suitable on diesel engine driven generators ranging
from 85 kW up to the largest diesel engine genera-
tor.
3-8. Governor/speed control.
A diesel engine used in an auxiliary generator must
have a governor to regulate and control engine
speed. Since an automatic governor functions only
with a change in speed, constant engine speed may
not be totally possible and “hunting” can occur due
to over-correction. The governor’s sensitivity is de-
termined by the minimum change in speed of the
prime mover which will cause a change in governor
setting; its speed regulation is the difference in gen-
erator speeds at full-load and no-load divided by the
arithmetical mean of the two speeds. Refer to the
glossary for descriptions of governor characteristics.
a. Usually, this ratio is stated as a percentage,
with synchronous speed considered rather than
mean speed. For example, a generator with a syn-
chronous speed of 1,200 rpm, operated at 1,190 rpm
when fully loaded and 1,220 rpm with no load, has
2.5 percent speed regulation.
b. The governor must be capable of speed adjust-0 20 40 60 80
ment so the proper governed speed can be selected.
PER CENT, LOAD
In most governors, this adjustment is made by
SPEED VS LOAD-MECHANICAL GOVERNOR
changing the tension of the main governor spring.
The governor should also be adjustable for speed
A 6% DROOP-RATED SPEED AT
LOAD
8 6% DROOP- RATED SPEED AT 0% L O A D
regulation so the droop of the speed-load curve can
C
6
DROOP
INTERMEDIATE SETTINGS
be altered as required to suit operating conditions.
E 4% DROOP-RATED SPEED AT 50% LOAD
Determine the curve by observing the generator
speed or frequency at various loads and plotting
Figure 3-11. Chart of speed droop characteristics.
them as abscissa against the loads (from no-load to
full-load) as ordinates. The curve droops at the full-
the speed. Speed droop is usually adjusted by
load end (hence, the expression “speed droop” of the
lengthening or shortening the governor operating
governor).
c. An example of speed droop characteristics is
levers, changing the ratio between governor move-
shown in figure 3-11. The characteristics are for a
ment and throttle or gate movement.
mechanical governor but the same principles can be
e. Alternating Current (AC) Generators. Gover-
used for other engine/governor applications. The
nors of prime movers driving AC generators which
chart is based on a six percent speed droop governor
operate in parallel with other generators must have
on an engine running at rated speed at no load.
enough speed regulation or speed droop to prevent
When full load is applied, engine speed drops to 94
surging of the load from one generator to another.
percent (94%) of rated value (line B). The engine
Ordinarily, three to five percent speed regulation is
can be brought to rated speed at full load by reset-
adequate. Some governors have antisurging devices
ting the governor (line A). However, with the load
to damp out the surges. Speed regulation should be
removed, engine speed would increase beyond its
increased if the surges continue. Speed regulation of
rated limit. Intermediate speed settings are shown
governors controlling AC generators affects the fre-
by lines C and D. Line E shows speed droop at 50
quency and the load division between generators
percent (50%) load.
but has almost no effect upon voltage.
d. Speed droop can be determined quickly by
f. Direct C urrent (DC) Generators. Regulation of
loading the generator to full-load, observing the
DC generators affects voltage regulation and the
speed, unloading the generator, and again observing
division of load between generators. In general, the
3-17
TM 5-685/NAVFAC MO-912
speed regulation of generators operated in parallel
and automatic equipment can be applied to the hy-
should be the same for each machine. Speed regula-
draulic governor.
tion for generators operating individually should be
(a) The hydraulic governor requires pressur-
as favorable as possible without causing generator
ized oil for operation. This oil can come from the
surge resulting from sudden load changes. Ordi-
engine or from a separate sump in the governor. Oil
narily, 2.5 percent speed regulation is satisfactory
is admitted to an auxiliary oil pump in the governor.
Voltage regulation of DC generators may be accom-
The auxiliary pump furnishes necessary pressure to
plished through adjustment of the speed droop of
actuate the governor mechanism. In the governor
the governor.
shown, the fuel to the engine is decreased by the
g. Types of governors. Usually four types of gov-
action of the fuel-rod spring (10) on the fuel rod ( 12)
ernors are used; mechanical, hydraulic, pneumatic,
and increased by the opposing action of the hydrau-
and electronic. When speed regulation must be
lic serve piston (14), the admission of oil to which is
more precise, such as Defense Communications
controlled by a pilot valve (4). The pilot valve is
Agency sites where no more than 0.8 percent varia-
controlled by flyweights of the governor (5) which
tion is permitted, an electronic (isochronous) gover-
are driven by the governor shaft through gearing to
nor is used.
