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Internal Combustion Engine

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Mechanical Features and Designs

An internal combustion engine is any engine in which the combustion of fuel occurs from inside the engine, usually inside a confined space known as a combustion chamber[1] and by which the mechanical work is performed through the expansion of gas that applies pressure on a piston inside a cylinder. This differs from an external combustion engine, such as a steam engine, by which combustion of fuel occurs outside the engine. Mechanical work is achieved through the release of steam and pressure applied to a steam actuated piston.

There are different types of internal combustion engines. The most common internal combustion engines are gasoline engines (sometimes called petrol engines), which are found in almost all cars, and diesel engines, used in some cars but more specifically in heavy-duty vehicles such as trucks, farming and industrial equipment, and other types of industrial applications. The gas turbine engine is another type of internal combustion engine used in airplanes, power plants, and helicopters.

Internal combustion engines operate by converting fuel into mechanical work based on what is known as a four-stroke combustion cycle or a two-stroke combustion cycle. The four-stroke internal combustion engine, like a gasoline engine, is used for automotive and industrial purposes and is far more efficient than the two-stroke combustion cycle engines commonly found in utility and recreational applications.[2]

An internal combustion engine can be further classified on the basis of what type of fuel it burns, whether gasoline, diesel, kerosene, hydrogen, methane, or propane, to do the mechanical work required to run. Other key differentiations include whether an internal combustion engine is a reciprocating or a rotary type, whether it uses a spark ignition system or compression ignition system.[3]

Contents

[edit] History

[edit] Early Concepts

In 1680, Dutch physicist Christian Huygens came up with the first working design of an internal combustion engine, using gunpowder as fuel. His engine was only a concept put onto paper and no engine actually was built.

After Huygens, attempts were made to invent a workable internal combustion engine but these did not prove to be promising. For example, in 1807, Francois Isaac de Rivaz of Switzerland invented an internal combustion engine for an automobile that burned a fuel mixture of hydrogen and oxygen. The experiment was not successful. Another attempt to design an internal combustion engine was made in 1824 when an English engineer by the name of Samuel Brown modified a Newcomen steam engine that burned gas to power a vehicle. The engine did so, but only briefly.[4]

[edit] Major 19th Century Contributions

It was not until around 1859 that Belgian-born engineer Jean Joseph Etienne Lenoir actually succeeded in inventing and then patenting a workable internal combustion engine fueled by coal gas. The engine, a double-acting, electric spark ignition design, was the first internal combustion engine that could run continuously.[5] A few years later, Lenoir developed an improved petroleum engine that featured a primitive carburetor and was attached to a three-wheeled wagon. The contraption managed to complete a 50-mile (80.5-km) road trip.[6]

In 1862, Alphonse Beau De Rochas, a French civil engineer, received a patent for a four-stroke engine that was not even built. This changed in 1876 when Sir Dougald Clerk achieved the first building of a two-stroke engine that remains widely in use to this day, though the original engine design has since been simplified.[7]

Perhaps one of the most substantial contributions made to internal combustion engine design and development was the invention and patent of the four-stroke engine otherwise known as the “Otto cycle” by Nicolaus August Otto in 1876.[8] The operation of the four-stroke engine can be explained in simple terms as four strokes of the piston for each explosion. It is based on the principle of thermodynamics. [9] Today, the four-stroke cycle engine is the most widely applicable type of internal combustion engine in use, powering practically all cars and trucks on the road.[10]

Another key contribution in internal combustion engine design was made by Gottlieb Daimler in 1885 when he developed what is notably the very first prototype of today’s modern gasoline engine. The engine featured a vertical cylinder with gasoline injected through a carburetor. The design was patented in 1887. Daimler went on to incorporate his engine into a two-wheeled vehicle and, a year later, into the world’s very first four-wheeled motor vehicle.[11]

[edit] How it Works

Internal combustion engines operate according to either a two-stroke combustion cycle or a four-stroke combustion cycle.

[edit] Four-stroke Combustion Cycle

The four-stroke combustion cycle is a four-step approach that essentially converts the fuel used by the engine into motion through an in-take stroke, compression stroke, combustion stroke (explosion), and exhaust stroke. Examples of four-stroke engines are the piston-type gasoline engines present in automobiles today, as well as diesel engines.

