Structure of the engine
Recently, I have come across a great website, which explains and shows in details the structure of most types of engines. I will try to retell the most important things in short. But first, I want to ask you a couple of questions.
Can you explain to your girlfriend the difference between a diesel and a gasoline engines? What is the difference between four and two stroke engines? No? Then I invite you to read this article.
Four stroke engine
The four stroke engine was first introduced by German engineer Nikolaus Otto in 1876, and it is also known as the Otto cycle from then on. But it is more correct to call it a four stroke cycle. This engine is probably one of the most common engine types of these days. It is used in almost all cars and trucks.
These four strokes means:, intake, compression, power, and exhaust. Each cycle corresponds to one stroke of the piston; hereupon working cycle in each of the cylinders is made of two turns of the crankshaft.
During the intake, the piston moves downward, drawing a fresh portion of air-fuel mixture through the intake valve. A distinctive feature of this engine is that the intake valve is opened by the vacuum that is made by the movement of the piston downward.
The torque raises the piston that compresses the air-fuel mixture. The inlet valve is closed by increasing pressure force, resulting from the upward piston.
At the top of the compression stroke, the spark ignites the compressed fuel. During the combustion of the fuel the energy is released, which affects the piston, forcing it to move downward.
When the piston reaches its lower point, the exhaust valve opens and the exhaust gases are driven from the cylinder by the upward moving piston.
Two stroke engine
A two stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft (an up stroke and a down stroke of the piston, compared to twice that number for a four stroke engine). This is accomplished by using the end of the combustion stroke and the beginning of the compression stroke to perform simultaneously the intake and exhaust functions. In this way, two stroke engines often provide high specific power, at least in a narrow range of rotational speeds. The functions of some or all of the valves required by a four stroke engine are usually served in a two-stroke engine by ports that are opened and closed by the motion of the piston(s), greatly reducing the number of moving parts. Wiki.
Gasoline (spark ignition) versions are particularly useful in lightweight (portable) applications, such as chainsaws, and the concept is also used in diesel compression ignition engines in large and weight insensitive applications, such as ships, locomotives and the light aircraft models.
This type of engines has an indisputable disadvantage, such as diseconomy, as a large proportion of the fuel does not burn out and it is ejected with the exhaust gases.
The air-fuel mixture is drawn in the crankcase by the vacuum, which is created during the upward movement of the piston.
Compression in the crankcase
The inlet valve is closed by the pressure in the crankcase during compression. The fuel mixture is compressed on the final stage of stroke.
Movement of the fuel mixture / exhaust
Toward the end of the stroke, the piston forces the compressed air-fuel mixture to move along the inlet port from the crankcase to the main cylinder. The air-fuel mixture forces out the exhaust gases that leave the main cylinder through the exhaust valve. Unfortunately, some unburned fuel also leaves the cylinder, causing a two stroke engine design to be considered as less economical.
The torque drives the piston upward that compresses the fuel mixture. (At this point, under the piston is taking place the next intake stroke).
At the top of the stroke, a spark plug ignites the fuel mixture. The resulting energy makes the piston to move downward to the end of the cycle. (At this point, the fuel is compressed in the crankcase under the cylinder).
Four stroke diesel engine
A special feature of the diesel engine is a modified system of fuel ignition.
This type of engine was creates by Rudolf Diesel in 1897. He stated that his engine is the most efficient ever created. So far, his creation is among the most efficient engines.
The inlet valve is opened and the fresh air (no fuel) is sucked into the cylinder.
As the piston rises, the air is compressed and the temperature increases in the cylinder. At the end of the stroke the air is heated enough to ignite the fuel.
Near the top of the compression stroke, the fuel injector injects fuel into the cylinder. The hot air ignites the fuel upon the contact.
During the combustion of the fuel, the energy is released, which effects the piston, forcing it to move downward.
Exhaust valve opens, causing the exhaust gases leave the cylinder.
Rotary piston internal combustion engine (Wankel engine)
Wankel rotary piston engine is a wonderful creation, offering very intricate redesign of the four elements of the Otto cycle. This engine was developed by Felix Wankel in the 1950s of last century.
In the Wankel engine, a triangular rotor with a central ring gear is driven around a fixed pinion within an extended chamber.
Nowadays, Mazda makes most efforts to develop and promote this type of engine, but still the four stroke engine remains the most popular. AutoVAZ also uses this type of engine in gyroplanes.
Here are some advantages over conventional gasoline engines:
•It has a low level of vibration. The rotary piston engine is fully balanced mechanically, thus enhancing the comfort of light vehicles, such as the micro-cars, moto-cars, and so on.
