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Diesel Engine

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(Redirected from Diesel engines)
Mechanical Features and Designs

A diesel engine is a type of internal combustion engine that uses diesel fuel. A diesel engine also uses a Compression ignition system. A small amount of fuel is injected into the cylinder at the end of the compression stroke after which is it then auto-ignited.

Diesel engines are similar to gasoline engines in that they are reciprocating engines utilizing a piston-and-cylinder assembly to convert chemical energy into mechanical energy or work. This cycle is based on the Otto cycle—a four-stroke combustion principle invented and patented by Nicolaus Otto in 1876 when he devised the earliest incarnation of today’s modern gasoline engine.[1]

As a result of their higher operating efficiency, diesel engines are primarily used in heavy-duty industrial applications such as powering trucks, ships, locomotives, trains, cranes, buses, power generators, farming equipment, and industrial and construction equipment.

Contents

[edit] History

[edit] Rudolph Diesel

The invention of the diesel engine has been credited to Rudolph Diesel, a German engineer. As a graduate of the Munich Polytechnic in Germany, Diesel was fascinated by engine design and the concept of energy efficiency throughout the 1880s—particularly its application in steam engines that were then being used as an industrial power source, though not a necessarily highly efficient one.[2]

Diesel was also a student of the Carnot cycle, which "formed the perfect process of a heat engine." This process, developed by Nicolas L. Sadi Carnot in 1824, was based on the hypothesis that the efficiency of a heat engine was dependent on the difference between the highest and lowest temperature reached in one cycle. Diesel dedicated his energy to building a more efficient type engine, basing his diesel engine design on Carnot’s original ideas.[3]

He went on to design many types of heat engines, including a solar-powered engine. In 1893 he published a paper describing the working of a type of internal combustion engine where combustion occurred inside a cylinder. The following year, Diesel applied for a patent for his new invention that he appropriately named after himself—the diesel engine.[4]

His prime model was a single 10-foot (3-m) iron cylinder with a flywheel at its base. He exhibited the engine’s potential at Augsburg, Germany in August 1893. The model was the first time one of his engines was successful running off its own power.[5] The model had an operating efficiency of 26 percent, which was double that of a steam engine.[6]

These early models did not perfectly encapsulate his idea for a new type of internal combustion engine. In one incident, he was almost killed when one engine exploded. What the early workings of these models showcased, however, was an internal combustion engine in which the fuel did not need to be ignited by a spark as in the already existing gasoline engine.[7]

Diesel continued to work out improvements in the mechanics and performance of his existing diesel engine design over the next few years. By 1896, he built a diesel engine that operated at a theoretical efficiency of 75 percent. In 1898, he was granted a patent for another version of a diesel engine. The engine worked much more efficiently and became widely used in various industries, making Diesel a millionaire. [8]

The diesel engine was powered by the biomass fuel peanut oil. He had originally conceived the idea for his diesel engine as a way to give farmers and small-scale business owners leverage to compete with larger businesses, as peanut oil was quite an economical fuel source and used in his engines up until the 1920s.[9]

By the 1920s, the diesel engine was reconfigured to be slighter and more compact, permitting it to be used in smaller machinery, such as trucks and vehicles. Before this time, it had existed as a rather heavy, cumbersome engine used primarily in large industrial applications.[10]

Rudolph Diesel mysteriously disappeared in 1913 and the cause of this death was never determined. Some speculate it was related to politics at the time as he held a vast amount of knowledge that he was willing to share with German enemies during World War I.[11]

[edit] Clessie Cummins

No other person, aside from Rudolph Diesel, made as substantial a contribution to the evolution of the diesel engine as Clessie Cummins. Cummins was a chauffer for a wealthy industrialist by the name of Will G. Irwin. Cummins drove Irwin around in a 1909 Packard touring car that only Cummins had the knack to keep running. At one point, Cummins insisted on a hefty pay hike from his employer and Irwin threatened to fire him. Upon reaching a compromise, Irwin agreed to equip the family garage with an arsenal of tools that Cummins could use to repair engines. In 1917, Cummins started making wagon hubcaps for the U.S. Army while at the same time, reading about the diesel engines used in German U-boats. Most diesel engines during this time were big and cumbersome and let off a lot of smoke, not practical for any form of transportation.[12]

