Operation, Maintenance and Repair of Auxiliary Generators by Department of the Army and the Navy - HTML preview

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(a) Proven dependability for sustained op-


eration at rated load.

a. The advantages of diesel engines include:

(b) Can use a variety of liquid and gaseous

(1) Proven dependability for sustained opera-


tion at rated load.

(c) Low vibration level.

(2) Efficiency.


TM 5-685/NAVFAC MO-912

(3) Adaptability for wide range of liquid fuels.

(4) Controlled fuel injection.

b. The disadvantages include:

(1) High initial cost.

(2) High weight per given output.

(3) High noise level.

(4) Specialized maintenance.

(5) Fuel injection system has fine mechanical

tolerances and requires precise adjustment.

(6) Difficult cranking.

(7) Cold starting requiring auxiliary ignition


(8) Vibration.

3-3. Types of Diesel Engines.

Various configurations of single and multiple diesel

engines, either two-cycle or four-cycle are used to

drive auxiliary generators. Multi-cylinder engines

Figure 3-2 Typical small stutionary diesel

generator unit, air cooled

of either type can be of “V” or in-line configurations.

Figure 3-3. Typical large stationary diesel generator unit.


TM 5-685/NAVFAC MO-912

Figure 3-4. Typical diesel power plant on transportable frame base.

The “V” configuration is favored when there is a

port (or the exhaust valve closes), then the scaveng-

lack of space because “V” engines are shorter and

ing air port is closed. The piston now compresses

more compact than in-line engines. Most engines in

the air to heat it to a temperature required for

use are liquid-cooled. Air cooling is sometimes used

ignition as the piston nears top dead center (TDC).

with single-cylinder and other small engines (driv-

As the piston nears TDC, a metered amount of fuel

ing generators with up to 10 kW output). Air-cooled

is injected at a certain rate. Injection atomizes the

engines usually reach operating temperature

fuel, which is ignited by the high temperature, and

quickly but are relatively noisy during operation.

combustion starts. Combustion causes the tempera-

a. Two cycle. The series of events that take place

ture and pressure to rise further.

in a two-cycle diesel engine are: compression, com-

(2) Power: As the piston reaches and passes

bustion, expansion, exhaust, scavenging, and air in-

TDC, the pressure of the hot gas forces and acceler-

take. Two strokes of the piston during one revolu-

ates the piston downward. This turns the crank-

tion of the crankshaft complete the cycle.

shaft against the load connected to the shaft. The

(1) Compression. The cycle begins with the pis-

fuel/air mixture continues to burn. As the piston

ton in its bottom dead center (BDC) position. The

passes eighty percent (80%) to eighty-five percent

exhaust valve is open permitting burned gases to

(85%) of the stroke travel towards BDC, it uncovers

escape the cylinder, and the scavenging air port is

the exhaust port (or the exhaust valve is opened).

uncovered, permitting new air to sweep into the

This allows exhaust gas to escape from the cylinder.

cylinder. With new air in the cylinder, the piston

As the piston continues downward, it uncovers the

moves upward. The piston first covers the exhaust

scavenging air port, allowing scavenging air (fresh


TM 5-685/NAVFAC MO-912

air at 3 pounds per square inch (psi) to 6 psi) to

sweep the cylinder, further purging the exhaust gas

and providing a fresh clean charge for the next

cycle. The piston reaches and passes through BDC.

The compression stroke then begins again.

b. Four-cycle. The series of events taking place in

a four-cycle engine are: inlet stroke, compression

stroke, expansion or power stroke, and exhaust

stroke. Four strokes (two revolutions of the crank-

shaft) are necessary to complete the cycle.

(1) Inlet stroke. As the piston starts downward

from TDC, the inlet (intake) valve opens and allows

the piston to suck a charge of fresh air into the

cylinder. This air may be supplied at a pressure

higher than atmospheric air by a supercharger.

(2) Compression stroke. As the piston nears

BDC, the air inlet valve closes, sealing the cylinder.


Energy supplied by the crankshaft from a flywheel,

or power from other cylinders, forces the piston up-

ward toward TDC, rapidly compressing the air and

increasing the temperature and pressure within the


A .

(3) Power stroke. As the piston approaches

TDC, an amount of fuel (modulated by the governor)

is injected (sprayed and atomized) into the cylinder

which is ignited by the high temperature, and com-



bustion starts. Combustion, at a controlled rate,

further increases the temperature and pressure to


accelerate the piston toward BDC. The expansion of

V A L V E O P E N S 7

the hot gases forces the piston down and turns the

crank against the load. Engine efficiency depends

on the fuel charge being completely burned during

the power stroke.

