Diesel Engine

TM 55-1905-223-24-4

c. Auto-Control Panel. Provides one way of starting the engine, automatically, if the power fails, or manually, for

test and maintenance. In addition, the control circuits provide for shut off of the engine if an overspeed, high water

temperature, or low oil pressure develops.

d. Automatic-Voltage Regulator. Controls the generator output voltage at a preset value regardless of the load.

e. Governor. The-governor assembly consists of three main components5, the actuator, assembly, the control unit

and the magnetic sensor. It maintains the engine at a constant speed during varying loads. The unit contains all solid

state electric circuits which sense speed from a magnetic sensor located in the flywheel housing. A pulse from the

sensor is directly proportional to the engine speed. It is compared with the control speed set point. It then supplies the

appropriate current output to the actuator to control the fuel pump throttle arm. During cranking, the speed control unit

causes the actuator to move the fuel pump lever to the full ON position. The actuator will regulate the engine speed

once the engine starts.

f. Circuit Breakers. The breakers are used to protect the system during an overload and certain short circuit

conditions. They are installed between the voltage regulator and the generator.

1-11. Diesel Engine. The following is a brief summary of the operation of the systems which make up the diesel engine.

a. Combustion System (Diesel Cycle). Diesel Engines are different from spark-ignited engines in a number of ways.

Compression ratios are higher, and the charge taken into combustion chamber during the intake stroke consists of air

only, with no fuel mixture. Injectors receive low pressure fuel from the fuel pump and deliver it into individual

combustion chambers at the proper time, in equal quantity and in an atomized. condition for burning. Ignition of fuel is

caused by heat of compressed air in the combustion chamber. The four strokes and order in which they occur are shown

in FIGURE 1-2 and described in the following paragraphs.

(1) Intake Stroke. During intake stroke, the piston travels downward; intake valve is open, and exhaust valve is

closed. The downward travel of the piston allows air from the turbocharger to enter the cylinder.

(2) Compression Stroke. At the end of the intake stroke, intake valve closes and piston starts upward on

compression stroke (exhaust valve remains closed). At the end of compression stroke, air in combustion chamber is

compressed into a small space causing temperature of the air to rise to a point high enough for ignition of fuel. During

last part of compression stroke and early part of power, stroke, a small metered charge of fuel is injected into combustion

chamber. Almost immediately after fuel charge is injected into combustion chamber, fuel is ignited by the hot

compressed air.

(3) Power Stroke. During the beginning of the power stroke, the piston is pushed downward by the burning and

expanding gases; intake and exhaust valves are closed. As more fuel is added and burns, gases get hotter and expand

more to further force piston downward and thus add driving force to crankshaft rotation.

1-5