diesel engine

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diesel engine,

type of internal-combustion engineinternal-combustion engine,
one in which combustion of the fuel takes place in a confined space, producing expanding gases that are used directly to provide mechanical power.
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 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.


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

[¦dē·zəl ′en·jən]
(mechanical engineering)
An internal combustion engine operating on a thermodynamic cycle in which the ratio of compression of the air charge is sufficiently high to ignite the fuel subsequently injected into the combustion chamber. Also known as compression-ignition engine.

Diesel engine

An internal combustion engine operating on a thermodynamic cycle in which the ratio of compression of the air charge is sufficiently high to ignite the fuel subsequently injected into the combustion chamber. Compared to an engine operating on the Otto cycle, the diesel engine utilizes a wider variety of fuels with a higher thermal efficiency and consequent economic advantage under many service applications. See Otto cycle

The true diesel engine, as represented in most low-speed engines, uses a fuel-injection system where the injection rate is delayed and controlled to maintain constant pressure during combustion. Adaptation of this injection principle to higher engine speeds has necessitated departure from the constant-pressure specification, because the time available for fuel injection is so short (often 2 ms or less). Nonvolatile (distillate) fuels are burned to advantage in these engines, which cannot be rigorously identified as true diesels but properly should be called commercial diesels. However, all such engines are ordinarily classified as diesels. Diesel engines give high intrinsic and actual thermal efficiency (20–40%).

The diesel engine in the automobile is usually a four-stroke-cycle engine with indirect injection into an auxiliary combustion chamber (see illustration). Most automobile diesel engines use a distributor-type injection pump. The fuel system often includes a fuel-conditioner assembly, which combines a water-in-fuel detector, water-fuel separator, fuel filter, fuel heater, and hand-priming pump in a single unit. See Combustion chamber

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Diesel engines in trucks and buses are usually larger and operate at lower speeds than diesel engines in passenger cars. Most truck diesel engines operate on the four-stroke cycle, although many buses and some trucks have two-stroke-cycle engines. These usually have intake ports in the cylinder and exhaust valves in the cylinder head, with scavenging air provided by a crankshaft-driven blower mounted on the crankcase. A unit fuel injector operated by the engine camshaft meters and injects the fuel into the combustion chamber at high pressure at the proper time.

In addition to a noticeable odor, the exhaust gas from the diesel engine contains gaseous and particulate emissions which contribute to air pollution. The particles, or soot, may be removed by a trap oxidizer that consists of a filter and a regeneration system, which burns the trapped particles and cleans the filter. Gaseous emissions of unburned hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) may be controlled through the use of electronically controlled fuel injection, exhaust-gas recirculation, and charge-air cooling. Operating the engine on low-sulfur fuel reduces sulfur and particulate emissions. See Fuel injection

diesel engine

, motor
a type of internal-combustion engine in which atomized fuel oil is sprayed into the cylinder and ignited by compression alone