Page 139 - The Jet Engine

Starting and ignition

21. An ignition unit may be supplied with direct ensure that any residual stored energy in the
current (D.C.) and operated by a trembler capacitor is dissipated within one minute of the
mechanism or a transistor chopper circuit, or system being switched off. A safety resistor is fitted to
supplied with alternating current (A.C.) and operated enable the unit to operate safely, even when the high
by a transformer. The operation of each type of unit tension lead is disconnected and isolated.
is described in the subsequent paragraphs.
23. Operation of the transistorized ignition unit is
22. The ignition unit shown in fig. 11-10 is atypical similar to that of the D.C. trembler-operated unit,
D.C. trembler-operated unit. An induction coil, except that the trembler-unit is replaced by a
operated by the trembler mechanism, charges the transistor chopper circuit. A typical transistorized unit
reservoir capacitor (condenser) through a high is shown in fig. 11-11; such a unit has many
voltage rectifier. When the voltage in the capacitor is advantages over the trembler-operated unit because
equal to the breakdown value of a sealed discharge it has no moving parts and gives a much longer
gap, the energy is discharged across the face of the operating life. The size of the transistorized unit is
igniter plug. A choke is fitted to extend the duration of reduced and its weight is less than that of the
the discharge and a discharge resistor is fitted to trembler-operated unit.

Fig. 11-10 A D.C. trembler-operated ignition unit.

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