lubricating oil (figure 2.9)

Figure 2.9 Underslung main bearing of the diesel D100

- In case of engines without thrust bearing, the main bearing toward the flywheel (flywheel side

Figure 2.10 Construction of a stop bearing