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The idea of utilizing the physical principle of reaction on a large scale by means of rockets is usually attributed to China in the thirteenth century. Not until after the Second World War, however, did rocket technology mature to a state which made the idea of space travel a practical possibility, owing largely to a giant step forward during the war itself. Although earliest models of the steam turbine date back as early as the 17 th century, practical applications of the turbine engine had to wait until the turn of the 20 th century. Today, the gas turbine engine is the most widespread and most effective method of aircraft propulsion, having almost totally displaced the reciprocating engine, which, up to the 1960 s, was the common power source in aviation. There are four types of engines I will be talking about; the turbojet, turbofan, turboprop, or the turbo shaft. The gas turbine represents one of the most technological achievements in aviation, the successful introduction of which made possible a tremendous acceleration of progress in all fields of aviation.
Some of the historical milestones that are major steps toward turbine engine development, ending in the use of the gas turbine for aircraft propulsion are as follows: 1687 - the English philosopher and mathematician Sir Isaac Newton formulates three laws of motion which form the basis of modern jet propulsion, according to which: 1) a body remains either at rest, or in motion of constant velocity, unless an external force acts on the body; 2) the sum of forces acting on a body equals the product of the bodys mass times acceleration produced by these forces (i. e. force = mass times acceleration); 3) for every force acting on a body, the body exerts a force of equal magnitude and opposite direction along the same line as the original force. 1791 - John Barber, an Englishmen, was granted a patent for a gas driven turbine engine which utilized the thermodynamic cycle of the modern gass turbine. The power plant was to be comprised of a gass generator with compressor, combustion chamber and a turbine wheel - components that are fundamental to todays engine. This engine was never built. 1918 - Sanford Moss, at General Electric in the United States, develops an exhaust turbo-charger for reciprocating are-engines. This is the first application of a gas turbine in an aircraft propulsion system. 1930 - Frank Whittle applied for his patent in which he describes a jet engine with multi-staged axial compressor followed by a centrifugal compressor, annular combustion chamber, single-stage axial turbine, and a nozzle.
The patent was titled Improvements relating to the Propulsion of Aircraft and other Vehicles. The engine, which ran on liquid fuel, was successfully run in April of 1937. These early steps laid the foundation of modern high-thrust engines. Engine Classification Different types of engines exist, according to their tasks. Turbojet and turbofan engines provide propulsion forces directly by reaction forces generated by the exhaust gas.
Turbofan engines, are classified according to the portion of mass airflow that is bypassed around the basic engine, and are typically denoted as high-bypass or low-bypass-ratio engines. The turbojet is made up of the following components: -Multi-stage compressor -Computer -Single or multi-stage turbine In order to function properly to produce thrust, an air intake and an exhaust system are required to process the airflow. The air first enters the intake section, which must deliver a smooth stream of air for the compressor. The compressors job is to raise the pressure of the air. This also leads to a rise not only in pressure, but also in temperature and density. On leaving the compressor, the pressurized air enters the combustion chamber, where fuel is injected and burned, thus adding more energy to the airflow.
It is here that the airflow is processed to take on the characteristics of a gas. The first station where energy is absorbed from the gas is in the gas turbine. The energy content of a hot gas is not depleted when the gas discharges from the turbine. A major part of the heat and pressure energy of the gas is still available to be converted into kinetic energy. This is the task of the exhaust nozzle. High exhaust velocity is a prerequisite to the generation of thrust.
Exhaust velocity maybe increased further by afterburning, a fuel-exhausting method of adding more heat downstream of the turbine. The turbofan has emerged as the most common type of a gas turbine engine for aircraft propulsion. Like that of the turboprop, the turbine section is designed to absorb more energy than would be necessary to drive the compressor alone. The excess power is used to drive a fan, a low-pressure compressor of larger diameter arranged upstream of a main compressor. Part of the air entering the engine intake by passes the inner engine and expands in a separate nozzle to provide cold rust. The amount of air that is bypassed in relation to the air that passes through the core engine that is turned bypassed-ratio.
A distinction is made between low and high bypass-ratio engines. Low bypass-ratio engines are used with supersonic combat aircraft. The high bypass-ratio engines are used with high subsonic military and commercial airliners. In a turboprop, the energy of the hot gas is used to drive an additional, but separate turbine, which in turn provides shaft power to drive a propeller. The gas when exhausting from the nozzle, has transmitted most of its energy to the turbines, which a small amount of energy remaining for the generation of thrust. The basic layout of a turboprop is slightly different then a turbojet because it has a additional turbine to drive the propeller, a two-spool arrangement of the rotational machinery, and a mechanical reduction gear to convert the high rotational speed of the turbine to the more moderate speed of the propeller.
A turboprop is designed to accelerate a high massed flow to a low velocity. This results in unsurpassed fuel efficiency, at the expense of flight speed and cabin noise. In a turbo shaft engine, all of the usable hot gas energy is extracted and converted into shaft power, by an additional (free) turbine. This type of engine is typically used with helicopter...
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