the engine. The centrifugal force of the flyweights in
(1) The mechanical governor used in small air-
rotation is opposed by the speeder spring (6), the
cooled engines may be part of the fly-wheel. The
compression of which determines the speed at
governor in multicylinder engines is usually a sepa-
which the governor will control the engine. The
rate assembly driven by gear or belt from a cam-
speeder-spring compression is adjusted through the
shaft or crankshaft. A typical mechanical governor,
rotation of the speed-adjusting shaft (8) which
shown in figure 3-12, operates as follows: the gov-
raises or depresses the spring fork (7) through its
ernor drive gear (2) drives the governor shaft (10)
and the governor weights (4). Centrifugal force
linkage lever.
moves the weights away from the shaft which push
(b) The droop of the speed-load characteristic
the operating-fork riser (6) against the operating
is adjusted by changing the effective length of the
fork (ll), rotating the operating-fork shaft (7) and
floating lever (11). This is accomplished by moving
moving the governor arm (9). In the external view,
the droop-adjusting bracket forward or backward in
the governor spring (A) is connected to the governor
the slot of the floating lever. The effective length of
arm and opposes movement of the governor weights
the lever should be shortened to decrease the speed
away from the shaft. Adjusting screw (c) adjusts the
droop and lengthened to increase the speed droop.
tension of the governor spring, establishing the
(3) The pneumatic governor (air-vane type) is
speed at which the prime mover operates. The
used in certain small generator plants (see fig
greater the governor-spring tension, the lower the
3-14). The engine flywheel includes an integral fan
governed speed. The auxiliary adjusting screw (D)
which forces air outward from the drive shaft. The
adjusts the droop of the governor. Turning this
amount of air flowing from the engine depends on
screw in closer to the arm decreases the droop of the
engine speed. A movable air vane is placed in the air
governor; this screw should be turned in as far as
stream. The air vane (blade) acts as a governor
possible without allowing the engine to surge. Aux-
since the air pressure depends upon engine speed.
iliary adjusting screw (B) is turned in to damp out
The air pressure on the vane is opposed by a gover-
surging of the engine at light-load or no-load; it
nor spring and these forces operate through linkage
should not be turned in so far that it increases the
to control the throttle of the engine.
speed of the generator at no-load.
(4) Electronic (isochronous) speed control is the
(2) The hydraulic governor (see fig 3-13) is
maintenance of constant engine speed independent
used on large prime movers as well as diesel en-
of the load being carried (zero droop). An isochron-
gines as small as 100 hp. The governor usually
ous governor will maintain, or can be adjusted to
includes: a speed-responsive device, usually fly-
maintain, constant engine speed (within 0.2 percent
weights; a valve mechanism; a regulating cylinder
variation). This type of governor can be a combina-
and piston; and a pressure pump and relief valve.
tion of a conventional hydraulic governor and an
The assembly is adjustable for various ranges of
electronic load-sensing system, or an all-electric
speed and sensitivity. The hydraulic principle pro-
system.
vides greater power than could be obtained from a
(a) Speed control by the hydraulic governor,
mechanical type. Since the flyweights only control
see paragraph 3-8 d(2), depends on variation in cen-
an easily moved pilot valve (which in turn controls
trifugal force created by flyweights (centrifugal
the hydraulic action), the governor can be made to
forces are not used in electric types). This force
operate accurately and smoothly. Remote control
operates a piston-type pilot valve which controls the
3 - 1 8
TM 5-685/NAVFAC MO-912
0 BEARING
OPERATING FORK
012 BUMPER SPRING
BUMPER SPRING SCREW
\
COCK NUT
- E X T E R N A L VIEW
0 BUMPER SPRING SCREW
ADJUSTING
SCREW
I
DRIVE
GEAR
ADJUSTABLE
I
SCREW
GOVERNOR
SPRING
Figure 3-12. Mechanical Governor.
3-19
TM
MO-912
flow of high-pressure oil to a servomotor, thereby
operating fuel controls.
(b) The isochronous system uses electronic
sensing and amplifying devices that actuate a type
of servomotor throttle control. The system is used
with power generation where precise frequency con-
trol is required. An isochronous system may be sen-
sitive to frequency changes (engine speed) or to both
frequency and load. When responsive to load
changes, the system corrects fuel settings before
load changes can appreciably modify engine speed
or frequency.
3-9. Air intake system.
Approximately 15 pounds of air is required to burn
one pound of fuel. Accordingly, the air requirement
for a 2000 horsepower engine is about 3600 cubic
feet per minute. The same horsepower-to-air rela-
tionship applies to engines for other power ratings.
