diesel engine, an internal combustion engine, which means that the fuel is burned inside the engine cylinders, as opposed to a steam engine where the fuel is burned externally in a boiler for steam propulsion. A diesel engine may operate on a two-stroke cycle or a four-stroke cycle. A two-stroke engine gives one power stroke for every two strokes (up or down) of the piston or for every one revolution of the crankshaft. A four-stroke engine gives one power stroke for every four strokes of the piston or for every two revolutions of the crankshaft. This means that for the same size and rotational speed a two-stroke engine is likely to develop twice as much power as a four-stroke engine. The engine has a number of cylinders, each with a piston which attaches to the crankshaft by means of a connecting rod.

Marine diesel engines for ships are of the crosshead type or the trunk piston type. The crosshead type is similar to a reciprocating steam engine, in that it is tall, and runs at relatively low speed. It is connected directly to the propeller shaft, which means the engine speed is changed to change the ship's speed, and it is stopped and reversed to make the ship go astern. It almost always operates on the two-stroke cycle, and is used to power container ships, tankers, and bulk carriers because there is plenty of space to fit such an engine into them. The trunk piston type of engine is similar to an outsize car engine. Most of these are not connected directly to the propeller shaft but via a gearbox, though some are used to drive an electric generator for electric propulsion. Unlike the crosshead-type engine, it is uncommon for them to be reversible and, as the engine's speed is constant, a controllable pitch propeller is used to change the ship's speed and direction. This type of engine is not as tall as a crosshead type which makes them ideal for ferries and cruise ships where low engine-room height means additional car or passenger decks can be fitted. Medium-speed trunk piston engines can also be used to drive electrical generators for purposes other than the ship's propulsion.

Diesel engines were introduced to ship propulsion in the early years of the 20th century. The first installations were for river and harbour craft, but as they became more reliable their use for marine propulsion gradually increased. The Fram, which in 1911 took Amundsen to the North Pole, had a diesel engine, and the first successful ocean-going ship powered by diesel machinery, the Danish Selandia, launched in 1912, showed that the diesel was a practical and economic alternative to coal- and oil-fired ships. By the end of the First World War (1914–18) many ships had diesel engines, although these tended to be the smaller cargo ships; and its lower fuel consumption, greater range, and the availability worldwide of bunkering stations, led to a further increase in diesel's popularity during the 1920s. One of the earliest diesel-engined passenger ships was the 18,815 gross ton Swedish American liner Gripsholm. Built in 1925, she remained in service with her original engines until 1966.

The early diesel engines burned diesel oil, similar to the diesel fuels used in modern diesel-engined road vehicles. This is a distillate fuel and much more expensive than the boiler oil used for oil-fired steamships. However, during the 1950s diesel engines were developed which could burn the residual oil used by oil-burning steamships, which is also known as fuel oil, bunker C, and heavy fuel oil. Residual oil is what remains after crude oil has been processed and the lighter, higher-value commodities, such as kerosene, gasoline, gas oil, and diesel oil, have been extracted. With the development of residual fuel oil-burning marine diesel engines in the 1950s, the last economic advantage the steam plant had over the diesel engine, using cheaper fuel, was gone; and from that time diesels gradually replaced steam engines for all forms of conventional ship propulsion.

With few exceptions, all commercial ships built from the late 1980s onwards have been fitted with diesel engines and some ships have been re-engined with diesels. For example, the liner Queen Elizabeth II had its steam turbine plant replaced in 1986/7 with nine diesel engines, and the ship is now powered by diesel electric propulsion. Not only did this reduce the fuel consumption, it reduced the number of engineers running the plant. The efficiency of diesel-powered ships is further increased by using the engine's exhaust gas to generate steam. This can be used for various heating purposes within the ship, and waste heat in the engine cooling water can be employed in evaporator plants to generate fresh water from sea water.

Apart from its economy, the diesel-engined cargo ship could also often travel twice as far as a similarly sized steamship on the fuel stored in its double-bottom tanks, and the diesel's thermal efficiency, just over 50%, means that just over half of the chemical energy in the fuel is converted into work at the engine crankshaft. This compares very favourably with the best marine steam-turbine plant which only achieves a thermal efficiency of about 30%.

