basically the same, but can be achieved by various methods. The type and power source for the starter varies in accordance with engine and aircraft require-ments. Some use electrical power, others use gas, air or hydraulic pressure, and each has its own merits. For example, a military aircraft requires the engine to be started in the minimum time and, when possible, to be completely independent of external equipment. A commercial aircraft, however, requires the engine to be started with the minimum disturbance to the passengers and by the most economical means. Whichever system is used, reliability is of prime importance.
4.
The starter motor must produce a high torque and transmit it to the engine rotating assembly in a manner that provides smooth acceleration from rest up to a speed at which the gas flow through the
Electric
5.
The electric starter is usually a direct current (D.C.) electric motor coupled to the engine through a reduction gear and ratchet mechanism, or clutch, which automatically disengages after the engine has reached a self-sustaining speed (fig. 11-2).
6.
The electrical supply may be of a high or low voltage and is passed through a system of relays and resistances to allow the full voltage to be progres-sively built up as the starter gains speed. It also provides the power for the operation of the ignition system. The electrical supply is automatically cancelled when the starter load is reduced after the engine has satisfactorily started or when the time cycle is completed. A typical electrical starting system is shown in fig. 11-3.
122
图11-2 一种电动起动机
Starting and ignition
图11-3 一种低压电起动系统
Fig. 11-3 A low voltage electrical starting system.
注:继电器示于‘起动’位置
减小电流
计时开关
火花塞
起动机马达
起动电路
再点火电路
吹除电路
高能点火装置
主继电器
点火继电器
全电流计时开
慢速起动电阻
点火开关
绝缘继电器
火药起动
7.火药筒起动有时用于某些军用发动机中，它是一种快速的独立起动方式。起动机马达基本上是一台小型冲击式涡轮，由火药燃烧的高速燃气驱动。涡轮的功率输出通过减速齿轮和自动脱开机构带动发动机转动。一个电发火起爆器开始点燃火药装药。当用无烟火药装药为这种起动机提供功率时，所要求的装药尺寸会大大限制火药筒起动机的使用。图11-4所示为三筒式起动机。
起动开始
截止计时开关
点火开关绝缘继电器
超转继电器
指示灯亮
起动
起动／再点火选择开关
再点火
吹除
起动机主开关
28伏直流供电
异丙基硝酸酯起动
8.这种起动机可产生大的功率输出，而且具有快速起动的特性。它有一个涡轮，通过减速齿轮将功率传给发动机。在这种情况丅，涡轮由异丙基硝酸酯燃烧产生的高压燃气带转。这种燃料喷入作为起动机一部分的一个燃烧室中，由高能点火系统进行电点火。油泵将燃料从储箱中供入燃烧室，在每次起动之前先由空气泵将起动机燃烧室中的雾气抽出去。燃料和空气泵、点火系统，以及起动循环终止的整个工作由继电器和定时开关进行电控制。一种异丙基硝酸酯起动系统示于图11-5。
Starting and ignition
喷口导向器
Fig. 11-4 A triple-breech cartridge starter.
Cartridge
7. Cartridge starting is sometimes used on military engines and provides a quick independent method of starting. The starter motor is basically a small impulse-type turbine that is driven by high velocity gases from a burning cartridge. The power output of the turbine is passed through a reduction gear and an automatic disconnect mechanism to rotate the engine. An electrically fired detonator initiates the burning of the cartridge charge. As a cordite charge provides the power supply for this type of starter, the size of the charge required may well limit the use of the cartridge starters. A triple-breech starter is illustrated in fig. 11-4.
Iso-propyl-nitrate
8. This type of starter provides a high power output and gives rapid starting characteristics. It has a turbine that transmits power through a reduction gear to the engine. In this instance, the turbine is rotated by high pressure gases resulting from the combustion of iso-propyl-nitrate. This fuel is sprayed into a combustion chamber, which forms part of the starter, where it is electrically ignited by a high-energy ignition system. A pump supplies the fuel to the combustion chamber from a storage tank and an air pump scavenges the starter combustion chamber of fumes before each start. Operation of the fuel and air pumps, ignition systems, and cycle cancellation, is electrically controlled by relays and time switches. An iso-propyl-nitrate starting system is shown in fig. 11-5.
Air
9.
Air starting is used on most commercial and some military jet engines. It has many advantages over other starting systems, and is comparatively light, simple and economical to operate.
10.
An air starter motor transmits power through a reduction gear and clutch to the starter output shaft which is connected to the engine. A typical air starter motor is shown in fig. 11-6.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：劳斯莱斯喷气引擎－中英(65)