•The main advantages of rotary piston engine are excellent dynamic characteristics, for example, it is possible using a low gear to accelerate the car without excessive load on the engine above 100 km / h at higher engine speeds (8000 turns / min or more) than in the case of conventional design of the piston internal combustion engine .
•It has the high specific power.
•It has in 1,5-2 times smaller dimensions.
•It has less number of parts by 35-40%.
Here are some disadvantages:
•Tendency to overheat.
•The difficulty in producing.
•The lower efficiency at low speeds.
The air-fuel mixture gets through the inlet valve at this stage of rotation.
The fuel mixture is compressed here.
The fuel mixture is ignited here, rotating the rotor around.
The exhaust gases get out here.
This type of engine could be powered by steam, but more often it could be met in small aircraft models, where it works on compressed air or carbon dioxide (CO2).
This animation displays the tank with CO2. Compressed CO2 is a liquid that is being released, and then it transforms into a gaseous state, in other words, under normal atmospheric temperature and pressure, the liquid carbon dioxide boils, so we cannot go wrong if we say that this type of engine works on the steam of CO2.
At the top of the cycle, the piston pin presses on the ball valve letting high pressure gas into the cylinder.
The gas expands, moving the piston downward.
When the piston opens the exhaust valve, the high pressure gas leaves the cylinder.
The torque brings the piston upward to complete the cycle.
The rocket and turbojet engines, according to the author are striking in their design, but the animation of their work is too boring in his opinion.
The rocket engine is the simplest of its kind, so we will start with it.
In order to operate in an outer space, the rocket engines require the supply of oxygen and the fuel for their operation. The air-fuel mixture is injected into the combustion chamber where it burns continuously. The high pressure gas goes through the nozzles, causing thrust in the opposite direction.
In order to test this method yourself, inflate a toy ball and release it from your hands – the rocket engine works much the same ;)
The turbojet engine works on the same principle as the rocket, except that it takes the oxygen from the atmosphere. This engine is most effective at high altitudes in the rarefied air.
Similarities: the fuel is being burned continuously in the combustion chamber as in a rocket. The expanding gas leaves the combustion chamber through nozzles, creating thrust in the opposite direction.
Differences: On its way out from the nozzle, the gas pressure is used to spin a turbine. The turbine is a series of rotors that are connected to a one shaft. Between each pair of fans is the stator, which helps the gas to pass through the propeller rotors more efficiently.
At the front of the engine, the turbine shaft spins a compressor. The compressor operates similar to a turbine, but in the opposite direction. Its function is to increase the pressure of air that is entering into the engine. The turbine pushes the air and the compressor sucks it.
Turboprop engine is similar to the turbojet, except the fact that the gas which leaves the combustion chamber rotates a turbine to a greater extent, and this turbine rotates the propeller in front of the engine. It creates the thrust. This engine is effective at low altitudes.
Turbofan engine is a compromise between the turbojet and turboprop. It works as a turbojet, but there is one peculiarity: a turbine shaft drives the external fan, which has more blades and spins faster than the propeller. It helps this engine to be effective at high altitudes where the air is discharged.
•Ultimate Visual Dictionary, DK Publishing Inc., 1999
•Building the Atkinson Cycle Engine, Vincent Gingery, David J Gingery Publishing, 1996
•The Stirling Engine Manual, James G. Rizzo, Camden Miniature Steam Services, 1995
•Modern Locomotive Construction, J. G. A. Meyer, 1892, reprinted by Lindsay Publications Inc., 1994.
•Five Hundred and Seven Mechanical Movements, Henry T. Brown, 1896, reprinted by The Astragal Press, 1995
•Model Machines / Replica Steam Models, Marlyn Hadley, Model Machine Co., 1999
•Air Board Technical Notes, RAF Air Board, 1917, reprinted by Camden Miniature Steam Services, 1997
•Internal Fire, Lyle Cummins, Carnot Press, 1976
•Toyota Web site Prius specifications
•Steam and Stirling Engines you can build, book 2, various authors, Village Press, 1994
•Knight's New American Mechanical Dictionary, Supplement Edward H. Knight, A.M., LL. D., Houghton, Mifflin and Company, 1884
•Thomas Newcomen, The Prehistory of the Steam Engine L. T. C. Rolt, David and Charles Limited, 1963
•An Introduction to Low Temperature Differential Stirling Engines James R. Senft, Moriya Press, 1996
•An Introduction to Stirling Engines James R. Senft, Moriya Press, 1993
I hope you will find this information useful and interesting!
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