Internal Combustion Engine - Assignment Example

Internal combustion engine ABSTRACT A small quantity of high energy fuel enclosed in a small chamber, on ignition, produces an enormous amount of energy. This principle is known as ‘internal combustion’. On the same lines, internal combustion engine works on the above principle. The combustion of fuel inside the compressed combustion chamber produces high temperature and high pressure gas flow. The force created by this high pressure gas flow is applied to the intended component of the engine which has to undergo displacement. Thus the main objective of an internal combustion engine is to convert chemical energy into mechanical energy. Hence the internal combustion engine is the core component of any aircraft or car. The two stroke and four stroke engine are the most popular types of internal combustion engine. It would be more feasible to first discuss the working of a four stroke engine and then the working of a two stroke engine, followed by its advantages and disadvantages. Working of four stroke engine Figure 1: Shows the various parts and working of a four stroke engine [1] The cylinder is the core of the engine. The piston is a cylindrical piece of metal that moves up and down within the cylinder. There may be more than one cylinder present in different alignments based on the nature of the vehicle. The spark plug supplies the spark at regular intervals which is required to ignite the air/fuel mixture present inside the cylinder [2]. Two valves are present. The inlet valve allows the flow of air and fuel into the cylinder. The outlet valve allows the exhaust to flow out of the cylinder. The most important point is that both the valves must be closed during the process of compression and combustion so that the cylindrical chamber remains sealed [3]. The connecting rod is a piece of metal that connects the piston and crankshaft. Both the ends of the connecting rod can rotate so that its angle can be adjusted according to the motion of the piston and crankshaft. The up and down motion of the piston is converted into circular motion with the help of the crankshaft. The crankshaft is surrounded by a sump and engine oil gets collected in the sump. The four strokes include intake stroke, compression stroke, combustion stroke, and exhaust stroke [4]. Initially the piston is at the top of the combustion chamber. First, the intake valve opens and this allows the piston to move down the cylindrical chamber. The descending motion of the piston allows the engine to take fuel (gasoline) and air inside the cylinder and the cylinder is gets filled with air and fuel. Air serves as an oxidizer for combustion. These events constitute the intake stroke. Next, the revolving crankshaft makes the piston to move upwards within the cylinder. The ascending motion of the piston compresses the air / fuel mixture creating a very high pressure within the cylinder. These events constitute the compression stroke. When the piston reaches the top of its stroke, the spark plug present at the top of the cylindrical chamber emits a spark [5]. This spark ignites the gasoline and the air/fuel mixture within the cylinder explodes. This explosion forces the piston to move down the cylinder. These events constitute the combustion stroke. The descending motion of the piston makes the exhaust valve to open. As the exhaust valve opens, the exhaust leaves the cylinder. These events constitute the exhaust stroke. After the above series of events, the piston is ready for the intake of another air/fuel mixture and the process gets repeated again and again. In a four stroke engine, “the linear motion of the piston is converted into rotational motion by the crankshaft” [6]. This rotational motion is most desirable in an automobile as the main intention is to rotate the wheel of the vehicle. Working of two stroke engine Figure 2: Shows the working of a two stroke engine [7] The main difference between a four stroke engine and a two stroke engine is that the two stroke engine does not contain any moving valves, so there is no intake or exhaust stroke. Also the spark plug of a two stroke engine emits the spark once for each revolution while the four stroke engine emits the spark once for every two revolutions [8]. The piston of a two stroke engine performs several complicated functions as compared to the four stroke engine. At one end, the piston compresses the air/fuel mixture and also captures large amount of energy received, when fuel in the compression chamber get ignited. On the other side, the crankcase is attached to the piston. The piston creates vacuum to suck the air/fuel mixture from the carburettor and pressurizes the crankcase forcing the air/fuel mixture into the cylindrical combustion chamber [9]. At the same time, the either sides of the piston act as valves closing the intake and exhaust openings. So the cylindrical chamber remains sealed during compression and combustion process. The opening which is present in the lower part of the cylindrical chamber allows the air/fuel mixture to enter the cylinder. The upward motion of the cylinder compresses the air/fuel mixture and this constitutes the compression stroke. The spark plug emits the spark to ignite the compressed air/fuel mixture as a result of which it explodes constituting the combustion stroke. The exhaust leaves the cylindrical chamber through another opening present at the upper part of the cylindrical chamber. Conclusions Both two stroke and four stroke engines have advantages and disadvantages. The two stroke engine’s construction is simpler compared to four stroke engine as the inlet and outlet valves are absent [10]. Due to the same reason, it is of light weight and low cost compared to a four stroke engine. As already mentioned the two stroke engine sparks for each revolution and hence its power is twice as that of a four stroke engine. Despite the several advantages of two stroke engine, almost all cars and other vehicles use four stroke engine. This is because the two stroke engine system lacks a dedicated lubricating system. Therefore a two stroke engine gets worn out faster than a four stroke engine. Two stroke engine needs oil to be added along with fuel. Usage of oil frequently in a way hikes the expense. Two stroke engine does not give proper mileage and also creates a lot of pollution. The above mentioned disadvantages of a two stroke engine make it less significant and almost all automobiles use four stroke engines only References [1] “Four-stroke-cycle Engine Cycle.” Merriam-Webster, n. d. Web. 31 Oct 2014. http://visual.merriam-webster.com/transport-machinery/road-transport/types- engines/four-stroke-cycle-engine.php [2] Brain, Marshall. “How Car Engines Work.” How stuff works, n. d. Web. 31 Oct 2014. http://auto.howstuffworks.com/engine1.htmm [3] Brain, Marshall. “How Car Engines Work.” [4] Woodford, Chris. “Car engines.” Explain that stuff!, 13 May 2014. Web. 31 Oct 2014. http://www.explainthatstuff.com/carengines.html [5] Woodford, Chris. “Car engines.” [6] Brain, Marshall. “How Two-stroke Engine Work.” How stuff works, n. d. Web. 31 Oct 2014. http://science.howstuffworks.com/transport/engines-equipment/two-stroke6.htm [7] “Two-stroke-cycle engine cycle.” Merriam-Webster, n. d. Web. 31 Oct 2014. http://visual.merriam-webster.com/transport-machinery/road-transport/types-engines/two-stroke-cycle-engine-cycle.php [8] Brain, Marshall. “How Two-stroke Engine Work.” [9] Brain, Marshall. “How Two-stroke Engine Work.” [10] Brain, Marshall. “How Car Engines Work.” Read More