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1、 Unit 2 The Basic Principle of Engine Text A Classification and Main Components of Engine The internal combustion engine is an engine in which the combustion of fuel occurs with oxygen(usually air) in a combustion chamber, as shown in Fig.2.1. 1 8 7 6 9 2 3 4 5 Fig.2.1 Internal Combustion Engine 1th
2、e cap of the cylinder head 2valve 3engine block 4flywheel 5crankshaft 6oil pan 7pulley 8cylinder 9timing gear Classification of Engine The engine can be classified in following ways: By Fuel System Gasoline engine and diesel engine are used. In a gasoline engine, the air-fuel mixture is exploded in
3、the engine. A diesel engine uses diesel fuel. It generates high power at low speeds. The fuel efficiency is better than that of a gasoline engine. 11 Unit 2 The Basic Principle of Engine By Cylinder Arrangement Most cars have more than one cylinder. Four, six and eight cylinders are common used. In
4、a multi-cylinder engine, the cylinders are usually arranged in one of three ways: in-line, V-type, or flat (Fig.2.2). Today the number of cylinders is growing, the cylinders also can be arranged as W-type. (a) flat (b) V-type (c) in-line Fig.2.2 Cylinder Arrangement By Cooling System Liquid-cooled e
5、ngines and air-cooled engines are being used. Liquid-cooled engines are the most common in the engine industry. There are also other ways to classify the engines. Despite of these classifications, the structure of the engine is basically the same. Main Components The engine consists of several diffe
6、rent mechanisms and systems including cylinder block, crankshaft and connecting rod mechanism, valve mechanism, fuel supply system, lubrication system, cooling system, ignition system and starting system. Cylinder Block The core of the engine is the cylinder, with the piston moving up and down insid
7、e the cylinder. Crankshaft and Connecting Rod Mechanism The crankshaft changes the linear movement of the piston into a rotational movement via a connecting rod. The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and
8、the crankshaft rotates. Valve Mechanism A valve mechanism is a group of components that opens and closes the intake and exhaust valves in the cylinder head at the appropriate time. The main functions of the valve gear are to provide timely admission of the fresh charge into the cylinders and exhaust
9、 of spent gases from them. 12 汽车专业英语 Fuel Supply System The fuel system supplies fuel to the engine. It also has the functions to regulate the volume of fuel supply. The fuel systems in diesel and gasoline engines are different. Lubrication System The lubrication system uses an oil pump to continuou
10、sly supply engine oil throughout the inside of the engine. This system reduces friction between parts with a film of oil. If the engine is run without oil, the friction can cause poor running, or cause even meltdown. In addition to lubrication, engine oil cools and cleans the engine. Cooling System
11、The cooling system regulates the engine temperature to an optimal level (80 to 90 at coolant temperature) by circulating the coolant throughout the engine under all operating conditions and during all seasons of the year. The cooling fan cools the coolant in the radiator and water pump circulates th
12、e coolant through the cylinder head and the cylinder block. Ignition System Internal combustion engines require ignition of the mixture, either by spark ignition (SI) or compression ignition (CI). Starting System The starting system forces the engine to crank with an electric motor, and starts the e
13、ngine. Text B Engine Operating Principles A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes：intake, compression, power and exhaustduring two separate revolutions of the engines crankshaft, and one single thermodynamic
14、 cycle.The main parts in four stroke engine are shown in Fig.2.3. Fig.2.3 Main Parts in Four Stroke Engine 1intake valve 2spark plug 3exhaust valve 4combustion chamber 5piston head 13 Unit 2 The Basic Principle of Engine As their name implies, four-stroke internal combustion engines have four basic
15、steps that repeat with every two revolutions of the crankshaft: Intake stroke Compression stroke, Power stroke, Exhaust stroke. The four strokes will be illustrated in Fig.2.4. They draw in an air-fuel mixture to the cylinders, compress it, ignite and combust it, then discharge it. Repeating these f
16、our actions gives gasoline engines their power. The cycle begins at Top Dead Centre (TDC), when the piston is farthest away from the crankshaft. A cycle refers to the full travel of the piston from TDC to Bottom Dead Centre (BDC). Intake Stroke On the intake stroke of the piston, the piston descends