(4) Exhaust stroke. As the piston passes

through BDC at the end of the power stroke, the

exhaust valve opens. The piston, using stored en-

ergy from the flywheel or from the power stroke of

another cylinder, forces the burned gases from the

cylinder through the exhaust port. As the piston

approaches TDC, the exhaust valve is closed and

the air intake valve opens to begin another cycle.


c. Engine timing. Engine timing is critical. Intake


and exhaust valves have to open and close to allow

O V E R L A P -


the greatest amount of work to be extracted from


combustion. They must also be open long enough to

allow fresh air to flow into and exhaust gas to flow

out of the cylinder. Fuel must be injected at proper

rates during certain periods of time to get smooth

Figure 3-5. Timing diagrams

pressure rise and complete combustion. Timing for


two-stroke cycle and four-stroke cycle engines dif-


fers (refer to the timing diagrams in fig 3-5). Dia-

gram A illustrates two forms of the two-stroke cycle

The outer portion covers a port control (uniflow)

engine. The inner portion covers the typical crank-

system. Diagram B illustrates timing for a four-

case scavenging type with uncontrolled fixed ports.

stroke cycle engine.


TM 5-685/NAVFAC MO-912

d. Advantages. Advantages of diesel power for

material can seriously damage moving parts. Con-

generating units include the ability: to utilize spe-

taminated fuel is a major vehicle by which dirt and

cific liquid or gaseous fuel other than highly volatile

water enter the system. Fuel must be filtered before

refined ones (gasoline, benzene, etc.); to meet load


by varying the amount of fuel injected; to utilize a

e. Starting fuels. Diesel engines used for auxil-

relatively slow design speed; and, to operate with-

iary generators usually use distillate fuel for

out external furnaces, boilers or gas generators.

quicker starting. These fuels are light oils that are

e. Disadvantages. Major disadvantages include: a similar to kerosene. Various additives are fre-need to reduce cranking power by use of compres-

quently used with fuel such as cetane improvers

sion relief during start and a powerful auxiliary

which delay ignition for smoother engine operation,

starting engine or starting motor and battery bank;

corrosion inhibitors, and dispersants. Appendix C

high-pressure, close-tolerance fuel injection systems

contains information related to fuel and fuel stor-

capable of being finely adjusted and modulated for


speed/load control; weight; and, noise.

f. Injection systems. Diesel engine manufacturers

usually use one of the following types of mechanical

3-4. Diesel fuel system.

fuel injection systems: unit injection, common rail

A typical diesel engine fuel system is shown in fig-

injection, or in-line pump and injection nozzle. A

ure 3-6. Information related to cooling, lubrication,

limited number of diesel engines currently in use

and starting systems is also shown. Functional re-

employ a common rail injection system. Electronic

quirements of a diesel engine fuel system include

fuel injection has been developed for use in modern

fuel injection, injection timing, and fuel pressuriza-

diesel engines refer to paragraph 3-4 b(4). Unit in-


jector, common rail injector, and in-line pump and

a. Fuel injection system. This system measures

injection nozzle systems are described in tables 3-1

and meters fuel supplied to each cylinder of the

through 3-3. Injection of fuel in any system must

engine. Either inlet metering or outlet metering is

start and end quickly. Any delay in beginning injec-

used. In inlet metering, fuel is measured within the

tion changes the injection timing and causes hard

injector pump or injector. In outlet metering, fuel is

starting and rough operation of the engine. Delay in

measured as it leaves the pumping element. Instan-

ending injection is indicated by heavy smoke ex-

taneous rate during injection must deliver fuel to

haust and loud, uneven exhaust sounds. The end of

attain correct propagation of the flame front and

injection (full shutoff) should be total with no

resulting pressure rise.

dribble or secondary injections. Some injection sys-

b. Timing. Fuel injection timing is critical. The

tems include a delivery or retraction valve for fuel

duration of fuel injection and the amount of fuel

shutoff. In other systems, camshafts have cam lobes

injected vary during starting and partial, full, or

designed with a sharp drop to assure rapid fuel

overload conditions, as well as with speed. The best


engine start occurs when fuel is injected at (or just

(1) Common rail injection. The common rail in-

before) TDC of piston travel because air in the com-

jection system is an older system where fuel is sup-

bustion chamber is hottest at that instant. During

piied to a common rail or manifold. A high-pressure

engine operation, the injection timing may need to

pump maintains a constant pressure in the rail

be advanced to compensate for injection lag. Many

from which individual fuel lines connect to the in-

modern injection systems have an automatic injec-

jection or spray nozzle at each cylinder. Fuel is

tion timing device that changes timing to match

drawn from the supply tank by the low-pressure

changes in engine speed.