However, residual fuel oil does have its drawbacks. It has a very high viscosity which, at room temperature, has the consistency of treacle. For it to be pumped and burned it must be heated, so that its viscosity is the same as diesel oil. It also creates a major pollution problem if it gets into the sea, particularly in large quantities from oil tankers that founder or run aground. It does not break down easily and if washed ashore it coats rocks and beaches with a tarlike substance which is very difficult to remove, destroying local fisheries and tourism. Such accidents raise important environmental issues as does the fact that residual oil emits chemical impurities when burnt. A large cruise or container ship may burn over of 200 tonnes per day and, if this contains 3% sulphur, over 12 tonnes of sulphuric acid can be directed into the atmosphere each day, a problem that MARPOL is addressing.

Before the introduction of nuclear power, and with the exception of K-boats, submarines used diesel engines when surfaced, or when employing a schnorkel.

Denis Griffiths

diesel engine type of internal-combustion engine invented by the German engineer Rudolf Diesel and patented by him in 1892. Although his engine was designed to use coal dust as fuel, the diesel engine now burns fuel oil.

The diesel engine does not require a large water supply or a long warming-up period and is highly efficient in converting heat energy into work. Diesels are widely used in both stationary and mobile installations where the power required is between that furnished by the gasoline engine and that of the steam turbine and where the relatively high initial cost can be written off over a long period. For example, diesels having capacities of 100 to 5,000 hp are employed on industrial and municipal electric generators and on continuously operating pumps (e.g., on oil pipelines). Moreover, they occupy relatively little space compared with steam units, since no boiler is needed—a factor of importance aboard ships.

The diesel engine differs from the gasoline engine in that the ignition of fuel is caused by compression of air in its cylinders instead of by a spark: the high compression ratio allows the air in the cylinder to become hot enough to ignite the fuel. Because of the high temperatures of operation, a diesel engine must be water-cooled. The construction of the diesel engine is heavier than that of the gasoline engine; there are usually three or more cylinders (supported on a framework and bedplate) and a heavy flywheel. The cylinders are set to work alternately to give a smooth-turning effect, and the flywheel contributes further to smooth action.

There are two classes of diesel engines. In the two-stroke, or two-cycle, type there is a complete cycle of operation in every two strokes of a piston. This type of engine requires a supply of compressed air for operating and for starting. In the four-stroke, or four-cycle, type the first downstroke of the piston draws in air, which is compressed on the upstroke to about 500 lb per sq in. (35 kg per sq cm). At the top of the stroke a jet of oil is sprayed in through a fuel injector. The oil is ignited and the rapid expansion of the gas created by the explosion forces the piston down in the working, or firing, stroke. The next upstroke drives the waste gases out through the exhaust valve, and the cycle is complete.

The speed and power of the diesel are controlled by varying the amount of fuel injected into the cylinder, not the amount of air admitted as in the gasoline engine. Small and medium-size ships may have several diesels producing as much as 50,000 hp. Heavy-duty land transports such as trains, trucks, buses, and tractors are often diesel-powered. Some automobiles—in Europe, roughly half—use diesel engines, and even some airplanes have had diesel engines.

Diesel engines, although more fuel efficient than gasoline engines, have in the past generated more smog-producing combustion products (although they produce less greenhouse gases). This has restricted the sale of diesel-powered automobiles in states such as California where smog has been a significant problem. The introduction of ultra-low-sulfur diesel fuel in 2006, undertaken in part to encourage the development of improved emission control technology for diesel engines, has spurred the development of cleaner burning diesel engines for automobiles. New rules for diesel engines in 2009 required them to match the emissions standards set for gasoline engines.

Bibliography: See W. R. Nitske and C. M. Wilson, Rudolf Diesel (1965); A. W. Judge, High Speed Diesel Engine (1967); S. D. Haddad and N. Watson, ed., Design and Applications in Diesel Engineering (1984); L. R. Lilly, Diesel Engine Reference Book (1984).

