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 TM 55-1905-223-24-3
(6) Coolant Heating. The engine is equipped with a coolant heater that operates on the principle of
thermosiphon when the engine is shut down. An oil pressure switch automatically turns the heater ON and OFF.
The heater comes on when the engine is shut down. Heated coolant expands and forces a flow check valve on
the water inlet closed. The heated coolant is forced up the outlet to the top of the engine. When the pressure
drops in the tank, cold coolant enters the tank and the cycle is repeated. A flow-through thermostat, installed in
the inlet line of the engine heater, measures the coolant at its coldest point and keeps the coolant within a
preset temperature range.
e. Air System. The diesel engine requires several hundred cubic feet of air for every gallon of fuel that it
burns. For the engine to operate efficiently, it must breathe freely. Intake and exhaust systems must not be
restricted. The intake air is always routed through an air cleaner. The cleaner is mounted on the engine. Air is
routed from the air cleaner directly to the turbocharger intake air manifold (aftercooler).
(1) Aftercooler. An aftercooler is a device in the engine intake system designed to reduce intake air
temperature and/or preheat intake air temperature. The aftercooler consists of a housing, used as a portion of
the engine intake air manifold, with an internal core. The core is made of tubes through which coolant
circulates. Air is cooled or heated by passing over the core before going into the engine combustion chambers.
Improved combustion results from the better control of intake air temperature, cooling or warming as applied by
the aftercooler.
(2) Turbocharger. The turbocharger forces additional air into combustion chambers so the engine can
burn more fuel and develop more horsepower than if it were naturally aspirated. The turbocharger consists of a
turbine wheel and a centrifugal blower, or compressor wheel, separately encased but mounted on and rotating
with a common shaft. The power to drive turbine wheel - which in turn drives the compressor - is obtained from
energy of the engine exhaust gases. Rotating speed of the turbine changes as the energy level of the gas
changes; therefore, the engine is supplied with enough air to burn fuel for its load requirements. The
turbocharger is lubricated and cooled by engine lubricating oil.
f. Electrical System. The electrical power to the engine is a 24 volt circuit coming from the batteries to a
magnetic switch, instrument panel, and starter motor and solenoid. Operational gauges and switches for local
control of the engine are mounted on the instrument panel on top of the engine. The engine crankshaft drives
a 250 kW generator which produces the ship's ac power. Each generator is equipped with automatic paralleling
controls and an automatic voltage regulator.
(1) Generator. Transforms the mechanical energy from the engine into electrical energy.
(a) When two or more generators furnish power to a common load, they are said to be operating in
parallel (maintaining equal voltage). The NTA 855-GC is equipped with automatic paralleling controls. These
controls are located remote from the generator units. For operating instructions, refer to TM 55-1905-223-10.
(b) The automatic voltage regulator (AVR) controls the generator voltage by controlling the
electrical current supplied to the exciter field. An internal motor-driven rheostat sets the required voltage. An
external exciter field circuit breaker monitors the field current output to the regulator. The breaker will trip if the
current level becomes excessive and extended. The AVR is located on the generator terminal box.
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