pump and passed through a filter to the suction side

c. Fuel pressurization. Fuel must be pressurized of the high-pressure pump. The high-pressure pump

to open the injector nozzle because the nozzle (or

raises the fuel to the engine manufacturer’s speci-

injector tip) contains a spring-loaded check valve.

fied operating pressure. Constant pressure is main-

The injection pressure must be greater than the

tained in the system by the high pressure pump and

compression pressure within the compression

related relief valve. If pressure is greater than the

chamber or cylinder. Between 1500 psi and 4000 psi

relief valve setting, the valve opens and permits

pressure is required for injection and proper fuel

some of the fuel to flow back (bypass) into the tank.

atomization. Specific information is provided in the

Check valves in the injection nozzle prevent the

engine manufacturer’s literature. Fuel system com-

return of fuel oil to the injection system by cylinder

ponents are listed in paragraph 3-4 c.

compression pressure.

d. Fuel contamination. Fuel injection equipment

(2) Unit injection. This system consists of an

is manufactured to precision accuracy and must be

integral fuel-injector pump and injector unit. A com-

very carefully handled. A small amount of abrasive

plete unit is required for each cylinder. Fuel oil is


TM 5-685/NAVFAC MO-912

Figure 3-6. Diagram of typical fuel, cooling, lubrication, and starting systems.


TM 5-685/NAVFAC MO-912

Table 3-l. Unit injector system.

of each other. Fuel from the supply tank is passed

through a filter to the injector pump supply pipe.

Component Purpose

The injector pump receives the fuel which is then

Gear pump

Low pressure pump; delivers fuel from tank to

injected into the cylinders in proper quantity and at

injector: fuel also lubricates the pump.

a prearranged time.


Meters, times, and pressurizes fuel: camshaft-

(3) Electronic Fuel Injection. The electronic

operated by pushrod and rocker arm; one injec-

fuel injection system is an advanced design for mod-

tor for each cylinder.

ern diesel engines, intended to produce improved


Protect machined components from dirt and

starting and operating characteristics. Several sys-

water in fuel.

tems have been developed, mainly for smaller and

Governor Controls engine speed. Varies position of the

intermediate-sized engines. Similarities to me-

injector plunger to vary amount of fuel in-

chanical injection systems include the following: a


fuel pump (or pumps), a governor or speed regula-

Table 3-2. Common rail injector system.

tor, filters, and fuel injectors. The major difference

between mechanical and electronic systems is the

Component Purpose

computer which replaces the mechanical compo-

Low and

Low-pressure pump delivers fuel from tank to

nents (cams and pushrods) used to control fuel in-

high-pressure pump

high-pressure pump; high-pressure pump deliv-

jection. The computer processes data inputs (such

ers fuel to injectors at the desired operating

as engine speed and load, desired speed or governor

pressure: fuel lubricates governor and pumps.

setting, engine temperature, and generator load).


Flyweight-type; controls maximum fuel pres-

Computer output is precisely timed electrical sig-

sure; prevents engine overfueling; controls en-

nals (or pulses) that open or close the fuel injectors

gine idle and prevents overspeeding by control-

ling fuel supply: contained within main pump

for optimum engine performance. Adjustment of in-


jection timing is seldom required after the initial

setup. Refer to the engine manufacturer’s literature


Controlled by the operator; regulates fuel flow

and pressure to injectors.

for maintenance of injectors, pumps, and other fuel

system components.


Meters, times and pressurizes fuel; camshaft-

operated by pushrod and rocker arm: one injec-

g. The main components of the fuel system. Fuel tor for each cylinder.

supply source, transfer pump, day tank, fuel injec-

tion pump, fuel injection nozzles, and filters and


Protect machined components from dirt and

water in fuel.

strainers. These components are matched by the

engine manufacturer for optimum performance and

Table 33. In-line pumps and injection nozzle system.

warranty protection.

(1) The fuel supply source is one or more stor-

age tanks. Each tank must have drain valves for

Injection pump Meters, times, pressurizes and controls fuel

removal of bottom water, see paragraph 2-4 for

delivered to the injection nozzles; consists of

genera! requirements. Additionally, the fuel system

single pumping element for each cylinder; tit-

should include a day tank and a transfer pump, see

ted into a common housing; operated by rocker

paragraph 2-4d.

arm or directly from the camshaft.