In 1919, Cummins got his start working on diesel engines when he convinced Irwin to negotiate a contract with Sears, Roebuck & Co. to buy three horsepower farm diesels made under a European patent. This venture witnessed the establishment of the Cummins Engine Co. Through his company, Cummins modified Diesel’s original diesel engine so that it could be used for mass transportation. In this regard, he has even been esteemed as the "father of the American truck diesel."[13]

At the time, engineers were adding on parts to the diesel engine to make it more powerful. Cummins, however, believed that the addition of these “add-on” parts to maximize engine power was not the solution to increasing the engine’s power at all. He accepted only one premise for diesel engine design: only a combustion ignition or fuel oil placed inside the cylinder to be ignited was the means to enhance engine. Cummins also reduced the diesel engine’s amount of horsepower yet got his diesel engines to run faster than other models. Years of experimentation led to 33 patents over 56 years.[14]

For example, he invented the Sneezer, a device used to inject every last bit of fuel oil into a cylinder to ensure that absolutely no oil could be released as smoke. Another development he can be attributed with was a fuel injector system described by experts to be as simple as a “fountain pen.” Eventually, his fuel pump and injector were regarded as the best in the diesel engine industry. Before long, his diesel engines were the preference of truck manufacturers still reliant on gasoline engines because they proved to be quite powerful, fuel-efficient and reliable.[15] As a result his business flourished making Cummins Engine Co. a dominant manufacturer of diesel engines for decades.[16]

Though the truck industry has shrunken over the years, Cummins diesel engines are still widely used in drilling rigs, boats, industrial locomotives, compressors, pumps, logging equipment, construction equipment, agricultural equipment, municipal and school buses, and various other applications.[17]

[edit] Features/How it Works

A diesel engine, similar to a gasoline engine, is a reciprocating piston-and-cylinder type internal combustion engine that converts the chemical energy of fuel, through the four-stroke combustion process, into mechanical energy. The primary difference between the two engines is how these explosions occur. In a gasoline engine, the fuel is mixed with air, compressed by pistons, and then ignited by sparks from spark plugs. With a diesel engine, air is taken in first, and then fuel is injected into the combustion chamber. The heat generated from compressed air is what lights the fuel within the engine. Therefore, a diesel engine uses what is called direct injection and uses a compression ignition system as opposed to a spark ignition system characteristic of gasoline engines.[18]

[edit] Diesel Fuel

A diesel engine uses diesel fuel, which is a type of petroleum fuel or crude oil found naturally in the earth and refined at factories to be turned into all kinds of fuel including gasoline, jet fuel, kerosene, and diesel.

Diesel fuel is very different from gasoline as evidenced by the difference in its odor and the fact that its texture of is heavier and oilier. In fact, diesel fuel is so oily it is often called diesel oil.

There are pros and cons to using diesel fuel as opposed to gasoline. One positive is that diesel emits smaller quantities of carbon monoxide, hydrocarbons, and carbon dioxide, emissions that lead to global warming. On a negative note, diesel nitrogen compounds and soot are let off into the air as a result of burning diesel fuel. Soot and these nitrogen compounds can lead to acid rain, smog, and poor health conditions.[19]

New types of diesel fuel have been produced to combat the environmental implications presented by using regular diesel fuel. An example is better, refined diesel fuels like ultra-low sulfur diesel that cut harmful emissions. Upgrading the compatibility of diesel engines to complement new types of diesel fuel also helps.[20]

[edit] Biodiesel Fuel

Biomass fuels are making a comeback. Biodiesel fuel can now be used with diesel engines with little or no modifications having to be made to the actual engines.[21]
Biodiesel, similar to the peanut oil that fueled Rudolph Diesel’s very first diesel engines, is a non-toxic and biodegradable fuel made out of a combination of vegetable oils, waste cooking oils, animal fats, or tall oil (oil by-product from pulp and paper processing). Taking all these different types of oils and reacting them with an alcohol such as methanol and a catalyst such as sodium hydroxide in a process called transesterification creates biodiesel fuel. The result is a fuel that is able to combust better with a higher cetane rating and one that emits lower levels of greenhouse emissions.[22] The other advantage of biodiesel is that it can be used on its own or in combination with diesel fuel.[23]

