1、1 中文 3214 字 外文原文 The Diesel Engine In 1892 Rudolf Diesel developed and obtained the German patent for the diesel engine. His goal was to create an engine that was highly efficient. Much more efficient than the gasoline engine that was invented in 1876 and was not very efficient at all, especially at
2、 that point in time. There are two main differences between a diesel engine and a gasoline engine: (1) A gasoline engine intakes a mixture of gas and air, compresses it and ignites the mixture with a spark. A diesel engine takes in just air, compresses it and then injects fuel into the compressed ai
3、r. The heat of the compressed air lights the fuel spontaneously.(2) A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency. Gasoline engines use eithe
4、r a carburetor or a fuel injection system to deliver the fuel to the cylinder. With a carburetor the fuel is mixed as it enters the intake manifold, long before it gets to the cylinders. In a fuel injection system the fuel is injected just before the intake stroke at the intake valve. Diesel engines
5、 use direct fuel injection (DI), that is to say the diesel fuel is injected directly into the cylinder. The diesel engine has no spark plugs. The air it takes in is compressed and the fuel is injected directly into the cylinder where the heat caused by the air compression ignites the fuel. In the ol
6、d days this meant that it exploded and expanded very quickly, making a noisy engine. This is why most diesel cars were IDI (indirect injection)； the rough behavior was fixed by injecting the fuel into a small pre-combustion chamber that is connected to the cylinder by a narrow passage. This slows do
7、wn the explosion, as the gasses have to escape from through the narrow passage into the cylinder. This gives a softer bang and a smoother engine, but the gasses have to work harder, which lowers the efficiency a little. However the newer breed of DI engines use other techniques to tame the behavior
8、of the engine, such as two stage injection, electronic control. The injector on a diesel engine is its most complex component and has been the subject of a great deal of development and innovation. On any specific engine it may be located in a 2 variety of places. The injector has to be able to with
9、stand the temperature and pressure inside the cylinder and still deliver the fuel in a fine mist. Getting the mist circulated in the cylinder so that it is evenly distributed is also a problem, so some diesel engines employ special induction valves, pre-combustion chambers or other devices to swirl
10、the air in the combustion chamber or otherwise improve the ignition and combustion process. One major difference between a gas engine and a diesel engine is in the injection process. Most car engines use port injection or a carburetor rather than direct injection. In a car engine all of the fuel is
11、loaded into the cylinder during the intake stroke and then compressed. The compression of the fuel/air mixture limits the compression ratio of the engine. If it compresses the air too much, the fuel/air mixture spontaneously ignites and causes knocking. A diesel compresses only air, so the compressi
12、on ratio can be much higher. The higher the compression ratio, the more power is generated. In the United States and Canada, diesel engines are most commonly found in trucks and buses. In Europe, where fuel prices fluctuate around $3.00 to $4.00 per gallon, the fuel efficiency of the diesel has made
13、 it a popular choice for cars, and most European-market cars are available with a diesel or a turbo-diesel engine. Compared to gasoline-powered vehicles, diesels are more fuel efficient. Diesel engines produce more torque, and they tend to be more durable. They dont need an electric ignition system,
14、 which reduces their complexity. However, they also create more noise, they can be difficult to start in extremely cold weather and they sometimes require more frequent routine maintenance than gasoline engines. Most passenger car diesel engines have a glow plug of some type. When a diesel engine is
15、 cold, the air compression may not raise the air to a high enough temperature to ignite the fuel. The glow plug is an electric heater that glows red-hot and helps to ignite the fuel when the engine is cold so that the engine can start. The amount of power which an engine can produce is limited by ho
16、w much fuel it can burn, and the amount of fuel it can burn is limited by the amount of oxygen in the cylinder. The amount of oxygen in the cylinder is limited by the amount of air in the cylinder. So, if more power is wanted then more air is needed, how do we achieve this? Well a large engine has m
17、ore air, so it can produce more power, or we can compress the air before it gets to the cylinders.This is what a super-charger does； it is a simple air compressor. A super-charger is a mechanically driven compressor run by a belt off the crankshaft. A diesel engine has no spark plugs. Because the ai
18、r is so compressed and hot at the top of the stroke, the fuel ignites right away when it is injected. This is why a diesel engine is called a Compression Ignition engine and gasoline engines are called Spark Ignition engine. 3 This also means that there are no ignition breakers, ignition coils, dist
19、ributors and ignition wires to go bad. This allows diesel engines to start no matter if it is dry or rainy and wet. The key to fuel efficiency is to squeeze as much energy as possible out of a given amount of fuel by burning it as completely as possible. Diesel fuel itself has the potential to produ
20、ce more power than a like quantity of gasoline. Furthermore, high compression ratios help diesels to burn their fuel more completely than gasoline engines. And because diesels always intake a full charge of air while varying the amount of fuel, the air-fuel mixture tends to be a very lean mixture at
21、 lower power outputs, which helps burn the fuel more completely. Some modern diesel engines are starting to come out with electronically controlled injection pumps, but the vast majority of them out there have purely mechanical pumps. No electricity is required to make a diesel engine run, except fo
22、r a simple fuel cut off solenoid so that you can hut the engine down. Turbo-charging a diesel is easier than turbo-charging a gasoline engine. One problem for a gasoline engine is that if the compression ratio is too high, and the pressure in the cylinder gets too high during the inlet stroke, then
23、the fuel/air mixture can start to burn too soon, while the piston is still on the way up. A turbo increases the pressure in the cylinder making this problem worse. With a diesel engine, there is no fuel in the cylinder during the compression stroke, so a turbo can be used to pack as much air in ther
24、e as desired without causing problems. The process of starting a diesel engine is less affected by temperature. When a gasoline engine is started from cold it needs a lot of fuel to make it run properly. If you do short trips all the time then youll get far below the fuel economy that youd normally
25、get. Since emissions are proportional to the amount of fuel consumed, youll be producing higher pollution levels. Diesel engines are ideal for short journeys because their efficiency is almost as high cold as when they are hot. Diesel engines last a lot longer than gasoline engines. This is because
26、gasoline destroys lubrication and diesel fuel doesnt. Cold start-ups are a real killer for gasoline engines because of all that extra gasoline needed to start a cold engine. A compression ratio of 19:1 to 25:1 gives significant engine braking, but it also makes the engine hard to start. Youll need a
27、 good battery, one of very high amperage, and starter motor. Glow plugs are needed. Diesel engines rely on the heat of compressed air to ignite their fuel. When the engine is cold, compression alone may not produce enough heat for the fuel to burn, so most car and truck diesels use glow plugs, electric elements that heat up the cylinder before a cold engine is started These electric heaters are switched on for anywhere from 5 to
