PART TWO. GAS TURBINE ENGINES
CHAPTER 3
PRINCIPLES, OPERATION, AND CONSTRUCTION
A gas turbine engine is an air-dependent, thermal jet propulsion device that us exhaust-gas-driven turbine wheels to drive a compressor, making continuous operation of the engine possible.
PRINCIPLES 项目符号在哪里
梦到船
Although the gas turbine engine differs radically in construction from the conventional four-stroke, five-event cycle reciprocating engine, both operate on the same principle. In the piston (reciprocating) engine, the functions of intake, compression, combustion, and exhaust all take place in the same combustion chamber therefore, each must completely occupy the chamber during its respective part of the combustion cycle. In the gas turbine engine, a parate ction is devoted to each function; all functions are performed at the sa
me time without interruption. The ctions are the air-inlet ction the compressor ction, the combustion ction, and a turbine and exhaust ction. The compressor brings in compress, and forces air into the combustion ction. Fuel is then injected into the combustion area, where it mixes with the compresd air. The fuel and air mixture is ignited by an electrical ignition plug; however, once started, ignition is shut off and combustion is continuous and lf-supporting. In gas turbine engines designed for Army u, nearly two-thirds of the energy available from the products of combustion is necessary to drive the compressor. The power turbine is designed to extract as much of the remaining energy as possible from the gas and transform it into shaft horpower which is ud to drive an output shaft or propeller from a power shaft.
A basic gas turbine engine is illustrated in Figure 3-1. A container of compresd air has been provided with an opening (nozzle) through which the air pass off into the atmosphere until the pressure is exhausted (A). This brief high-speed airflow (velocity) through the node produces a mild momentary reaction force (solid arrow). The density of the air can be incread by heating (B). The result of this incread volume is a greater v
elocity as indicated by the long arrow (heated air) as compared to the short broken arrow. In (C) the heated air (solid arrow) is directed (impinged) onto the airfoil-shaped blades attached to the rim of the disc (turbine) causing the turbine to rotate on its shaft. To provide for the continuous airflow, an opening is placed in the forward end of the container (D). A mechanical pump (compressor) forces air (solid arrow) into the container (E). With high-velocity air driving the turbine, the rotating motion of the turbine can be ud to drive the compressor by joining the two rotating parts with a shaft (F). Up to this point the air container has only provided for the heating of the air by an outside means. The container becomes an engine combustion chamber when fuel is introduced mixed with the air, and ignited internally. Not all of the air entering the combustion chamber is needed for combustion. However, all of it is heated and expands rapidly. It exhausts as hot, high-velocity gas through the nozzle and is directed (impinged) onto the turbine. As the gas pass across the turbine, approximately two-thirds of the available energy is ud The remaining energy still posss a high work potential. Therefore, a cond turbine is placed in the flow path of the hot, high-velocity gas and is driven in the same
manner as the compressor-driven turbine. The cond turbine (power turbine), by means of a shaft system mechanically independent of the compressor turbine system drives a system of reduction gears and the output shaft. The output shaft is externally splined for turboprop application or internally splined for helicopter application (G).
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ENGINE OPERATION分娩球
The front or inlet duct is almost entirely open to permit outside air to enter the front of the engine. The compressor works on the incoming air and delivers it to the combustion ction with as much as twelve times or more the pressure the air had when it entered the engine. In the combustion ction fuel is sprayed and mixed with the compresd air. The air-fuel mixture is then ignited by igniter or spark plugs. Once the mixture is lighted the igniter is turned off as the burning process will continue without further assistance, providing the engine is supplied with the right air-fuel mixture. This air-fuel mixture bums at a relatively constant pressure with only about 25 percent of the air taking part in the actual combustion process The rest of the air is ud for cooling some of the components of the combustion ction, This heated expanding air is then directed to the turbine. The turbines are connected to the compressor and accessories. They will extract a major portion (nearly two-thirds) of the energy to drive them. The remaining energy will be ud to either propel the aircraft through a jet nozzle or to turn other times (power turbines). Power turbines will take this energy and transform it into shaft horpower, which in turn
心电感应808习俗是什么drives an output shaft or propeller from a power shaft. 爱的魔法歌词
TYPES OF GAS TURBINE ENGINES
The gas turbine engines most commonly ud today are divided into four types:
▪Turbojet engine -- a gas turbine engine in which the net energy available is ud by the air or hot gas solely in the form of the jet issuing through a propelling nozzle or nozzles or a jet engine who air is supplied by a turbine-driven compressor, the turbine being driven by exhaust gas.
▪Turboshaft engine -- an engine in which the net energy available is transmitted from the exhaust gas-driven turbine wheel through a planetary gear, which may be integral to the engine or externally provided by the aircraft manufacturer, to turn a helicopter transmission-driven powertrain system.
▪Turboprop engine -- a turboshaft engine in which power is transferred from the power shaft through reduction gearing to a propeller. The major difference between the two engi
nes is the gear reduction.
▪Turbofan engine -- in principle, the same as a turboprop, except that the geared propeller is replaced by a duct-enclod axial-flow fan driven at engine speed (优秀班主任Figure 3-2).
The term "turbo" means "turbine." Therefore, a truboshaft engine is an engine that delivers power through a shaft, which, in turn is powered by a turbine wheel. Army aircraft gas turbine engines are generally the free-type power turbine turboprop or turboshaft engines. Having a free power turbine enables the power output shaft to turn at a constant speed while the power-producing capability of the engine can be varied to accommodate the incread loads applied to the power output shaft. Turbine engines may also be classified into two general groups, centrifugal-flow and axial-flow, depending on the type of compressor ud. However, most gas turbine engines in Army aircraft employ a combination of both types.