[edit] The Four-stroke Combustion Process

The four-stroke combustion process in a gasoline engine is fairly similar to that of a diesel engine. During the intake stroke, a valve opens up and the intake of air into the cylinder occurs, pushing the piston inside the cylinder downwards. In the compression stroke, the piston is directed upwards and compresses the air. As the piston hits the top again, fuel is injected just at the right moment and ignited. This results in a combustion stroke that forces the piston into a downward position again. During the exhaust stroke -- the fourth and final stroke -- the piston goes back up, pushing out the exhaust created from combustion out an exhaust valve.[24]

[edit] Direct Injection

Diesel engines use direct injection (DI) to ignite the fuel inside the cylinder whereas a gasoline engine uses a carburetor or fuel injection system to inject fuel inside the cylinder. With no spark plugs in a diesel engine, the air is taken into the cylinder, compressed, and the fuel is directly injected. The heat caused by the compression of air ignites the fuel.

This explains why diesel engines used to be very noisy. After being ignited, the fuel inside the cylinder of a diesel engine would expand and combust very quickly as a result of using an indirect diesel injection (IDI) system. The problem was overcome by forming a small pre-combustion chamber connected to the cylinder via a narrow passage that the fuel could be injected into. The gases released through combustion take longer to escape from the narrow passageway and into the cylinder. This makes for a smoother running engine but decreases efficiency since the gases have to work harder.[25]

An injector on a diesel engine is probably the most complicated component and can be located in a number of places. The component is so complicated because it has to be able to face both the pressure and temperature inside a cylinder and still be able inject the fuel as a mist evenly through the entire inside of the cylinder. This is why diesel engines now come with special pre-combustion chambers or induction valves.[26]

There is a new category of direct injection diesel engines being built that employ different technologies such as two stage-injection, electronic control, acoustic shrouds, and shock absorbing engine mounts to reduce noise and mask engine rattling.[27]

[edit] Glow Plugs

Some diesel engines employ the use of glow plugs. These devices are like the hot wires found inside a toaster. The purpose of glow plugs is to provide electrical heat and raise the heat inside the combustion chamber when the engine is too cold to start. The compressed air inside of a diesel engine may not reach a high enough temperature to ignite the fuel.[28]

[edit] Common Manufacturers

[edit] References

  1. Diesel. Howstuffworks.com. 2008-09-29.
  2. The History of the Diesel Engine. Helium. 2008-09-29.
  3. The Carnot Cycle. Start Your Engines. 2008-09-29.
  4. Diesel. About.com. 2008-09-29.
  5. Diesel. About. 2008-09-29.
  6. Diesel Engine History. Whatprice. 2008-09-29.
  7. Diesel. About.com. 2008-09-29.
  8. Diesel. About.com. 2008-09-29.
  9. Diesel Engine History. Whatprice. 2008-09-29.
  10. Diesel Engine History. Whatprice. 2008-09-29.
  11. Diesel Engine History. Whatprice. 2008-09-29.
  12. Cummins Inc. Answers.com. 2008-09-29.
  13. Biblio. Powells. 2008-09-29.
  14. Biblio. Powells. 2008-09-29.
  15. Cummins Inc. Answers.com. 2008-09-29.
  16. Cummins Inc. Answers.com. 2008-09-29.
  17. Cummins Inc. Answers.com. 2008-09-29.
  18. Diesel. Howstuffworks. 2008-09-29.
  19. Diesel. Howstuffworks.com. 2008-09-29.
  20. Diesel. Howstuffworks.com. 2008-09-29.
  21. Diesel. Howstuffworks.com. 2008-09-29.
  22. Biodiesel. OEE. 2008-09-29.
  23. Diesel. Howstuffworks.com. 2008-09-29.
  24. Diesel. Howstuffworks.com. 2008-09-29.
  25. Autorepair. About.com. 2008-09-29.
  26. Autorepair.About.com. 2008-09-29.
  27. Autorepair. About.com. 2008-09-29.
  28. Diesel. Howstuffworks.com. 2008-09-29