Internal Combustion Engine and the Four Stroke Engine
Today, we have massive jets that can fly us around the world in a matter of hours, generators that can generate electricity efficiently in the most remote places, tractors and pumps that help us cultivate crops faster, and of course our very own personal automobiles to cruise down on the highway. But what made all this possible? The answer is the Internal Combustion Engine. The internal combustion engine has become an integral part of every person on earth. It offers a relatively small, lightweight source for the amount of power it produces. The simple objective of these heat engines is to convert the chemical energy in fuel to mechanical energy which is usually passed on to the rotating shaft.
One of the most significant applications of the internal combustion engine is the automobile. Transportation technology changed forever with the mass production of automobiles with an internal combustion engine. An internal combustion engine is an engine that uses the explosion of fuel called combustion, to push a piston within a cylinder. As the piston is pushed out of the cylinder, it turns the crankshaft that turns the car wheels. The most common type of fuel that is used for this combustion is gasoline.
Early History and Development
The technology that we see today is the product of centuries of evolution and development, starting all the way in the early 16th century with Leonardo Da Vinci and his early description of compression less engine. The first experimental internal combustion engine, however, was made more than a century later, in 1680, by Christian Huygens, a Dutch astronomer who applied a principle for drawing water. This principle was based on the fact that the explosion of a small amount of gunpowder in a closed chamber provided with escape valves would create a vacuum when the gases of combustion cooled. Using a cylinder containing a piston, Huygens was able to move it in this manner by the external atmospheric pressure.
This was followed by the first commercially practical internal combustion engine built by a French engineer, Etienne Lenoir in around 1859–1860, using illuminating gas as fuel. Two years later, in 1862, Alphonse Beau de Rochas patented but did not build the four-stroke engine. It was only fourteen years later, in the year 1876, that the first ancestor of the Internal Combustion Engine used today, was born. This feat was accomplished by Nickolaus August Otto who succeeded in creating an engine with much higher efficiency compared to earlier designs, by compressing the fuel prior to combustion. This came to be known as the “Otto Cycle”.
Components of the Internal Combustion Engine
The essential parts of the Otto-cycle include a combustion chamber consisting of a cylinder. The cylinder is usually fixed and is closed at one end and in which a close-fitting piston slide. The motion of the piston changes the volume of the chamber between the closed end of the cylinder and the inner face of the piston. In order to transform the reciprocating motion of the piston to rotary motion, a connecting rod is used to attach a crankshaft to the outer face of the piston. There are two holes cut on the top surfaces of the cylinder, also called the cylinder head, which houses valves that operate with the help of a can mechanism. These are the intake manifold and the exhaust manifold. The internal combustion engine makes use of a fuel system that consists of a tank, a fuel pump and a carburettor to vaporize the liquid fuel. The vaporized fuel is then conveyed through the intake manifold, while the gases produced by the combustion is carried off through the exhaust manifold. The valves are normally held closed by the pressure of springs and are opened at the proper time during the operating cycle by cams on a rotating camshaft that is geared to the crankshaft.
The mixture of air and gasoline vapour delivered to the cylinder from the carburettor ignited by causing a spark to jump the gap between the electrodes of a spark plug, which projects through the walls of the cylinder. One electrode is insulated by porcelain or mica; the other is grounded through the metal of the plug, and both form the part of the secondary circuit of an induction system.
The Four-Stroke Cycle
Almost every car with a gasoline engine uses a four-stroke combustion cycle to convert gasoline into motion. The four strokes are:
1. Intake stroke
2. Compression stroke
3. Combustion stroke
4. Exhaust stroke
In the first stroke, also known as the Intake Stroke or Induction, the piston travels from the top dead centre (TDC) to the bottom dead centre (BDC) with the intake valve open and exhaust valve closed. This creates a vacuum due to the increase in volume in the combustion chamber. The pressure difference between the atmospheric pressure on the outside and the vacuum on the inside, causes air to be pushed into the cylinder. A carburettor is then used to add the desired amount of fuel to the system.
This is followed by the compression stroke, where the intake valve closes and the piston moves back to TDC with all valves closed. This causes the air-fuel mixture to compress, raising both the pressure and temperature in the cylinder. At the end of the compression stroke, the combustion is initiated by firing the spark plug. The combustion of the air-fuel mixture occurs in a very short but finite length of time with the piston near TDC. Combustion changes the composition of the gas mixture to that of exhaust products and increases the temperature in the cylinder to a very high peak value causing the pressure in the cylinder to rise to a very high peak value.
Next, the Expansion of Stroke or Power Stroke takes place. This stroke produces the main work output of the cycle. With all valves closed, the high pressure created by the combustion process pushes the piston away from TDC. As the piston travels from TDC to BDC, cylinder volume is increased, causing pressure and temperature to drop. While the piston approaches BDC, the exhaust valve is opened, and the gases produced by the combustion is blown out. Opening the exhaust valve before BDC reduces the work obtained during the power stroke but is required because of the finite time needed for exhaust blowdown.
Finally, the last stroke is the Exhaust stroke. While the exhaust valve remains open, the piston moves from BDC to TDC, expelling the remaining exhaust gases out of the cylinder into the exhaust system. Close to the end of the exhaust stroke, the intake valve begins to open such that it is fully open by the time the piston reaches the TDC. Similarly, the exhaust valve starts to close and fully closes around the time the piston reaches the TDC. This period when both the intake valve and exhaust valve are open is called valve overlap.
With the piston back at TDC, the next intake stroke takes place, starting the cycle again.
References
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Garden, H., Hood, U. and Engines, T. (2019). How Car Engines Work. [online] HowStuffWorks. Available at: https://auto.howstuffworks.com/engine1.htm [Accessed 3 Jun. 2019].
Newworldencyclopedia.org. (2018). Internal combustion engine — New World Encyclopedia. [online] Available at: https://www.newworldencyclopedia.org/entry/Internal_combustion_engine [Accessed 3 Jun. 2019].
Scienceclarified.com. (2009). Internal-Combustion Engine — body, used, process, life, type, form, energy, gas, air. [online] Available at: http://www.scienceclarified.com/He-In/Internal-Combustion-Engine.html [Accessed 3 Jun. 2019].
InfoPlease. (2019). internal-combustion engine: Evolution of the Internal-Combustion Engine | Infoplease. [online] Available at: https://www.infoplease.com/encyclopedia/science/tech/terms/internalcombustion-engine/evolution-of-the-internalcombustion-engine [Accessed 3 Jun. 2019].