Diesel engine

A diesel engine is a type of internal-combustion engine developed by German engineer Rudolf Diesel (1858–1913) in the late nineteenth century. His original design called for the use of coal dust as fuel, but most modern diesel engines burn low-cost fuel oil. Whereas gasoline engines (found in the majority of present-day automobiles) use an electric spark to ignite the premixed fuel-air blend, diesel engines use compressed air to ignite the fuel.

In both gasoline and diesel engines, fuel is ignited in a cylinder, or chamber. Inside the sealed, hollow cylinder is a piston (a solid cylinder) that is attached at the bottom to a crankshaft. The movement of the piston up and down turns the crankshaft, which transfers that movement through various gears to the drive wheels in an automobile.

In a diesel engine cylinder, the piston completes one up-and-down cycle in four strokes: intake, compression, power, and exhaust. During the intake stroke, the piston moves downward, sucking air into the cylinder through an open intake valve. On the compression stroke, the intake valve closes and the piston rises, compressing the air in the cylinder and causing it to become heated. While the air is being compressed, a fuel pump sprays fuel into the cylinder to mix with the air. When the compressed, hot air reaches the right temperature, it ignites the fuel, driving the piston down on the power stroke. As the piston rises on the exhaust stroke, the exhaust valve opens and the gases created by explosion of the fuel (exhaust) pass out of the cylinder. Then the cycle repeats.

The entire combustion cycle takes but a fraction of a second. Diesel engines can operate from several hundred up to almost one thousand revolutions per minute. The high pressure created in the cylinders during compression requires diesel engines to be strongly constructed and, thus, much heavier than gasoline engines. This weight cuts into their fuel efficiency. Diesel engines also emit high levels of foul-smelling exhaust.

However, diesel engines are more powerful than conventional gasoline engines and run on a less costly fuel. First installed on a ship in 1910 and in an automobile in 1922, they are generally used in large vehicles such as locomotives, trucks, and buses, and in heavy construction and agricultural machinery. Because of their ability to burn crude fuels while delivering an efficient amount of the fuel's energy as usable power, diesel engines are almost the only choice for industrial power throughout the world.

[See also Internal-combustion engine ]

Diesel

Rudolf Christian Karl Diesel (1858–1913), a German thermal engineer, invented the diesel engine and patented it in 1893. Unlike their gasoline counterparts, which ignite an air/fuel mixture using spark plugs, diesel engines compress air to a very high pressure and then inject the fuel. The fuel then ignites due to the high temperature of the compressed air. Diesel engines are relatively fuel-efficient engines commonly used in heavy construction equipment, ships, locomotives, commercial trucks, and some large pickups, as well as in the production of electricity at some power plants or in factories.

Diesel-powered automobiles gained popularity in the United States during the oil crisis of the 1970s because they tend to result in better fuel economy than their gasoline counterparts. But diesel-powered cars have declined in popularity with American drivers since their peak in the mid-1970s because of quality-related problems in early models and because earlier diesel engines did not accelerate as quickly as those powered by gasoline. Diesel passenger cars have also declined in popularity because they are more expensive and they emit more smog-forming pollutants and toxic soot than other conventional internal-combustion engines. For eighteen-wheel trucks and other large vehicles, however, diesel engines are currently the standard.

see also Vehicular Pollution.

Internet Resource

"How Diesel Engines Work." Available at http://auto.howstuffworks.com/diesel1.htm.

David Friedman

die·sel / ˈdēzəl; -səl/ • n. (also diesel engine) an internal combustion engine in which heat produced by the compression of air in the cylinder is used to ignite the fuel: [as adj.] a diesel locomotive. ∎  a heavy petroleum fraction used as fuel in diesel engines: eleven liters of diesel. DERIVATIVES: die·sel·ize / -ˌlīz/ v.

diesel engine Internal combustion engine, invented by Rudolf Diesel (1897). Heat for igniting the light fuel oil is produced by compressing air.

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