17、 from (TDC,BDC) to (TDC, BDC), reducing the pressure inside the cylinder. A mixture of fuel and air, or just air in a diesel engine, is forced by atmospheric pressure into the cylinder through the intake port. The intake valve(s) then (open,close). Compression Stroke With both intake and exhaust val
18、ves (open,close), the piston returns to the top of the cylinder compressing the fuel-air mixture into the combustion chamber of the cylinder head. Power Stroke It is also named as combustion stroke. While the piston is close to (TDC,BDC), the compressed airfuel mixture is ignited. The resulting mass
19、ive pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward (TDC,BDC). Exhaust Stroke During the exhaust stroke, the piston once again returns to (TDC,BDC) while the exhaust valve is (open,close). This action evacuates the burnt products of combustion from
20、the cylinder by expelling the spent fuel-air mixture out through the exhaust valve(s). . (1) intake (2) compression (3) power (4) exhaust Fig.2.4 Four Stroke Cycle 14 汽车专业英语 NEW WORDS AND PHRASES principle n. 原理，法则 classification n. 种类，类别 configuration n. 布局，构造 oxygen n. 氧气 combustion n. 燃烧 chamber
21、n. 室，房间 component n. 成分，部件，零件 force n. 力 gasoline n. 汽油 diesel n. 柴油；柴油机 explode n. 爆炸，爆发 rotational adj. 旋转的 in-line adj. (汽缸)直列的 flat adj. (汽缸)水平对置 cooling system 冷却系 liquid-cooled 水冷 air-cooled 风冷 cylinder block 汽缸体 crankshaft n. 曲柄轴，机轴 connecting rod 连杆 valve mechanism 配气机构 fuel supply system 燃油
22、供给系 lubrication 润滑 lubrication system 润滑系 ignition system 点火系 starting system 起动系 linear adj. 线性的 piston n. 活塞 intake n. 吸入；进气口，入口 exhaust n. 排气；废气 valve n. 气门，阀门 oil pump 机油泵 friction n. 摩擦(力) part n. 零件, 部位 appropriate adj. 恰当的，适当的 15 Unit 2 The Basic Principle of Engine volume U.S. n. 容量，容积 a fil
23、m of oil 一层油膜 meltdown n. 熔毁 optimal adj. 最佳的，最优的 coolant n. 冷却液，冷冻剂 radiator n. 散热器 water pump 抽水机，水泵 spark ignition (SI) 火花点火 compression ignition (CI) 压缩点火 four-stroke 四冲程的(内燃机) power n. 做功 illustrate vt. 说明，阐明 revolution n. 旋转(一周) spark plug 火花塞 discharge vt. 释放；排出 Top Dead Centre (TDC) 上止点 Bott
24、om Dead Centre (BDC) 下止点 descend vi. 下降，降临 evacuate vi. 散离，释放 NOTES TO THE TEXT 1. The internal combustion engine is an engine in which the combustion of fuel occurs with oxygen(usually air) in a combustion chamber. 内燃机是一种由燃料和氧气(通常是空气)在燃烧室中燃烧而产生动力的发动机。 2. The engine consists of several different mec
25、hanisms and systems including cylinder block, crankshaft and connecting rod mechanism, valve mechanism, fuel supply system, lubrication system, cooling system, ignition system and starting system. 发动机由不同的机构和系统构成，包括汽缸体、曲轴和连杆机构、配气机构、燃油供 给系、润滑系、冷却系、点火系和起动系。 3. The crankshaft changes the linear movement
26、 of the piston into a rotational movement via a connecting rod. 曲轴把活塞的线性运动通过连杆转换成旋转运动。 4. A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes, intake, compression, power and exhaustduring two separate revolutions of the
27、 engines crankshaft, and one single thermodynamic cycle. 四冲程发动机也叫做四循环发动机，这种内燃机在发动机曲轴转两周和一个热力学循 环中完成四个独立的冲程即进气、压缩、做功和排气。 16 汽车专业英语 5. While the piston is close to Top Dead Center, the compressed airfuel mixture in a gasoline engine is ignited, usually by a spark plug, or fuel is injected into the die
28、sel engine, which ignites due to the heat generated in the air during the compression stroke. 活塞接近上止点时，汽油机中的压缩空气与燃料混合气通常被火花塞点燃，而柴油机 中燃油直接喷入发动机，由压缩冲程压缩空气产生的热量压燃。 6. They draw in an air-fuel mixture to the cylinders, compress it, ignite and combust it, then discharge it. 空气与燃料混合气被吸入汽缸里，被压缩，点燃、燃烧，然后被排出
29、。 EXERCISES 1. Translate the following words to English. 发动机工作原理 发动机结构 内燃机 起动系 曲轴和连杆机构 配气机构 燃油供给系统 上止点 四冲程发动机 空燃混合气 活塞 汽缸排列 水冷 多缸发动机 柴油机 上下运动 润滑系统 冷却系统 点火系 油膜 2. Translate the following sentences to Chinese. (1) In an internal combustion engine, the expansion of the high-temperature and 17 Unit 2 Th
30、e Basic Principle of Engine high-pressure gases produced by combustion apply direct force to some component of the engine. (2) The air-fuel mixture is exploded in the engine, and this force is converted into a rotational movement to move the vehicle. (3) In a multi-cylinder engine, the cylinders usu
31、ally are arranged in one of three ways: inline, V-type or flat. (4) The crankshaft changes the linear movement of the piston into a rotational movement via a connecting rod. (5) Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. (6) As their