The execution of the four-stroke combustion cycle occurs with four strokes of a piston inside a cylinder connected to a crankshaft by a connecting rod. On the first stroke, the piston is driven downward to allow for the intake of fuel and air that are drawn inside the cylinder. The piston is then driven upwards. This compresses the fuel-air mixture inside the cylinder and it becomes ignited by a spark plug. The expansion of gas and heat inside the cylinder forces the piston downward in a third stroke. The fourth and final stroke upwards expels the gas from the cylinder through an exhaust pipe or tailpipe.[12]

[edit] Two-stroke Combustion Cycle

The two-stroke combustion cycle is less complicated mechanically than the four-stroke, requiring fewer moving parts. As a result, it is a lot less efficient and used primarily to fuel lower-power applications and devices such as lawn and garden equipment, dirt bikes, mopeds, jet skis, and small outboard motors.[13]

The two-stroke engine works essentially double time in that it has to deliver one power stroke for every two strokes as opposed to one stroke for every four, as in four-stroke engines. The engine, lighter and more compact, can give out the same amount of power as a four-stroke engine.

Drawbacks are present that ultimately restrict the two-stroke engine's use. Twice as many power strokes during operation in a two-stroke engine means this kind of engine is predisposed to overheating, thereby having a shorter product shelf life. Another disadvantage is that fuel in a two-stroke engine is mixed with lubricating oil, causing the emission of a high level of hydrocarbons. Currently a more efficient and pollutant-free two-stroke automobile engine is under development.[14]

[edit] Reciprocating Engines

Both the gasoline engine and the diesel engine are examples of reciprocating engines. A reciprocating engine consists of either the compression of air or pre-compressed air within the cylinder of the engine through piston action. Heat energy is added to the compressed air by combusting the fuel in the compressed air. This results in the expansion of hot gas inside the cylinder, in turn activating the piston to move and produce a useful mechanical working energy.[15]

[edit] Rotary Engines

The rotary engine is a type internal combustion engine but works quite differently from a conventional gasoline piston type engine, in which all four tasks occur in the same amount of space inside the cylinder. In a rotary engine, each job occurs within its own space, much like having a separate cylinder for each given job and by which the piston moves continuously from one to the next. A rotary engine is also called a Wankel engine or Wankel rotary engine after its inventor Dr. Felix Wankel, a German engineer who devised its design in 1956.[16]

The Wankel engine has a distinctive form resembling a triangular disc with bulging sides that rotates inside a figure eight-shaped, thick waist cylinder. The engine has 48 percent fewer parts and about one-third the bulk of a reciprocating engine. Advantages of the rotary engine over the gasoline engine are that advanced pollution control devices are easier to design for it and that higher engines speeds (calculated in horsepower) are more attainable with a rotating motion over a reciprocating motion.[17]

[edit] Spark Ignition vs. Compression Ignition Systems

Diesel engines differ slightly from gasoline engines in that heat generated by compression rather than a spark plug is used to ignite the intake of fuel and air mixture inside the cylinder. This is known as a compression ignition system. In gasoline engines, spark plugs provide an electrical spark used for igniting the air-fuel mixture outside the cylinder; this is called a spark ignition system.

[edit] Direct Injection System

Most gasoline engines now use an electronic injection system, commonly referred to as a direct injection system, which is quickly replacing the conventional carburetion system. For example, with multi-point injection, fuel is injected into the engine through various ports. This allows for more greater control and precision over the ignition process, resulting in better fuel efficiency.[18]

[edit] Types

[edit] References

  1. Internal Combustion Engine. Speedace. 2008-09-29.
  2. Internal Combustion. About.com. 2008-09-29.
  3. Bartleby. About.com. 2008-09-29.
  4. The History of the Automobile. About.com. 2008-09-29.
  5. Evolution of the Internal Combustion Engine. 2008-09-29.
  6. Inventors. About.com. 2008-09-29.
  7. Evolution of the Internal Combustion Engine. 2008-09-29.
  8. Evolution of the Internal Combustion Engine. 2008-09-29.
  9. Otto Cycle. Science World. 2008-09-29.
  10. Otto. Keveney. 2008-09-29.
  11. Inventors. About.com. 2008-09-29.
  12. Engine. Howstuffworks.com. 2008-09-29.
  13. Engine. Howstuffworks.com. 2008-09-29.
  14. Inventors. About.com. 2008-09-29.
  15. Inventors. About.com. 2008-09-29.
  16. Rotary Engine. Howstuffworks.com. 2008-09-29.
  17. Inventors. About.com. 2008-09-29.
  18. Direct Injection. Freescale. 208-09-29.