“不落的星尘”全力打造，华丽的一个金币，传说中的物美价廉
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…………分割线…………割了烦恼…………毕业愉快…………工作愉快……
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（本文来自《汽车专业英语》/陈勇、边明远主编）
The Engine’s System
The engine is an important part of the automobile; it acts as the heart of a person, which provides the power that the cars need to run on the road. All the automotive engines today are the Internal Combustion Engines ( ICEs ) because the fuel is burnt inside their cylinders and the energy is provided.
ICEs are those heat engines that burn their fuel inside the engine cylinder. In ICEs, the chemical energy stored in their fuel converted into heat energy during the burning part of their operation. The heat energy is converted into mechanical energy by the expansion of gases against the piston attached to crankshaft that can rotate. The engines that burn petrol are known as petrol engine. Other types of ICEs burn heavier oils, of these types the diesel engine has come into the widest use.
Diesel and petrol engines have the same mechanical parts, except that diesel components are generally stronger and heavier. Both engines are internal combustion engines, but they have different fuel system and use different fuels. With a diesel, only air enters the cylinder during the intake stroke. A petrol engine takes in an air-fuel mixture. Following are some general comparisons between diesel and petrol engines:
In a diesel, the fuel is injected into the cylinder as a fine spray near the top of the compression stroke. With a petrol engine, the fuel is injected into the exhaust ports at the start of the induction stroke.
Ignition in a diesel is by the high temperature from the highly compressed air. A petrol engine needs a spark for ignition.
Diesel engines generally operate at lower engine rpm than petrol engines.
Diesel engines use distillate for fuel, which is less volatile than petrol.
The design of diesel engines makes them noisier than petrol engines and they have a unique diesel knock.
Small diesel engines, as well as petrol engines, are used in passenger cars and light commercial vehicles. Larger diesel engines are used in all heavy commercial vehicles, earthmoving equipment, and farm machinery.
1. Engine Configurations
The term engine configuration refers to the way that the cylinders of an engine are arranged. The cylinders can be in-line, or at an angle ( V-type ). Within these three basic arrangements, there are a number of variations.
In-line engine
With in-line engines, the cylinders are arranged in a straight line, one behind the other. Most in-line engines have their cylinders vertical, but some are slanted. That is, the engine is tilted at an angle to reduce the overall height. These engines are sometimes referred to as slanted engines.
Some in-line engines have their cylinders horizontal, so that the engine is more or less on its side. This reduces the overall height of the engine. This arrangement is
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used mainly in larger commercial vehicles with the engine mounted under part of the cab. The mechanical arrangement of a four-cylinder in-line for a passenger car is shown in Fig.1-
9. The cut-away view in Fig.1-10 enables the various parts to be identified.
Horizontally opposed engine
This arrangement has its cylinders arranged in two flat blanks with the crankshaft between them. The engine shown has a short rigid crankshaft with five bearings. A horizontally opposed engine has even firing impulses and good balance. Movement of a piston in direction is opposed by movement of a piston in the opposite direction.
Horizontally opposed engines, with their flat design, give the engine a low height and also help to keep the center of gravity of the vehicle low. A low center of gravity gives the vehicle stability.
V-type engines
With V-type engines, the cylinders are arranged in two blanks at an angle. This reduces the length of the engine and makes it more compact. This also reduces the length of the crankshaft, which can be designed to be more rigid than a long shaft.
2. The Engine Assembly and Components
The complete engine assembly consists of the mechanical components that make up the engine itself and also a number of associated systems. These are the systems that are needed to start the engine and also to control it and keep it running. The mechanical parts of the engine assembly can be broken down into a number of sub-assemblies, or groups of associated components, although these are usually referred to merely as assemblies, for example, cylinder-head assembly and piston assembly. Some parts of an engine are internal, other parts are external, this illustration identifies a number of external parts.
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