内燃机专业英语英文.doc

内燃机专业英语自编讲义部分：1. Engine Classification and Overall MechanicsThe automobile engines can be classified according to: 1. number of cylinders; 2. arrangement of cylinders; 3. arrangement of valves; 4. type of cooling; 5. number of cycles (two or four); 6. type of fuel burned; 7. type of ignition.The engine is the source of power that makes the wheels go around and the car move. The automobile engine is an internal-combustion engine because the fuel (gasoline) is burned inside it. The burning of gasoline inside the engine produces high pressure in the engine combustion chamber. This high pressure forces piston to move, the movement is carried by connecting rods to the engine crankshaft. The crankshaft is thus made to rotate; the rotary motion is carried through the power train to the car wheels so that they rotate and the moves.The engine requires a fuel system to supply it with a mixture of air and fuel. The fuel system does this by pumping liquid gasoline from a tank into the carburetor, a mixing device that mixes the gasoline with air. The mixture is delivered to the engine where it is burned.The engine also needs a cooling system, the combustion of the air-fuel mixture in the engine creates a very high temperature (as high as 2000 to 2700 ). The cooling system takes heat away from the engine by circulating a liquid coolant (water mixed with antifreeze) between the engine and a radiator. The coolant gets hot as it goes through the engine. It cools off as it goes through the radiator. Thus, the coolant continually takes heat away from the engine, where it could do damage, and delivers it to the radiator. Air passing through the radiator takes heat away from the radiator.The engine also includes a lubricating system. The purpose of the lubricating system is to supply all moving parts inside the engine with lubricating oil; the oil keeps moving parts from wearing excessively.The engine requires a fourth system, the ignition system. The ignition system provides high-voltage electric sparks that ignite, or set fire to, the charges of air-fuel mixture in the engine combustion chambers.The fifth is starting system and its purpose is to change the electrical current into the mechanical energy to push the crank-shaft around. By means of this, the engine can be started.These five systems are discussed briefly in following sections.Words and Expressionscombustion chamber 燃烧室；ignition. 点燃；power train 动力传动系统；carburetor 化油器；antifreeze 防冻的；coolant 冷却剂（液态）；crankshaft 曲轴282. Four-stage-engine OperationThe action taking place in the engine cylinder can be divided into four stages, or strokes. “Stroke” refers to piston movement; as stroke occurs when the piston moves from one limiting position to the other. The upper limit of piston movement is called TDC （top dead center）. The lower limit of piston movement is called BDC (bottom dead center). A stroke is piston movement from TDC to BDC or from BDC to TDC. In other words, the piston completes a stroke each time it change its direction of motion.Where the entire cycle of events in the cylinder requires four strokes (or two crankshaft revolutions), the engine is called a four-stroke-cycle engine, or a four-cycle engine. The four piston strokes are intake, compression, power, and exhaust.Intake stroke. On the intake stroke, the intake valve has opened, the piston is moving downward, and a mixture of air and vaporized gasoline is entering the cylinder through the valve port. The mixture of air and vaporized gasoline is delivered to the cylinder by the fuel system and carburetor.Compression stroke. After the piston reaches BDC, or the lower limit of its travel, it begins to move upward. As this happens, the intake valve closes. The exhaust valve is also closed, so that the cylinder is sealed. As the piston moves upward (pushed now by the revolving crankshaft and connecting rod), the air-fuel mixture is compressed. By the time the piston reaches TDC, the mixture has been compressed to as little as one-tenth of its original volume, or even less. This compression of the air-fuel mixture increases the pressure in the cylinder. When the air-fuel mixture is compressed, not only does the pressure in the cylinder go up, but the temperature of the mixture also increases.Power stroke. As the piston reaches TDC on the compression stroke, an electric spark is produced at the spark plug. The ignition system delivers a high-voltage surge of electricity to the spark plug to produce the spark. The spark ignites, or sets fire to, the air-fuel mixture. It now begins to burn very rapidly, and the cylinder pressure increases to as much as 3-5 MPa or even more. This terrific push against the piston forces it downward, and a power impulse is transmitted through the connecting rod to the crankpin on the crankshaft. The crankshaft is rotated as the piston is pushed down by the pressure above it.Exhaust stroke. As the piston reaches BDC again, the exhaust valve opens. Now, as the piston moves up on the exhaust stroke, it forces the burned gases out of the cylinder through the exhaust-valve port. Then, when the piston reaches TDC, the exhaust valve closes and the intake valve opens. Now, a fresh charge of air-fuel mixture will be drawn into the cylinder as the piston moves down again toward BDC. The above four strokes are continuously repeated.Words and Expressions stroke 行程，冲程；BDC 上止点；TDC 下止点；surge 冲击，脉动；terrific 了不起的，绝妙的；crankpin 曲柄销，连杆轴颈；intake stroke 吸气冲程；compression stroke 压缩冲程；power stroke 做功冲程；exhaust stroke 排气冲程；fresh charge （发动机）吸入的新鲜混合油气 3. Two-stage-engine OperationIn the four-stroke-cycle engine, already discussed in lesson 1、2, the complete cycle of events requires four piston strokes (intake, compression, power, and exhaust). In the two-stroke-cycle, or two-cycle, engine, the intake and compression strokes and power and exhaust strokes are in a sense combined. This permits the engine to