32、name implies, four-stroke internal combustion engines have four basic steps that repeat with every two revolutions of the engine:Intake stroke, Compression stroke, Power stroke，Exhaust stroke. 3. The diagrams(Fig.2.5) below show the four strokes of a 4-cycle gasoline engine offers many advantages, F
33、rom word group A, select the words that are applicable to the numbers given in parentheses. From word group B, select the phrases that appropriately describe the respective strokes. Fig.2.5 (1) ( ) Stroke (2) ( ) Stroke (3) ( ) Stroke (4) ( ) Stroke Group A a) Compression b) Exhaust c) Intake d) Com
34、bustion Group B e) The exhaust valve closes and the intake valve opens. The downward stroke of the piston causes the air-fuel mixture to be drawn into the cylinder via the open intake valve. f) Both the intake and exhaust valves are closed. The compressed air-fuel mixture combusts and explodes. The
35、force of this explosion pushes the piston downward. g) Both the intake and exhaust valves are closed. The air-fuel mixture that is drawn into the cylinder is compressed by the upward stroke of the piston. h) The intake valve closes and the exhaust valve opens. The exhaust gases that result from the
36、combustion are discharged outside of the cylinder. 18 汽车专业英语 READING MATERIAL Wankel engine The Wankel engine is a rotary engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. The rotary engine is sometimes called a Wankel engine,
37、or Wankel rotary engine,for it was invented by Dr. Felix Wankel, a German Engineer. In a piston engine, the same volume of space (the cylinder) alternately does four different jobsintake, compression, combustion and exhaust. A rotary engine does these some four jobs, but each one happens in its own
38、part of the housing. Its kind of like having a dedicated cylinder for each of the four jobs, with the piston moving continually from one to the next. As shown in Fig.2.6, the single rotor Wankel engine is consist of several different parts, intake port, exhaust port, rotor, housing and two spark plu
39、gs. The rotor has three convex faces, each of which acts like a piston. Each face of the rotor has a pocket in it, which increases the displacement of the engine, allowing more space for air/fuel mixture. The housing is roughly oval in shape. The shape of the combustion chamber is designed so that t
40、he three tips of the rotor will always stay in contact with the wall of the chamber, forming three sealed volumes of gas. 1 2 5 4 3 Fig.2.6 Basic Structure of Single-rotor Wankel Engine 1intake port 2exhaust port 3housing 4spark plug 5rotor The best way to visualize the action of the engine in the a
41、nimation at left is to look not at the rotor itself, but the cavity created between it and the housing. The rotary engine is actually a variable-volume progressing-cavity system. Thus there are 3 cavities per housing, all repeating the same cycle. As the rotor rotates and orbit ally revolves, each s
42、ide of the rotor is brought closer to and then away from the wall of the housing, compressing and expanding the combustion chamber like the strokes of a piston in a reciprocating engine. The power vector of the combustion stage goes through the center of the offset lobe. While a four-stroke piston e
43、ngine 19 Unit 2 The Basic Principle of Engine makes one power stroke per cylinder for every two revolutions of the crankshaft, each combustion chamber in the Wankel generates one power stroke per each driveshaft rotation. Thus, power output of a Wankel engine is generally higher than that of a four-
44、stroke piston engine of similar engine displacement in a similar state of tune; and higher than that of a four-stroke piston engine of similar physical dimensions and weight. For comparison purposes between a Wankel Rotary engine and a piston engine, displacement and corresponding power output can m
45、ore accurately be compared on the basis of displacement per revolution of the eccentric shaft. A Wankel Rotary engine is still a 4-stroke engine and pumping losses from non-power strokes still apply, but the absence of throttling valves and a 50% longer stroke duration result in a significantly lowe
46、r pumping loss compared against a four-stroke reciprocating piston engine. Measuring a Wankel rotary engine in this way more accurately explains its specific output, as the volume of its air fuel mixture put through a complete power stroke per revolution is directly responsible for torque and thus power produced. eccentric adj. 偏心的 single rotor 单转子 intake port 进气口 exhaust port 排气口 spark plug 火花塞 convex Adj. 凸出的，凸面的 displacement n. 排量 oval adj. 椭圆形的 visualize vt. 想象，设想 throttling valve 节气门 torque n. 转矩，项圈 power n. 功率