关于发动机的英语介绍

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Passage A    Kinds of Engines
    The engine is the heart of an automobile. The purpose of an automobile engine is to convert fuel into engine that moves the automobile. Currently the easiest way to create motion from fuel is to burn the fuel inside an engine. Therefore, an automotive engine is an internal combustion into engine, which burns fuel within cylinders and converts the expanding force of the combustion into rotary force used to drive the automobile.
   There are several types of internal combustion engines classified as reciprocating or rotary engine; spark ignition engine; and alternative-fuel engine or hybrid-electric vehicle.
Reciprocating Engine
The most familiar combination is the reciprocating spark-ignited, four-stroke gasoline engine, shown in Fig.1-1.a. The modern automobile is usually driven by a water-cooled, piston-type internal combustion engine, mounted in the front of the automobile; its power may be transmitted either to the front heels, or to all four wheels. Some automobile use air-cooled engines, but these are generally less efficient than the liquid-cooled type. The other main type of reciprocating engine is the diesel engine, which is employed both for heavy vehicles, such as trucks and buses, and for a small number of family sedans. Both diesel and gasoline engines generally employ a four- stroke cycle.
Rotary Engine
    A rotary combustion engine, also called Wankel engine, developed    by Felix Wankel of Germany in 1954, might provide an alternative to the reciprocating internal combustion engine because of its low exhaust emissions and feasibility for mass production. In this engine a three-sided rotor revolves within a combustion chamber in which the free space contracts or expands as the rotor turns, see Fig.1-2. Fuel is inhaled, compressed, and fired by the ignition system. The expanding gas turns the rotor and the exhausted gas is expelled, shown in 1-3. The rotary engine has no valves, pistons, connecting rods, reciprocating parts, or crankshaft. It develops a high horsepower, an essentially, produces no vibration, but its fuel consumption is higher than that of the conventional piston engine.
    Alternative –fuel Engine
    Internal combustion engines consume relatively high amounts of petroleum, and contribute heavily to air-pollution; therefore, other types of fuels and non-conventional engines are being studied and   developed.
    An alternative-fuel vehicle (AFV) is a dedicated flexible-fuel vehicle with a common fuel tank designed to run on varying blends of unleaded gasoline with either ethanol or methanol or a dual-fuel vehicle designed to run on a combination of an alternative fuel and a conventional fuel. An advanced-technology vehicle (ATV) combines a new engine, power train, and drive train system to significantly   improve fuel economy. The ideal alternative-fuel engine would burn fuel much more cleanly than conventional gasoline-powered internal combustion engines and yet still be able to use the existing gas stations.
Hybrid-electric Vehicle
    A hybrid vehicle, or a hybrid-electric vehicle (HEV) (shown in Fig.1-4), is powered by two or more energy sources, one of which is electricity, to produce a high-mile-per-gallon, low-emission drive. There are two types of HEVs, series and parallel. In a series hybrid, all of the vehicle power is provided from one source. For example, an electric motor drives the vehicle from the battery pack and the internal combustion engine powers a generator that charges the battery. In a parallel hybrid, power is delivered through both paths,     the electric motor and the internal combustion engine powering the vehicle. Thus, the electric motor may help power the vehicle while idling and during acceleration. The internal combustion engine takes over while cruising, powering the drive train and recharging the electric motor’s battery.
In current production hybrids both the engine and the electric motor are connected to the wheels by the same transmission. With the assistance of the electric motor the engine can be much smaller.

Passage B   Engine Types and Operating Principle
There are several engine types which are identified by the number of cylinders and the way the cylinders are laid out. Automobiles will have from 4to 12 cylinders or more, which are arranged in the engine block in several configurations. In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: in-line engine or V-type engine or flat engine (also known as horizontally opposed boxer), as shown in the following figures.
In-line engine has the cylinders arranged, one after the other, in a straight line. Almost all four-cylinder engines use this arrangement like Fig.1-5 shown. There are some five- and six-cylinder-in-line engines.
An in-line four-cylinder engine fires every 180º, which means that always two pistons are in the same position and moving up are moving at different speeds than pistons that are moving down. So there are vibrations that have to be cancelled by balancer shafts.
An in-line six engine consists basically of two three-cylinder engines. So there isn’t even end-to-end vibration. Because the crankshaft is identical with the one of a three cylinder, only twice  as long and with twice as much pistons. That is the reason why in-line six cylinder engines run so smoothly.
The V-type engine has two banks of cylinders side-by-side and is commonly used in V-6, V-8, and V-12 configurations at a ninety or sixty degree angle to each other. Its advantages are its short length, the great rigidity of the block. This type of engine lends itself to very high, resistance to torsional vibration, and a shorter car length without losing passenger room. Fig.1-6 show V6 engine.
A flat engine or horizontal-opposed engine uses two opposing banks of cylinders and are less common than the other  two  design, see Fig.1-7. It is ideal for installations where vertical space is limited, because it has a very low height. Flat engine are usually either four or six cylinders, and have been used by Porsche and Subaru. Flat engines are used in some Ferrari’s with 12 cylinders.
Different configurations have different advantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.
How an engine works
Almost all cars currently use a four-stroke combustion cycle to convert gasoline into motion. That is to say that the Intake stroke, Compression stroke, Power stroke and Exhaust stroke are one engine cycle. When the fourth stroke is completed, the cycle begins again. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four-strokes are illustrated in Fig.1-8. They are:
Intake stroke
The first stroke is the intake stroke. As the piston starts down, the intake valve opens and the air-fuel mixture enters into the cylinder. When the piston reaches the bottom of the intake stroke, the intake valve closes, trapping the air-fuel mixture in the cylinder. During this stroke, the exhaust valve stays closed.
Compression stroke
The second stroke is the compression stroke. The piston moves in the cylinder with both valves closed and compresses the trapped air-fuel mixture. When the piston reaches the top of the cylinder, the pressure rises.
Power stroke
The third stroke is the power stroke. Near the end of the compression stroke, the spark plug fires, igniting the compressed air-fuel mixture that produces a powerful explosion. The combustion process pushes the piston down the cylinder with great force turning the crankshaft to provide the power to drive the car.
Exhaust stroke
The fourth stroke is the exhaust stroke. With the piston at the bottom of the cylinder, the exhaust valve opens, and the piston moves up again and forces the burned gases out of the cylinder. The piston travels up to the top of the cylinder pushing all the exhaust out before closing the exhaust valve in preparation for starting the four-stroke process over again.

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