produce a power stroke every two piston strokes, or every crankshaft rotation.In the two-cycle engine, the piston acts as a valve, clearing valve ports in the cylinder wall as it nears BDC.A fresh air-fuel charge enters through the intake port, and the burned gases exit through the exhaust port. The complete cycle of operation is as follows: As the piston nears TDC, ignition takes place. The high combustion pressures drive the piston down, and the thrust through the connecting rod turns the crankshaft. As the piston nears BDC，it passes the intake and exhaust ports in the cylinder wall. Burned gases, still under some pressure, begin to stream out through the exhaust port. At the same time, the intake port, now cleared by the piston, begins to deliver air-fuel mixture, under pressure, to the cylinder. The top of the piston is shaped to give the incoming mixture an upward movement. This helps to sweep the burned gases ahead and out through the exhaust port.After the piston has passed through BDC and stars up again, it passes both ports, thus sealing them off. Now the fresh air-fuel charge above the piston is compressed and ignited. The same series of events takes place again and continue as long as the engine runs.We mentioned that the air-fuel mixture is delivered to the cylinder under pressure. In most engines, this pressure is put on the mixture in the crankcase. The crankcase is sealed except for a leaf, or reed, valve at the bottom. The reed valve is a flexible, flat metal plate that rests snugly against the floor of the crankcase. There are holes under the reed valve that connect to the engine carburetor. When the piston is moving up, a partial vacuum is produced in the sealed crankcase. Atmospheric pressure lifts the reed valve off the holes, and air-fuel mixture enters the crankcase. After the piston passes TDC and starts down again, pressure begins to build up in the crankcase. This pressure closes the reed valve so that further downward movement of the piston compresses the tapped air-fuel mixture in the crankcase. The pressure which is built up on the air-fuel mixture then causes it to flow up through the intake port into the engine cylinder when the piston moves down far enough to clear the intake port.The two-stroke engine is not only very simple but gives nearly twice the power of a four stroke engine from a cylinder of given size, but it is wasteful of gasoline, as some mixture inevitably finds its way into the exhaust system on the combines intake/exhaust stroke, and there are always some combustion products left in the cylinder which reduce the rapid burning of the fuel. This kind of engine is always used in motorcycles.Words and Expressionssweep 扫气；connecting rod 连杆；crankcase 曲轴箱；seal off 密封；leaf （reed） valve 片簧阀；air-fuel charge 可燃混合油气4. Diesel Engine Operating FeaturesWe all know that diesel engines, in principle, work in the same way as gasoline engines do. Both kinds of engines are internal-combustion engines, but each of them has its characteristic features. As their names suggest this type of engines burn their fuel inside the working parts of the engines. “Internal” means “inside”, “combustion” means “catching fire or burning”. In any internal combustion engine, burning fuel heats air which consequently expands, and in expanding exists a push to a piston which, in turn, rotates the engine crankshaft through a connecting rod.Now let us compare the diesel engine with the gasoline engine. Firstly, the explosive mixture of the gasoline engine is provided by a carburetor, but in the case of the diesel engine the supply is affected by an injection or “jerk” pump which forces a “short” of fuel into each cylinder in turn according to the correct firing sequence. Secondly, the fundamental difference between gasoline and diesel engines is that in the gasoline engine the source of the heat for igniting the charge, namely, an electric spark, is generated outside the engine, and is taken, as it were, into the waiting charge at the required instant. In the diesel engine the source of heat for igniting the charge is created within the engine by compressing pure air to a degree that will initiate combustion and then injecting the fuel at the right time in relation to the movement of the crankshaft. Both classes of engines are of very similar construction. But as the diesel engine is called upon to withstand very much greater stresses due to higher pressures in cylinders, it has to be of more substantial construction, and is thus heavier. In general, the diesel engine may weigh about 9.25 kilograms per kilowatt. The most important advantage of the gasoline engine is its lower weight per kilowatt. The gasoline engine for automobiles weighs about 6.17 kilograms per kilowatt, and gasoline engines for airplanes may weigh as little as 0.77 kilograms per kilowatt. This advantage prevents the diesel engine from replacing the gasoline engine in some automobiles and airplanes.However, the diesel engine is more efficient, because it has higher compression ration. Its ratio may be as high as 16 to 1. Up to 40 percent of the chemical energy of the burning fuel may be changed into mechanical energy. In addition, the diesel engine runs cooler than the gasoline engine. This advantage is especially obvious at lower speeds. Diesel oil is not only cheaper than gasoline, but also safer to store.Words and Expressions：diesel：柴油机； internal-combustion engines：内燃机； jerk pump：脉动史喷油泵；compression ration：压缩比5. Engine Cylinder Block CrankcaseWe have seen how the mixture of air and fuel is delivered by the fuel system to the engine cylinder, where it is compressed, ignited, and burned. We have noted that this combustion produces a high pressure that pushes the piston down so that the crankshaft is rotated. Now let us examine the various parts of the engine in detail.Engine cylinder blockThe cylinder block of liquid-cooled engines forms the