system consists of engine-mounted accessories and
means you are able to make repairs and replace a variety
sensors, an electronic control system, and panel-
of engine-related components without having to ship the
mounted controls and indicators. AU engine harnesses
complete engine to a depot repair facility.
are designed to withstand salt spray, sand, dust, fungi,
vibrations, immersion during washdown and steam
Operation
cleaning, and fuel and oil residues. The connector ends
Study figure 6-3 as you read about the operation of
are molded for wiring integrity and suitable strain relief.
the TF40B. The compressor rotor assembly is turned by
The cable assemblies provide electrical continuity
the air starting system as air enters the inlet housing
between the engine accessories and engine interfaces.
module. The inlet air is directed into the compressor
All molded ends of the harness assemblies are stamped
rotor assembly and is compressed. The compressed air
with their respective plug numbers, making it easier for
then flows through the air diffuser assembly and into the
you to locate and identify these assemblies in the
atomizing combustor chamber assembly. When the
appropriate engine electrical control system wiring
engine reaches 2,246 rpm, the fuel valve assembly and
schematic.
fuel flow divider allow metered main fuel to flow to the
28 main fuel injection nozzles. The air mixes with fuel
CAUTION
from the fuel injection nozzles to form a combustible
mixture. Two igniter assemblies provide spark and
System ground is isolated and should not be
ignite the mixture, creating the hot, expanding gases
which are discharged through the turbine section. Some
connected to frame ground.
energy from the hot gases drives the two gas producer
disk assemblies which, in turn, drive the compressor
IGNITION SYSTEM. The ignition system is
rotor assembly. The remaining energy from the hot gases
used for start procedures only. It consists of a single-box,
drives the integral third turbine wheel shaft assembly
high-energy, capacitor-discharge ignition exciter that is
and fourth turbine rotor disk assembly which, in turn,
used with two ignition leads and two shunted surface
drive the power output shaft assembly.
gap-type igniter assemblies.
Ignition Exciter. The ignition exciter is designed
Systems
to operate in ambient temperatures of -30 to 250F
The operation of the TF40B is supported by the
(-34 to 121C). It uses an input voltage of 16 to
following major systems:
30 V dc and will produce an output voltage of at
least 2,400 V at the igniter assemblies. Its duty cycle is
1. Electrical control system
2 minutes on, 3 minutes off, 2 minutes on, 23 minutes
2. Ignition system
off.
3. Engine gas temperature (EGT) system
Ignition Leads and Igniter Assemblies. The
ignition leads will operate in ambient air temperatures
4. Speed sensing system
of 30 to 500F (34 to 260C). Both the ignition
5. Fuel system
leads and the igniter assemblies are designed to operate
in a marine environment.
6. Lubrication system
ENGINE GAS TEMPERATURE SYSTEM.
7. Electronic control system
The EGT system works with the electronic control
8. Air system
system to sense turbine speeds and provide monitoring
information. First, the gas temperature is sensed by a
In the following paragraphs, we will give you a brief
chromel-alumel parallel thermocouple averaging
overview of these systems. You will need to become
arrangement. Then, it is biased by the air inlet
familiar with the fundamental systems of this engine
temperature sensing device assembly and finally
before you read about your general maintenance
applied to the electronic control system for automatic
responsibilities. For detailed descriptions of these
monitoring purposes.
systems, you should consult the appropriate technical
manuals.
SPEED SENSING SYSTEM. The gas producer
ELECTRICAL CONTROL SYSTEM. The
(N1) and power turbine (N2) speeds are sensed by their
magnetic pickups located nearby. The N1 speed
electrical control system is energized by a separate 24-
magnetic pickup is located on the rear face of the
to 28-V dc ungrounded two-wire power source. The