(2) The following paragraphs cover the fuel in-

Governor Usually the flyweight-type: may be mounted on

jection pump, fuel injection nozzles, and filters and

main injection pump housing; controls fuel de-


livery: variable-speed or limiting-speed type is


(3) A fuel injection pump accomplishes the

functions described in paragraph 3-4 b(3). Addi-

Fuel lines High-pressure type; transports fuel from pump

tional details are provided in the following para-

to injection nozzles.


Injection nozzle Spring-loaded; hydraulically operated valve that (a) The fuel injection pump must perform

is inserted in the combustion chamber: one

two functions: first, deliver a charge of fuel to the

nozzle for each cylinder.

engine cylinder at the proper time in the engine

Filters Protect machined components from dirt and

operating cycle, usually when the piston has almost

water in fuel.

reached the end of the compression stroke; and sec-

ond, measure the oil charge delivered to the injector

supplied to the cylinders by individual pumps oper-

so the amount of fuel is sufficient to develop the

ated from cams located on a camshaft or on an

power needed to overcome the resistance at the

auxiliary drive. The pumps operate independently



TM 5-685/NAVFAC MO-912

(b) The fuel injection pump consists of a bar-

quency of cleaning and replacing filter elements.

rel and a reciprocating plunger. The reciprocating

Adjust the frequency to meet unusual local operat-

plunger takes a charge of fuel into the barrel and

ing conditions. Generally, all metal-edge and wire-

delivers it to the fuel-injecting device at the engine

mesh devices are called strainers, and all replace-


able absorbent cartridge devices are called filters.

(4) Fuel injection nozzles for mechanical injec-

Fuel filters approved for military use consist of re-

tion systems are usually of the spring-loaded,

placeable elements mounted in a suitable housing.

needle-valve type. These nozzles can be adjusted to

Simplex and duplex type fuel filters are available.

open at the predetermined pressure. Consult the

Fuel strainers and filters must not contain pressure

manufacturer’s specifications before adjusting fuel

relief or bypass valves. Such valves provide a means

injection valves. The nozzle components are as-

for the fuel to bypass the strainer or filter, thereby

sembled carefully at the factory and must never be

permitting the fuel-injection equipment to be dam-

intermixed. Most manufacturers use an individual

aged by contaminated fuel. Filter capacity is gener-

pump for each cylinder (pump injection system) and

ally described in terms of pressure drop between the

provide each cylinder with a spring-loaded spray

input and output sides of the filter. However, fuel oil

valve. The spring keeps the needle from lifting until

filters must be large enough to take the full flow of

the pump has delivered oil at a pressure greater

the fuel oil pumps with a pressure drop across the

than the spring loading. As soon as the pressure

filter not to exceed the engine manufacturer’s speci-

lifts the needle, oil starts to spray into the engine

fications. Fuel filter elements should be changed

cylinder through an opening in the valve body.

whenever the pressure drop across the filter nears

(5) Diesel fu 1

e suppliers try to provide clean

or reaches a specified value. Refer to manufactur-

fuel. However, contaminants (water, sand, lint, dirt,

er’s instructions for information on the replacement

etc.) are frequently found even in the best grades. If

of filter elements. Filter capacity at a given pres-

foreign material enters the fuel system, it will clog

sure drop is influenced by the viscosity of the fuel.

the nozzles and cause excessive wear of fuel pumps

The filter should have ample capacity to handle fuel

and injection valves.

demand of the engine at full load. The larger the

(6) Sulphur, frequently found in fuel oil, is very

filter, the less frequently it will have to be cleaned

undesirable. When sulfur is burned (during combus-

and the better the filtering performance will be.

tion), sulfur dioxide and sulfur trioxide form. Both

substances will combine with water condensates to

3-5. Diesel cooling system.

form sulfuric acid. The maximum amount of sulfur

Diesel engines are designed to be either air cooled

acceptable in fuel oil must not exceed one percent.

or liquid cooled. Cooling is used to prevent the cyl-

The engine manufacturer’s recommendation should

inder walls, the head, the exhaust manifold, and the

be used if acceptable sulfur in fuel oil requirements

lube oil from overheating.

are more restrictive. Strainers and filters capable of

a. An air-cooled system depends on an engine

removing fine particles are placed in the fuel line

driven fan to blow ambient air over the fluted or

between supply tank and engine, or between engine

finned surfaces of the cylinder head and through a

transfer pump and injection pump, or sometimes at

radiator type oil cooler, and over the exhaust mani-

both places. The basic rule for placement of strain-

fold. The exterior surfaces must be kept free of