F R O M E N G I N E
Intake air carries dust particles, water vapor and
other foreign material. Since these materials can
damage moving parts within the engine, filtration
Figure 3-13. Hydraulic Governor.
of the intake air is necessary. A 2000 horsepower
1) PLUNGER, 2) GEAR PUMP DRIVE, 3) GEAR PUMP
engine, breathing air containing three parts per
IDLER, 4) PLUNGER PILOT VALVE, 5) FLYWEIGHT,
million dust contamination, would take in 25
6) SPEEDER SPRING, 7) SPRING FORK,
8) SPEED-ADJUSTING SHAFT, 9) SPEED-ADJUSTING
pounds of foreign material in 1000 operating hours.
LEVER, 10) SPRING, 11) FLOATING LEVER,
An air intake system must collect, filter, and dis-
12) FUEL ROD, 13) TERMINAL LEVER,
tribute the required air to the engine cylinders. This
14) SERVO PISTON
must be accomplished with a minimum expenditure
of energy (pressure drop). The objective of air filtra-
tion is the reduction of engine component wear. Sev-
eral types of air filters or air cleaners are used. The
pleated-paper type are strainers, porous enough to
THROTTLE ADJUSTING SCREW
pass air but able to remove solid particles larger
than 0.002 of an inch. Larger engines use an oil-
GOVERNOR
bath air cleaner (see fig 3-15). In oil-bath cleaners
air is drawn through an oil bath. Solid particles are
trapped and settle in the unit’s bottom pan.
a. Supercharging. Supercharging increases the
amount of air taken into a working cylinder. This
provides the injected fuel oil with more oxygen to
enable combustion of a larger charge of air/fuel mix-
ture. Power output of a certain size engine is
thereby increased, enabling use of smaller engines
where space prohibits larger engines.
(1) Advantages. The power output of a natu-
rally aspirated engine is limited by the normal pres-
sure and oxygen content of the atmosphere. When
NEEDLE VALV
supercharging is used, the intake valve (port) closes
with the cylinder under the initial pressure. Super-
charging is particularly effective at higher alti-
ADJUSTING
tudes. The supercharged engine can develop greater
horsepower than the standard naturally-aspirated
unit. The fuel consumption of a supercharged unit
will not exceed that of comparable horsepower sizes
Figure 3-14. Carburetor and pneumatic governor.
of naturally-aspirated units.
3-20
TM 5-685/NAVFAC MO-912
but the coolant should be allowed to circulate
through the supercharger.
(4) Operating instructions. Manufacturer’s in-
structions must be followed to ensure proper opera-
tion of superchargers. Filtered air only should enter
the air inlet, because foreign matter can cause rotor
imbalance and damaging vibration. The manufac-
turer’s recommendations for lubrication must be fol-
lowed. Proper lubrication is necessary because the
unit operates at high speed and at high tempera-
ture. Not more than 15 seconds should elapse be-
tween the start of rotation and an oil pressure indi-
cation of 12 to 71 psi. Coolant circulation through
the turbocharger should be regulated so the tem-
perature rise does not exceed 30” Fahrenheit at full
engine load. A rise in excess of 30” Fahrenheit indi-
cates faulty circulation. Coolant should be allowed
to circulate through the turbocharger for about 5
minutes after the engine is shutdown.
b. Aspiration. The term “naturally-aspirated” is
applied to engines that are not supercharged. A four
stroke cycle engine performs its own air pumping
action with the piston intake stroke. When it is
supercharged, a four-stroke engine with a blower or
turbocharger provides pressure in the intake mani-
fold greater than atmospheric. The increased pres-
Figure 3-15. Oil bath air cleaner:
sure in the intake manifold is referred to as “boost”.
(2) Methods. The most successful method of su-
Two stroke cycle engines require an air supply un-
der pressure to provide scavenging air.
percharging is the use of a turbocharger driven by
exhaust gas (see fig 3-16). The heat and energy
3-10. Exhaust system.
pulsations in the exhaust gas, which are usually
Components. The exhaust system consists of the
lost in the exhaust silencer, are used to drive a
engine exhaust manifold and includes piping, ex-
single-stage centrifugal turbine. The exhaust gas
pansion joints, silencers, and exhaust pipe. Also the
turbine is coupled to a centrifugal compressor that
system may include exhaust waste heat recovery
compresses the air to a pressure of four or five
equipment. The purpose of the system is to remove
psi. The engine’s pressurized air is then delivered to
exhaust gas from engine cylinders to the atmo-
the individual cylinders through the intake mani-
sphere. Parts of the system are shown in figure 3-6.
fold.
