说New words

•        Dictatedto 指使

•        Shafthorse-power 轴马力

•        Assess评估

•        Fuelconsumption 燃料消耗

•        Frontalarea 迎风面积

•        Impartedto 传授给

•        Altitude海拔高度

•        Climatic气候

•        Specificfuel consumption 燃油消耗率

•        Latter后者

•        Curve 曲线

•        Graph 图形

•        Benchtesting 试车台

•        Simulate模拟

•        Symbol符号

•        Denote表示

•        Slightly稍微

•        Incorporated合并

•        Standardize标准化

•        Conventional传统的、常用的

•        InternationalStandard Atmosphere 国际标准大气

•        Lapse 失效、间隔、流逝

•        Approximately大约

•        Ambient环境

•        Notation符号

•        Tropopause对流层

•        Facility设施

•        Derive获得、得到

•        Waterinjection 喷水

•        Density密度

•        Hence 因此

•        Rotational旋转

•        Correction修正

•        Observe观察

•        Mercury水星、水银

•        Inpractice 在实际中

•        Distinguish区分

•        Aspect方面

•        Equivalent相等的、相同的、等量

•        Netjet thrust 净喷气推力

•        Estimation估计

•        Extra额外的

•        Comparison比较

•        Conversion转换

•        Convert转换

•        Quote 引用

•        Knot 节（海里/小时）

•        Nautical海上的、航海

•        Gross 总量

•        Diagrammatic图解

•        Ramratio 冲压比

•        Machnumber 马赫数

•        Offset抵消

•        Unavoidable不可避免的

•        Shockwave 激波

•        Suitably合适地、恰当地

•        Permissible允许的

•        Limitation限制

•        Irrespective  无关的

•        Deteriorate恶化

•        Negligible可忽略的

•        Augmentation增强

•        Utilization利用

•        Compensate补偿

•        Whereupon因此

•        Schedule安排

•        Governor调节器

•        Passive被动的

•        Pressureratio 增压比

•        Kineticenergy 动能

•        Internalefficiency 内部效率

•        Externalefficiency 外部效率

•        Wasteenergy 无用能

•        Dissipate消散

•        Multi-bladed  多叶片

•        Sweptback design 后掠设计

•        Configuration配置

•        Swirl 旋转

•        Substitute代替、取代

•        Triple-spool  三转子

•        Rearmounted后置式

•        Contra-rotatingfan 对转风扇

•        Efflux流出

•        Theoretically理论上

•        Diameter直径

•        Duty 职责

•        Contributory有贡献的

•        Scale 规模、范围

•        Power-to-weightratio 功重比

读Sentence

•        2.Since the thrust or s.h.p. developed is dependent on the mass of air enteringthe engine and the acceleration imparted to it during the engine cycle, it isobviously influenced, as subsequently described, by such variables as theforward speed of the aircraft, altitude and climatic conditions, Thesevariables influence the efficiency of the air intake, the compressor, theturbine and the jet pipe; consequently, the gas energy available for theproduction of thrust or s.h.p. also varies.

•        7. Toenable the performance of similar engines to be compared, it is necessary tostandardize in some conventional form the variations of air temperature andpressure that occur with altitude and climatic conditions. There are in useseveral different definitions of standard atmospheres, the one in most commonuse being the International Standard Atmosphere (I.S.A.). This is based on atemperature lapse rate of approximately 1.98 K. degrees per 1,000ft,, resultingin a fall from 288.15 deg.K. (15 deg.C) at sea level to 216.65 deg.K (-56.5deg.C.) at 36,089 ft. (the tropopause). Above this altitude the temperature isconstant up to 65.617ft. The I.S.A. standard pressure at sea level is 14.69pounds per square inch falling to 3.28 pounds per square inch at the tropopause(refer to I.S.A. table fig. 21-10).

•        8. Thethrust of the turbo-jet engine on the test bench differs somewhat from thatduring flight. Modern test facilities are available to simulate atmosphericconditions at high altitudes thus providing a means of assessing some of theperformance capability of a turbo-jet engine in flight without the engine everleaving the ground. This is important as the changes in ambient temperature andpressure encountered at high altitudes considerably influence the thrust of theengine.

•        19.Since reference will be made to 'ram ratio' and Mach number, these terms aredefined as follows:

Ramratio is the ratio of the total air pressure at the engine compressor entry tothe static air pressure at the air intake entry.

