13-08-2012, 10:54 AM
OVER VIEW OF DIESEL ENGINE
OVER VIEW OF DIESEL.docx (Size: 137.52 KB / Downloads: 63)
HISTORY:
Rudolf Diesel, of German ethnicity, was born in 1858 in Paris where his parents were German immigrants. He was educated at Munich Polytechnic. After graduation he was employed as a refrigerator engineer, but his true love lay in engine design .Diesel’s story actually begins with the invention of the gasoline. “Nikolas August Otto” had invented and patented the gasoline engine in 1876. In 1878, Rudolf diesel was attending the polytechnic high school of Germany when he learned about the low efficiency of gasoline. This disturbing information inspired him to create an engine with high efficiency.Rudolf Diesel's prime model, a single 10-foot (3.0 m) iron cylinder with a flywheel at its base, ran on its own power for the first time. Diesel spent two more years making improvements and in 1896 demonstrated another model with a theoretical efficiency of 75 percent, in contrast to the 10 percent efficiency of the steam engine. By 1898, Diesel had become a millionaire. The diesel engine is modeled on the diesel cycle. The diesel engine and thermodynamic cycle were both developed by Rudolf Diesel in 1896. Diesel demonstrated is engine at the exhibition fair in Paris, France in 1898. Diesel engine initially intended to run on coal dust. The engine was fuel by pea-nut oil, the original bio-diesel. Diesel engines are manufactured in two strokes and four strokes. First diesel race car placed 13th in the Indianapolis 500.Indianapolish 500 is an American automobile race, held annually.
What is diesel engine?
A diesel engine (also known as a compression-ignition engine and sometimes capitalized as Diesel engine) is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. This is in contrast to spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which uses a spark plug to ignite an air-fuel mixture. The diesel engine is modeled on the Diesel cycle. The engine and thermodynamic cycle were both developed by Rudolf Diesel in 1897.
The diesel engine has the highest thermal efficiency of any regular internal or external combustion engine due to its very high compression ratio. Low-speed diesel engines (as used in ships and other applications) often have a thermal efficiency which exceeds 50 percent.
How diesel engine works?
The diesel internal combustion engine differs from the gasoline powered Otto cycle by using highly compressed, hot air to ignite the fuel rather than using a spark plug (compression ignition rather than spark ignition).
In the true diesel engine, only air is initially introduced into the combustion chamber. The air is then compressed with a compression ratio typically between 15:1 and 22:1 resulting in 40-bar (4.0 MPa; 580 psi) pressure compared to 8 to 14 bars (0.80 to 1.4 MPa) in the petrol engine. This high compression heats the air to 550 °C (1,022 °F). At about the top of the compression stroke, fuel is injected directly into the compressed air in the combustion chamber. This may be into a void in the top of the piston or a pre-chamber depending upon the design of the engine. The fuel injector ensures that the fuel is broken down into small droplets, and that the fuel is distributed evenly. The heat of the compressed air vaporizes fuel from the surface of the droplets. The vapour is then ignited by the heat from the compressed air in the combustion chamber, the droplets continue to vaporize from their surfaces and burn, getting smaller, until all the fuel in the droplets has
been burnt. The start of vaporization causes a delay period during ignition, and the characteristic diesel knocking sound as the vapor reaches ignition temperature and causes an abrupt increase in pressure above the piston. The rapid expansion of combustion gases then drives the piston downward, supplying power to the crankshaft.
COMPRESSION RATIO:-
The compression ratio of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines.
In a piston engine it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.
Picture a cylinder and its combustion chamber with the piston at the bottom of its stroke containing 1000 cc of air (900 cc in the cylinder plus 100 cc in the combustion chamber). When the piston has moved up to the top of its stroke inside the cylinder and the remaining volume inside the head or combustion chamber has been reduced to 100 cc, then the compression ratio would be proportionally described as 1000:100, or with fractional reduction, a 10:1 compression ratio.
Moving component:
Piston - A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall.
Drawback of piston--Since the piston is the main reciprocating part of an engine, its movement creates an imbalance. This imbalance generally manifests itself as a vibration, which causes the engine to be perceivably harsh. The friction between the walls of the cylinder and the piston rings eventually results in wear, reducing the effective life of the mechanism
What is a Diesel fuel system?
Over the past few decades, scientists and engineers have experimented with different types of fuels for use in cars, trucks, construction equipment, planes and other machines. Although fuels such as electricity and hydrogen have been developed or considered for this purpose, the most common fuels are still derived from petroleum. Gasoline is the most common type of fuel used in fuel systems. Another common type of fuel system, however, is the diesel fuel system.
Common rail injection system:-
In recent years, more and more drivers have been drawn to diesel-powered vehicles. The Common Rail system in particular gives engine developers the freedom they need to reduce exhaust emissions even further, and especially to lower engine noise. The particular design of Common Rail, with its flexible division of injection into several pre-, main and post-injections, allows the engine and the
Injection system to be matched to each other in the best possible way. In the Common Rail accumulator injection system, the generation of the injection pressure is separate from the injection itself. A high-pressure pump generates in an accumulator – the rail – a pressure of up to 1,600 bar (determined by the injection pressure setting in the engine control unit), independently of the engine speed and the quantity of fuel injected. The fuel is fed through rigid pipes to the injectors, which inject the correct amount of fuel in a fine spray into the combustion chambers.