basic framework of the engine. Other parts are attached to the cylinder block or are assembled in it. The block is cast in one piece from gray iron or iron alloyed with other metals, such as nickel or chromium. Some blocks are cast from aluminum. The block contains not only the cylinders but also the water jackets that surround them. In aluminum blocks, cast-iron or steel cylinder sleeves (also called bore lines) are used. These metals have better wearing qualities than aluminum and can better withstand the wearing effect of the pistons and ring moving up and down in the cylinders. For most engines, cast iron has been found to be a satisfactory cylinder-wall material. However, in some small engines, the cylinder walls are plated with chromium, a very hard metal, to reduce wall wear and lengthen their life.Cylinder HeadThe cylinder head is usually cast in one piece from iron, from iron alloyed with other metals, or from aluminum alloy. Aluminum has the advantage of combining lightness with high heat conductivity. That is, an aluminum head tends to turn cooler, other factors being equal. There are two types of head, L head and I head. Cylinder head contains water jackets for cooling; in the assembled engine, these water jackets are connected through openings to the cylinder-block water jackets. Spark-plug holes are provided, along with pockets into which the valves can move as they open.GasketsThe joint between the cylinder block and the head must be tight and able to withstand the pressure and heat developed in the combustion chambers. The block and head cannot be machined flat and smooth enough to provide an adequate seal. Thus, gaskets are used. Head gaskets are made of thin sheets of soft metal or asbestos and metal. All cylinder, water, valve, and head-bolt openings are cut out. When the gasket is placed on the block and the head installed, tightening of the head bolts (or nuts) squeezes the soft metal so that the joint is effectively sealed. Gaskets are also used to seal joints between other parts, such as between the oil pan, manifolds, or water pump and the block.Oil PanThe oil pan is usually formed of pressed steel. It usually holds 5 to 10 litres of oil, depending on the engine design. The oil pan and the lower part of the cylinder block together are called the crankcase; they enclose, or encase, the crankshaft. The oil pump in the lubricating system draws oil from the oil pan and sends it to all working parts in the engine. The oil drains off and runs down into the pan. Thus, there is constant circulation of oil between the pan and the working parts of the engine.Words and Expressionscylinder block 气缸体；block crankcase 曲轴箱；framework 结构，车架； gray iron 灰铸铁；water jacket 水套； platewith 镀金属；cylinder head 气缸盖；gaskets 密封垫；asbestos 石棉；manifold 岐管；oil pan 油盘； pocket 凹槽；bore liner 气缸衬套 6. Piston Connecting RodPistonThe piston is essentially a cylindrical plug that moves up and down in the engine cylinder. It is equipped with piston rings to provide a good seal between the cylinder wall and piston. The piston absorbs heat from the gas, and this heat must be carried away if the metal temperature is to be carried away if the metal temperature is to be held within safe limits. The constant reversal of the piston travel sets up inertial forces, which increase both with the weight of the piston and with its speed. For this reason, designers try to keep piston weight low, particularly in high-speed engines. As lower hood lines and over-square engines became popular, the semi-slipper and full-slipper pistons came into use. On these pistons the number piston rings was reduced to three, two compression and one oil-control. One reason for the slipper piston is that, on the short stroke, over-square engine, the piston skirt had to be cut away to make room for the counterweights on the crankshaft. Also, the slipper piston, being shorter and having part of its skirt cut away, is lighter. This reduces the inertial load on the engine bearings and, in addition, makes for a more responsive engine. The lighter the piston, the less the bearing load and the longer the bearings will last. Another way to lighten the piston is to make it of light metal. The idea piston material would be light and strong, conduct heat will, expand only slight when heated, resist wear, and be low in cost. Thus, most automotive-engine pistons today are made of aluminum, which is less than half as heavy as iron. Iron pistons were common in the earlier engines. Aluminum expands more rapidly than iron with increasing temperature, however, and since the cylinder block is of iron, special provisions must be made to maintain proper piston clearance at operating temperatures. To take care of it, the crown is machined on slight taper, the diameter being greatest where the crown meets the skirt and becoming less toward the top.Piston RingsA good seal must be maintained between the piston and cylinder wall to prevent blow-by. “Blow-by” is the name that describes the escape of burned gases from the combustion chamber, past the piston, and into the crankcase. In other words, these gases “blow by” the piston. It is not practical to fit the piston to the cylinder closely enough to prevent blow-by. Thus, piston rings must be used to provide the necessary seal. The rings are installed in grooves in the piston. Actually, there are two types of rings, compression rings and oil-control rings. The compression rings seal in the air-fuel mixture as it is compressed and also the combustion pressures as the mixture burns. The oil-control rings scrape off excessive oil from the cylinder wall and return it to the oil pan.The rings have joints (they are split) so that they can be expanded and slipped over the piston head and into the recessed grooves cut in the piston. Rings for automotive engines usually have butt joints, but in some heavy-duty engines, the joints may be angles, lapped, or