Machnumber is an additional means of measuring speed and is defined as the ratio ofthe speed of a body to the local speed of sound. Mach 1.0 therefore representsa speed equal to the local speed of sound.

•        20.From the thrust equation in para. 18, it is apparent that if the jet velocityremains constant, independent of aircraft speed, then as the aircraft speedincreases the thrust would decrease in direct proportion. However, due to the'ram ratio' effect from the aircraft forward speed, extra air is taken into theengine so that the mass airflow and also the jet velocity increase withaircraft speed. The effect of this tends to offset the extra intake momentumdrag due to the forward speed so that the resultant loss of net thrust ispartially recovered as the aircraft speed increases. A typical curveillustrating this point is shown in fig. 21-3. Obviously, the 'ram ratio'effect, or the return obtained in terms of pressure rise at entry to thecompressor in exchange for the unavoidable intake drag, is of considerableimportance to the turbo-jet engine, especially at high speeds. Above speeds ofMach 1.0, as a result of the formation of shock waves at the air intake, thisrate of pressure rise will rapidly decrease unless a suitably designed airintake is provided (Part 23); an efficient air intake is necessary to obtainmaximum benefit from the ram ratio effect.

•        22.With an increase in forward speed, the increased mass airflow due to the 'ramratio' effect must be matched by the fuel flow (Part 10) and the result is anincrease in fuel consumption. Because the net thrust tends to decrease withforward speed the end result is an increase in specific fuel consumption(s.f.c.), as shown by the curves for a typical turbo-jet engine in fig, 21-4.

•        30.This larger increase in thrust is invaluable for obtaining higher speeds andhigher altitude performances. The total and specific fuel consumptions arehigh, but not unduly so for such an increase in performance.

•        32.With increasing altitude the ambient air pressure and temperature are reduced.This affects the engine in two interrelated ways:

Thefall of pressure reduces the air density and hence the mass airflow into theengine for a given engine speed. This causes the thrust or s.h.p. to fall. Thefuel control system, as described in Part 10, adjusts the fuel pump output tomatch the reduced mass airflow, so maintaining a constant engine speed.

Thefall in air temperature increases the density of the air, so that the mass ofair entering the compressor for a given engine speed is greater. This causesthe mass airflow to reduce at a lower rate and so compensates to some extentfor the loss of thrust due to the fall in atmospheric pressure. At altitudesabove 36,089 feet and up to 65,617 feet, however, the temperature remains constant,and the thrust or s.h.p. is affected by pressure only.

•        43. Toobtain good propulsive efficiencies without the use of a complex propellersystem, the by-pass principle (Part 2) is used in various forms. With thisprinciple, some part of the total output is provided by a jet stream other thanthat which passes through the engine cycle and this is energized by a fan or avarying number of LP. compressor stages. This bypass air is used to lower themean jet temperature and velocity either by exhausting through a separatepropelling nozzle, or by mixing with the turbine stream to exhaust through acommon nozzle.

•        46.Primary engine design considerations, particularly for commercial transportduty, are those of low specific fuel consumption and weight. Considerableimprovement has been achieved by use of the by-pass principle, and by advancedmechanical and aerodynamic features, and the use of improved materials. Withthe trend towards higher by-pass ratios, in the range of 15:1, the triple-spooland contra-rotating rear fan engines allow the pressure and by-pass ratios tobe achieved with short rotors, using fewer compressor stages, resulting in alighter and more compact engine.

50. For a given mass flow less thrust is produced by the by-pass enginedue to the lower exit velocity. Thus, to obtain the same thrust, the by-passengine must be scaled to pass a larger total mass airflow than the pureturbo-jet engine. The weight of the engine, however, is still less because ofthe reduced size of the H.P. section of the engine. Therefore, in addition tothe reduced specific fuel consumption, an improvement in the power-to-weightratio is obtained.

读全文并回答以下问题：

•       Whichkind of engine is measured in the shaft horse-power ?

•       Definethe specific fuel consumption.

•       Describethe methods to further increase the thrust.

•       Definethe total thrust and the net thrust.

•       How toprevent the overstressing causing by high forward speeds at low altitudes fromhappening?

•       Listthe factors which determined the limit to the obtainable thrust.

•       Listthe effect of temperature.

•       Definethe thermal efficiency and the propulsive efficiency.

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