Diesel cycle
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The Diesel cycle is a combustion process of a reciprocating internal combustion engine, in which fuel is ignited by heat generated compressing air in the combustion chamber, into which fuel is injected, as opposed to igniting it with a spark plug as in the Otto cycle (four-stroke/petrol) engine. Diesel engines (heat engines using the Diesel cycle) are used in automobiles, power generation, diesel-electric locomotives, and submarines.
Invented by Rudolph Diesel in 1897, it was originally intended to run on Peanut oil, this engine, generates power (while continuously injecting fuel) to maintain the cylinder at constant pressure during its power stroke.
The Diesel cycle refers to a compression ignition engine, called the Diesel engine that can have a two or four stroke power cycle, drawing in air by its piston, or by a mechanically or exhaust driven supercharger. As air is compressed, its temperature rises from adiabatic compression until the piston reaches the top of its compression stroke. At that point fuel is injected directly into the cylinder with an atomizing fuel injector and ignites immediately; however, because diesel fuel has a higher molecular weight than gasoline, it vaporizes and burns more slowly. The piston is already moving down by the time combustion begins. Fuel injection can be limited to a short part, or continue to near the bottom of the power stroke. If combustion is incomplete when the piston reaches the bottom of its stroke, smoke is generated and fuel is wasted. [verification needed]
Diesel engines are nevertheless more efficient than Otto cycle engines overall, but only during partial load with fuel cut-off at part of the power stroke. Most land vehicles rarely run at the maximum rated power of an engine. Unless the vehicle is at full stroke injection, when the pedal is 'floored', it is at partial rated power. Since diesel engines use the heating effect of compressing air to ignite fuel, it can inject as little or as much fuel as the situation demands. It is important to note that Otto cycle engines can be more efficient than Diesel cycle engines, but only when the engine is running at or near maximum power.
[edit] General information
The diesel engine has the lowest specific fuel consumption of any large internal combustion engine, 0.26 lb/hp.h (0.16 kg/kWh) for very large marine engines. In fact, two-stroke diesels with high pressure forced induction, particularly turbocharging, make up a large percentage of the very largest diesel engines.
In North America, diesel engines are primarily used in large trucks, where the low-stress, high-efficiency cycle leads to much longer engine life and lower operational costs. These advantages also make the diesel engine ideal for use in the heavy-haul railroad environment.
[edit] Other internal combustion engines without spark plugs
Many model airplanes use very simple "glow" and "diesel" engines. Glow engines use glow plugs. "Diesel" model airplane engines have variable compression ratios. Both types depend on special fuels (easily obtainable in such limited quantities) for their ignition timing.
Some 19th century or earlier experimental engines used external flames, exposed by valves, for ignition, but this becomes less attractive with increasing compression. (It was not until Nicolas Léonard Sadi Carnot that the thermodynamic value of compression was known.) An historical implication of this is that the diesel engine would eventually have been invented without the aid of electricity.