(a) Leak-free. Exhaust systems must be leak free
(3) Disadvantages. Although the supercharged
to protect personnel from asphyxiation, and equip-
engine has many advantages over nonsupercharged
ment from fire and explosion. Exhaust from gaso-
engines, its disadvantages are not insignificant. The
line engines can contain dangerous carbon monox-
turbocharger is another piece of equipment to main-
ide. Diesel engine exhaust includes objectionable
tain and operate. It operates at varying speeds de-
smoke and odors. On supercharged engines, leaks
pending on engine load, barometric pressure, inlet
ahead of the turbine cause a loss of power.
air temperature, exhaust temperature, smoke con-
(b) Piping. Exhaust piping must be the correct
tent of the exhaust, or accumulations of dust and
size to minimize exhaust back pressure. Connec-
dirt on the impeller and diffuser. It may operate at
tions between exhaust manifold and piping should
very high speed (up to 120,000 rpm) with a full load
have an expansion joint and the exhaust pipes
on the engine and thus be subjected to all the
should slope away from the engine. Also the exhaust
troubles of high-speed equipment. With proper
pipes should have suitable devices to prevent entry
maintenance, however, the turbocharger can be op-
of rainwater. The length of tail pipes from silencer
erated very successfully. If the turbocharger fails,
to atmosphere should be kept to a minimum.
the engine can usually be operated at reduced load
(c) Silencers. Silencers are used to reduce or
as a nonsupercharged engine. The turbocharger can
muffle engine exhaust noise. Silencing engine ex-
be partially dissembled and the opening blocked off,
haust sounds consists of trapping and breaking up
3-21
TURB’ IMPELLER
GAS INLET
ENGINE
CYLINDER
EXHAUST GAS
DISCHARGE
ENGINE EXHAUST GAS FLOW
AMBIENT AIR
COMPRESSED AIR FLOW
Figure 3-16. Diagram of turbocharger operation.
the pressure waves. Usually, a cylindrical unit with
2744 is provided at the back of this publication. A
baffles, expansion chambers, and sound absorption
completed example of DD Form 2744 is located in
materials is used.
appendix F, figure F-l. It is authorized for electronic
generation.
3-11. Service practices.
(1) Record keeping. Engine log sheets are an
a. Maintenance program. Service practices for
important part of record keeping. The sheets must
diesel engines consist of a complete maintenance
be developed to suit individual applications (i.e.,
program that is built around records and observa-
auxiliary use) and related instrumentation. Accu-
tions. The maintenance program includes appropri-
rate records are essential to good operations. Notes
ate analysis of these records. DD Form 2744
should be made of all events that are or appear to be
(Emergency/Auxiliary Generator Operation Log)
outside of normal range. Detailed reports should be
should be used to record inspection testing of
logged. Worn or failed parts should be tagged and
emergency/auxiliary generators. A copy of DD Form
protectively stored for possible future reference and
3-22
TM 5-685/NAVFAC MO-912
analysis of failure. This is especially important
Table 3-5. Diesel engines troubleshooting-Continued
when specific failures become repetitive over a pe-
EXCESSIVE SMOKING AT IDLE
riod of time which may be years.
Cause Remedy
(2) Log sheet data. Log sheets should include
engine starts and stops, fuel and lubrication oil con-
Clogged injector. Clean all injectors, refer to appendix G. Refer Leaking head gasket to manufacturer’s instruction and correct as sumption, and a cumulative record of the following:
or blowby. Engine due required. Schedule the overhaul and correct as (a) Hours since last oil change.
for overhaul. Incorrect required. Perform timing procedures. refer to (b) Hours since last overhaul.
timing. appendix G.
(c) Total hours on engine.
EXCESSIVE SMOKING UNDER LOAD
(d) Selected temperatures and pressures.
The same causes for
The same remedies for “idle” apply.
b. Troubleshooting. Perform troubleshooting pro-
“idle” apply.
cedures when abnormal operation of the equipment
Air intake restricted.
Check air intake and correct as required.
is observed. Maintenance personnel should then re-
fer to log sheets for interpretation and comparison
High exhaust back
Check exhaust system and turbocharger; correct
pressure.
as required.
of performance data. Comparisons of operation
should be made under similar conditions of load and
Poor quality fuel.
Replenish fuel supply with fresh, proper quality
ambient temperature. The general scheme for
fuel.
troubleshooting is outlined in the following para-
Engine overloaded. Reduce load to proper ievel.
graphs.
LOW POWER OR LOSS OF POWER
(1) Industrial practices. Use recognized indus-
Air intake restricted.
Check air intake and correct as required.
trial practices as the general guide for engine ser-
vicing. Service information is provided in the manu-
Poor quality fuel.
Replenish fuel supply with fresh, proper quality
facturer’s literature and appendixes